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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    International journal of flexible manufacturing systems 12 (2000), S. 145-163 
    ISSN: 1572-9370
    Keywords: inventory ; modeling ; postponement ; supply chain management
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract This paper studies the impact of a reduction in hardware complexity on the supply-chain inventory against various customer on-time delivery alternatives and manufacturing environments. Different methods of reducing hardware complexity are proposed, and their impact on total supply-chain inventory and customer serviceability quantified. An analytical inventory optimization scheme taking into account multistage supply networks, product structure, forecast accuracy, lead-time variability, and supplier reliability is used to determine optimal inventory levels in a stochastic modeling environment. The analysis is based on a business case for an IBM midrange computer family consisting of more than 200 models and upgrades with hundreds of features. We investigate different hardware complexity reduction strategies, including low-usage feature reduction, low-volume feature reduction, and feature substitution, as well as quick response and postponement mechanisms. Our computational results show that, in a fabrication-fulfillment center environment, reducing hardware complexity results in significantly higher inventory savings than in an integrated manufacturing environment. The results presented in this paper were used to reduce hardware complexity in IBM's midrange computer division.
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  • 2
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    Plasma chemistry and plasma processing 20 (2000), S. 65-86 
    ISSN: 1572-8986
    Keywords: thermal plasma ; waste processing ; fly-ash vitrification ; optical emission spectroscopy ; volatilization ; lead ; modeling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract Results are presented of optical emission spectroscopy (OES) application asa control tool to improve fly-ash plasma vitrification. A twin-torch plasmasystem has been used for the fly-ash processing, and a new OES method hasexamined metallic vapors above the melt. The method allows the study ofnonhomogeneous optically thin plasmas exhibiting a symmetry plane withoutsophisticated tomographic systems. The dc arc torches are mounted above acold crucible filled with a synthetic glass. The arc intensity is from200 to 400 Å. Argon is introduced into the torches along the cathodeand the anode, while argon, oxygen or hydrogen are injected through thelance between the torches. Local plasma temperatures above the melt havebeen evaluated using measured relative intensities of spectral lines ofthe plasma-forming gas. Metallic vapor concentration in the plasma isdeduced from the intensity ratio of the metal–gas spectral lines. Leadoxide has been used to study heavy-metal behavior at the fly-ash plasmavitrification. Distribution of the lead along the crucible surface,depending on the plasma-forming gas composition as well as the concentrationevolution with time, have been examined. The elemental analysis of theresultant glass has been measured by scanning electron microscopy (SEM)with energy-dispersive spectrometry (EDS). A predictive model has beenadapted to simulate the noncongruent vaporization of heavy metals from themelt. According to the data obtained, steep variations of the volatility ofthe elements depend strongly on reducing properties of gases controllingthe plasma composition near the melted surface. In addition, the melttemperature and the redox potential of the gas phase are found to be themost critical parameters.
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  • 3
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    Plasma chemistry and plasma processing 20 (2000), S. 521-553 
    ISSN: 1572-8986
    Keywords: thermal plasma ; transferred arc ; fumed silica ; modeling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract The volatilization of quartz in a transferred arc plasma followed byquench and recondensation is a promising route to the production offumed silica. In this work, an existing model of a transferred arcwas modified and combined with a newly developed model of a moltensilica anode to predict the behavior of a transferred arc evaporatoras a function of current and plasma gas flow rate. The model predictstemperature, current, and flow fields in both the plasma and anode aswell as evaporation rates. Although quantitative agreement withexperimental results was not possible because of insufficient propertydata for silica at high temperature, the results were within an orderof magnitude of those measured experimentally. The model developed isuseful for the design and scaleup of this type of reactor.
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  • 4
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    Journal of materials synthesis and processing 8 (2000), S. 139-144 
    ISSN: 1573-4870
    Keywords: TiO2 ; phase transformations ; mechanical alloying ; kinetics ; modeling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A high-pressure and high-temperature phase of TiO2 : TiO2 II is formed transiently during room-temperature high-energy ball milling of anatase TiO2 : TiO2 anatase → TiO2 II → TiO2 rutile. Rutile is the only phase present after prolonged ball milling. The present paper focuses on the influences of physical and chemical processing conditions on the transformation kinetics. The effects of two milling parameters on the kinetics of phase transformation of anatase TiO2 were investigated: the nature of milling tools and the powder-to-ball weight ratio R. Granulometric characterizations and TEM observations have demonstrated that the transformation of TiO2 anatase into TiO2 II occurs without fracturing of particles and that TiO2 II nanograins form at the surface of anatase particles. The parameter R affects only the transformation rate. For a given R, the transformation rate is the largest with alumina grinding tools, intermediate with zirconia tools, and the smallest with steel tools. The parameters involved in current models of the mechanical alloying process do not suffice to explain the differences in transformation rates observed here. A parameter, which takes into account the influence of the mechanical properties of grinding materials, is considered.
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  • 5
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    Oxidation of metals 53 (2000), S. 49-75 
    ISSN: 1573-4889
    Keywords: FeCrAl ; α Al2O3 ; high-temperature resistance ; residual stresses ; thermal stresses ; X-ray diffraction ; relaxation ; modeling ; elasto-viscoplastic model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The stresses generated in alumina scales during different oxidation stepscontrol the protective character of such scales and their lifetime. Laboratoryand industrial Fe–Cr–Al alloys, differing by their impuritycontent and preparation, and for which the oxidation kinetics werepreviously characterized, were studied here to experimentally determine ortheoretically calculate the stress level in the alumina scales. Theexperiments were performed by X-ray diffraction (XRD) at room temperature,using the sin2psi method. The oxide-stress level wascorrelated with many parameters, such as the scale microstructure andmorphology, the nature of the substrate, the substrate and oxide thickness,the oxide grain size, the cooling rate, etc. A numerical elasto-viscoplasticmodel was developed to calculate the thermal stresses and to point out theeffect of the relaxation phenomena either during cooling or duringisothermal treatment after oxidation. The results obtained by theelasto-viscoplastic model are in good agreement with the experimental ones.
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  • 6
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    Journal of materials synthesis and processing 8 (2000), S. 73-85 
    ISSN: 1573-4870
    Keywords: Chemical vapor deposition (CVD) ; diamond films ; modeling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The evolution of grain size, grain-size distribution, morphological and crystallographic texture, surface roughness, and the contribution of various surface facets to the growth of polycrystalline diamond films is performed by carrying out a series of two-dimensional computer simulations. The films are assumed to grow from a set of randomly oriented, {100}- and {111}-faceted nuclei by the motion of their vertices (the points where the adjoining facets of the same or neighboring grains meet). The vertex velocities are found to be a function of the orientation and the growth rate of the adjoining facets. To quantify the latter, a {100} to {111} growth-rate parameter is used. The results show that the evolution of the grain size and its distribution, surface roughness, morphological and crystallographic texture, and the portion of the film grown from different surface facets are all mutually linked and governed by the magnitude of the growth-rate parameter. The latter can be controlled by the CVD processing conditions, such as the substrate temperature, reactor pressure, mole fraction of carbon-source gas (e.g., CH4, C2H2).
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  • 7
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    Autonomous robots 8 (2000), S. 25-42 
    ISSN: 1573-7527
    Keywords: visual servoing ; robust control ; mobile robot ; vehicles ; modeling ; vision
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract We have been interested in Automatic Guided Vehicles (AGV) for several years. In this paper, we synthesize controllers for AGV applications using monocular vision. In particular, we are interested in road following and direction change tasks, and in analyzing the influence of extrinsic camera parameter perturbations on vehicle behavior. We use the bicycle as the kinematic vehicle model, and we choose the position of the white band on the road as the sensor signal. We define an interaction between the camera, which is mounted inside the vehicle, and the white band detected in the image space. Using this kind of interaction, we present how to use a pole assignment technique to solve the servoing task. We show the simulation and experimental results (1/10 scale demonstrator) with and without perturbations. We then investigate the use of a robust controller to slow down the effect of perturbations on the behavior of the vehicle.
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  • 8
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    Transport in porous media 41 (2000), S. 105-116 
    ISSN: 1573-1634
    Keywords: flow ; integration ; Gassmann ; acoustics ; reservoir ; characterization ; modeling ; simulation ; Newton–Raphson
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract Integrated flow modeling is the combination of a traditional flow simulator with a petrophysical model. By combining a petrophysical model with a traditional flow model, it is possible to perform calculations that improve our ability to monitor fluid movement in porous media. This paper outlines the formulation of an integrated flow model IFLO and its multi-variable, Newton–Raphson IMPES solution procedure. The benefits of integrated flow modeling and the underlying principles involved in the integration of a flow model with a petrophysical model are presented. Results from the IFLO model are used to illustrate the principles.
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  • 9
    ISSN: 1573-1634
    Keywords: NAPLs ; radon ; modeling ; monitoring ; partitioning ; tracer ; emanation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract The recently developed natural radon tracer method has potential as a rapid, low‐cost, nondestructive, and noninvasive method for quantifying NAPL contamination. In the subsurface, radon‐222 (radon) is produced by the decay of naturally occurring radium‐226 contained in the mineral fraction of aquifer solids. In groundwater radon occurs as a dissolved gas, with a half‐life of 3.83 days. In the absence of NAPL, the radon concentration in groundwater quickly reaches a maximum value that is determined by the mineral composition of the aquifer solids, which controls the rate of radon emanation. In the presence of NAPL, however, the radon concentration in the groundwater is substantially reduced due to the preferential partitioning of radon into the organic NAPL phase. A simple equilibrium model and supporting laboratory studies show the reduction in radon concentration can be quantitatively correlated with residual NAPL saturation. Thus, by measuring the spatial distribution in radon it may be possible to identify locations where residual NAPL is present and to quantify the NAPL saturation. When the basic processes of partitioning, radon emanation from the aquifer solids, and first‐order decay are incorporated into an advective/dispersive transport model, good agreement is obtained with the results of laboratory and field experiments. Model sensitivity analyses shows many factors can contribute to the radon concentration response, including the length of the NAPL zone, NAPL saturation, groundwater velocity, porosity, and radon emanation. Thus, care must be taken when applying the radon method to locate and quantify NAPL contamination in the subsurface.
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  • 10
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    Transport in porous media 41 (2000), S. 47-60 
    ISSN: 1573-1634
    Keywords: unsaturated flow ; peat ; filters ; septic ; modeling ; hydraulics ; soil moisture retention curve
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract Peat is an alternative filter medium for the treatment of various waste streams including septic tank effluent. The water holding capacity and adsorption capacity of peat make it a favorable filter medium over sand or gravel which are commonly used as the filter medium for the drainage field of septic systems. This paper presents the results of a field study to evaluate the hydraulics of a peat filter used to treat the septic tank effluent from a public school west of Ottawa, Canada. An experimental box was placed within the filter during its construction to provide access to the vertical profile of the peat layer. The filter is periodically pulsed with septic tank effluent, which is distributed over the top of the filter and flows vertically through the peat. The filter was instrumented with tensiometers and transducers to monitor the pore water pressures in response to a pulse of septic tank effluent. An in-depth study of the hydraulics of the system was completed. The soil moisture retention curve and the hydraulic conductivity as a function of density were determined in laboratory experiments. A one-dimensional unsaturated flow model was used to predict the pressure response due to a pulse. A comparison of the field and model results illustrates the impact of the density variations, and the corresponding hydraulic conductivity variations, on the model predictions. The compaction of the peat is an important design consideration for the filter since it directly impacts the flow characteristics and the hydraulic retention time within the filter.
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  • 11
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    Journal of electroceramics 5 (2000), S. 153-182 
    ISSN: 1573-8663
    Keywords: modeling ; SOFC ; internal reforming ; cermet
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Approaches to models and computer simulations of conductivity, polarization resistance, and impedance of composite electrodes in solid oxide fuel cells (SOFC) are reviewed with respect to the more important experimental findings. The approaches are classified according to how they model the highly disordered structure of composite SOFC electrodes: As corrugated layers of electrode material covered by a thin film of electrolyte or vice versa (thin film model), as a random packing of particles (Monte Carlo calculations), or using a macroscopic, averaged description of the disordered electrode structure (macroscopic porous-electrode model). Thin film models appear to be useful rationalizations of some experimental measurements of polarization resistance, but in the stricter sense fail to predict a number of important electrode characteristics. The Monte Carlo method, on the other hand, apparently meets with most of the more prominent experimental results reported so far, although some issues concerning parameter choices, among other things, remain to be resolved. The macroscopic porous-electrode theory may serve as a useful simplification of the Monte Carlo method, but with a more limited scope. Modeling of composite electrodes for SOFC thus appears to have reached a level where it can be used for practical engineering applications. As an example of this, the rate of methane reforming at Ni-YSZ cermet anodes under current load is calculated using the framework of the macroscopic porous-electrode theory, modified to include non-linear kinetics and gas-phase diffusion. The reforming reaction is quite evenly distributed in the anode, and its overall rate is therefore strongly dependent on thickness. However, most of the electrochemical reaction is likely to occur in a region closer than 10 μm to the bulk electrolyte. For an anode thickness larger than this, the current-collector potential at a given current is by and large independent of thickness. The ratio between the rates of the reforming and the electrochemical reactions can therefore be balanced to a certain degree by optimizing thickness, without significant loss in cell power. In addition, cermet porosity, volume fraction of Ni and Ni-particle size, appears to have a moderate effect in controlling the rate balance, which will have to be manipulated within the constraints set by the requirement of percolation in the gas-phase and the Ni- and YSZ-networks.
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  • 12
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    Flow, turbulence and combustion 63 (2000), S. 1-21 
    ISSN: 1573-1987
    Keywords: turbulence ; RANS ; modeling ; length-scale
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract We derive an equation for the average length-scale in a turbulent flow from a simple physical model. This is a tensorial length-scale. We use as a model the evolution of a blob of turbulent kinetic energy under the influence of production, dissipation, and transport, as well as distortion by the mean motion. A single length-scale is defined which is biased toward the smallest of the scales in the various directions. Constants are estimated by consideration of homogeneous decay. Preliminary computations are carried out in a mixing layer and a two-dimensional jet, using the new length-scale equation and the equation for the turbulent kinetic energy. The results are compared with data and with the predictions of the classical k-epsilon equations; the new results are quite satisfactory. In particular, the plane jet/round jet anomaly is approximately resolved.
