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  • STRUCTURAL MECHANICS  (884)
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  • 201
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    A New Uncoupled Viscoplastic Constitutive Model (1983)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: A new uncoupled viscoplastic model has been proposed along with experiments and analysis to define the various material constraints. Distinguishing between rate sensitive and rate insensitive strain allows the rate sensitive strain to be modelled over a wide range of temperatures with very little variation in the stress component 'n'. Furthermore, it allows the rounded corners on stress-strain hysteresis loops to be achieved very naturally.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA. Lewis Research Center Nonlinear Constitutive Relations for High Temp. Appl.; p 217-234
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  • 202
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    Application of an Uncoupled Elastic-plastic-creep Constitutive Model to Metals at High Temperature (1983)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: A uniaxial, uncoupled constitutive model to predict the response of thermal and rate dependent elastic-plastic material behavior is presented. The model is based on an incremental classicial plasticity theory extended to account for thermal, creep, and transient temperature conditions. Revisions to he combined hardening rule of the theory allow for better representation of cyclic phenomenon including the high rate of strain hardening upon cyclic reyield and cyclic saturation. An alternative approach is taken to model the rate dependent inelastic deformation which utilizes hysteresis loops and stress relaxation test data at various temperatures. The model is evaluated and compared to experiments which involve various thermal and mechanical load histories on 5086 aluminum alloy, 304 stainless steel and Hastelloy-X.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA. Lewis Research Center Nonlinear Constitutive Relations for High Temp. Appl.; p 185-190
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  • 203
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    Some Recent Developments in the Endochronic Theory with Application to Cyclic Histories (1983)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: Constitutive equations with only two easily determined material constants predict the stress (strain) response of normalized mild steel to a variety of general strain (stress) histories, without a need for special unloading-reloading rules. The equations are derived from the endochronic theory of plasticity of isotropic materials with an intrinsic time scale defined in the plastic strain space. Agreement between theoretical predictions and experiments are are excellent quantitatively in cases of various uniaxial constant amplitude histories, variable uniaxial strain amplitude histories and cyclic relaxation. The cyclic ratcheting phenomenon is predicted by the present theory.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA. Lewis Research Center Nonlinear Constitutive Relations for High Temp. Appl.; p 191-216
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  • 204
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    On the Application of Deformation Kinetics to Nonlinear Constitutive Relations at Higher Temperatures (1983)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: A single phenomenological constitutive equation is derived theoretically from first principles and applied to aluminum, tin and lead. The theory is based on deformation kinetics of steady creep in which the fundamental mechanism is atomic transport over potential barriers whose conformation is distorted by the application of a stress field. The form of the functional dependence of barrier distortion and stress over the entire temperature range is found to be a sigmoidal curve which tends to straight lines of a unit slope in the small and high stress regions. With this form of barrier distortion, the constitutive equation prediction the steady creep behavior of aluminum, tin and lead over a wide range of temperature and stress.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA. Lewis Research Center Nonlinear Constitutive Relations for High Temp. Appl.; p 139-152
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  • 205
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    Evaluation of Inelastic Constitutive Models for Nonlinear Structural Analysis (1983)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: The influence of inelastic material models on computed stress-strain states, and therefore predicted lives, was studied for thermomechanically loaded structures. Nonlinear structural analyses were performed on a fatigue specimen which was subjected to thermal cycling in fluidized beds and on a mechanically load cycled benchmark notch specimen. Four incremental plasticity creep models (isotropic, kinematic, combined isotropic-kinematic, combined plus transient creep) were exercised. Of the plasticity models, kinematic hardening gave results most consistent with experimental observations. Life predictions using the computed strain histories at the critical location with a Strainrange Partitioning approach considerably overpredicted the crack initiation life of the thermal fatigue specimen.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: Nonlinear Constitutive Relations for High Temp. Appl.; p 89-106
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  • 206
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    Multiaxial Cyclic Thermoplasticity Analysis with Besseling's Subvolume Method (1983)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: A modification was formulated to Besseling's Subvolume Method to allow it to use multilinear stress-strain curves which are temperature dependent to perform cyclic thermoplasticity analyses. This method automotically reproduces certain aspects of real material behavior important in the analysis of Aircraft Gas Turbine Engine (AGTE) components. These include the Bauschinger effect, cross-hardening, and memory. This constitutive equation was implemented in a finite element computer program called CYANIDE. Subsequently, classical time dependent plasticity (creep) was added to the program. Since its inception, this program was assessed against laboratory and component testing and engine experience. The ability of this program to simulate AGTE material response characteristics was verified by this experience and its utility in providing data for life analyses was demonstrated. In this area of life analysis, the multiaxial thermoplasticity capabilities of the method have proved a match for the actual AGTE life experience.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA. Lewis Research Center Nonlinear Constitutive Relations for High Temp. Appl.; p 69-88
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  • 207
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    Evaluation of Three Constitutive Models for the Prediction of Hastelloy X Elevated Temperature Cyclic Response (1983)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: The approach for the method development assumes that, for a thermally loaded structure, the overall strain history is defined by linear elastic analysis. The local stress history at a fatigue critical location is then determined from a one dimensional material behavior model and the local strain and temperature conditions. Three material models are currently being evaluated to assess their ability to predict relevant high temperature cyclic material response characteristics. They are: a time independent classical plasticity and creep representation, a time dependent viscoplastic model capable of predicting combined creep and plasticity effects, and an approximate elastic analysis approach that uses a series of stress-strain curves and a cyclic hardening model to determine reverse plasticity.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA. Lewis Research Center Nonlinear Constitutive Relations for High Temp. Appl.; p 43-46
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  • 208
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    Correlation of Rupture Life, Creep Rate, and Microstructure for Type 304 Stainless Steel (1983)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: The stress and temperature sensitivites of the rupture life and secondary creep rate were examined in detail for a single heat of type 304 stainless steel (9T2796). Assuming that the rupture life has a power law stress dependency, relatively small differences in the stress exponent were observed over a broad range of stress and temperature. In contrast, large changes were observed for equivalent parameter for secondary creep rate. As a result of these differences, the Monkman-Grant correlation was sensitive to stress and temperature below 650 C. Metallurgical studies based on light and transmission electron microscopy suggested that the temperature and stress sensitivities of secondary creep rate at temperatures below 650 C were related to features of the substructure not present at higher temperature. Specifically, the presence of a fine dislocation network stabilized by precipitates altered the stress and temperature sensitivities relative to what might be expected from high temperature studies.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA. Lewis Research Center Nonlinear Constitutive Relations for High Temp. Appl.; p 1-12
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  • 209
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    A new method for generating and maintaining rigid formats in NASTRAN (1983)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: A new method for generating and updating Rigid Formats in NASTRAN is discussed. The heart of this method is a Rigid Format data base that is in card-image format and that can therefore be easily maintained by the use of standard text editors. Each Rigid Format entry in this data base will contain the Direct Matrix Abstraction Program (DMAP) for that Rigid Format along with the related restart, subset and substructure control tables. NASTRAN will read this data base directly in every NASTRAN run and perform the necessary transformations to allow the DMAP to be processed and compiled by the NASTRAN executive. This approach will permit Rigid Formats to be changed without unnecessary compilations and relinking of NASTRAN. Furthermore, this approach will also make it very easy for users to make permanent changes to existing Rigid Formats as well as to generate their own Rigid Formats. This new method will be incorporated in a future release of the public version of NASTRAN.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: COSMIC 11th NASTRAN User's Colloq.; p 249-254
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  • 210
