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  • Articles  (11)
  • American Geophysical Union
  • Blackwell Publishing Ltd
  • Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics  (11)
  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 80 (1997), S. 0 
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: X-ray diffraction (XRD) patterns from nominally β-SiC specimens often differ from those expected for the cubic crystal structure. These differences include the presence of additional peaks, enhanced background intensities, peak broadening, changes in relative peak heights, and shifts in peak positions. It has long been recognized that they are due to the presence of stacking faults, and models relating the experimental observations to stacking fault population have continued to evolve. The presence and relative magnitude of these features vary among different β-SiC specimens. In this work, computer simulations were used to show that the variations are closely related to differences in the type and spatial distribution of stacking faults in each specimen. In these simulations, stacking sequences were generated using a selectively activated 1-D Ising model with a Boltzmann-type probability function for specifying errors, which allows a wide variety of fault configurations to be generated. Direct correlations between different features in the XRD data to the underlying fault population are demonstrated, which are discussed in this paper. It is also shown that this computer model is general, in the sense that many of the models presented in prior work can be interpreted as limiting cases of it.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Fatigue & fracture of engineering materials & structures 19 (1996), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— Constant and variable amplitude (VA) loading fatigue studies were carried out on a 6261 aluminium alloy using cylindrical plain hour-glass specimens. Crack growth was monitored via surface replication using cellulose acetate.Crack growth results at constant amplitude loading show the typical intermittent high and low periods of growth rate associated with crack-microstructure interactions. Acceleration in growth rate during an overload block depends on crack length and stress amplitude ratio. It appears to pass through a maximum at a crack length corresponding to the first microstructural barrier. Microstructural-based modelling is therefore required for small fatigue cracks, rather than solely closure-based modelling. The Navarro-de los Rios model of short fatigue crack growth appears able to provide good indications of crack growth rates under VA block loading, and gives reasonable life predictions.For short cracks (surface length 〈 80 μm) and a small overload ratio (6.7%), crack growth may show severe retardation during the overload block. This is ascribed to crack tip blunting being more important than the increase in stresses when closure is low. It appears from a Miner's rule type exercise, that VA block loading has its major effect on growth at a surface crack length of 20 μm. This means that the crack initiation period cannot be ignored in life prediction models for small fatigue cracks.
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Fatigue & fracture of engineering materials & structures 3 (1980), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— Linear-elastic fracture mechanics techniques were used to characterize the effect of temperature on the fatigue-crack propagation behaviour of precipitation heat-treated. Inconel X-750 in an air environment over the temperature range 24 to 649°C. In general, crack growth rates were found to increase with increasing temperature, particularly at the highest test temperature (649°C). The effect of stress ratio on the fatigue-crack growth behaviour of Inconel X-750 was examined at 538°C, and results indicated that the elevated temperature fatigue response of this nickel-base superalloy was relatively insensitive to stress ratio level at the growth rate levels studied. Metallographic and electron fractographic examination of Inconel X-750 fatigue fracture surfaces revealed operative crack growth mechanisms to be a function of temperature and prevailing stress intensity factor. Under room temperature and intermediate temperature conditions (up to 538°C), all fatigue fracture surfaces exhibited a faceted crystallographic morphology at low crack growth rates followed by striations in the higher growth rate regime. At the highest test temperature (649°C), the fatigue crack was found to propagate by an intergranular mechanism.
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Fatigue & fracture of engineering materials & structures 19 (1996), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract —The load interaction effects that occur under variable amplitude loading conditions following single peak overloads, low-high blocks and high-low blocks have been investigated on a commonly used structural steel. A detailed investigation has been carried out on long cracks which aims at developing and assessing the efficacy of a simple predictive model based on closure and plastic zone effects.The material was tested in a quenched and tempered condition. All the tests were carried out in the four point bending mode, in both the Paris regime and near the threshold, with overloads ranging from 10% to 100%.An attempt to relate crack closure to crack growth rates in the transient growth rate region (which follows a load change) was made.The trends observed for a wide range of loading parameters are presented.
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Fatigue & fracture of engineering materials & structures 14 (1991), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: In the presence of a notch, fully compressive loading has been shown to develop fatigue cracks, typically less than 1 mm in length, from the notch root in metals, cemented carbides and ceramics. The crack length is dependent on factors like load range, stress ratio, frequency and environmental influences. This paper examines the influence of these factors on crack growth in β-alumina under compression fatigue. Results obtained support the constitutive microcracking model advanced by Brockenborough and Suresh, but are influenced by crack tip shielding and, at low frequencies, a small stress corrosion component of growth.