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  • 13
    ISSN: 1573-1839
    Keywords: virtual reality ; modeling ; constructionism ; astronomy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Natural Sciences in General , Technology
    Notes: Abstract In this manuscript we describe an introductory astronomy course for undergraduate students in which we moved from the large-lecture format to one in which students were immersed in a technologically-rich, inquiry-based, participatory learning environment. Specifically, undergraduate students used 3-D modeling tools to construct virtual reality models of the solar system, and in the process, build rich understandings of various astronomical phenomena. For this study, primarily naturalistic inquiry was used to gain a holistic view of this semester-long course. These data are presented as two case studies focusing on: (1) the role of the teacher in this participatory learning environment; (2) the particular dynamics that formed in each group; (3) the modeling process; (4) the resources used, specifically student-developed inscriptions; and (5) the role of technology and whether learning the technology interfered with learning astronomy. Results indicated that VR can be used effectively in regular undergraduate university courses as a tool through which students can develop rich understandings of various astronomical phenomena.
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  • 14
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    Applied mathematics and mechanics 21 (2000), S. 19-26 
    ISSN: 1573-2754
    Keywords: structure ; optimization ; topology optimization ; modeling ; dual programming ; O223 ; TU323
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Mathematics , Physics
    Notes: Abstract Topology optimization design of continuum structures that can take account of stress and displacement constraints simultaneously is difficult to solve at present. The main obstacle lies in that, the explicit function expressions between topological variables and stress or displacement constraints can not be obtained using homogenization method or variable density method. Furthermore, large quantities of design variables in the problem make it hard to deal with by the formal mathematical programming approach. In this paper, a smooth model of topology optimization for continuum structures is established which has weight objective considering stress and displacement constraints based on the independent-continuous topological variable concept and mapping transformation method proposed by Sui Yunkang and Yang Deqing. Moreover, the approximate, explicit expressions are given between topological variables and stress or displacement constraints. The problem is well solved by using dual programming approach, and the proposed element deletion criterion implements the inversion of topology variables from the discrete to the continuous. Numerical examples verify the validity of proposed method.
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  • 15
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    Journal of intelligent manufacturing 10 (1999), S. 323-329 
    ISSN: 1572-8145
    Keywords: Computer-aided design ; rapid prototyping ; modeling ; simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The direct slicing of CAD models created in CADDS V to generate geometric data for rapid prototyping using fused feposition modeling technique (FDM) is presented in this paper. The report file from an explicit model is accessed for obtaining model data. Algorithms have been developed for determining the volumes of model material as well as support materials. New algorithms have been developed for filling the sheet solid. A simulation module has been developed to verify whether the filling is correctly done. Example of a model is manufactured using this approach is also presented in this paper.
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  • 16
    ISSN: 1572-896X
    Keywords: particle population ; fluid mechanics ; flame synthesized aerosols ; CFD ; modeling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics , Technology
    Notes: Abstract The interaction of fluid mechanics and particle dynamics at the very early stages of flame synthesis largely affects the characteristics of the product powder. Detailed simulations provide a better understanding of these processes, which take place in a few milliseconds, and offer the possibility to influence the product characteristics by intelligent selection of the process parameters. The present paper reports on the simulation of titania powder formation by TiCl4 oxidation in an aerosol flow reactor. A commercially available fluid mechanics code is used for the detailed calculation of the fluid flow and the chemical reaction at non-isothermal conditions. This code is then interfaced with a model for aggregate particle dynamics neglecting the spread of the particle size distribution. The simulation shows the onset of the particle formation in the reactor and calculates the dynamic evolution of the aggregate particle size, number of primary particles per aggregate and the specific surface area throughout the reactor. The presented, newly developed calculation technique allows for the first time the simulation of particle formation processes under the authentic, complex conditions as found in actual aerosol reactors.
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  • 17
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    Plasma chemistry and plasma processing 19 (1999), S. 341-362 
    ISSN: 1572-8986
    Keywords: Thermal rf plasma ; modeling ; spectroscopy ; plasma flash evaporation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract The evaporation process of zirconia powders injected in a thermal rf plasma is investigated. Both model calculations and optical emission spectroscopy are used to study the evaporation behavior. Gas temperatures and velocity distributions are determined numerically from conservation laws and Maxwell equations. The influence of plasma and particle parameters on the thermal history of entrained particles is discussed. Asymmetric Abel inversion is applied to detect asymmetric emission profiles in the plasma source. Spectroscopic measurements reveal that evaporated zirconium is concentrated near the axis of the plasma. Numerical calculations show that line-integrated emission profiles can be used to distinguish the cases of complete and incomplete evaporation. Axial emission profiles confirm that the evaporation zone is shifted upstream of the plasma when smaller precursor particles are used.
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  • 18
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    Plasma chemistry and plasma processing 19 (1999), S. 467-486 
    ISSN: 1572-8986
    Keywords: He-plasma ; excitation spectra ; modeling ; comparison with experiments
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract A collisional-radiative model was used to study the kinetics of an atmospheric pressure helium discharge. The electron kinetics was obtained from a two-term solution of the Boltzmann equation with electron–electron collisions included. The distribution of the helium electronic excited states was compared to measured values and used to calculate excitation temperatures. The results show that a unique value of the excitation temperature cannot be used to characterize the whole electronic states distribution, because the plasma is not in local thermodynamical equilibrium under the conditions considered. Other calculated discharge parameters, such as the electron temperature, the maintenance electric field, the density of metastable atoms in the 2 3 S state, and the ion densities are presented and compared to experimental data when available.
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  • 19
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    Plasma chemistry and plasma processing 19 (1999), S. 445-466 
    ISSN: 1572-8986
    Keywords: Dielectric barrier discharge ; CARS on N2 and NO ; NO reduction ; chemical and vibrational kinetics ; modeling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract Dielectric barrier discharges (DBD) with planar- and knife-shaped electrodes are operated in N2O2NO mixtures under a pressure of 20 and 98 kPa. They are excited by means of consecutive unipolar or bipolar high-voltage pulse packages of 10 kV at a pulse repetition rate of 1 and 2 kHz. The rotational and vibrational excitation of N 2 molecules and the reduction of nitric oxide (NO) in the discharge have been investigated using coherent anti-Stokes Raman scattering (CARS) technique. Rotational (gas) temperatures near the room temperature and vibrational temperatures of about 800 K at atmospheric pressure and 1400 K at a pressure of 20 kPa are observed. Therefore, chemical reactions of NO with vibrationally excited N 2 are probably insignificant. One-dimensional kinetic models are developed that balance 35 chemical reactions between 10 species and deliver equations for the population density of excited vibrational levels of N 2 together with a solution of the Boltzmann equation for the electrons. A good agreement between measured vibrational temperatures of N 2 , the concentration of NO, and calculated data is achieved. Modeling of the plasma discharge verifies that a DBD operated with a N2NO mixture reduces the NO content, the simultaneous presence of O 2 , already 1%, is enough to prevent the NO reduction.
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  • 20
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    Applied composite materials 6 (1999), S. 99-119 
    ISSN: 1573-4897
    Keywords: damage ; modeling ; fiber composites ; crack-density ; strain energy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A new model for the damage factor in terms of strain energy densities is derived and proposed. The damage factor values can be predicted directly from the stress–strain data using the aforementioned model. Moreover, an expression of crack density ratios in terms of total strain energy densities is inferred. Their validity has been shown by comparing their results with the limited experimental data. The proposed model compares well with the model and the experimental data of Voyiadjis performed on metal-matrix laminates. A new technique, used to predict reasonably the values of crack density ratios at any fiber orientation angle using measured data in the principal material directions, is also developed. Due to difficulties encountered in the evaluation of amount of damage in composite materials up to failure, especially, when using experimental techniques, it was shown that the proposed method for finding the damage factor and crack-density ratios is sufficient and gives reasonable predictions.
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  • 21
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    Journal of science education and technology 8 (1999), S. 3-19 
    ISSN: 1573-1839
    Keywords: levels ; complexity ; simulation ; modeling ; science education ; mathematics education ; dynamic systems ; systems thinking
    Source: Springer Online Journal Archives 1860-2000
    Topics: Natural Sciences in General , Technology
    Notes: Abstract The concept of emergent "levels" (i.e., levels that arise from interactions of objects at lower levels) is fundamental to scientific theory. In this paper, we argue for an expanded role for this concept of levels in science education. We show confusion of levels (and "slippage" between levels) as the source of many of people's deep misunderstandings about patterns and phenomena in the world. These misunderstandings are evidenced not only in students' difficulties in the formal study of science but also in their misconceptions about experiences in their everyday lives. The StarLogo modeling language is designed as a medium for students to build models of multi-leveled phenomena and through these constructions explore the concept of levels. We describe several case studies of students working in StarLogo. The cases illustrate students' difficulties with the concept of levels, and how they can begin to develop richer understandings.
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  • 22
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    Transport in porous media 35 (1999), S. 49-65 
    ISSN: 1573-1634
    Keywords: modeling ; biodegradation ; microbial transport ; dual-porosity ; kinetics.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract A mathematical model describing microbial transport and growth in a heterogeneous aquifer domain, composed of overlapping subdomains of high-permeability and low-permeability materials, is developed. Each material is conceptually visualized as a continuum which occupies the entire considered spatial aquifer domain. Based on the assumption that advection in the low-permeability domain is negligible, the mathematical model is solved by using a publically available reactive transport code. The importance of modeling microbial transport and growth in such a dual-porosity system is demonstrated through a hypothetical case study.
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  • 23
    ISSN: 1573-2711
    Keywords: scanning force microscope ; lateral force microscope ; force modulation ; normal and lateral modulation ; elasticity ; friction ; contact stiffness ; Young modulus ; shear modulus ; modeling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Results and an analysis are presented on elastic and friction imaging by indirect force modulation with a scanning force microscope. Two techniques are compared, normal modulation (Z-modulation, perpendicular to the surface of the sample) and lateral modulation of the contact (X-modulation in the plane of the sample, perpendicular to the axis of the cantilever). Theoretical and experimental results show that lateral modulation offers great advantages compared to normal modulation: the images are free of artifacts and can be easily quantified.
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  • 24
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    Autonomous robots 6 (1999), S. 89-103 
    ISSN: 1573-7527
    Keywords: virtual reality ; modeling ; man-machine interaction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract In order to avoid the complex calculation and poor robustness in automatic visual modeling process, a man-machine interaction based stereo vision system is developed for modeling an unknown environment. The operator's knowledge about a scene is used as a guidance for modeling 3D environment. The modeling technique has advantage in terms of reliability and robustness over other automatic modeling approaches. The data points needed for modeling an objects are obtained through the intersection of lines, or calculation from equations of curve, derived via fitting from human guided edge detection. The modeling accuracy is ensured by using image feature extraction. A multi-viewpoint modeling approach has been developed in order to deal with occlusion problems. Both accuracy and speed issues are addressed in this paper. The system implementation and some 3D measurements on real scene have been performed using cameras lenses of 16 mm and 8 mm with an accuracy 0.5 mm and 0.8 mm over the field of view, respectively. The virtual environment rendering based on the modeling data of real scenes with known model of mobile robot is given at the end of this paper.
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    Plasma chemistry and plasma processing 18 (1998), S. 73-89 
    ISSN: 1572-8986
    Keywords: Thermal plasma ; CVD ; modeling ; liquid precursor ; diamond
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract In this paper, a comprehensive model for thermal plasma chemical vapor deposition (TPCVD) with liquid feedstock injection is documented. The gas flow is assumed to be steady, of a single temperature. Radiation and charged species contributions are excluded, but extensive homogeneous and heterogeneous chemistry is included. The liquid phase is traced by considering individual droplets. Discussion on the model's application to diamond production from acetone in a hydrogen–argon plasma is included. The major conclusions are: (1) Liquid injection possesses a capability to deliver the hydrocarbon precursor directly onto the deposition target. (2) For the case of complete evaporation of the droplet before reaching the substrate, the deposition rate is similar to that obtained with gaseous precursors. (3) The computational results compare well with experimental data. The modeling results can be used to optimize the injection parameters with regard to the deposition rate.
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    Plasma chemistry and plasma processing 18 (1998), S. 189-214 
    ISSN: 1572-8986
    Keywords: Remote PECVD ; silicon dioxide ; modeling ; deposition rate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract Plasma-enhanced chemical vapor deposition has become one of the most important thin film deposition technologies. To avoid direct plasma exposure the substrates may be placed in the remote region. A carrier gas conveys the plasma energy to the deposition area where the reactions with the monomer molecules take place. For the engineering of such a process the modeling of the achievable deposition rate is of great interest. Among different possibilities semiempirical models provide a fast and easily utilizable tool without intensive computer simulations or the necessity of detailed knowledge about the chemistry involved. From deposition experiments with oxygen and an organosilicon monomer (hexamethyldisiloxane, HMDSO) the remote composite parameter is suggested. It combines microwave power, monomer and carrier gas flow rate, and the distance of the substrate from the plasma source. This parameter was derived from the ratio between atomic oxygen and monomer flow rate. In the parameter range considered the deposition rate is described as well ordered and the energy- and monomer-deficient regions are clearly separated.
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    Plasma chemistry and plasma processing 18 (1998), S. 285-303 
    ISSN: 1572-8986
    Keywords: Fullerenes ; carbon arc ; plasma process ; modeling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract A mathematical model of the carbon arc process for the synthesis of fullerenes (C 60 , C 70 ) is developed. The two-dimensional model solves for the velocities, temperature, and total concentration of carbon species. The net emission coefficient method is used for the radiation term. The carbon species conservation equations consider the evaporation of carbon from the anode, cathode surface deposition, and carbon condensation. The thermodynamic and transport properties are calculated as a function of temperature and carbon mass fraction, using the method of Chapman–Enskog. Erosion rates used by the model are determined experimentally. Calculated fields of the velocities, temperatures, carbon mass fraction and current intensity are presented. Comparison is made of the behavior of the arc at 1 and 4 mm interelectrode gaps, and between operation in argon and in helium. The results of simulations provide a justification for the higher yields observed in helium compared to the argon case.