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    Elastic-plastic analysis of annular plate problems using NASTRAN (1983)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: The plate elements of the NASTRAN code are used to analyze two annular plate problems loaded beyond the elastic limit. The first problem is an elastic-plastic annular plate loaded externally by two concentrated forces. The second problem is stressed radially by uniform internal pressure for which an exact analytical solution is available. A comparison of the two approaches together with an assessment of the NASTRAN code is given.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: COSMIC 11th NASTRAN User's Colloq.; p 281-292
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  • 211
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    Implementation of elastic-plastic structural analysis into NASTRAN (1983)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: Elastic-plastic analytic capabilities were incorporated into the NASTRAN program. The present implementation includes a general rigid format and additional bulk data cards as well as to two new modules. The modules are specialized to include only perfect plasticity of the CTRMEN and CROD elements but can easily be expanded to include other plasticity theories and elements. The practical problem of an elastic-plastic analysis of a ship's bracket connection is demonstrated and compared to an equivalent analysis using Grumman's PLANS program. The present work demonstrates the feasibility of incorporating general elastic-plastic capabilities into NASTRAN.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: COSMIC 11th NASTRAN User's Colloq.; p 255-280
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  • 212
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    Bolt in bore boundaries (1983)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: The factors that must be taken into consideration when applying NASTRAN's linear analysis to structures whose principle boundaries are formed by bolting, and for which localized stress peaking is important are discussed. An illustration is given in an application to a mounting bracket.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: COSMIC 11th NASTRAN User's Colloq.; p 293-303
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  • 213
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    The effect of matrix properties and fiber properties on impact failure mechanics (1983)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-01-25
    Beschreibung: The low-velocity impact problem in graphite/epoxy composite sheets must be solved before large amounts of that material can be used in commercial aircraft. Many of the low-velocity impacts that affect aircraft parts occur during normal ground operations and maintenance. Service equipment and tools have masses above 1 kg, and at velocities of less than 3 m/s can impact structural parts with energies higher than composites can endure without degradation of stiffness or strength. Simple solutions were developed for large-mass, low-velocity impacts which can be modeled as quasi-static events. Static test data and impact data show that the fiber properties control the impact energy which can be absorbed before penetration. Matrix shear strength and peel resistance control the extent of delamination. Comparison of results from tough matrix and brittle matrix composites show that although tough matrices reduce the extent of delamination, they lead to more fiber damage in the contact area.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: Delaware Univ. Abstr. of the 20th Ann. Meeting, Society of Engineering Science, Inc.; p 57
    Format: text
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  • 214
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    A nonlinear fracture mechanics approach to the growth of small cracks (1983)
    In:  CASI
    Details
    Publikationsdatum: 2017-10-02
    Beschreibung: An analytical model of crack closure is used to study the crack growth and closure behavior of small cracks in plates and at notches. The calculated crack opening stresses for small and large cracks, together with elastic and elastic plastic fracture mechanics analyses, are used to correlate crack growth rate data. At equivalent elastic stress intensity factor levels, calculations predict that small cracks in plates and at notches should grow faster than large cracks because the applied stress needed to open a small crack is less than that needed to open a large crack. These predictions agree with observed trends in test data. The calculations from the model also imply that many of the stress intensity factor thresholds that are developed in tests with large cracks and with load reduction schemes do not apply to the growth of small cracks. The current calculations are based upon continuum mechanics principles and, thus, some crack size and grain structure exist where the underlying fracture mechanics assumptions become invalid because of material inhomogeneity (grains, inclusions, etc.). Admittedly, much more effort is needed to develop the mechanics of a noncontinuum. Nevertheless, these results indicate the importance of crack closure in predicting the growth of small cracks from large crack data.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: AGARD Behaviour of Short Cracks in Airframe Components; 26 p
    Format: text
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  • 215
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    Cannon launched electromechanical control actuation system development (1983)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: The evolution of an electromechanical control actuation system from trade study results through breadboard test and high-g launch demonstration tests is summarized. Primary emphasis is on design, development, integration and test of the gear reduction system.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: JPL The 17th Aerospace Mech. Symp.; p 181-198
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  • 216
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    Optimal damping for a two-dimensional structure (1983)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: Criteria for selection of optimal damper locations are presented. A damping synthesis problem was formulated and applied to a NASA grillage model.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA. Langley Research Center Structual Dyn. and Control of Large Space Struct., 1982; p 249-262
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  • 217
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    Active control of a flexible beam (1983)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: Because of inherent low damping and high flexibility, large space structures may require some form of active control of their dynamics. Because of the apparent inability to accurately model the dynamics of these structures, methods for parameter adaptive control are now being developed at Langley. This approach uses a digital computer to process discrete sensor data, identify modal parameters, calculate modal control gains, and then convert the modal forces to real forces. Some of the problems considered are: (1) the possibility that there may be modes to control with limited amounts of hardware, and (2) the required accuracy of identified structural parameters.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: Structural Dyn. and Control of Large Space Struct., 1982; p 235-247
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  • 218
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    Structural design for dynamic response reduction (1983)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: A computer program for redesigning structural modes to reduce response has been initiated. The linear regulator approach in modal coordinates has been implemented. It is noted that the transformation of solution to physical structure is a major problem. It is concluded that the solution of stiffness equations and damping equations can be done separately as NXN set of (matrix Riccati) equations.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: Structural Dyn. and Control of Large Space Struct., 1982; p 141-150
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  • 219
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    Nonlinear effect on modal data analysis method (1983)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: How the presence of nonlinearities in structural test data can be detected when using modern linear modal data analysis methods is discussed. The extent to which linear algorithms can provide useful information on nonlinear systems was discussed. The modal data analysis method successfully identified the frequency components (but not damping) of the true solution of a nonlinear systems. It was found that the approximate modal parameters of the linear system can be identified by the modal method when low levels of nonlinearities are present. The modal method successfully identified the modal parameters of a linear mode in the presence of a nonlinear response.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: Structural Dyn. and Control of Large Space Struct., 1982; p 135-140
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  • 220
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    Decoupling and observation theory applied to control of a long flexible beam in orbit (1983)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: Techniques which use decoupling theory and state variable feedback to control the pitch attitude and the flexible mode amplitudes of a long, thin beam are discussed. An observer based on the steady state Kalman filter was incorporated into the control design procedure in order to estimate the values of the modal state variables required for the feedback control law.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: Structural Dyn. and Control of Large Space Struct., 1982; p 9-38
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  • 221
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    Active damping of a flexible beam (1983)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: The development of an algorithm that will determine actuator and sensor locations on a flexible beam is discussed. Large space structures will have many locations where actuators can be placed. This research seeks to determine the optimum locations. In addition, the best locations are determined while certain constraints are satisfied which guarantee that mission performance requirements are achieved. The approach adopted is to consider actuators and sensors to be collocated so as to produce an equivalent viscous damper. Ultimately, the experimental results of measuring the log decrement during free decay will correlate with the analytical predictions.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: Structural Dyn. and Control of Large Space Struct., 1982; p 1-8
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  • 222