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  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Fatigue & fracture of engineering materials & structures 12 (1989), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— —This paper reports the results of an investigation of the closure, growth rate and COD behaviour of small cracks in A533B steel. A laser-based interferometric strain/displacement measurement system was used in the work to quantify closure and COD values in both fine and coarse grained microstructures at stress ratios of - 1 and 0.1. The data obtained clarify the relative dominance of closure or microstructure in the two conditions of the steel and appear to shed some light on the size of crack tip plastic zones for small cracks in the two microstructures.
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Fatigue & fracture of engineering materials & structures 12 (1989), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— In low cycle fatigue situations, the plastic behaviour of the material at the root of stress concentrators is of prime importance in determining the cyclic life. However, simple procedures such as Neuber's rule do not adequately describe the development of plastic behaviour at a notch root, while the expense of a finite element analysis is not justified in many instances. This paper describes a simple, approximate numerical method of calculating plastic notch stresses and strains that would be of use in such situations. The usefulness of the technique is demonstrated by comparing low cycle fatigue lives predicted from notch plastic strains with those determined by fatigue testing of smooth specimens subjected to similar plastic strain ranges.
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  • 8
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Fatigue & fracture of engineering materials & structures 8 (1985), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— The paper addresses some aspects of the differences in fatigue crack growth rate behaviour and threshold values obtained for long through-cracks, short through-cracks and surface cracks. Attention is focused on plasticity induced closure in the wake behind the growing crack tip. For long cracks at high Kmax, closure is found to depend in a linear manner on Kmax, i.e. Kop, increases with the size of the monotonic plastic zone. Closure increases at low δK and this is primarily a consequence of the load shedding procedure. If short through-cracks are prepared by machining specimens containing long cracks, a substantial part of the plastic wake is removed and this can produce marked effects on the closure contribution during subsequent growth. The length of crack “closed” in a long crack threshold test was found to be of the order of 1 mm. Cracks less than this length exhibited “short crack” behaviour: greater than this length, they behaved as “long cracks”, with plastic wake effects apparently fully operative. Small surface cracks exhibit “long crack” behaviour at lengths as short as 0.2 mm and reasons for this are discussed.
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  • 9
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Fatigue & fracture of engineering materials & structures 6 (1983), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— Evidence is presented that the cyclic stress intensity threshold for fatigue crack growth in A1 2219-T851 is associated with a critical maximum value of stress intensity, Kc. This relationship is discovered by measuring the local value of stress intensity at the crack tip which is less than the applied stress intensity because of fatigue induced compressive residual stresses in the plastic zone. Crack growth rates and values of the crack tip residual stress are measured as functions of load ratio. For local stress intensities greater than Kc, the growth rate follows a power-law relationship, increasing monotonically with δK. For local stress intensities below Kc, growth rates are also sensitive to the cyclic stress range, δσ. If the stress range is small, a threshold to growth, typical of long cracks, is seen. When the cracks are short and δσ exceeds a critical value, growth rates are a complex function of both δσ and δK. This behavior is attributed to the effect of δσ on the propagation of the crack front past obstacles such as grain boundaries.
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  • 10
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Typically, the debonding and sliding interface enabling fiber pullout for SiC-fiber-reinforced SiC-matrix composites with BN-based interphases occurs between the fiber and the interphase. Recently, composites have been fabricated where interface debonding and sliding occur between the BN interphase and the matrix. This results in two major improvements in mechanical properties. First, significantly higher failure strains were attained due to the lower interfacial shear strength with no loss in ultimate strength properties of the composites. Second, significantly longer stress-rupture times at higher stresses were observed in air at 815°3C. In addition, no loss in mechanical properties was observed for composites that did not possess a thin carbon layer between the fiber and the interphase when subjected to burner-rig exposure. Two primary factors were hypothesized for the occurrence of debonding and sliding between the BN interphase and the SiC matrix: a weaker interface at the BN/matrix interface than the fiber/BN interface and a residual tensile/shear stress-state at the BN/matrix interface of melt-infiltrated composites. Also, the occurrence of outside debonding was believed to occur during composite fabrication, i.e., on cooldown after molten silicon infiltration.
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