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    Plasma chemistry and plasma processing 18 (1998), S. 325-362 
    ISSN: 1572-8986
    Keywords: Microwave plasma ; diamond deposition ; modeling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract One-dimensional transport models of moderate-pressure H 2 and H 2 /CH 4 plasmas obtained in a diamond deposition microwave reactor are presented. These models describe the plasma as a thermochemically nonequilibrium flow with three different energy modes. The solution of the one-dimensional plasma transport equations enabled the estimation of plasma species concentrations and temperatures on the axis of the reactor. As far as pure H 2 plasmas are concerned, results showed that the model predictions of gas and vibration temperatures are in good agreement with experimental measurements. The model also yields a relatively good qualitative prediction of the variations of H-atom mole fraction with the power density absorbed by the plasma. The results obtained for H 2 /CH 4 discharges showed that the model prediction on the variations of H-atom mole fraction with methane percentage in the discharge is in good qualitative agreement with experimental results. They also showed that methane is rapidly converted to acetylene before reaching the discharge zone. The concentrations of neutral hydrocarbon species in the reactor are mainly governed by thermal chemistry. The addition of methane strongly affects the ionization kinetics of the plasma. Three major ions are generally obtained in H 2 /CH 4 plasmas: C 2 H 2 + , C 2 H 3 + , and C 2 H 5 + . The relative predominance of these ions depends on the considered plasma region and on the discharge conditions. The ionic species concentrations are also mainly governed by chemistry, except very near the substrate surface. Finally the use of this transport model along with the surface chemistry model of Goodwin (1) enabled us to estimate the diamond growth rate for several discharge conditions.
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    Plasma chemistry and plasma processing 18 (1998), S. 429-446 
    ISSN: 1572-8986
    Keywords: Pulsed microwave discharge ; plasma ignition ; Ar/CF4 mixture ; plasma processing ; etching ; chemical kinetics ; modeling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract The present work deals with a pulsed microwave discharge in an Ar/CF 4 gas mixture under a low pressure (1–10 mbar). The discharge chamber developed has a cylindrical geometry with a coupling window alternatively made of quartz or alumina. The setup allows one to investigate the plasma–wall interactions (here etching of the quartz window) and the ignition process of the pulsed microwave plasma. Microwave pulses with a duration of 50–200 μs and repetition rate between 1 and 10 kHz are typical for the experiments. The space-time behavior of the fluorine number density in the discharge has been investigated experimentally by optical actinometry. The discharge kinetics is modeled using electron-transport parameters and rate coefficients derived from solutions of the Boltzmann equation. Together with the solution of the continuity and electron balance equations and the rate equations describing the production of CF x (x=2, 3, 4) radicals and F atoms, a good agreement between experimental and theoretical data can be achieved.
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    ISSN: 1573-4897
    Keywords: metal matrix composites ; ceramic matrix composites ; short fibres ; fracture behaviour ; powder metallurgy ; modeling ; multi-scale model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract An experimental study of the fracture behaviour of metal- and ceramic-based composites containing randomly oriented short fibres, related to fabrication parameters of those composites produced by a powder metallurgy method, yields a suggestion to describe the failure of such composites with a multi-scale model. A most important feature of the failure behaviour is an occurrence of the maximum strength of a composite at rather low values of the fibre volume fraction. A multi-scale model is built of a non-homogeneous body which accounts for changes in the structure of the body during its formation and fracture. Despite the simplicity of the model it supplies an adequate description of the macroscopic behaviour of composites. In particular, the non-monotonic relationships between the composite strength and the fabrication parameters can be understood, and therefore the possibility to optimize a composite fabrication process becomes visible. The micro-level of the model is related to the fibre/matrix interactions in a composite. The meso-level of the model describes both formation of a structure on the many-fibres agglomerate scale when obtaining a composite body and its fracture on loading of the body.
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    ISSN: 1573-7527
    Keywords: autonomous robots ; agent architectures ; action selection and planning ; diagnosis ; integration and coordination of multiple activities ; fault protection ; operations ; real-time systems ; modeling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract This paper describes the New Millennium Remote Agent (NMRA) architecture for autonomous spacecraft control systems. The architecture supports challenging requirements of the autonomous spacecraft domain not usually addressed in mobile robot architectures, including highly reliable autonomous operations over extended time periods in the presence of tight resource constraints, hard deadlines, limited observability, and concurrent activity. A hybrid architecture, NMRA integrates traditional real-time monitoring and control with heterogeneous components for constraint-based planning and scheduling, robust multi-threaded execution, and model-based diagnosis and reconfiguration. Novel features of this integrated architecture include support for robust closed-loop generation and execution of concurrent temporal plans and a hybrid procedural/deductive executive. We implemented a prototype autonomous spacecraft agent within the architecture and successfully demonstrated the prototype in the context of a challenging autonomous mission scenario on a simulated spacecraft. As a result of this success, the integrated architecture has been selected to fly as an autonomy experiment on Deep Space One (DS-1), the first flight of NASA';s New Millennium Program (NMP), which will launch in 1998. It will be the first AI system to autonomously control an actual spacecraft.
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    Journal of engineering mathematics 34 (1998), S. 277-300 
    ISSN: 1573-2703
    Keywords: modeling ; supercell storm ; nonlinear ; inertial oscillation ; mesonetwork data.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Technology
    Notes: Abstract The pulsing inertial oscillation (PIO) model is a nonlinear, time-dependent, translating vortex solution of the inviscid, compressible fluid dynamic equations in the middle troposphere. The translation of this vortex during a pulse is strikingly similar to that of a supercell storm – a rotating thunderstorm that can generate tornadoes and hail. Two studies were performed to test the hypothesis that some supercell storms are manifestations of a PIO pulse. The first study applied the model to an intense interior draft whose buoyancy was bounded by a temperature excess of ± 12 K. The peak updraft speed achieved was 41·5 m s−1 and the peak Rossby number was 92·9. The study also pointed to an advanced concept for attaining higher values. The second study applied the PIO model to a supercell storm as a whole and succeeded in replicating its bulk properties, such as mesocylonic circulation, net mass and moisture influxes, and time track. This study also identified a critical feature of the PIO model that could be tested against storm data: The average vertical draft is downward before the turn in the storm track and upward afterwards. In the conventional theory, the average vertical draft is upward from storm inception until dissipation. These differing draft predictions were compared with the best available data, which are surface mesonetwork data. These data were found to support the PIO model. However, surface data alone are not conclusive, and further measurements are warranted.
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    Materialwissenschaft und Werkstofftechnik 29 (1998) 
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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    Materialwissenschaft und Werkstofftechnik 29 (1998), S. 153-153 
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
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    Materialwissenschaft und Werkstofftechnik 29 (1998), S. A21 
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
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    Materialwissenschaft und Werkstofftechnik 29 (1998), S. 51-56 
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Application of Wear Resistant PACVD-Coatings in Aluminium Diecasting under Economical and Ecological AspectsAluminium pressure diecasting is a frequently applied manufacturing process for the near netshape production of precision parts. State of the art production techniques still demand considerable amounts of die lubricants. But the side effects of these lubricants include a decrease in surface quality of the cast part as well as a prolongation of the casting cycle time. The job quality decreases and the waste and exhaust disposal during production and application of lubricants is ecologically risky. In this study different wear resistant coating systems have been developed in order to minimize the use of die lubricants in the casting process while at the same time increasing the service life of the diecasting tools.Nitrides, carbides and borides of titanium were synthesized by means of DC-pulse-PACVD. The influence of the process parameters gas composition, pressure, voltage and pulse/pulse repetition ratio was investigated. Compositional analysis was performed by analytical methods such as XRD, EDS, WDS and SIMS. Hardness, adhesion and friction behaviour of the layers were determined in order to describe their mechanical properties. The wetting angle was determined and the corrosion resistance was evaluated in dip tests in aluminium melt. A selection of the best coatings was then compared in diecasting praxis tests under tightened-up conditions reducing the amount of lubricants.TiN, Ti(B,N), TiC and multilayers of the system Ti-C-N were deposited exhibiting a wide range of stoichiometry. The coatings reached hardness values of up to 4400 HK0.005 and the friction coefficient μ was in the range of 0.3. In the diecasting praxis test the amount of die lubricant could be reduced by 97%. Under most severe conditions all layer types led to a minimum increase in the lifetime of the tool of factor 60 compared to an untreated dummy. A strong dependence on the layer type and on its stoichiometry could be observed. Ti(B,N) as the most successful coating in this study has not yet shown any sign of failure and already achieved an increase in lifetime of 300 times.
    Notes: Der heutige Stand der Technik in Aluminiumdruckguß erfordert den Einsatz von Formtrennmitteln. Zu deren Nebenwirkungen gehört aber eine Verschlechterung der Oberflächenqualität des Gußteils. Formtrennmittel beeinträchtigen die Arbeitsplatzqualität und sind unter ökologischen Gesichtspunkten als bedenklich zu betrachten. Um den Einsatz von Trennmitteln zu vermeiden und gleichzeitig die Standzeit der Druckgußwerkzeuge zu erhöhen, wurden nitridische, karbidische und boridische Schichten auf Titanbasis mittels DC-Plus-PACVD abgeschieden und im Hinblick auf ihren Einsatz im Aluminiumdruckguß optimiert. Durch die Beschichtung konnte bei gleichzeitiger Steigerung der Qualität der abgegossenen Teile die notwendige Trennmittelmenge um 97% reduziert werden. Die Standzeit der beschichteten Druckgußkerne im Vergleich zu unbeschichteten erhöhte sich durch die Beschichtung um über das 300-fache.
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    Materialwissenschaft und Werkstofftechnik 29 (1998), S. 77-79 
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Über die Sinterung mit festen EinlagerungenDas Sintern von porösen Matrixwerkstoffen mit steifen, im speziellen nicht verdichtenden Einlagerungsphasen wird mit Hilfe des sphärischen Verbundwerkstoff-Modells von Scherer diskutiert. Ein neuer Zusammenhang zur Berechnung der Verdichtungsdichte des Verbundwerkstoffs unter Berücksichtigung der durch die nicht-verdichtenden Einlagerungen hervorgerufenen Eigenspannungen, wird vorgeschlagen. Drei Komponenten der Dehnungsrate werden betrachtet: (i) die freie, von den vorhandenen Spannungen unabhängige Verdichtungs-Dehnungsrate, (ii) die sich aus den mikroskopischen Spannungseffekten bei den Sintermechanismen ergebende Dehnungsrate und (iii) die aus der Spannung resultierende makroskopische Dehnungsrate. Die Ergebnisse deuten darauf hin, dass bei steifen Einlagerungen höhere innere Spannungen entstehen, als mit dem originalen Modell von Scherer berechnet.
    Notes: The sintering of porous matrices containing rigid, i.e. non-densifying, inclusions is discussed on the basis of the composite sphere model of Scherer. Recognizing that internal stresses are generated by the presence of the non-densifying inclusions, a new equation for the densification rate of the composite is proposed. It takes into account three contributions: (i) the free densification strain rate, which is independent of the stresses present, (ii) the strain rate due to the microscopic effect of the stresses on the sintering mechanism and (iii) the macroscopic deformation strain rate induced by the stresses. This result indicates that the presence of rigid inclusions may generate higher internal stresses in the densify ing compact than those calculated by the original Scherer's approach.
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    Materialwissenschaft und Werkstofftechnik 29 (1998), S. A38 
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
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    Materialwissenschaft und Werkstofftechnik 29 (1998), S. 97-130 
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Valve Materials for Combustion EnginesAn overview is being given on production numbers, requirements and properties of valve materials. Their development from the beginning till today's state of the art is reviewed with a focus on Chromium-Manganese-Nitrogen-alloys. Valve materials are grouped by the criteria of density - heavy, lightweight - and alloying elements. The multiple stresses of the material in the valve are being met with a few standardised grades and specific ways of manufacture. The path of the material from bar stock to the finished valve is being followed. Engine development in the past decades increased the load on the valves which could be met by continuously developing their structural strength. Also the strength of all valve materials could be raised to nominal strength above 1100 Mpa by applying specific methods. Higher strength at the surface is being effectuated by work hardening effects. The technology to increase reliability of hollow valves and new aspects of valve seat facing including residual stress is explicitly discussed. General aspects of alloy utilisation is followed by a discussion of lightweight valve materials as Titanium alloys, intermetallic Titaniumaluminide alloys and ceramic materials, spec. Silicon Nitride, which all have a potential as forthcoming valve materials capable of reducing fuel consumption of the engines.
    Notes: Nach einem Überblick über Produktionszahlen, allgemeine Anforderungen und Eigenschaften von Ventilen für Verbrennungsmotoren, wird in einem Rückblick die Werkstoffentwicklung für die Ventilstähle von den ersten Anfängen bis zum heutigen Stand aufgezeigt. Schwerpunktmäßig wird die Gruppe der Chrom-Mangan-Stickstoff-Stähle behandelt. Daneben werden die Ventilwerkstoffe geordnet nach schweren und leichten und innerhalb dieser Gruppen nach Legierungsmerkmalen beschrieben. Es wird über die vielfältigen Werkstoffanstrengungen am Ventil informiert, die mit wenigen genormten Werkstoffgüten und speziellen Fertigungsverfahren problemlos mit niedrigsten Fehlerraten beherrscht werden. Der Weg des Werkstoffes vom Halbzeug bis zum fertigen Ventil wird in allen Schritten verfolgt. Die in den letzten Dekaden forcierte Motorenentwicklung führte zu verschärften Betriebsbedingungen auch für die Ventile, die mit einer kontinuierlichen Weiterentwicklung bestehender Werkstoffgüten und Verbesserungen der Gestaltsfestigkeit der Ventile aufgefangen wurden. In diesem Zusammenhang werden spezielle Lösungen zur Festigkeitssteigerung aller Ventilwerkstoffe bis in den Bereich von über 1100 MPa erläutert, die nach bekannten metallkundlichen Gesetzen ermöglicht wurden. Als wesentliches Prinzip werden ortsabhängig, besonders an der Oberfläche, erhöhte Festigkeits- und Verschleißeigenschaften zur Optimierung der Gestalts- und Betriebsfestigkeit eingesetzt. Über Entwicklungen zur Technologie der Hohlventile und von erweiterten Lösungen beim Auftragschweißen von Ventilsitzen im Zusammenhang mit Eigenspannungen wird ausführlich berichtet. Einer kurzen allgemeinen Betrachtung zum Legierungsaufwand der wichtigsten Ventilwerkstoffe folgt ein Kapitel über Titan, Intermetallische Verbindungen und Keramik, die möglicherweise als zukünftige leichte Ventilwerkstoffe Verwendung finden können.