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    Results from recent NASA tire thermal studies (1983)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: The testing technique and some results from an experimental study to determine tire temperature profiles to aid in defining the strength and fatigue limitations of the tire carcass structure are described. This effort is part of a program to explore analytically and through experiment the temperature distribution in an aircraft tire during free roll and braked and yawed rolling conditions.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: Tire Modeling; p 211-222
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  • 223
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    Adhesion testing of aircraft tires (1983)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: Adhesion testing appeared to offer a less burdensome alternative to replace some of the dynamometer tests. Accordingly, test results and data were requested from retreaders who had used adhesion testing.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA. Langley Research Center Tire Modeling; p 175-192
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  • 224
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    Heat generation in aircraft tires (1983)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: A method was developed for calculating the internal temperature distribution in an aircraft tire while free rolling under load. The method uses an approximate stress analysis of each point in the tire as it rolls through the contact patch, and from this stress change the mechanical work done on each volume element may be obtained and converted into a heat release rate through a knowledge of material characteristics. The tire cross-section is then considered as a body with internal heat generation, and the diffusion equation is solved numerically with appropriate boundary conditions of the wheel and runway surface. Comparison with data obtained with buried thermocouples in tires shows good agreement.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA. Langley Research Center Tire Modeling; p 193-210
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  • 225
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    Overview of NASA tire experimental programs (1983)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: Ongoing aircraft tire experimental programs are reported. These programs are designed to measure profile growth due to inflation pressure and vertical loading, contact pressures in the tire footprint, and a number of tire mechanical properties including spring, damping, and relaxation characteristics.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: Tire Modeling; p 163-174
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  • 226
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    Experimental and finite element study of a standing torus under normal and tangential loads (1983)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: The effect of a combined external load consisting of a normal component and a tangential braking force applied to an inflated torus is addressed. Experimental results obtained by photographic study of the contact area between the torus and load plate are presented as well as measurements of the vertical and horizontal displacement of the torus under load. A numerical procedure for displacement analysis is developed in which the finite element program STAGS (Structural Analysis of General Shells) is used in an iterative manner to produce a flat, horizontal footprint surface under force loading. The redistributed force distribution obtained by the iterative process is displayed along with computed meridional and circumferential stresses. Finally, an extension of the iterative method is introduced which eliminates the need to experimentally determine the footprint area.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA. Langley Research Center Tire Modeling; p 141-162
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  • 227
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    A tire contact solution technique (1983)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: An efficient method for calculating the contact boundary and interfacial pressure distribution was developed. This solution technique utilizes the discrete Fourier transform to establish an influence coefficient matrix for the portion of the pressurized tire surface that may be in the contact region. This matrix is used in a linear algebra algorithm to determine the contact boundary and the array of forces within the boundary that are necessary to hold the tire in equilibrium against a specified contact surface. The algorithm also determines the normal and tangential displacements of those points on the tire surface that are included in the influence coefficient matrix. Displacements within and outside the contact region are calculated. The solution technique is implemented with a finite-element tire model that is based on orthotropic, nonlinear shell of revolution elements which can respond to nonaxisymmetric loads. A sample contact solution is presented.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA. Langley Research Center Tire Modeling; p 95-122
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  • 228
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    Analytical and experimental study of a standing torus with normal loads (1983)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: Finite element analysis is applied to study the large deflection and stress of a thin-walled pressurized torus loaded by normal contact with a plane. Experimentally determined stresses are compared to those resulting from finite element analysis at various meridional and circumferential coordinates of the torus, including the footprint area. Circumferential strains compare favorably while meridional strains are higher in the finite element analysis, probably due to slippage of the boundary at the rim. The STAGS finite element computer program was used. The purpose of the study was to evaluate the various program options for structural loading, for material modeling, for stress analysis, and for grid refinement. The experimental model, a thin-walled rubber tube mounted on a steel cylindrical rim, provided measured results to compare with various analytical trade-offs. It was found that there was almost no difference in predicted deflections or stress distributions between linear and nonlinear material description. However, the difference between linear analysis and that of geometric nonlinearities utilizing incremental loading was marked.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA. Langley Research Center Tire Modeling; p 123-140
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    Application of tire dynamics to aircraft landing gear design analysis (1983)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: The tire plays a key part in many analyses used for design of aircraft landing gear. Examples include structural design of wheels, landing gear shimmy, brake whirl, chatter and squeal, complex combination of chatter and shimmy on main landing gear (MLG) systems, anti-skid performance, gear walk, and rough terrain loads and performance. Tire parameters needed in the various analyses are discussed. Two tire models are discussed for shimmy analysis, the modified Moreland approach and the von Schlippe-Dietrich approach. It is shown that the Moreland model can be derived from the Von Schlippe-Dietrich model by certain approximations. The remaining analysis areas are discussed in general terms and the tire parameters needed for each are identified. Accurate tire data allows more accurate design analysis and the correct prediction of dynamic performance of aircraft landing gear.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA. Langley Research Center Tire Modeling; p 71-94
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  • 230
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    Finite element methods for nonlinear elastostatic problems in rubber elasticity (1983)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: A number of finite element methods for the analysis of nonlinear problems in rubber elasticity are outlined. Several different finite element schemes are discussed. These include the augmented Lagrangian method, continuation or incremental loading methods, and associated Riks-type methods which have the capability of incorporating limit point behavior and bifurcations. Algorithms for the analysis of limit point behavior and bifurcations are described and the results of several numerical experiments are presented. In addition, a brief survey of some recent work on modelling contact and friction in elasticity problems is given. These results pertain to the use of new nonlocal and nonlinear friction laws.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA. Langley Research Center Tire Modeling; p 39-70
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  • 231
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    Finite element modeling and analysis of tires (1983)
    In:  CASI
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    Publikationsdatum: 2016-06-07
    Beschreibung: Predicting the response of tires under various loading conditions using finite element technology is addressed. Some of the recent advances in finite element technology which have high potential for application to tire modeling problems are reviewed. The analysis and modeling needs for tires are identified. Reduction methods for large-scale nonlinear analysis, with particular emphasis on treatment of combined loads, displacement-dependent and nonconservative loadings; development of simple and efficient mixed finite element models for shell analysis, identification of equivalent mixed and purely displacement models, and determination of the advantages of using mixed models; and effective computational models for large-rotation nonlinear problems, based on a total Lagrangian description of the deformation are included.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA. Langley Research Center Tire Modeling; p 1-38
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  • 232
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    Inelastic work and thermomechanical coupling in viscoplasticity (1983)
    In:  Other Sources
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    Publikationsdatum: 2018-12-01
    Beschreibung: The inelastic deformation of engineering alloys was recently shown to be rate (time)-dependent at room temperature. Experiments reported herein demonstrate that inelastic strain path length is a suitable measure for the modeling of work hardening for these materials, whereas inelastic work is not appropriate. The measured deformation induced temperature change is well predicted by a previously proposed theory of thermomechanical coupling. It has been derived by neglecting the stored energy of cold work and by assuming tha the internal energy expression for thermoelasticity is valid even when the mechanical deformation is inelastic.