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    Materialwissenschaft und Werkstofftechnik 29 (1998), S. 141-152 
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Hartstoffschichten auf Leichtmetall-Komponenten unter mechanischer OberflächenbeanspruchungIn der vorliegenden Studie wurde das Verhalten von hartstoffbeschichteten Leichtmetallkomponenten unter mechanischer Oberflächenbeanspruchung untersucht. Hierzu wurden drei Leichtmetallegierungen (Ti-6Al-4V, A1Si7Mg und AlMgSi0.5) sowie 100Cr6 - Stahl (als Vergleichsmaterial) mit zwei unterschiedlichen PVD-Verfahren beschichtet: radio frequency magnetron sputtering und electron beam evaporation. Als Schichtmaterialien wurden CrN und TiN verwendet. Um die verschiedenen Substrat/Schicht-Kombinationen hinsichtlich ihres Belastungsvermögens zu beurteilen, wurden Standard-Testmethoden angewendet, die jeweils eine andere Lastsituation simulieren: der Härtetest (der eine statische Normalkraft aufbringt), der Ritztest (der eine statische Normalkraft mit einer statischen Tangentialkraft überlagert) und der Impacttest (der eine dynamische Normalkraft aufbringt).Es wurde beobachtet, daß das Belastungsvermögen beschichteter Materialien von der vorherrschenden Lastsituation abhängt. Die beschichteten Aluminiumlegierungen wiesen unter allen getesteten Lastsituationen ein geringes Belastungsvermögen auf. Allerdings zeigten sie eine höhere Oberflächenhärte als unbeschichteter Stahl. Beschichtetes Ti-6Al-4V wies ein hohes Belastungsvermögen auf, vergleichbar mit beschichtetem Stahl. Bei sämtlichen beschichteten Leichtmetallsubstraten war eine signifikante Verbesserung des Belastungsvermögens mit zunehmender Schichtdicke zu erkennen.An den Ergebnissen des Ritztests, welcher weitverbreitet zur Untersuchung der Haftung dünner Schichten eingesetzt wird, war auf den Aluminiumsubstraten ein sofortiger Durchbruch des Prüfdiamanten durch die Schichten zu beobachten. Es traten keinerlei Abplatzungen auf. Aufgrund dieses Verhaltens erscheint der Ritztest nicht geeignet, um die Schichthaftung auf Leichtmetallsubstraten zu untersuchen. Im Gegensatz dazu wies das Schadensbild des Impacttests auch auf den Aluminiumsubstraten Schichtabplatzungen auf, was auf dessen Eignung zur Beurteilung des Haftungsvermögens dünner Schichten auf sehr weichen Substraten schließen läßt.Die Studie zeigt, daß in bestimmten Anwendungsgebieten eine Substitution des Stahls durch hartstoffbeschichtete Leichtmetallegierungen möglich ist.
    Notes: In this work the behaviour of hard coated light-metal components was investigated when they are mechanically loaded. Three lightmetal alloys, Ti-6Al-4V, AlSi7Mg and AlMgSi0.5 and 100Cr6 steel (as a reference material) were coated by two different physical vapour deposition processes: radio frequency magnetron sputtering and electron beam evaporation. The coating materials utilised were CrN and TiN. Standard test methods with different loading conditions were used to evaluate the substrate/coating-combinations: the hardness test (applying a static normal load), the scratch test (applying a combination of a static normal and a static tangential force) and the impact test (applying a dynamic normal load).It was observed that the load support of coated materials depends on the loading conditions. The coated aluminium alloys showed poor load support under all loading test conditions but produced a higher surface hardness than uncoated steel. Coated Ti-6Al-4V showed very good load support properties, similar to coated steel. All coated light-metal substrates demonstrated significant improvement in load support behaviour with an increase in coating thickness.The results of the scratch test, which is commonly used to asses adhesion properties of thin coatings, showed an immediate indenter-breakthrough on the aluminium alloy substrates, but causing no coating delamination. Due to this behaviour, the scratch test is not suitable to evaluate adhesion properties on coated soft light-metals. Yet the impact test allowed assessment of coating delamination on the aluminium alloys, proving its usefulness for adhesion measurement even on soft substrates.The study indicates that substitution of steel with coated lightmetal alloys is a viable proposition for certain applications.
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    Materialwissenschaft und Werkstofftechnik 29 (1998), S. 154-162 
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: A concept to describe the fatigue lifetime by using statistical methodsIn order to spend time and money, cyclic loading tests have been usually undertaken with a relative small number of specimens. On the other hand, it is well established that fatigue life data, i.e. the cycle number of crack initiation Ni as well as the cycle number of total failure Nf show a scatter for a given load level. Therefore, fatigue live predictions must be undertaken using statistical methods. In this case it has to be taken into account that the quantity Nf consists of two parts, i.e. crack initiation and propagation. The first one has to be calculated in a statistical manner, whereas the second one with deterministic methods. Therefore, a superposition of statistical and deterministic parts has to be taken into account. Up to now it was estimated that in all cases the failure results from the same damage mechanism. In this case a scatter of fatigue life may be described by the Weibull distribution and characterised by the location parameter and the Weibull exponent. By using the correct density function, all fatigue life data Ni can be plotted in a failure probability Pv(Ni) vs. Ni plot. In case of some Al-alloys no linear dependence between Pv and Ni has been found, indicating that more than one type of defect spectrum may initiate the failure. Indeed, in AlMgSi cold worked specimens two types of cracks, e.g. surface as well as corner cracks, have been found that initiate the failure of the specimens. If was possible to correlate each type of crack with an individual Weibull distribution. By using this procedure, fatigue life can be estimated better than before.
    Notes: Zur experimentellen Lebensdauervorhersage an bauteilnahen Proben werden Schwingfestigkeitsuntersuchungen üblicherweise aus Zeit- und Kostengründen mit einer relativ kleinen Anzahl von Proben durchgeführt. Andererseits ist auf einem vorgegebenen Lastniveau grundsätzlich mit einer Streuung der Versuchsergebnisse, d. h. der Anrißlastspielzahl Ni bzw. der Lastspielzahl bis zum Bruch Nf, Zu rechnen. Um Lebensdauervorhersagen auf statistischer Grundlage durchführen zu können, muß beim Merkmalswert Nf in Betracht gezogen werden, daß die Rißausbreitung im Gegensatz zur Rißbildung in vielen Fällen deterministisch bestimmbar ist. Es ist daher abzuschätzen, in wie weit dieser Beitrag die Streuung der Gesamtlebensdauer beeinflußt. Desweiteren wurde bislang vorausgesetzt, daß der Versagensmechanismus immer auf dem selben Schädigungstyp beruht. In diesem Fall kann die Lebensdauer z. B. mit einer zweiparametrigen Weibull-Verteilung durch Angabe des Streu-und Lageparameters statistisch beschrieben werden. Bei der Verwendung einer geeigneten Dichtefunktion lassen sich die Schwingspielzahlen über die Ausfallwahrscheinlichkeiten auftragen. Im Fall von Al-Basislegierungen hat sich gezeigt, daß diese Auftragung keinen linearen Zusammenhang mehr aufweist, was dafür sprechen könnte, daß mindestens zwei unterschiedliche Defektsorten die Anrißbildung im Bauteil einleiten. Dies konnte für AlMgSi-Bleche anhand von Bruchflächenanalysen direkt nachgewiesen werden. Dazu wurden Ermüdungsrisse klassiert, die sich entweder an den Probenkanten oder direkt an Kratzern der Walzhaut bildeten. Die zwei Ereignisse ließen sich bei sonst gleichbleibenden Versuchsbedingungen in einzelne Weibull-Verteilungen zerlegen. Damit läßt sich im Fall von bauteilnahen Proben die Lebensdauer für kleine Ausfallwahrscheinlichkeiten genauer abschätzen als dies bislang der Fall ist.
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  • 42
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    Materialwissenschaft und Werkstofftechnik 29 (1998), S. 206-214 
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: The size effect on the fatigue properties of weldmentsConstant amplitude fatigue tests (R = - 1 and 0)have been carried out in order to investigate the influence of specimen size and manufacturing conditions on the high-cycle fatigue behaviour of large welded I-beams (web height 500 mm, total length 12 and 7 m respectively). The specimens contained transverse butt welds and longitudinal fillet welds, mainly produced by manual metal arc welding. The Δs̰-concept, as proposed in international standards for fatigue related design is supported by the test results as far as transverse butt welds or longitudinal fillet welds in large sections are concerned. The HCF-behaviour of butt joints in large sections, welded under site conditions, are reasonably covered by Eurocode 3 category 90. EC 3-Category 100 does not conservatively cover the HCF-behaviour of longitudinal fillet joints in large sections.
    Notes: Der Einfluß von Bauteilgröße und Fertigungsbedingungen auf die Ermüdungsfestigkeit von Stumpfstößen und Längskehlnähten wurde anhand von Einstufen-Wöhlerversuchen (R = - 1 und 0) mit großen geschweißten I-Blechträgern (Stelghöhe 500 mm, Länge 12 m bzw. 7 m) untersucht. Die Mehrzahl der Schweißnähte wurde im Lichtbogenhandschweißverfahren hergestellt. Das Konzept der Mittelspannungsunabhängigkeit der zulässigen Spannungen, das in den neueren Stahlbauvorschriften propagiert wird, wird für die Nahtformen Stumpfstoß und Längsnaht durch die Ergebnisse der Großbauteilversuche gestüzt. Das HCF-Verhalten von unter Baustellenbedingungen geschweißten Stumpfstößen in großen Bauteilen wird durch die Kerbfallklasse 90 im Eurocode 3 hinreichend abgedeckt. Die im Eurocode 3 für Längskehlnähte vorgesehene Kerbfallklasse 100 deckt die Versuchsergebnisse nicht vollständig ab.
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  • 43
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    Materialwissenschaft und Werkstofftechnik 29 (1998), S. A61 
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 44
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    Materialwissenschaft und Werkstofftechnik 29 (1998), S. 424-443 
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Deficiency and Surplus of Electrons, a Possibility to explain the most different Phenomenons of Materials Science?The dream to explain all phenomenons with a few principles is very old. It has been tried to explain the transformation and the process of destruction with the help of binding ratios between the atoms at the example of iron, iron-alloys and iron-compounds. The binding ratios depend on the mode, the motion and the distribution of the atoms of a material, on the temperature, on the pressure and on the surrounding (mode, distribution and state of aggregate of the surrounding atoms and particles, redox-potential, fields…).The system „Material and surrounding“ is characterized by deficiency and surplus of electrons in a disequilibrium (in the material as well as in the surrounding). Regardless whether a system is in equilibrium or in disequilibrium, there is a steady exchange of electrons (and also of other particles) between material and surrounding. The ratio of binding electrons to non-binding electrons should be suitable for the characterization of the binding ratios in the material.An universal material testing system for material testing corresponding to load is suggested with the aim of estimation of endurance.The UMTS should allow a better valuation of materials and constructional elements and also a better material sampling and constructing corresponding to load on the basis of Load-Energy-Occurence-Graphs and data files as well as the guarantee of endurance of constructional elements, machines, cars, aircrafts as well as constructions.
    Notes: Der Traum, alle Erscheinungen mit wenigen Prinzipien erklären zu können, ist schon recht alt.Am Beispiel von Eisen, Eisenlegierungen und Eisenverbindungen wird versucht, die Modifikationswechsel, Umwandlungsvorgänge und den Zerstörungsprozeß mit den Bindungsverhältnissen zwischen den Atomen zu erklären. Die Bindungsverhältnissen hängen von der Art, Bewegung und Verteilung der Atome eines Stoffes, von der Temperatur, vom Druck und von der Umgebung (Art, Verteilung und Aggregatzustand der umgebenden Atome und Teilchen, Red-Ox-Potential, Felder…) ab.Das System „Stoff und Umgebung“ ist im Ungleichgewicht (sowohl im Stoff als auch in der Umgebung) durch Elektronenmangel bzw. -überschuß gekennzeichnet. Unabhängig davon, ob sich ein System im Gleichgewicht oder im Ungleichgewicht befindet, findet ein ständiger Austausch von Elektronen (und mit Sicherheit auch von anderen Teilchen) zwischen Stoff und Umgebung statt. Zur Charakterisierung der Bindungsverhältnisse im Stoff sollte das Verhältnis „Bindungselektronen zu nicht an der Bindung beteiligten Elektronen“ beitragen können.Ein universelles Werkstoffprüfsystem zur beanspruchungsgerechten Werkstoffprüfung mit dem Ziel der Lebensdauerabschätzung wird vorgeschlagen. Das UMTS sollte eine bessere Werkstoff- und Bauteilbewertung, eine verbesserte Werkstoffauswahl und ein beanspruchungsgerechtes Konstruieren auf der Grundlage von Belastungs-Energie-Ereignis-Schaubildern und -Dateien sowie die Übernahme von Lebensdauergarantien für Bauteile, Maschinen, Fahr- und Flugzeuge sowie Konstruktionen ermöglichen.
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    Materialwissenschaft und Werkstofftechnik 29 (1998), S. 48-50 
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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    Materialwissenschaft und Werkstofftechnik 29 (1998), S. 50-50 
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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    Materialwissenschaft und Werkstofftechnik 29 (1998), S. 338-338 
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
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  • 48
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    Materialwissenschaft und Werkstofftechnik 29 (1998), S. 365-370 
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The corrosion inhibition of mild steel by some naturally occuring substance was evaluated in absence and presence of 600 and 1200 mg H2S/l in 3% NaCl aqueous solution and pH of 3 and temperature of 25 °C. These naturally occurring substance included the water extracts, coumarines and fatty matters extracts of some Egyptian plants. These plants included:(1) Nigella Sativa (Family Ranunculacease) (Extract (1), 2) Coriandrum Sativum (Family Umbelliferea) (Extract II), 3) Ricinus communis (Family Euphorbiaceae) (Extract III). The galvanostatic anodic and cathodic polarization measurements were used for studying the corrosion behavior of mild steel and evaluation of the percentage inhibition of the undertesting extracts of these three plants and also preparation of fatty matters and coumarin fractions were mentioned.
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  • 49
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    Materialwissenschaft und Werkstofftechnik 29 (1998), S. 397-411 
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Mechanische und Physikalische Eigenschaften von Vermiculargraphit - Gußeisen GGV
    Notes: The mechanical and physical properties of compacted graphite iron (CGI) have been studied. While it is known that CGI provides at least 70% higher tensile strength, 35% higher elastic modulus and 80% higher fatigue limits than conventional grey cast iron, the objective of this paper was to determine how the properties change with varying nodularity (graphite shape) and pearlite content. Tensile properties, hardness, damping capacity and thermal conductivity were determined over the range 0-90% nodularity and 25-100% pearlite. Compressive properties, wear resistance and fatigue behaviour of CGI are also reported upon. Of greatest importance is the influence of patches of flake graphite in predominantly CGI microstructures. As soon as flake patches appear, which can occur with a loss of as little as 0.001% active magnesium, the mechanical properties of CGI abruptly decrease by 25-40%. Proper foundry control technology and quality procedures are therefore required to ensure the reliable production of this improved material.
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    Materialwissenschaft und Werkstofftechnik 29 (1998), S. A1 
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 51
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    Materialwissenschaft und Werkstofftechnik 29 (1998), S. 1-8 
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Protective coating systems for fasteners in contact with light weight metalsA review of the recent use of fasteners for light weight alloys in automotive car production is given. Mechanical design, materials selection and protective coating concepts for Magnesium- and Aluminum-alloys are presented. The specific problems caused by galvanic corrosion are discussed by the use of electrochemical data of the protective coating systems on fasteners for joining Magnesium. Experience from outdoor exposure in automotive applications up to date are considered.
    Notes: Es wird ein Überblick über die derzeit im Kraftfahrzeugbau verwendeten Verschraubungselemente für Leichtmetallegierungen gegeben. Dabei werden konstruktive Auslegungen, Werkstoffauswahl und Beschichtungskonzepte für Magnesium- und Aluminiumlegierungen vorgestellt. Die spezielle Problematik der Kontaktkorrosion wird anhand elektrochemischer Messungen f ür verschiedene Beschichtungssysteme im Verbau mit Magnesium diskutiert. Bisherige Felderfahrungen im Automobilbereich fließen jeweils in die Betrachtungen mit ein.
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  • 52
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    Materialwissenschaft und Werkstofftechnik 29 (1998), S. 16-22 
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Activation energy of repeated carbide precipitation processes in steelsDispersion microstructures in steels can be formed from the martensitic condition by repeated precipitation and coarsening of M3C (or M6C) particles. The precipitation stage comprehends the nucleation and the growth of one particle generation according to r ∝ t1/2 (r - particle radius, t - time), and already after some minutes it turns into the dominating coarsening according to r ∝ t1/3 (OSTWALD-ripening). The coarsening of the first precipitated particle generation is superposed with the following precipitation of further generations. They can be proved by the coercive field strength, the yield strength, microstructural mean values from scanning electron micrographs and by hardness tests. The occurring maxima of precipitation allow the evaluation of the activation energy for the effective volume diffusion in the α - Fe phase. By including the electronegativity (after L. Pauling ) the covalent bond in the M3C phase is considered. With that is possible to attach the estimated activation energy to the main alloying (and diffusing) element and also to the total composition of the steel.
    Notes: Dispersionsgefüge in Stählen werden aus dem martensitischen Zustand durch wiederholte Ausscheidung und Vergröberung von M3C-Partikeln (oder M6C) gebildet. Das Ausscheidungsstadium umfaßt gemäß r ∝ t1/2 (r - Partikelradius, t - Zeit) die Keimbildung und das Wachstum einer Partikelgeneration und geht schon nach wenigen Minuten in die dominierende Vergröberung gemäß der OSTWALD-Reifung r ∝ t1/3 über. Die Vergröberung zuerst ausgeschiedener Partikelgenerationen überlagert sich mit der nachfolgenden Ausscheidung und Vergröberung weiterer Partikelgenerationen. Sie können mit Hilfe der Koerzitivfeldstärke, der unteren Streckgrenze, mit Gefügemittelwertsdaten rasterelektronenmikroskopischer Abbildungen des Dispersionsgefüges und durch Kleinlasthärteprüfungen nachgewiesen werden. Die auftretenden Ausscheidungsmaxima gestatten die Abschätzung der Aktivierungsenergie für die effektive Volumendiffusion in der α - Fe - Phase. Durch Einbeziehung der Elektronegativitätswerte (hier nach L. PAULING) wird die vorliegende kovalente Bindung der M3C-Partikel berücksichtigt. Durch sie ergibt sich eine Zuordnung der abgeschätzten Aktivierungsenergie zu dem Hauptlegierungselement und darüber hinaus zur Gesamtzusammensetzung eines Stahles.
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    Materialwissenschaft und Werkstofftechnik 29 (1998), S. A24 
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 54
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    Materialwissenschaft und Werkstofftechnik 29 (1998), S. 57-65 
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: With TiN particles lasermodified Al2O3 ceramic under oscillating sliding contact at different humidities and temperaturesA slightly porous, commercially available alumina ceramic was surface modified up to 170 μm thickness by adding TiN particles. The multiphase surface structure of this laser treated ceramic consisted of about 12 vol.% TiN, 16 vol.% grain boundary phase and 72 vol.% Al2O3. Tribological tests on the modified ceramic and for reference also on a highly dense alumina and titania were carried out in oscillating sliding contact against Al2O3 balls. In these tests, the temperature of the specimens was varied between 28°C and 500°C. At room temperature the relative humidity of the surrounding air was changed between 3% and 70% and additional tests were run by using distilled water as interfacial medium. The resulting multiphase microstructure showed substantially reduced friction and wear at different temperatures and also above relative humidities of about 35% at room temperature compared with the highly dense, commercially available alumina.
    Notes: Über einen zweistufigen Laserprozeß wurde eine handelsübliche Al2O3-Keramik in einer Randschicht von 170 μm Dicke durch Einlagerung von TiN-Partikeln modifiziert. Das entstandene mehrphasige Gefüge setzte sich aus ca 12 Vol.-% TiN, 16 Vol.-% Korngrenzenphase und 72 Vol.-% Aluminiumoxid zusammen. Die tribologische Charakterisierung erfolgte im reversierenden, ungeschmierten Gleitkontakt gegen Al2O3-Gegenkörper. Variiert wurde die Versuchstemperatur zwischen 28°C und 500°C und die relative Luftfeuchte bei Raumtemperatur zwischen 3% und 70%. Zusätzlich wurden Versuche in destilliertem Wasser unter Mischreibung durchgeführt. Als Referenzmaterialien wurden je eine handelsübliche, dichte Al2O3-und TiO2-Keramik mit in die Untersuchungen einbezogen.Die durch Oberflächenmodifizierung entstandenen, mehrphasigen Gefüge zeigten in verschiedenen Temperaturbereichen deutlich reduzierte Reibungszahlen und Verschleißbeträge im Vergleich mit der hochdichten, monolithischen Al2O3-Referenzkeramik. Aus den Untersuchungen zum Einfluß der relativen Luftfeuchte (rF) folgte, daß sich die mit TiN-Partikeln modifizierte Al2O3-Keramik oberhalb von 35 % rF durch niedrigere und von der Feuchte unabhängige Reibungszahlen und Verschleißbeträge auszeichnete.
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    Materialwissenschaft und Werkstofftechnik 29 (1998), S. 594-594 
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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    Materialwissenschaft und Werkstofftechnik 29 (1998), S. 605-608 
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Das Grenzflächenverhalten eines mit Stahlkörnern verfestigten Kupfer-Basis-VerbundwerkstoffesEs wird ein neuer, mit Körnern verstärkter, Guß-Verbundwerkstoff vorgestellt. Zur Verstärkung [VZE]dienen grobe Stahlkörner mit einem Durchmesser von 0.6 bis 1 mm in einer Matrix aus Zinnbronze. Der Verschleißwiderstand dieses Verbundwerkstoffes ist zehnmal besser als der der Matrix, die Zugfestigkeit erreicht einen dreifach höheren Wert. In der vorliegenden Veröffentlichung wird schwerpunktmäßig das Grenzflächenverhalten zwischen den Körnern und der Matrix beschrieben. Als Ergebnis wird die Bildung der Grenzfläche durch Diffusion von Eisen und Kupfer, die zu einer Verfestigung führt, beschrieben.
    Notes: A new type of grain reinforcing cast composite is introduced. The reinforcing component is the coarse steel grain (0.6∼1.0mmφ) with the matrix of tin bronze. The wearing resistance of this material is 10 times as much as the matrix and regarding the tensile strength, 3 times. In this paper, the interface behaviour between grains and the matrix is emphasised. The results show the formation of an interface layer, caused by the diffusion of Fe and Cu, which strengthens the bonding.
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    Materialwissenschaft und Werkstofftechnik 29 (1998), S. 595-604 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Survival Rate and Reliability of Ceramic Femoral Heads for Total Hip ArthroplastyFemoral heads and sockets made of alumina ceramics are successfully used in total hip replacement. The in vivo fracture rate of Biolox heads is lower than 0.02%. An extremely high load (e. g. accident) can initiate subcritical crack growth causing fracturing.107 retrieved Biolox heads were investigated. When measuring their fracture load no fatigue was detected. This result can be explained by the relation between crack velocity and stress intensity (v-K-diagram). The stress intensity of ceramic heads when loaded with standard conditions (e. g. walking, max. load 3 kN) is in the order of 0.6 MPa m1/2. Stress intensities like that are below alumina's fatigue limit KIo which is in the order on 1 MPa m1/2.Biolox alumina heads are examples for engineering ceramics that are reliable despite tensile stress over very long periods of time.
    Notes: Der totale Ersatz eines Hüftgelenkes mit Kugelköpfen und Pfannen aus Aluminiumoxidkeramik ist klinisch bewährt. Die in vivo Bruchrate eines Biolox Kugelkopfes liegt unter 0,02 %. Ausgelöst durch eine extrem hohe Belastung (z. B. Unfall) kann der Bruch nach unterkritischem Rißwachstum erfolgen.An 107 Biolox Explantaten wurde die Restfestigkeit bestimmt. Es konnte keine Materialermüdung nachgewiesen werden. Dies kann mit Hilfe des Zusammenhanges zwischen der Geschwindigkeit des Rißfortschritts und der Spannungsintensität (v-K-Diagramm)b erklärt werden. Normal belastete keramische Kugelköpfe (z. B. beim Gehen max. 3 kN) haben in vivo Spannungsintensitäten K1 von ca. 0,6 MPa m1/2. Hiermit befindet man sich mit der Spannungsintensität im Bereich unter der Ermüdungsgrenze KIo, für die ca. 1 MPa m1/2 abgeschätzt werden kann.Biolox Kugelköpfe sind ein Beispiel für den Einsatz von Keramik, die trotz Zugspannungen als Dauerbelastung und mit hohen Anforderungen an die Sicherheit über large Zeiten sicher im Einsatz sind.
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Differences in the cyclic deformation behaviour of quenched and tempered steel 42 CrMo 4 (AISI 4140) due to stress- and strain-controlCyclic stress-strain-curves and Manson-Coffin-plots of quenched and tempered steel 42 CrMo 4 (AISI 4140) strongly depend on whether they are determined under stress- or total-strain-control. At total-strain-controlled experiments, this is caused on the one hand by comparatively high initial stress-amplitudes which lead to distinctive cyclic worksoftening. On the other hand, the occurring differences in the evolution of inhomogeneous deformation patterns at both types of loading, which can be recorded by means of photoelasticity and microscopy, lead to differently distributed plastic deformations and to different integral values of plastic strain.
    Notes: Die bei nennspannungs- und totaldehnungskontrollierter Zug-Druck-Wechselverformung von vergütetem 42 CrMo 4 erhaltenen Zyklischen Spannungs-Dehnungs-kurven und Manson-Coffin-Auftragungen hängen stark von der Versuchsführung ab. Ursachen dafür sind einerseits die bei Totaldehnungskontrolle vergleichsweise großen Anfangsspannungsamplituden, die zu ausgeprägten Wechselentfestigungen führen. Andererseits bilden sich bei beiden Beanspruchungsarten, wie sich spannungsoptisch und lichtmikroskopisch nachweisen läßt, unterschiedliche inhomogene Deformationserscheinungen aus, die voneinander abweichende plastische Dehnungsverteilungen und integrale Dehnungswerte ergeben.
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    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Stress-strain hysteresis measurements of cyclically loaded unidirectional SiC-short-fiber reinforced alkali-lime-silicate-glassFor the technical application of fiber reinforced glasses, the knowledge of their fatigue behavior is important. Therefore, AR-glass specimens and SiC-short-fiber reinforced glass-compound specimens were produced by extrusion and investigated in stress controlled cyclic 3-point bending tests. The cyclic deformation behavior was characterized and the failure mechanisms were evaluated as a function of stress amplitude, number of cycles and fiber volume fraction by hysteresis measurements and microscopical investigations of the specimens surfaces. Selected results are presented and discussed.
    Notes: Im Hinblick auf die technische Anwendung faserverstärkter Gläser ist die Kenntnis des Ermüdungsverhaltens dieser Werkstoffe eine unabdingbare Voraussetzung. Hierzu wurden AR-Glasproben sowie SiC-kurzfaserverstärkte AR-Glas-Verbundproben durch Strangpressen hergestellt und in spannungskontrollierten 3-Punkt-Biegeversuchen im Schwellbereich schwingend beansprucht. Die Charakterisierung des zyklischen Verformungsverhaltens und die Bewertung der Versagensmechanismen in Abhängigkeit von Beanspruchungsamplitude, Beanspruchungsdauer und Faservolumengehalt erfolgte mit Hilfe des Hysteresismeßverfahrens sowie lichtmikroskopischer Strukturuntersuchungen an den Probenoberflächen. Ausgewählte Versuchsergebnisse werden vorgestellt und diskutiert.