    Schlagwort(e): STRUCTURAL MECHANICS
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  • 233
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    Preliminary investigation of dynamic lateral stability characteristics of a configuration of the north american x-15 research airplane (1957)
    In:  CASI
    Details
    Publikationsdatum: 2019-05-23
    Beschreibung: Dynamic lateral stability of configurations of X-15 research aircraft
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NACA-RM-L56L27
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  • 234
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    Demonstration test of burner liner strain measurement systems: Interim results (1983)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: Work is in progress to demonstrate two techniques for static strain measurements on a jet engine burner liner. Measurements are being made with a set of resistance strain gages made from Kanthal A-1 wire and via heterodyne speckle photogrammetry. The background of the program is presented along with current results.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA. Lewis Research Center Turbine Eng. Hot Sect. Technol. (HOST); p 41-44
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  • 235
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    Transverse vibration and buckling of a cantilevered beam with tip body under constant axial base acceleration (1983)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: The planar transverse bending behavior of a uniform cantilevered beam with rigid tip body subject to constant axial base acceleration was analyzed. The beam is inextensible and capable of small elastic transverse bending deformations only. Two classes of tip bodies are recognized: (1) mass centers located along the beam tip tangent line; and (2) mass centers with arbitrary offset towards the beam attachment point. The steady state response is studied for the beam end condition cases: free, tip mass, tip body with restricted mass center offset, and tip body with arbitrary mass center offset. The first three cases constitute classical Euler buckling problems, and the characteristic equation for the critical loads/accelerations are determined. For the last case a unique steady state solution exists. The free vibration response is examined for the two classes of tip body. The characteristic equation, eigenfunctions and their orthogonality properties are obtained for the case of restricted mass center offset. The vibration problem is nonhomogeneous for the case of arbitrary mass center offset. The exact solution is obtained as a sum of the steady state solution and a superposition of simple harmonic motions.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA-CR-175567 , NAS 1.26:175567 , CSDL-R-1675
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  • 236
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    Planar dynamics of a uniform beam with rigid bodies affixed to the ends (1983)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: The planar dynamics of a uniform elastic beam subject to a variety of geometric and natural boundary conditions and external excitations were analyzed. The beams are inextensible and capable of small transverse bending deformations only. Classical beam vibration eigenvalue problems for a cantilever with tip mass, a cantilever with tip body and an unconstrained beam with rigid bodies at each are examined. The characteristic equations, eigenfunctions and orthogonality relations for each are derived. The forced vibration of a cantilever with tip body subject to base acceleration is analyzed. The exact solution of the governing nonhomogeneous partial differential equation with time dependent boundary conditions is presented and compared with a Rayleigh-Ritz approximate solution. The arbitrary planar motion of an elastic beam with rigid bodies at the ends is addressed. Equations of motion are derived for two modal expansions of the beam deflection. The motion equations are cast in a first order form suitable for numerical integration. Selected FORTRAN programs are provided.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA-CR-175566 , NAS 1.26:175566 , CSDL-R-1629
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    Analyses of large quasistatic deformations of inelastic bodies by a new hybrid-stress finite element algorithm - Applications (1983)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: A new hybrid-stress finite element algorithm suitable for analyzing large quasistatic deformations of inelastic solids is presented and its feasibility and performance are demonstrated with examples. The algorithm provides extremely accurate bifurcation analysis which is stable with respect to variation in the finite element mesh, so long as the same type of element is used in every mesh. When the mesh element is varied, the result changes in a predictable manner. The method does not necessarily lead to an upper or lower bound for the critical load. An explicit forward gradient scheme is used to improve stability and is shown to be useful also for elongation-dominated deformations. The application of the method to the onset of necking in plane extension and to deformation and stress in plane extension of an elasticoviscous fluid with an array of cylindrical voids is given in detail.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: Computer Methods in Applied Mechanics and Engineering (ISSN 0045-7825); 40; 171-198
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    Analyses of large quasistatic deformations of inelastic bodies by a new hybrid-stress finite element algorithm (1983)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: A new hybrid-stress finite element algorithm, suitable for analyses of large, quasistatic, inelastic deformations, is presented. The algorithm is base upon a generalization of de Veubeke's complementary energy principle. The principal variables in the formulation are the nominal stress rate and spin, and thg resulting finite element equations are discrete versions of the equations of compatibility and angular momentum balance. The algorithm produces true rates, time derivatives, as opposed to 'increments'. There results a complete separation of the boundary value problem (for stress rate and velocity) and the initial value problem (for total stress and deformation); hence, their numerical treatments are essentially independent. After a fairly comprehensive discussion of the numerical treatment of the boundary value problem, we launch into a detailed examination of the numerical treatment of the initial value problem, covering the topics of efficiency, stability and objectivity. The paper is closed with a set of examples, finite homogeneous deformation problems, which serve to bring out important aspects of the algorithm.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: Computer Methods in Applied Mechanics and Engineering (ISSN 0045-7825); 39; 245-295
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  • 239
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    Theoretical and software considerations for nonlinear dynamic analysis (1983)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: In the finite element method for structural analysis, it is generally necessary to discretize the structural model into a very large number of elements to accurately evaluate displacements, strains, and stresses. As the complexity of the model increases, the number of degrees of freedom can easily exceed the capacity of present-day software system. Improvements of structural analysis software including more efficient use of existing hardware and improved structural modeling techniques are discussed. One modeling technique that is used successfully in static linear and nonlinear analysis is multilevel substructuring. This research extends the use of multilevel substructure modeling to include dynamic analysis and defines the requirements for a general purpose software system capable of efficient nonlinear dynamic analysis. The multilevel substructuring technique is presented, the analytical formulations and computational procedures for dynamic analysis and nonlinear mechanics are reviewed, and an approach to the design and implementation of a general purpose structural software system is presented.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA-CR-174504 , NAS 1.26:174504 , SM-8
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    Research and development program for the development of advanced time-temperature dependent constitutive relationships. Volume 2: Programming manual (1983)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: The results of a 10-month research and development program for nonlinear structural modeling with advanced time-temperature constitutive relationships are presented. The implementation of the theory in the MARC nonlinear finite element code is discussed, and instructions for the computational application of the theory are provided.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA-CR-168191-VOL-2 , NAS 1.26:168191-VOL-2 , R83-956077-2
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  • 241
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    Research and development program for the development of advanced time-temperature dependent constitutive relationships. Volume 1: Theoretical discussion (1983)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: The results of a 10-month research and development program for the development of advanced time-temperature constitutive relationships are presented. The program included (1) the effect of rate of change of temperature, (2) the development of a term to include time independent effects, and (3) improvements in computational efficiency. It was shown that rate of change of temperature could have a substantial effect on the predicted material response. A modification to include time-independent effects, applicable to many viscoplastic constitutive theories, was shown to reduce to classical plasticity. The computation time can be reduced by a factor of two if self-adaptive integration is used when compared to an integration using ordinary forward differences. During the course of the investigation, it was demonstrated that the most important single factor affecting the theoretical accuracy was the choice of material parameters.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA-CR-168191-VOL-1 , NAS 1.26:168191-VOL-1 , R83-956077-1
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    A total life prediction model for stress concentration sites (1983)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: Fatigue crack growth tests were performed on center crack panels and radial crack hole samples. The data were reduced and correlated with the elastic parameter K taking into account finite width and corner crack corrections. The anomalous behavior normally associated with short cracks was not observed. Total life estimates for notches were made by coupling an initiation life estimate with a propagation life estimate.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA-CR-168225 , NAS 1.26:168225 , UDR-TR-83-57
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  • 243
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    Vertical drop test of a transport fuselage section located forward of the wing (1983)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: A Boeing 707 fuselage section was drop tested at the NASA Langley Research Center to measure structural, seat, and occupant response to vertical crack loads. Post-test inspection showed that the section bottom collapsed inward approximately 2 ft. Preliminary data traces indicated maximum normal accelerations of 20 g on the fuselage bottom, 10 to 12 g on the cabin floor, and 6.5 to 8 g in the pelvises of the anthropomorphic dummies.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA-TM-85679 , NAS 1.15:85679
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    The crack problem in a specially orthotropic shell with double curvature (1983)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: The crack problem of a shallow shell with two nonzero curvatures is considered. It is assumed that the crack lies in one of the principal planes of curvature and the shell is under Mode I loading condition. The material is assumed to be specially orthotropic. After giving the general formulation of the problem the asymptotic behavior of the stress state around the crack tip is examined. The analysis is based on Reissner's transverse shear theory. Thus, as in the bending of cracked plates, the asymptotic results are shown to be consistent with that obtained from the plane elasticity solution of crack problems. Rather extensive numerical results are obtained which show the effect of material orthotropy on the stress intensity factors in cylindrical and spherical shells and in shells with double curvature. Other results include the stress intensity factors in isotropic toroidal shells with positive or negative curvature ratio, the distribution of the membrane stress resultant outside the crack, and the influence of the material orthotropy on the angular distribution of the stresses around the crack tip. Previously announced in STAR as N83-16782