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    Materialwissenschaft und Werkstofftechnik 29 (1998) 
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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    Materialwissenschaft und Werkstofftechnik 29 (1998), S. 339-344 
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Zerstörungsfreie Zustandsermittlung von GasturbinenschaufelnDie Restlebensdauer von sich in Einsatz befindenden Gasturbinenschaufeln wird durch die Bestimmung von Gefügeveränderungen des Grundwerkstoffes während der Betriebszeit ermittelt. Da man versucht Turbinenschaufelstufen in kompletten Sätzen zu halten, ist die Zerstörungsfreie Untersuchung (ZfU) sehr attraktiv. Ziel dieser Untersuchung war es deshalb, die Möglichkeiten eines ZfU Verfahrens zur Bestimmung von Strukturveränderungen im Basismaterial zu bewerten.Das einstufige Oberflächenabdruckverfahren (kombiniert mit REM-Untersuchungen) zeigt sich als relativ einfaches Verfahren, das allen Anforderungen entspricht. Auf unbeschichteten Turbinenschaufeln ist dieses Verfahren direkt anwendbar. Um es auf beschichteten Turbinenschaufeln anzuwenden, muß die Beschichtung lokal entfernt werden.
    Notes: In order to determine the remaining life of service exposed turbine blades it is necessary to characterize the degeneration of the microstructure of the base metal during service. Since turbine blades of industrial gas turbines are kept in complete stages, non-destructive inspection (NDI) is very attractive. Hence the goal of the investigation reported here was to evaluate a NDI technique able to detect microstructural changes of the base metal. It was found that single-stage replication (in combination with investigation in a Scanning Electron Microscope) is a relatively simple technique that fulfils all requirements. This technique can be used in-situ on uncoated buckets. For coated turbine blades local removal of the coating is necessary to perform base metal replication.
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    Materialwissenschaft und Werkstofftechnik 29 (1998), S. A97 
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
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    Materialwissenschaft und Werkstofftechnik 29 (1998), S. A77 
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Materialwissenschaft und Werkstofftechnik 29 (1998), S. 389-396 
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Plasma Pretreatment and Coating of Polymer Films. Part 3: Analysis of the Experimental Results and DiscussionThe food packaging industry demands cheap polymer films possessing a high barrier against permeation of gases, moisture and flavour. Candidates for the most successful materials fulfilling these requirements are vacuum web coated biaxial oriented polypropylene (BOPP) films containing a thin inorganic barrier layer. For a good adhesion of the barrier layer on the BOPP films, the polymer film must be pretreated. The industry uses the Corona atmosphere plasma. This work is separated in three parts. The first part describes the experimental setup and the properties of vacuum web coated layers on polymer films[1] The next part contains the results of the systematic modification of polymer surface by atmosphere and low pressure plasmas[2]. The influence of the surface properties on the final functionality of the coated films is given. In the last part, the discussion of the results of the first and second part reveals systematic relations between the production parameters of the high barrier films and their final functionality. These results firstly reveal the adhesion mechanism of the inorganic barrier layers of the polymer films and the necessary surface properties of the polymer films, in order to get cheap high barrier films by vacuum web coating.
    Notes: Die lebensmittelverpackende Industrie verlangt nach immer billigeren Kunststoffolien mit immer höheren Barrieren gegenüber Gasen, Wasserdampf und Aromastoffen. Ein sehr erfolgreicher Schritt, um diese Anforderungen zu erfüllen, besteht in der vakuumtechnischen Beschichtung mit dünnen anorganischen Schichten von biaxial orientierten Polypropylenfolien (BOPP). UM gute Haftungen der aufgedampften Aluminiumschichten zu erzielen, müssen die BOPP-Folie vorbehandelt werden. Industriell steht dafür das Corona-Atmosphärendruckplasma zur Verfügung. In dieser Arbeit aufgeteilt in drei Abschnitte wird zuerst der Versuchsaufbau und die Eigenschaften beschichteter Kunststoffolien allgemein dargestellt[1]. Im nächsten Schritt erfolgt die systematische Modifikation der Folienoberfläche mittels verschiedener Atmosphärendruck- und Niederdruckplasmen [2]. Die Plasmen werden mittels Langmuir-Sonde und Quadrupolmassenspektrometer charakterisiert. Nach Beschichtung der mittels verschiedener Plasmen modifizierten Kunststoffolien zeigen Haftung und Permeabilitätsmessungen den Einfluß der Vorbehandlung auf die Funktionalität der Folie/Schicht-Systeme. Im letzten Abschnitt werden aus den Ergebnissen der Analysen der unbeschichteten und beschichteten Folien systematische Zusammenhänge zwischen Herstellungsparametern und funktionellen Eigenschaften der beschichteten Folien hergestellt. Daraus lassen sich erstmals die zu einer guten Schichthaftung führenden Mechanismen aufzeigen und die notwendigen Oberflächeneigenschaften der unbeschichteten Folie identifizieren, so daß durch die vakuumtechnische Beschichtung preisgünstige Hochbarrierefolien produziert werden können.
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    Materialwissenschaft und Werkstofftechnik 29 (1998), S. 336-338 
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Es wird die Präparation und die temperaturabhängige Lichtdurchlässigkeit thermotroper Gelnetzwerke in Abhängigkeit von ihrer Zusammensetzung auf der Basis von Polyvinylalkohol (PVA), ethoxyliertem Polydimethyl-siloxan (ePS) und Wasser beschrieben. Diese thermotropen Materialien sind für den Einsatz in sogenannten „intelligenten“ Fenstern geeignet.
    Notes: The aim of this study has been to examine the possibility of preparing thermotropic aqueous gel networks that exhibit multiphase transitions in connection with changing the transparency of the system depending on temperature variation. As polymers polyvinyl alcohol (PVA) and ethoxylated polydimethylsiloxane (ePS) were chosen. Thermotropic materials can be used as intelligent shadegivers.
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    Materialwissenschaft und Werkstofftechnik 29 (1998), S. 345-364 
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Plasma Pretreatement and Coating of Polymer Films. Part 2: Experimental Results of the Plasma Pretreatment of Polymer FilmsThe food packaging industry demands cheap polymer films possessing a high barrier against permeation of gases, moisture and flavor. Candidates for the most successful materials fulfilling these requirements are vacuum web coated biaxial oriented polypropylene (BOPP) films containing a thin inorganic barrier layer. For a good adhesion of the barrier layer on the BOPP films, the polymer film must be pretreated. The industry uses the Corona atmosphere plasma. This work is separated in three parts. The first part describes the experimental setup and the properties of vacuum web coated layers on polymer films [1]. The next part contains the results of the systematic modification of po } ymer surface by atmosphere and low pressure plasmas. The influence of the surface properties on the final functionality of the coated films is given. In the last part, the discussion of the results of the first and second part reveals systematic relations between the production parameters of the high barrier films and their final functionality. These results firstly reveal the adhesion mechanism of the inorganic barrier layers of the polymer films and the necessary surface properties of the polymer films, in order to get cheap high barrier films by vacuum web coating.
    Notes: Die lebensmittelverpackende Industrie verlangt nach immer billigeren Kunststoffolien mit immer höheren Barrieren gegenüber Gasen, Wasserdampf und Aromastoffen. Ein sehr erfolgreicher Schritt, um diese Anforderungen zu erfüllen, besteht in der vakuumtechnischen Beschichtung mit dünnen anorganischen Schichten von biaxial orientierten Polypropylenfolien (BOPP). Um gute Haftungen der aufgedampften Aluminiumschichten zu erzielen, müssen die BOPP-Folie vorbehandelt werden. Industriell steht dafür das Corona-Atmosphärendruckplasma zur Verfügung. In dieser Arbeit aufgeteilt in drei Abschnitte wird zuerst der Versuchsaufbau und die Eigenschaften beschichteter Kunststoffolien allgemein dargestellt [1]. Im nächsten Schritt erfolgt die systematische Modifikation der Folienoberfläche mittels verschiedener Atmosphärendruck- und Niederdruckplasmen. Die Plasmen werden mittels Langmuir-Sonde und Quadrupolmassenspektrometer charakterisiert. Nach Beschichtung der mittels verschiedener Plasmen modifizierten Kunststoffolien zeigen Haftung und Permeabilitätsmessungen den Einfluß der Vorbehandlung auf die Funktionalität der Folie/Schicht-Systeme. Im letzte Abschnitt werden aus den Ergebnissen der Analysen der unbeschichteten und beschichten Folien systematische Zusammenhänge zwischen Herstellungsparametern und funktionellen Eigenschaften der beschichteten Folien hergestellt. Daraus lassen sich erstmals die zu einer guten Schichthaftung führenden Mechanismen aufzeigen und die notwendigen Oberflächeneigenschaften der unbeschichteten Folie identifizieren, so daß durch die vakuumtechnischen Beschichtung preisgünstige Hochbarrierefolien produziert werden können.
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    Materialwissenschaft und Werkstofftechnik 29 (1998), S. 412-423 
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Weldability of Aluminium and Al AlloysAluminium is behind steel the most used metal. Advantages of Al-materials are the low weight, the favourable strength and deformation properties, the good corrosion resistance and the good electrical and thermal conductivity. Welding of aluminium encounters difficulties due to high melting oxide layer at the surface, the strong heat dissipation from the welding region, the tendency to form craters or pores and the high heat extension. This contribution describes the basic facts and special features of arc welding and weld properties of aluminium and Al-alloys during welding.
    Notes: Aluminium ist das nach dem Stahl am häufigsten eingesetzte Metall. Vorteile der Aluminiumwerkstoffe sind das geringe Gewicht, günstige Festigkeits- und Verformungseigenschaften, der hohe Korrosionswiderstand sowie die hohe elektrische und Wärmeleitfähigkeit. Beim Schweißen ergeben sich vielfach Schwierigkeiten, die u. a. durch die hochschmelzende Oxidhaut, die starke Wärmeableitung, die Neigung zur Riß- oder Porenbildung sowie durch die große Wärmedehnung verursacht werden. Im vorliegenden Beitrag werden die Grundlagen und Besonderheiten von Reinaluminium und unterschiedlicher Legierungen hinsichtlich der Lichtbogen-Schweißtechnologie und der Nahteigenschaften dargestellt.
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    Materialwissenschaft und Werkstofftechnik 29 (1998), S. 447-450 
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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    Materialwissenschaft und Werkstofftechnik 29 (1998), S. 451-451 
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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    Materialwissenschaft und Werkstofftechnik 29 (1998), S. 466-475 
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Low energy IBAD: correlation between process parameters ans film properties for ion beam assisted evaporation and sputter depositionBinary nitride films with Al, Cr and Ti as metal components have been deposited with ion beam assisted evaporation and sputtering (IBAD) and the film properties are investigated in terms of the individual deposition parameters.In the case of ion beam assisted evaporation the flux ratio between the film forming metal atoms and the nitrogen ions from the ion source was shown to enable a quantitative control of the composition and the chemical phases of the films. Detailed studies for TiN reveal the possibilities to manipulate texture and stress, the average grain size and the morphology of the films. Such results are discussed with an extended structure zone model, introducing the energy input per film forming particle as the relevant parameter. Also, the structural film properties and the deposition parameters are quantitatively correlated with the hardness and the beginning of TiN deposition on stainless steel resulted in distinctly improved adhesion properties.For the deposition of TiN with a dual ion beam arrangement in which one beam bundle was directed onto a Ti-target and an other onto the substrate with the growing film, a strong influence of the particle energies and the incidence angles on the film texture and its directional orientation was found. Such effects are quantitatively related to the minimization of the free energy of the films and the influence of preferential re-sputtering effects. For ion beam sputter deposition without simultaneous ion bombardment of the growing film, the texture and the film stress are found to be controlled by energetic particles resulting from elastic backscattering at the target surface.
    Notes: Mittels ionenstrahlunterstütztem Aufdampfen und Aufsputtern (IBAD)wurden binäre Nitridschichten mit Al, Cr und Ti als Metallkomponente deponiert und hinsichtlich ihrer Eigenschaften in Abhängigkeit von den Depositionsparametern Charakterisiert.Beim ionenstrahlunterstützten Aufdampfen konnten durch Variation des Flußratenverhältnisses zwischen den schichtbildenden Metallatomen und den aus der Ionenquelle extrahierten Stickstoffionen die Schichtzusammensetzung und die chemischen Phasenverhältnisse kontrolliert eingestellt werden. Ausführliche Untersuchungen an den TiN-Schichten zeigen, daß auch Textur, Eigenspannungen, mittlere Korngröße und Morphologie der Schichten in weiten Grenzen manipuliert werden können. Ausgehend vom Energieeintrag pro schichtbildendem Teilchen werden die Ergebnisse anhand eines erweiterten Strukturzonenmodells diskutiert. Weiter lassen sich die strukturellen Schichteigenschaften und die Depositionsparameter mit der Härte und der Haftfestigkeit der Schichten quantitativ korrelieren. Durch dynamische Prozeßführung in der Anfangsphase des Schichtwachstums konnte eine deutliche Verbesserung der Haftung von TiN auf Werkzeugstahl erzielt werden.Für die Deposition von TiN mit einer Zweistrahlanordung, bei der ein Ionenstrahlbündel auf ein Ti-Target und ein weiteres auf das Substrat mit der aufwachsenden Schicht trifft, ergibt sich ein deutlicher Einfluß der Teilchenenergien und -auftreffwinkel auf die Schichttextur und deren Ausrichtung. Betrachtungen zur Minimierung der freien Energie in den Schichten und zum Einfluß von präferentiellen Rücksputtereffekten liefern ein quantitatives Verständnis der Effekte bei der Texturbildung. Bei der Ionenstrahl-Sputterdeposition ohne simultanem Substratbeschuß werden Textur und Schichtspannungen durch die vom Sputtertarget kommenden energiereichen Rückstreuteilchen bestimmt.
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    Materialwissenschaft und Werkstofftechnik 29 (1998), S. 518-524 
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Custom-Tailored Coating-Interface Systems by Means of lon Beam Assisted DepositionA coated sample represents in its most simple form a threefold junction consisting of substrate interface and top layer. In many cases the top layer consists again of several sublayers or the interface contains a modified substrate surface and an interconnection between top layer and interface. An ideal coating technique is evaporation under simultaneous ion bombardment with an ion source it is possible because of several free parameters to come close to an ideal system.For the coating Al/Al2O3 on steel it is shown that the width of a composition gradient between the sublayers Al and Al2O3 can be optimized with respect to excellent corrosion resistance.The example CrxN coating on steel or corrosion and wear resistence demonstrate the ability to optimize the corrosion and wear resistence by modifying the microstructure via variation of the parameters ion energy, ion impact angle, ion to atom ratio and process temperature.Finally, TiN layers on steel were chosen to show that the ion beam parameters influence the porosity and the crystal structure of the coatings. This fact can be used to optimize the corrosion protection or wear reduction obtained by the coating. Especially the multilayer Ti/TiO2/TiN exhibits very interesting properties.
    Notes: Ein beschichtetes Bauteil stellt in seiner einfachsten Form einen Dreierverbund aus Substrat, Interface und Schicht dar, in vielen Fällen kann die Schicht aus mehreren Untersystemen bzw. das Interface aus der modifizierten Substatrandschicht und einem Zwischenbereich zur Schicht bestehen. Eine ideale Beschichtungsmethode sollte es daher erlauben, alle diese Schichten bzw. Schichtbereiche in kontrollierter und aufeinander abgestimmter Form zu erzeugen.Mittels des IBAd-Verfahrens, bei dem Aufdampfschichten während ihrer Abscheidung mit Ionen aus einer Ionenquelle beschossen werden, ist es möglich, infolge der zahlreichen frei wählbaren Parameter sich an das ideale System heranzutasten.Anhand des Verbunds Stahl/Al/Al2O3 wird erlätert, wie durch einen in der Ausdehnung optimierten Zusammensetzungsgradienten das Interface zwischen den Subschichten Al und Al2O3 bezüglich des Korrosionsschutzvermögens der Schicht verbessert werden kann.An CrxN-Schichten wird demonstriert, daß durch die Wahl der Parameter Ionenenergie, Ioneneinfallswinkel, Ionen/Atom-Verhältnis und Prozeßtemperatur über die Mikrostruktur von Schicht und Oberfläche das Verschleiß-und Korrosionsverhalten sowie die Härte angepaßt werden können.Am Beispiel TIN auf Stahl zeigt sich, daß je nach Ionenstrahlparameter die Porosität und damit das Korrosionsverhalten bzw. die Kristallinität und damit Härte und Verschleißverhalten optimiert werden können. Besonders Mehrlagenschichten Ti/TiO2/TiN zeigen interessante Eigenschaften.
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    Materialwissenschaft und Werkstofftechnik 29 (1998) 
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Coatings in polymer processingCrxN coatings produced by PVD-magnetron sputtering (MSPVD) open unitsFor several years hard coatings have been used in plastic processing. The reduction of adhesion and contamination effects play a more and more important role besides the wear protection of injection moulds and extrusion tools. Applications of hard coatings in the field of highly stressed screws and barrels of plastification units are very seldom. In these cases the tribological effects are very intense so that the demanded wear resistance of hard coatings in the range 10μm is not sufficient. Different hard coatings based on titanium and chromium were tested according to their applicability for wear protection of screws in plastification units. Thickness, hardness, internal stresses and adhesion of the coatings were studied.Afterwards tribological tests in a model testing unit were investigated. Here the coatings were studied under tribological conditions, similar to those in a real plastification unit. The CrxN multilayer coatings showed extremely better wear resistance than the titanium based coatings. For this reason the CrxN coatings were optimized by help of the deposition parameters. These optimized coatings have been investigated according to their applicability for different polymers in comparison to other coating systems. First tests of CrCN/TiCN coated screw elements in practice showed very pleasing results. The test in practice with the optimized CrxN multilayer coating has yet to take place, but in the model tests the CrxN coatings showed excellent results.
    Notes: Hartstoffschichten werden bereits seit langem in der Kunststoffverarbeitung eingesetzt. Neben dem Verschleißschutz von Spritzguß-und Extrusionswerkzeugen stehen häufig auch die Verringerung von Klebneigungen und Formverschmutzungen im Vordergrund. Anwendungen im Bereich der hochbeanspruchten Schnecken und Zylinder von Plastifizieraggregaten sind noch selten. Die Verschleißeffekte sind hier so heftig, daß in der Praxis eine große Verschleißreserve gefordert wird, die Hartstoffschichten mit maximal 10 μm Schichtdicke naturgemäß nicht mitbringen. Verschiedene Hartstoffschichten auf Titan- und Chrombasis wurden hinsichtlich ihrer Eignung für den Verschleißschutz von Schnecken für Plastifizieraggregate untersucht. Schichtdicke, Härte, Eigenspannungen und Haftfestigkeit der Schichten wurden bestimmt.Anschließend wurden Verschleißversuche mit Hilfe einer Modellprüfapparatur, die die Schichten ähnlichen tribologischen Belastungen aussetzt, wie sie in einer Plastifiziereinheit auftreten, durchgeführt. Die CrxN-Mehrlagenschichten waren hierbei den auf Titan basierenden Schichten deutlich überlegen. Deshalb wurden für die CrxN-Schichten optimale Beschichtungsparameter bestimmt. Diese optimierten Schichten wurden mit verschiedenen anderen Schichtsystemen im Hinblick auf Ihre Eignung für unterschiedliche Kunststoffmaterialien verglichen. Erste Praxisversuche mit CrCN/TiCN-beschichteten Schneckenlementen sind sehr vielversprechend. Ein Praxistest der optimierten CrxN-Mehrlagenschichten steht zwar noch aus, jedoch konnten die guten Ergebnisse der CrxN-Schichten bei den Modellversuchen stets bestätigt werden.
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    Materialwissenschaft und Werkstofftechnik 29 (1998), S. 569-572 
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Predicting the fatigue strength of fillet-rolled crankshaftsSince three years Darmstadt University of Technology uses finite element method for simulation of fillet rolling process. Now, together with Daimler-Benz AG, a fracture mechanics based concept has been successfully applied predicting the fatigue strength of fillet-rolled crankshafts. For these parts conventional assessment of fatigue behaviour shows several disadvantages. The new concept reduces time and costs for development and design. It consists of three parts: calculation of residual stresses induced by fillet rolling and affected by crankshaft and roller geometry, rolling load and work hardening data of materialsimulation of residual stress redistribution due to cyclic loadassessment of fatigue cracks starting from notch root and propagating under compressive residual stresses by means of linearelastic fracture mechanics.
    Notes: Nachdem vor drei Jahren an der TU Darmstadt erstmals das Festwalzen erfolgreich mit Finite-Elemente-Methoden simuliert wurde [1], gelang nun in Zusammenarbeit mit der Daimler-Benz AG die rechnerische Abschätzung der Schwingfestigkeit festgewalzter Kurbelwellen mit Methoden der Bruchmechanik. Mit dem auch in der Vorentwicklung einsetzbaren Berechnungskonzept - hier zeigen die klassischen Berechnungsmöglichkeiten für festgewalzte Bauteile deutliche Defizite - können sowohl Entwicklungszeiten als auch Kosten der Versuchserprobung reduziert werden. Die Berechnung erfolgt dabei in drei Stufen: Berechnung der beim Festwalzen induzierten Eigenspannungen mit Hilfe der geometrischen Daten von Kurbelwelle und Festwalzrolle bei vorgegebener Werkstofffließkurve und Festwalzkräften.Berücksichtigung der Umlagerung der Eigenspannungen aufgrund der zyklischen Beanspruchung des Bauteils.Bruchmechanische Bewertung der sich im Radiusbereich der Kurbelwelle bildenden Anrisse und deren Verhalten in der druckeigenspannungsbehafteten Zone.
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    Materialwissenschaft und Werkstofftechnik 29 (1998), S. 629-631 
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    Keywords: Chemistry ; Polymer and Materials Science
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    Materialwissenschaft und Werkstofftechnik 29 (1998), S. A132 
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
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    Description / Table of Contents: Influence of mean stresses and mean strains on the cyclic deformation behavior and the plasticity-induced martensite formation of X6CrNiTi1810 stainless steelThis paper describes some aspects of the fatigue behavior of the metastable austenitic stainless steel X6CrNiTi1810 (German material number 1.4541). The aim of the present investigation is to determine the influence of plasticity-induced martensite formation on the cyclic deformation behaviour at room temperature and T = 300°C. Several specimen batches were tested under stress and total strain control with different R-values, a frequency of 5 Hz and triangular load-time functions, s̰-hysteresis and nondestructive magnetic measurements are used to characterize the fatigue behavior. Characteristic results are presented and discussed.
    Notes: Anhand von einstufigen spannungs- und totaldehnungskontrollierten Versuchen werden Zusammenhänge zwischen dem zyklischen Verformungsverhalten und der verformungsinduzierten Martensitbildung des metastabilen austenitischen Stahls X6CrNiTi1810 (Werkstoff-Nr. 1.4541) bei Raumtemperatur und T = 300°C untersucht. Besondere Beachtung findet hierbei der Einfluß von Mittelbeanspruchungen. Alle Versuche wurden mit einem dreieckförmigen Beanspruchung-Zeit-Verlauf und einer Frequenz von 5 Hz durchgeführt. Zur Charakterisierung des Wechselverformungsverhaltens dient neben den aus σ-Hysteresen ermittelten mechanischen Kennwerten, der on-line mittels eines Wirbelstromsensors gemessene magnetische Phasenanteil. Ausgewählte Versuchsergebnisse werden vorgestellt und diskutiert.
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    Materialwissenschaft und Werkstofftechnik 29 (1998), S. 713-713 
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
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    Materialwissenschaft und Werkstofftechnik 29 (1998), S. 152-152 
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
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    Materialwissenschaft und Werkstofftechnik 29 (1998), S. 300-311 
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Fiber composites of raw renewable materials for the ecological lightweight designDue to their low density natural fibers have the potential to be outstanding reinforcements in lightweight structures. Since most natural fibers are hollow they also bear great potentials in offering an increased bending resistance and buckling strength.By imbedding natural fibers in organic polymers instead of in conventional petroleumbased polymers a unique completely renewable and if wanted biodegradable composite can be created. Structural components made up of this new composite material cannot only be recycled or burned (in this case even CO2-neutral), but also be reintegrated in the cycle of natural decomposition.Presently e.g. car door linings or instrument panels have no supporting function in the car structure. In the future generation of cars weight reduction can be achieved giving these elements reinforcing functions by integrating hollow natural fibers aligned in the main loading directions. Furthermore critical regions in therms of stiffness and strength where loads are applied, like e.g. fastenings for side airbags, can be realised in the the same material without addition of metals. This can also be achieved for any other application.In this paper the potential of hallow natural fibers for reinforcements of lightweight structures, the renewable and (if wanted) biodegradable composites and their application in technical constructions will be discussed.
    Notes: Naturfasern weisen aufgrund ihrer niedrigen Dichte ein hohes Leichtbaupotential auf. Da viele Naturfasern zudem auch hohl sind, kann dieses Potential hinsichtlich Biege-, Knick- und Beulsteifigkeit verstärkt genutzt werden.Werden Naturfasern statt in herkömmlichen Polymeren auf petrochemischer Basis in neuartigen Biopolymeren auf der Basis nachwachsender Rohstoffe zu Faserverbundwerkstoffen verarbeitet, so können entsprechende Strukturen sogar die Eigenschaft der Bioabbaubarkeit haben. D. h., Faserverbundbauteile könnten nicht nur rezykliert oder verbrannt (hier sogar CO2-neutral) werden, sondern bieten zusätzlich über die Kompostierung die Möglichkeit der geschlossenen Kreislaufwirtschaft.Während heute z. B. Türinnenverkleidungen oder Armaturenbretter im Fahrzeugbau im wesentlichen verkleidenden Charakter aufweisen, kann im Zuge konsequenten Leichtbaus für zukünftige Automobilgenerationen auch an mittragende Strukturen gedacht werden, indem gerichtet hohle Naturfasern in die Kraftpfade eingearbeitet werden. Zudem können auch steifigkeits- und festigkeitskritische Lasteinleitungen z. B. für die Aufnahme von (Seiten-) Airbags aus gleichem Material ohne zusätzliche Metallinserts realisiert werden. Gleiches läßt sich auch auf beliebige andere Ingenieursanwendungen übertragen.Im Rahmen des Aufsatzes soll über das Leichtbaupotential hohler Naturfasern, über nachwachsende und biologisch abbaubare Faserverbundwerkstoffe und deren Anwendung berichtet werden.
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    Materialwissenschaft und Werkstofftechnik 29 (1998), S. 39-47 
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: The growth of the oxide protective layer on different Ni-Cr-Fe-alloys with variation of oxygen partial pressureHigh temperature alloys e.g. Incoloy 800 H, Hastelloy X and Ni75Cr25 model alloy are in-situ oxidized with variation potentials oxidation of PO2 = 4,41 × 10-19 bar, PO2 = 4,41 × 10-17 bar and PO2 = 176 × 10-16 bar by temperature, 800°. The behaviour of the scales which are oxidized at different oxidizing atmospheres has been investigated in this work, with deuterium permeation. The test of scales as corrosion barrier had been done in sulfidizing atmospheres with PS2 = 1,82 × 10-7 bar. The microstructure of the oxide layers has been investigated with Light Microscopy (LM), Scanning Electron Microscopy (SEM), Analytical Transmission Electron Microscopy (ATEM) and High Resolution Transmission Electron Microscopy (HRTEM). It is found that the deuterium permeation measurement can be correlated as a method for characterization corrosion layer at high temperature alloys. The structure of the oxide layer, the influence of sulfidizing atmospheres, additions of small amounts of reactive elements such as Ti before oxidation, the interface structure between oxide layers and matrix, as well as crystal defects and grain boundaries is explainable.
    Notes: Hochtemperaturlegieungen wie Incoloy 800 H, Hastelloy X und die pulvermetallurgisch hergestellte Modellegierung Ni-Cr/75-25 wurden mit ihren Oxiddeckschichten, die in verschiedenen Oxidationspotentialen mit Sauerstoffpartialdrucken von PO2 = 4.41 × 10-19 bis PO2 = 1.76 × 10-16 bar und bei einer Betriebstemperatur von T = 800° gewachsen sind, untersucht. Während der Oxidation wurde die Deuterium-Permeation gemessen. Gefügeuntersuchungen mit Hilfe der Lichtmikroskopie, der Rasterelektronenmikroskopie und vor allem der Transmissionselektronenmikroskopie unterstützen dabei die Aussagefähigkeit der Permeationsmessungen. Insbesondere werden Aufbau der Oxidschicht, der Einfluß von Schwefel, eine zusätzliche Titanbeschichtung vor der Oxidation, eine eventuell vorhandene Korngrenzenkorrosion und die Struktur der Grenzfläche Werkstoff-Oxidschicht vorgestellt und diskutiert.