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: Engineering Fracture Mechanics (ISSN 0013-7944); 18; 3 19; 1983
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  • 245
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    Dynamic fields near a crack tip growing in an elastic-perfectly-plastic solid (1983)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: A full asymptotic solution is presented for the fields in the neighborhood of the tip of a steadily advancing crack in an incompressible elastic-perfectly-plastic solid. There are four findings for mode I crack growth in the plane strain condition. The first is that the entire crack tip in steady crack growth is surrounded by a plastic region and that no elastic unloading is predicted by the complete dynamic asymptotic solution. The second is that, in contrast to the quasi-static solution, the dynamic solution yields strain fields with a logarithmic singularity everywhere near the crack tip. The third is that whereas the stress field varies throughout the entire crack tip neighborhood, it does not exhibit behavior that can be approximated by a constant field followed by an essentially centered-fan field and then by another constant field, especially for small crack growth speeds. The fourth finding is that there are two shock fronts emanating from the crack tip across which certain stress and strain components undergo jump discontinuities. After reviewing the mode III steady-state crack growth, it is concluded that ductile fracture criteria for nonstationary cracks must be based on solutions that include the inertia effects and that for this purpose quasi-static solutions may be inadequate.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: Mechanics of Materials (ISSN 0167-6636); 2; April 19
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    The determination of the elastodynamic fields of an ellipsoidal inhomogeneity (1983)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: The determination of the elastodynamic fields of an ellipsoidal inhomogeneity is studied in detail via the eigenstrain approach. A complete formulation and a treatment of both types of eigenstrains for equivalence between the inhomogeneity problem and the inclusion problem are given. This approach is shown to be mathematically identical to other approaches such as the direct volume integral formulation. Expanding the eigenstrains and applied strains in the polynomial form in the position vector and satisfying the equivalence conditions at every point, the governing simultaneous algebraic equations for the unknown coefficients in the eigenstrain expansion are derived. The elastodynamic field outside an ellipsoidal inhomogeneity in a linear elastic isotropic medium is given as an example. The angular and frequency dependence of the induced displacement field, as well as the differential and total cross sections are formally given in series expansion form for the case of uniformly distributed eigenstrains.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: ASME PAPER 83-APM-19 , (ISSN 0021-8936)
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    Vibrations of cantilevered circular cylindrical shells Shallow versus deep shell theory (1983)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: Free vibrations of cantilevered circular cylindrical shells having rectangular planforms are studied in this paper by means of the Ritz method. The deep shell theory of Novozhilov and Goldenveizer is used and compared with the usual shallow shell theory for a wide range of shell parameters. A thorough convergence study is presented along with comparisons to previously published finite element solutions and experimental results. Accurately computed frequency parameters and mode shapes for various shell configurations are presented. The present paper appears to be the first comprehensive study presenting rigorous comparisons between the two shell theories in dealing with free vibrations of cantilevered cylindrical shells.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: International Journal of Mechanical Sciences (ISSN 0020-7403); 25; 5 19; 1983
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    A quasi-Newton versus a homotopy method for nonlinear structural analysis (1983)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: The globally convergent quasi-Newton minimization algorithm and the homotopy algorithms are discussed in detail and their effectiveness in solving certain classes of highly nonlinear problems of structural analysis is demonstrated. The application of the double dogleg strategy controls the directions and step-lengths of the quasi-Newtonian algorithm and overcomes the problem of nonpositive definite Hessians being produced during the iteration process. The algorithms are applied to a centrally loaded clamped beam, the snap-through of a shallow arch, and a shallow reticulated dome.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: Computers and Structures (ISSN 0045-7949); 17; 4 19; 1983
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  • 249
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    Some analysis methods for rotating systems with periodic coefficients (1983)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: Two of the more common procedures for analyzing the stability and forced response of equations with periodic coefficients are reviewed: the use of Floquet methods, and the use of multiblade coordinate and harmonic balance methods. The analysis procedures of these periodic coefficient systems are compared with those of the more familiar constant coefficient systems. Previously announced in STAR as N82-23702
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: AIAA Journal (ISSN 0001-1452); 21; June 198
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    A three degree-of-freedom, typical section flutter analysis using harmonic transonic air forces (1983)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: Typical section flutter solutions are obtained using generalized air forces calculated with OPTRAN2, a program based on the transonic small perturbation potential equation, which uses potentials from a nonlinear solution to the steady flow to obtain linear unsteady air forces. Flutter results are calculated with a conventional, linear V-g type solution. Results are presented for a NACA 64A010 airfoil oscillating in plunge and pitch, and with a quarter-chord control surface in the Mach number range of 0.80 to 0.90. The flutter boundary shows a significant 'transonic' bucket, together with changes in flutter mode as, with increasing Mach numbers, a shock appears on the airfoil and then moves aft. Single degree-of-freedom instabilities associated with both the pitch and the control surface motions are identified.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: AIAA PAPER 83-0960
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  • 251
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    Edge effects in composites by moire interferometry (1983)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: The very high sensitivity of moire interferometry has permitted the present edge effect experiments to be conducted at a low average stress and strain level, assuring linear and elastic behavior in the composite material samples tested. Sensitivity corresponding to 2450 line/mm moire was achieved with a 0.408 micron/fringe. Simultaneous observations of the specimen face and edge displacement fields showed good fringe definition despite the 1-mm thickness of the specimens and the high gradients, and it is noted that the use of a carrier pattern and optical filtering was effective in even these conditions. Edge effects and dramatic displacement gradients were confirmed in angle-ply composite laminates.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: Experimental Techniques; 7; Jan. 198
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  • 252
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    Development of mixed time partition procedures for thermal analysis of structures (1983)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: (Previously announced in STAR as N82-23484)
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: International Journal for Numerical Methods in Engineering; 19; Jan. 198
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  • 253
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    CLFE2D: A generalized plane strain finite element program laminated composites subject to mechanical and hygrothermal loading (1983)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: CLFE2D is a two dimensional generalized plane strain finite element code, using a linear, four node, general quadrilateral, isoparametric element. The program is developed to calculate the displacements, strains, stresses, and strain energy densities in a finite width composite laminate. CLFE2D offers any combination of the following load types: nodal displacements, nodal forces, uniform normal strain, or hygrothermal. The program allows the user to input one set of three dimensional orthotropic material properties. The user can then specify the angle of material principal orientation for each element in the mesh. Output includes displacements, stresses, strains and strain densities at points selected by the user. An option is also available to plot the underformed and deformed finite element meshes.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA-CR-173507 , NAS 1.26:173507 , VPI-E-84-40 , IR-38
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  • 254
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    Experimental study of uncentralized squeeze film dampers (1983)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: The vibration response of a rotor system supported by a squeeze film damper (SFD) was experimentally investigated in order to provide experimental data in support of the Rotor/Stator Interactive Finite Element theoretical development. Part of the investigation required the designing and building of a rotor/SFD system that could operate with or without end seals in order to accommodate different SFD lengths. SFD variables investigated included clearance, eccentricity mass, fluid pressure, and viscosity and temperature. The results show inlet pressure, viscosity and clearance have significant influence on the damper performance and accompanying rotor response.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA-CR-168317 , NAS 1.26:168317 , NAUFP-202-2
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  • 255
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    Transient thermal stresses in a reinforced hollow disk or cylinder containing a radial crack (1983)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: The transient thermal stress problem in a hollow cylinder or a disk containing a radial crack is considered. It is assumed that the cylinder is reinforced on its inner boundary by a membrane which has thermoelastic constants different than those of the base material. The transient temperature, thermal stresses and the crack tip stress intensity factors are calculated in a cylinder which is subjected to a sudden change of temperature on the inside surface. The results are obtained for various dimensionless parameters and material constants. The special cases of the crack terminating at the cylinder-membrane interface and of the broken membrane are separately considered and some examples are given.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA-CR-173292 , NAS 1.26:173292
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    A cylindrical shell with a stress-free end which contains an axial part-through or through crack (1983)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: The interaction problem of a through or a part through crack with a stress free boundary in a semi-infinite cylindrical shell is considered. It is assumed that the crack lies in a meridional plane which is a plane of symmetry with respect to the external loads as well as the geometry. The circular boundary of the semi-infinite cylinder is assumed to be stress free. By using a transverse shear theory the problem is formulated in terms of a system of singular integral equations. The line spring model is used to treat the part through crack problem. In the case of a through crack the interaction between the perturbed stress fields due to the crack and the free boundary is quite strong and there is a considerable increase in the stress intensity factors caused by the interaction. On the other hand in the problem of a surface crack the interaction appears to be much weaker and consequently the magnification in the stress intensity factors is much less significant.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA-CR-173290 , NAS 1.26:173290