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    Materialwissenschaft und Werkstofftechnik 29 (1998), S. 66a 
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    Keywords: Chemistry ; Polymer and Materials Science
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    Materialwissenschaft und Werkstofftechnik 29 (1998), S. 72-76 
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Although the characteristics of PVD coatings in research and development papers are very promising, in the field of tribology the industrial application of these coating types is restricted to special market segments up to now: the deposition of hard coatings is state of the art on tools, whereas PVD coated machine components are quite rare.This is caused by the coatings profile of properties, the various surroundings and the demands for application reliability. The last aspect is the main topic of this contribution. Reliability is especially important for machine components, because tools may fail after relative short life time compared to machine parts. Besides this tools and the corresponding production equipment are designed for fast tool replacement in contrast to other machines, which should work without standstill and with a minimum of maintenance.Characteristics of coated systems must be guaranteed in practice theory and laboratory experiments have to show what is possible. On the one hand reproduction of the deposition process must be guaranteed to enter application fields with high demands for reliability, on the other hand characterization of coated systems must be standardized with admissible deviations for communication between coaters and users. These aspects are important for decisions concerning the use of coating substrate systems in tribology besides the topics of technical function.The present investigation shows main reasons for deviations in results of PVD coatings.
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    Materialwissenschaft und Werkstofftechnik 29 (1998), S. 93-93 
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    Keywords: Chemistry ; Polymer and Materials Science
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    Materialwissenschaft und Werkstofftechnik 29 (1998), S. A33 
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    Keywords: Chemistry ; Polymer and Materials Science
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    Materialwissenschaft und Werkstofftechnik 29 (1998), S. 131-136 
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Einfluß der Substratstruktur auf das Erscheinungsbild von Lacken und die relevanten CharakterisierungsmethodenIn diesem Artikel werden die relevanten mechanischen und optischen Methoden (mech. Profilometrie, wave-scan, Autospect) zur Untersuchung der Oberflächenstruktur lackierter und unlackierter Proben vorgestellt. Im ersten Teil des Artikels werden die verschiedenen Methoden diskutiert und verglichen, während in einem zweiten Teil ein Beispiel bezüglich des Einflusses von Substratrauhigkeit und Einbrennposition auf die endgültige Decklackstruktur gezeigt wird. Ein dritter Teil präsentiert eine Studie an verformten und nicht-verformten Substraten verschiedenen Blech-Typs und den Effekt auf das Decklack-Erscheinungsbild. Zusätzlich wird ein Vergleich zwischen zwei Lacksystemen gegeben.
    Notes: In this paper the relevant mechanical and optical measuring methods (mech. Profilometry, wave-scan, Autospect) for studying the surface structure of painted and unpainted samples will be presented. The various methods were discussed and compared in the first part of the paper, while in a second part an example concerning the influence of substrate roughness and baking position on the final topcoat structure will be given. A third part presents a study on deformed and undeformed substrates of different sheet type and the effect on topcoat appearance. In addition, a comparison of two paint systems will be shown.
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    Materialwissenschaft und Werkstofftechnik 29 (1998), S. A45 
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    Keywords: Chemistry ; Polymer and Materials Science
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    Materialwissenschaft und Werkstofftechnik 29 (1998), S. 163-169 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Near surface properties of Mg-alloy AZ 31 after mechanical surface treatmentsNear surface materials properties are investigated for Mg-alloy AZ 31 after different shot peening or deep rolling treatments resp. Surface topography as well as depth distributions of hardness, residual stresses and X-ray interference line half-width values are analysed for individual process parameters. In addition, stability of residual stress distributions during fatigue loading is investigated.
    Notes: Am Beispiel der Magnesiumbasislegierung AZ 31 wird gezeigt, welche randnahen Werkstoffzustände sich nach Kugelstrahl- bzw. Festwalzbehandlungen einstellen. Dazu werden die Oberflächentopographie sowie die Tiefenverteilungen der Härte, der Eigenspannungen und der Halbwertsbreiten von Röntgeninterferenzlinien nach Behandlungen mit unterschiedlichen Verfahrensparametern betrachtet. Außerdem wird die Stabilität der Eigenspannungszustände bei Schwingbeanspruchung an Luft untersucht.
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    Materialwissenschaft und Werkstofftechnik 29 (1998), S. 185-192 
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Application of the Weakest-Link Model to the Fatigue Limit of the Steel SAE 52100 in a Bainitic ConditionThe influence of notches and loading condition on the fatigue limit of the high strength steel SAE 52100 is investigated on specimens with ground surfaces. The behaviour can be described quantitatively by a three-parametric high-cycle fatigue criterion and the weakest link model. This includes the possibility of calculating local and total survival probabilities depending on the nominal stress amplitude. Crack initiation sites and the fatigue limit can be predicted, too. The basic relation between the size distribution of crack initiating inclusions and the fracture probability was proved on push-pull specimens.
    Notes: As Proben des hochfesten Stahls 100Cr6 im bainitischen Zustand wird der Einfluß von Kerben und Belastungsart auf die Dauerfestigkeit aufgezeigt. Das Verhalten der Proben, die so geschliffen waren, daß an der Oberfläche Druckeigenspannungen vorlagen, kann mit einer räumlich darstellbaren Schwingfestigkeitshypothese und dem Fehlstellenmodell, angewandt auf Volumenfehler, quantitativ beschrieben werden. Hieraus ergibt sich die Möglichkeit, für jede Nennspannungsamplitude örtliche Bruchwahrscheinlichkeiten und Gesamtbruchwahrscheinlichkeiten sowie Anrißort und Dauerfestigkeit vorherzusagen. An ungekerbten Zug-Druck-Proben wurde der Zusammenhang zwischen der Überlebenswahrscheinlichkeit und der Größenverteilung der bruchauslösenden Einschlüsse nachgewiesen.
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    Materialwissenschaft und Werkstofftechnik 29 (1998), S. 238-238 
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Description / Table of Contents: Crack Initiation Life Prediction Method for Arbitrary Multiaxial Stresses Based on continuous Damage EvaluationA consideration of arbitrary proportional and non-proportional multiaxial fatigue stresses in the finite life range in crack initiation life predication methods causes still considerable difficulties. In the present investigation a new method has been developed, which led to promissing results as it was applied to a mean stress sensitive high strength aluminium alloy. The new method considers the incremental plastic work that accumulates at each point of a speciman or component which is represented by elastic plastic FEM. In contrast to conventional predication methods the new methods accounts for the instantaneous mean stresses of the stress path in the stress space. From viewpoint of practical application the new method offers advantages because it does not require a definition of damage events like closed hysteresis loops under uniaxial conditions and does not need a special algorithm for the damage events.
    Notes: Das Problem der Anrißlebensdauervorhersage bei beliebigen proportionalen und nicht-proportionalen mehrachsigen Schwingbeanspruchungen im Zeitfestigkeitsbereich ist immer noch nicht befriedigend gelöst. In der vorliegenden Arbeit wird eine neue Methode vorgeschlagen, mit der an hochfesten mittelspannungsempfindlichen Aluminiumlegierungen positive Ergebnisse erzielt wurden. Diese Methode benutzt die plastische Arbeit, die in jedem Punkt eines mittels der elastisch-plastischen FE-Methode dargestellten Prüfkörpers während der mehrachsigen schwingbelastunginkrementell akkumuliert wird, als Indikator für die auftretende Ermüdungsschädigung. Eine neue Formulierung berücksichtigt zusätzlich die momentane Mittelspannungen. Aus Anwendersicht ist die vorgeschlagene Methode vorteilhaft, weil besondere ermüdungsbezogene Beanspruchungsereignisse, wie z. B. geschlossene Hystereseschleifen, nicht definiert und „gezählt“ werden müssen.
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    Materialwissenschaft und Werkstofftechnik 29 (1998), S. 253-253 
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    Keywords: Chemistry ; Polymer and Materials Science
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    Materialwissenschaft und Werkstofftechnik 29 (1998), S. 258-262 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Strength of Materials in Case of Mechanical ImpactThe resistance of materials to mechanical impact was investigated in the context of safety of guards used in machine tools. Such guards are meant to protect persons from injuries caused by parts which, in the case of technical failure, are projected at high speeds out of the work zone of the machine. Impact tests with blunt, cylindrical projectiles were carried out on steel and aluminium sheets and on polycarbonate and polymethylmetacrylate shields. The measure of impact strength was the ultimate projectile energy which could be applied to the specimen without causing perforation. The impact strength of new 8-mm-polycarbonate shields turned out to be approximately comparable to that of 3-mm-steel sheets St 12.03. Polycarbonate, however, when it is exposed to cooling lubricants as they are used in machining processes, suffers from a strong reduction of its impact strength. In the tests, there was good proportionality between the impact strength of the materials and their thickness, ultimate tensile strength and fracture elongation. In addition, the impact strength increased as the projectile diameter got bigger.
    Notes: Die Festigkeit von Werkstoffen bei Aufprallbeanspruchungen wurde im Hinblick auf deren Verwendung für trennende Schutzeinrichtungen an Werkzeugmaschinen ermittelt. Solche Schutzeinrichtungen sollen Personen vor Verletzungen durch Teile schützen, die im Versagensfall mit hoher Geschwindigkeit aus dem Arbeitsraum der Maschine fortgeschleudert werden. Durch Beschußversuche mit stumpfen, zylindrischen Stahlprojektilen wurde das verhalten von Stahl- und Aluminiumblechen sowie Polycarbonat- und Polymethylmetacrylat-Scheiben bei Aufprallbeanspruchungen untersucht. Als Maß für die Aufprallfestigkeit diente dabei diejenige Geschoßenergie, bei der gerade noch kein Durchriß in den Prüfmustern auftrat. Im Neuzustand entsprach die Aufprallfestigkeit von 8 mm dickem Polycarbonat in etwa derjenigen von 3 mm dickem Stahlblech St 12.03. Unter dem Einfluß von Kühlschmierstoffen, wie sie in der spanenden Fertigung verwendet werden, kann bei Polycarbonat jedoch eine deutliche Minderung der Aufprallfestigkeit eintreten. Die Aufprallfestigkeit der untersuchten Werkstoffe nahm unter den gewählten Versuchsbedingungen in guter Näherung proportional mit der Dicke, der Zugfestigkeit und der Bruchdehnung zu. Darüber hinaus hatte eine Vergrößerung des Geschoßdurchmessers eine Erhöhung der Aufprallfestigkeit zur Folge.
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    Materialwissenschaft und Werkstofftechnik 29 (1998), S. 270-276 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Assessment of the influence of residual and mean stresses on the fatigue limit of a quenched and tempered low alloyed steelThe effect of mean and residual stresses on the fatigue limit of steels is known qualitatively since a long time. The quantitative description of the effect of residual stresses seems yet not sufficiently solved since the special characteristics of residual stresses like instability during loading, multiaxiality, strong gradients and occasionally great differences between surface and volume are not totally considered by the known methods. An application of different concepts for the assessment of residual and mean stresses on the fatigue limit of a quenched and tempered low alloyed steel is presented. If the applied concept takes account of the characteristics of residual stresses it is not necessary to distinguish between residual and mean stress sensitivity.
    Notes: Seit langem ist die qualitative Wirkung von Mittel- und Eigenspannungen auf die Dauerfestigkeit von Stählen bekannt. Die quantitative Beschreibung der Wirkung der Eigenspannungen erscheint jedoch unzureichend, da die Besonderheiten des Eigenspannungszustandes wie Nichtstabilität während der Belastung, Mehrachsigkeit, starke Gradienten sowie gelegentliche große Unterschiede zwischen Oberfläche und Volumen in den gängigen Konzepten nicht berücksichtigt werden. Es werden Untersuchungen zur Dauerfestigkeit eines vergüteten Stahls vorgestellt, auf die verschiedene Konzepte zur Bewertung von Eigen- und Mittelspannungen angewandt werden. Hierbei zeigt sich, daß auf die Unterscheidung zwischen Eigenspannungs- und Mittelspannungsempfindlichkeit verzichtet werden kann, wenn das Bewertungskonzept die oben genannten Charakteristika der Eigenspannungen berücksichtigt.
    Additional Material: 7 Ill.
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  • 96
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    Electronic Resource
    Weinheim : Wiley-Blackwell
    Materialwissenschaft und Werkstofftechnik 29 (1998), S. A77 
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
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  • 97
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    Electronic Resource
    Weinheim : Wiley-Blackwell
    Materialwissenschaft und Werkstofftechnik 29 (1998), S. 281-291 
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Investigation of Laser Beam Joining Properties for Eye Glass Frame ManufactureIn the production of high-grade eye glass frames of stainless steel increase the application of laserbeam joining technology in comparison to conventional processes. In a study it should be established, with which process (brazing or welding), the practical requirements of eye glass frames could be realized. Profiles made of Cr-Ni-steel which are used in practice due to their corrosion resistance, were joined with laser beam. To characterize the properties of joints, the quality of specimens were tested concerning mechanical properties (hardness, strength, ductility) and structural constitution. In relation to the requirement of good ductility of the joints, it was possible to proof the advantages of the welded samples.
    Notes: Bei der Fertigung von hochwertigen Brillengestellen aus nichtrostenden Stählen gewinnt der Einsatz der Laserstrahlfügeverfahren im Vergleich zu konventionellen Verfahren zunehmend an Bedeutung. Im Rahmen einer Studie sollte festgestellt werden, welches der beiden Verfahren Löten und Schweißen die in der Praxis gestellten Anforderungen an Brillengestelle besser erfüllt. Hierzu wurden Profile aus Cr-Ni-Stahl, wie sie in der Praxis wegen ihrer besonderen Langzeitstabilität gegenüber Korrosion eingesetzt werden, mittels Laserstrahl gefügt. Zur Charakterisierung der metallurgischen Eigenschaften der Fügeverbindungen wurden die Qualitätsmerkmale der Proben hinsichtlich mechanischer Eigenschaften (Härte, Festigkeit und Verformbarkeit) sowie die Gefügeausbildung untersucht. Im Hinblick auf die geforderte gute Verformbarkeit der Verbindungen konnte für die geschweißten Proben ein Vorteil gegenüber dem Laserstrahllöten nachgewiesen werden.
    Additional Material: 13 Ill.
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  • 98
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Materialwissenschaft und Werkstofftechnik 29 (1998) 
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 99
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Materialwissenschaft und Werkstofftechnik 29 (1998), S. A86 
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
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  • 100
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Materialwissenschaft und Werkstofftechnik 29 (1998), S. 694-696 
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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