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  • 257
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    A pressurized cylindrical shell with a fixed end which contains an axial part-through or through crack (1983)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: A cylindrical shell having a very stiff and plate or a flange is considered. It is assumed that near the end the cylinder contains an axial flaw which may be modeled as a part through surface crack or a through crack. The effect of the end constraining on the stress intensity factor which is the main fracture mechanics parameter is studied. The applied loads acting on the cylinder are assumed to be axisymmetric. Thus the crack problem under consideration is symmetric with respect to the plane of the crack and consequently only the Mode 1 stress intensity factors are nonzero. With this limitation, the general perturbation problem for a cylinder with a built in end containing an axial crack is considered. Reissner's shell theory is used to formulate the problem. The part through crack problem is treated by using a line spring model. In the case of a crack tip terminating at the fixed end it is shown that the integral equations of the shell problem has the same generalized Cauchy kernel as the corresponding plane stress elasticity problem.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA-CR-173291 , NAS 1.26:173291
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  • 258
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    Propagation of crazing in viscoelastic media (1983)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: In response to a tensile stress glassy polymers exhibit crazing (surface cracks) which is a phenomenon of considerable practical and theoretical importance in the use of many plastics. An attempt is made to demonstrate how craze growth behavior is affected by the craze density (which is defined as the total number of crazes per unit surface area) surrounding the craze.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA-CR-173244 , NAS 1.26:173244
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  • 259
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    Restricted maximum principles for elastic bodies (1983)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: A maximum principle for the equilibrium of an elastic material body which is free of body forces is described not all of the components of the displacement vector or of the principal stresses can simultaneously have a strict maximum or minimum at any point in the body which does not be either on the surface or on a material interface.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA-CR-172255 , NAS 1.26:172255
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  • 260
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    Theoretical basis for design of thermal-stress-free fasteners (1983)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: A theoretical basis was developed for the design of fasteners which are free of thermal stress. A fastener can be shaped to eliminate the thermal stress which would otherwise result from differential thermal expansion between dissimilar fastener and sheet materials for many combinations of isotropic and orthotropic materials. The resulting joint remains snug, yet free of thermal stress at any temperature, if the joint is uniform in temperature, if it is frictionless, and if the coefficients of thermal expansion of the materials do not change with temperature. In general, such a fastener has curved sides; however, if both materials have isotropic coefficients of thermal expansion, a conical fastener is free of thermal stress. Equations are presented for thermal stress free shapes at both initial and final temperature, and typical fastener shapes are shown.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA-TP-2226 , L-15658 , NAS 1.60:2226
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  • 261
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    An improved finite-difference analysis of uncoupled vibrations of tapered cantilever beams (1983)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: An improved finite difference procedure for determining the natural frequencies and mode shapes of tapered cantilever beams undergoing uncoupled vibrations is presented. Boundary conditions are derived in the form of simple recursive relations involving the second order central differences. Results obtained by using the conventional first order central differences and the present second order central differences are compared, and it is observed that the present second order scheme is more efficient than the conventional approach. An important advantage offered by the present approach is that the results converge to exact values rapidly, and thus the extrapolation of the results is not necessary. Consequently, the basic handicap with the classical finite difference method of solution that requires the Richardson's extrapolation procedure is eliminated. Furthermore, for the cases considered herein, the present approach produces consistent lower bound solutions.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA-TM-83495 , E-1828 , NAS 1.15:83495
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  • 262
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    Three-dimensional analysis of chevron-notched specimens by boundary integral method (1983)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: The chevron-notched short bar and short rod specimens was analyzed by the boundary integral equations method. This method makes use of boundary surface elements in obtaining the solution. The boundary integral models were composed of linear triangular and rectangular surface segments. Results were obtained for two specimens with width to thickness ratios of 1.45 and 2.00 and for different crack length to width ratios ranging from 0.4 to 0.7. Crack opening displacement and stress intensity factors determined from displacement calculations along the crack front and compliance calculations were compared with experimental values and with finite element analysis.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA-CR-172225 , NAS 1.26:172225
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  • 263
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    Stability, vibration and passive damping of partially restrained imperfect columns (1983)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: A theoretical and experimental study of slender tubular columns for possible use in space structures is conducted in the presence of partial rotational end restraints. Explicit formulas are derived for computing the buckling load and the lowest natural frequency of perfectly straight uniform elastic members with rotational end restraints possessing linear moment-rotation characteristics. An exact solution in the form of a transcendental equation, and a numerical solution using second-order finite-differences are also presented. The presence of an initial imperfection is also incorporated into the numerical procedure. Vibration tests are conducted on an imperfect tubular steel member in the absence of an axial load. A damping concept consisting of a string-mass assembly is explored. Three passive damping configurations involving combinations of three lead shots were investigated. The three lead shot configurations provided considerably greater damping than the single lead shot.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA-TM-85697 , NAS 1.15:85697
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  • 264
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    Vertical drop test of a transport fuselage center section including the wheel wells (1983)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: A Boeing 707 fuselage section was drop tested to measure structural, seat, and anthropomorphic dummy response to vertical crash loads. The specimen had nominally zero pitch, roll and yaw at impact with a sink speed of 20 ft/sec. Results from this drop test and other drop tests of different transport sections will be used to prepare for a full-scale crash test of a B-720.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA-TM-85706 , NAS 1.15:85706
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  • 265
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    Aeroelastic analysis for propellers - mathematical formulations and program user's manual (1983)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: Mathematical development is presented for a specialized propeller dedicated version of the G400 rotor aeroelastic analysis. The G400PROP analysis simulates aeroelastic characteristics particular to propellers such as structural sweep, aerodynamic sweep and high subsonic unsteady airloads (both stalled and unstalled). Formulations are presented for these expanded propeller related methodologies. Results of limited application of the analysis to realistic blade configurations and operating conditions which include stable and unstable stall flutter test conditions are given. Sections included for enhanced program user efficiency and expanded utilization include descriptions of: (1) the structuring of the G400PROP FORTRAN coding; (2) the required input data; and (3) the output results. General information to facilitate operation and improve efficiency is also provided.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA-CR-3729 , NAS 1.26:3729 , UTRC83-6
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  • 266
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    Nonlinear dynamics and control of a vibrating rectangular plate (1983)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: The von Karman equations of nonlinear elasticity are solved for the case of a vibrating rectangular plate by meams of a Fourier spectral transform method. The amplification of a particular Fourier mode by nonlinear transfer of energy is demonstrated for this conservative system. The multi-mode system is reduced to a minimal (two mode) system, retaining the qualitative features of the multi-mode system. The effect of a modal control law on the dynamics of this minimal nonlinear elastic system is examined.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA-CR-172215 , NAS 1.26:172215
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  • 267
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    Vibration response of geometrically nonlinear elastic beams to pulse and impact loading (1983)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: The governing equations for the geometrically nonlinear deformation of elastic beams subjected to dynamic bending loads are developed and solved for various initial conditions. Of primary interest is the response to pulse loading and simulated impact. Both transient and several cycle solutions are generated for the free vibration response to pulse loading. The results obtained are compared to a first mode analysis approximation. A model is developed to simulate impact loading by the distribution of additional mass to the elastic system and subjecting it to a velocity pulse. The governing equations are solved using second order finite differences in space and time. The solutions obtained are in reasonable agreement with experimental results.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA-CR-174495 , NAS 1.26:174495
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  • 268
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    Effect of crack curvature on stress intensity factors for ASTM standard compact tension specimens (1983)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: The stress intensity factors (SIF) are calculated using the method of lines for the compact tension specimen in tensile and shear loading for curved crack fronts. For the purely elastic case, it was found that as the crack front curvature increases, the SIF value at the center of the specimen decreases while increasing at the surface. For the higher values of crack front curvatures, the maximum value of the SIF occurs at an interior point located adjacent to the surface. A thickness average SIF was computed for parabolically applied shear loading. These results were used to assess the requirements of ASTM standards E399-71 and E399-81 on the shape of crack fronts. The SIF is assumed to reflect the average stress environment near the crack edge.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA-CR-168280 , NAS 1.26:168280
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  • 269
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    Stress intensity factors in two bonded elastic layers containing cracks perpendicular to and on the interface. I Analysis. II - Solution and results (1983)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: The basic crack problem which is essential for the study of subcritical crack propagation and fracture of layered structural materials is considered. Because of the apparent analytical difficulties, the problem is idealized as one of plane strain or plane stress. An additional simplifying assumption is made by restricting the formulation of the problem to crack geometries and loading conditions which have a plane of symmetry perpendicular to the interface. The general problem is formulated in terms of a coupled systems of four integral equations. For each relevant crack configuration of practical interest, the singular behavior of the solution near and at the ends and points of intersection of the cracks is investigated and the related characteristic equations are obtained. The edge crack terminating at and crossing the interface, the T-shaped crack consisting of a broken layer and a delamination crack, the cross-shaped crack which consists of a delamination crack intersecting a crack which is perpendicular to the interface, and a delamination crack initiating from a stress-free boundary of the bonded layers are some of the practical crack geometries considered. Previously announced in STAR as N80-18428 and N80-18429
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: Engineering Fracture Mechanics (ISSN 0013-7944); 18; 3 19; 1983
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  • 270
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    Vibrations of cantilevered doubly-curved shallow shells (1983)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: Vibrational characteristics are determined for a previously unsolved class of problems, that of doubly-curved shallow shells having rectangular planforms, clamped along one edge and free on the other three. The solution procedure uses the Ritz method with algebraic polynomial trial functions. Convergence studies are made, and accurate frequencies and contour plots of mode shapes are presented for various curvature ratios, including spherical, circular cylindrical and hyperbolic paraboloidal shells. Particular emphasis is given to the effect of adding spanwise curvature to shells having chordwise curvature; numerous published references already exist for the case of zero spanwise curvature. The effects of changing aspect ratio, thickness ratio and Poisson's ratio are also studied.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: International Journal of Solids and Structures (ISSN 0020-7683); 19; 5 19; 1983
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  • 271
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    Dynamic analysis of constant-lift and free-tip rotors (1983)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: (Previously cited in issue 12, p. 2022, Accession no. A81-29479)
    Schlagwort(e): STRUCTURAL MECHANICS
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    Wrinkling phenomenon in structures. I - Model formulations (1983)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: Those structural element models which can suffer the wrinkling phenomenon are analyzed. A laminated elastic material, defined as a one-parametrical family of surfaces whose in-plane strains are negligible in comparison to the strains in the transverse direction, is analyzed in terms of its geometry, geometrical compatibility equations, layer geometry, kinematics, kinematical compatibility equations, and governing dynamical equations. These aspects are also examined for the case of a soft shell, defined as a shell for which the in-plane strains of the middle surface are negligible compared to the strains in the transverse direction, and for the case of a soft rod, defined as a rod for which the strains along the axis are negligible compared to the strains in the transverse direction. The influence of internal fluid flow on the wrinkling phenomenon for layers of laminated material and for a flexible pipe containing an inviscid and incompressible fluid is also analyzed.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: Solid Mechanics Archives (ISSN 0376-7426); 8; 3 19; 1983
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  • 273
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    Analysis of a thin-walled pressurized torus in contact with a plane (1983)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: Finite element analysis is applied to study the large deflection of a standing torus loaded by a plane. The internally pressurized thin-walled structure is found to have an elliptical footprint area. Considerable bulge occurs in the sidewall in the region of the load plane. Stress distributions throughout the torus are shown for various load levels and for various modeling strategies at a given load level. In large load ranges finite element calculations show compressive circumferential stress and negative curvature in the footprint region. Results are compared with inelastic wall analysis.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: AIAA PAPER 82-0702 , (ISSN 0001-1452)
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  • 274
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    Generic buckling curves for specially orthotropic rectangular plates (1983)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: Using a double affine transformation, the classical buckling equation for specially orthotropic plates and the corresponding virtual work theorem are presented in a particularly simple fashion. These dual representations are characterized by a single material constant, called the generalized rigidity ratio, whose range is predicted to be the closed interval from 0 to 1 (if this prediction is correct then the numerical results using a ratio greater than 1 in the specially orthotropic plate literature are incorrect); when natural boundary conditions are considered a generalized Poisson's ratio is introduced. Thus the buckling results are valid for any specially orthotropic material; hence the curves presented in the text are generic rather than specific. The solution trends are twofold; the buckling coefficients decrease with decreasing generalized rigidity ratio and, when applicable, they decrease with increasing generalized Poisson's ratio. Since the isotropic plate is one limiting case of the above analysis, it is also true that isotropic buckling coefficients decrease with increasing Poission's ratio.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: AIAA Journal (ISSN 0001-1452); 21; Aug. 198
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  • 275
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    Improvement of a large analytical model using test data (1983)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: Previously cited in issue 13, p. 2107, Accession no. A82-30108
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: (ISSN 0001-1452)
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    On the three-dimensional vibrations of the cantilevered rectangular parallelepiped (1983)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: A solution is presented for the three-dimensional problem of determining the free vibration frequencies and mode shapes for a rectangular parallelepiped which is completely fixed on one face and free on the other five faces. This problem apparently is previously unsolved in the published literature. The Ritz method is used, with displacements assumed in the form of algebraic polynomials. Convergence is studied. Numerical results are given for the first five frequencies of each of the four symmetry classes of vibration, for five thick parallelepiped configurations, including the cube. Contour plots are exhibited for the modal displacements of the cube. The effects of varying Poisson's ratio are also observed.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: Acoustical Society of America, Journal (ISSN 0001-4966); 73; June 198
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  • 277
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    Transient thermal stress problem for a circumferentially cracked hollow cylinder (1983)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: The paper is concerned with the transient thermal stress problem for a long hollow circular cylinder containing an internal axisymmetric circumferential edge crack that is suddenly cooled from inside. It is assumed that the transient thermal stress problem is quasi-static, i.e., the inertial effects are negligible. Also, all thermoelastic coupling effects and the possible temperature dependence of the thermoelastic constants are neglected. The problem is considered in two parts. The first part is the evaluation of transient thermal stresses in an uncracked cylinder; the second part is the isothermal perturbation problem for the cracked cylinder in which the crack surface tractions, equal and opposite to the thermal stresses obtained from the first problem, are the only external loads. The superposition of the two solutions gives results for the cracked cylinder.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: Journal of Thermal Stresses (ISSN 0149-5739); 6; Jan
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    A new strategy for stress analysis using the finite element method (1983)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: In the paper the authors examine the effectiveness of the Powell-Toint strategy for evaluating the Hessian of the potential energy surface of a finite element model that can be used for linear stress analysis and transient response predictions of structures. Cases for which the Powell-Toint strategy may be cost-effective with the conventional method of stress analysis are identified.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: Computers and Structures; 16; 5, 19; 1983
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    The effect of low velocity impact in the strength characteristics of composite materials laminates (1983)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: The nonlinear vibration response of a double cantilevered beam subjected to pulse loading over a central sector is studied. The initial response is generated in detail to ascertain the energetics of the response. The total energy is used as a gauge of the stability and accuracy of the solution. It is shown that to obtain accurate and stable initial solutions an extremely high spatial and time resolution is required. This requirement was only evident through an examination of the energy of the system. It is proposed, therefore, to use the total energy of the system as a necessary stability and accuracy criterion for the nonlinear response of conservative systems. The results also demonstrate that even for moderate nonlinearities, the effects of membrane forces have a significant influence on the system.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA-CR-170059 , NAS 1.26:170059
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    Documentation of computer program GRIDDEL (1983)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: The GRIDDEL computer program which generates finite element meshes for NASTRAN in a manner convenient to the study of laminated composite flat plates is discussed. The program is capable of creating 8 node HEXA elements, GRID coordinates, and PSOLID data in the appropriate NASTRAN format. It is more convenient for this purpose than use of NASTRAN's preprocessors.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA-CR-168123 , NAS 1.26:168123
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    Structures and Dynamics Division: Research and technology plans for FY 1983 and accomplishments for FY 1982 (1983)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: The objectives, expected results, approach, and milestones for research projects of the IPAD Project Office and the impact dynamics, structural mechanics, and structural dynamics branches of the Structures and Dynamics Division are presented. Research facilities are described. Topics covered include computer aided design; general aviation/transport crash dynamics; aircraft ground performance; composite structures; failure analysis, space vehicle dynamics; and large space structures.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA-TM-85661 , NAS 1.15:85661
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  • 282
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    Fixture for environmental exposure of structural materials under compression load (1983)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: A device for stressing a deformable material specimen consists of top plate and a bottom plate sandwiching a guide cylinder. The specimen is positioned on the bottom plate and attached to a load piston. Force is applied through the top plate into the guide cylinder. Once the specimen is loaded, the stress is maintained by tightening tie bolt nuts.
    Schlagwort(e): STRUCTURAL MECHANICS
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    On the suppression of zero energy deformation modes (1983)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: Based on the Hellinger-Reissner principle and the deformation energy due to assumed stresses and displacements, the problem of the kinematic deformation modes in assumed stress hybrid/mixed finite elements has been examined. Basic schemes are developed for the choice of assumed stress terms that will suppress all kinematic deformation modes. Quadrilateral membrane and axisymmetric elements, and three-dimensional hexahedral elements, are used to illustrate the suggested procedure.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: International Journal for Numerical Methods in Engineering (ISSN 0029-5981); 19; 1741-175
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    Potential of minicomputer/array-processor system for nonlinear finite-element analysis (1983)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: The potential of using a minicomputer/array-processor system for the efficient solution of large-scale, nonlinear, finite-element problems is studied. A Prime 750 is used as the host computer, and a software simulator residing on the Prime is employed to assess the performance of the Floating Point Systems AP-120B array processor. Major hardware characteristics of the system such as virtual memory and parallel and pipeline processing are reviewed, and the interplay between various hardware components is examined. Effective use of the minicomputer/array-processor system for nonlinear analysis requires the following: (1) proper selection of the computational procedure and the capability to vectorize the numerical algorithms; (2) reduction of input-output operations; and (3) overlapping host and array-processor operations. A detailed discussion is given of techniques to accomplish each of these tasks. Two benchmark problems with 1715 and 3230 degrees of freedom, respectively, are selected to measure the anticipated gain in speed obtained by using the proposed algorithms on the array processor.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA-TM-84566 , L-15532 , NAS 1.15:84566
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    Application of advanced reliability methods to local strain fatigue analysis (1983)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: When design factors are considered as random variables and the failure condition cannot be expressed by a closed form algebraic inequality, computations of risk (or probability of failure) might become extremely difficult or very inefficient. This study suggests using a simple, and easily constructed, second degree polynomial to approximate the complicated limit state in the neighborhood of the design point; a computer analysis relates the design variables at selected points. Then a fast probability integration technique (i.e., the Rackwitz-Fiessler algorithm) can be used to estimate risk. The capability of the proposed method is demonstrated in an example of a low cycle fatigue problem for which a computer analysis is required to perform local strain analysis to relate the design variables. A comparison of the performance of this method is made with a far more costly Monte Carlo solution. Agreement of the proposed method with Monte Carlo is considered to be good.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA-CR-168198 , NAS 1.26:168198
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    Vibration characteristics of a deployable controllable-geometry truss boom (1983)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: An analytical study was made to evaluate changes in the fundamental frequency of a two dimensional cantilevered truss boom at various stages of deployment. The truss could be axially deployed or retracted and undergo a variety of controlled geometry changes by shortening or lengthening the telescoping diagonal members in each bay. Both untapered and tapered versions of the truss boom were modeled and analyzed by using the finite element method. Large reductions in fundamental frequency occurred for both the untapered and tapered trusses when they were uniformly retracted or maneuvered laterally from their fully deployed position. These frequency reductions can be minimized, however, if truss geometries are selected which maintain cantilever root stiffness during truss maneuvers.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA-TP-2160 , L-15580 , NAS 1.60:2160
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  • 287
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    Statistical correlation of structural mode shapes from test measurements and NASTRAN analytical values (1983)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: The software and procedures of a system of programs used to generate a report of the statistical correlation between NASTRAN modal analysis results and physical tests results from modal surveys are described. Topics discussed include: a mathematical description of statistical correlation, a user's guide for generating a statistical correlation report, a programmer's guide describing the organization and functions of individual programs leading to a statistical correlation report, and a set of examples including complete listings of programs, and input and output data.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA-TM-86044 , NAS 1.15:86044
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  • 288
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    Aeromechanical stability of a hingeless rotor in hover and forward flight: Analysis and wind tunnel tests (1983)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: A research effort of analysis and testing was conducted to investigate the ground resonance phenomenon of a soft in-plane hingeless rotor. Experimental data were obtained using a 9 ft. (2.74 m) diameter model rotor in hover and forward flight. Eight model rotor configurations were investigated. Configuration parameters included pitch flap coupling, blade sweep and droop, and precone of the blade feathering axis. An analysis based on a comprehensive analytical model of rotorcraft aerodynamics and dynamics was used. The moving block was used to experimentally determine the regressing lead lag mode damping. Good agreement was obtained between the analysis and test. Both analysis and experiment indicated ground resonance instability in hover. An outline of the analysis, a description of the experimental model and procedures, and comparison of the analytical and experimental data are presented.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA-TM-85683 , NAS 1.15:85683 , AVRADCOM-TR-83-B-5 , AD-A134612
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  • 289
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    Parametric tip effects for conformable rotor applications (1983)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: A research study was initiated to systematically determine the impact of selected blade tip geometric parameters on aeroelasticity conformable rotor performance and loads characteristics. The model articulated rotors included baseline and torsionally soft blades with interchangeable tips. Seven blade tip designs were evaluated on the baseline rotor and three tip designs were tested on the torsionally soft blades. The designs incorporated a systematic variation in three geometric parameters: sweep, taper, and anhedral. The rotors were evaluated in the NASA Langley Transonic Dynamics Tunnel at several advance ratios, lift and propulsive force values, and tip Mach numbers. Based on the test results, tip parameter variations generated significant rotor performance and loads difference for both baseline and torsionally soft blades. Azimuthal variation of elastic twist generated by the tip parameters strongly correlated with rotor performance and loads, but the magnitude of advancing blade elastic twist did not correlate.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA-TM-85682 , NAS 1.15:85682 , AVRADCOM-TR-83-B-4 , AD-A134633
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  • 290
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    Vibration control of large linear quadratic symmetric systems (1983)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: Some unique properties on a class of the second order lambda matrices were found and applied to determine a damping matrix of the decoupled subsystem in such a way that the damped system would have preassigned eigenvalues without disturbing the stiffness matrix. The resulting system was realized as a time invariant velocity only feedback control system with desired poles. Another approach using optimal control theory was also applied to the decoupled system in such a way that the mode spillover problem could be eliminated. The procedures were tested successfully by numerical examples.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA-CR-174536 , NAS 1.26:174536
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  • 291
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    A note on the cracked plates reinforced by a line stiffener (1983)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: The problem of a cracked plate reinforced by a line stiffener is reconsidered. The original solution of this problem was given in the literature. Also, a variation of the problem with debonding between the plate and the stiffener near the cracked region was reported in the literature. However, the special case of the problem in which the crack tip terminates at the stiffener does not appear to have been studied. In practice, the solution may be necessary in order to assess the crack arrest effectiveness of the stiffener. The problem of a stiffened plate with a crack is reformulated, the asymptotic stress state near the crack tip terminating at the stiffener is examined, and numerical results are given for various stiffness constants. Previously announced in STAR as N83-21388
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: Engineering Fracture Mechanics (ISSN 0013-7944); 18; 6 19; 1983
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    The crack problem for a nonhomogeneous plane (1983)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: The plane elasticity problem for a nonhomogeneous medium containing a crack is considered. It is assumed that the Poisson's ratio of the medium is constant and the Young's modulus E varies exponentially with the coordinate parallel to the crack. First the half plane problem is formulated and the solution is given for arbitrary tractions along the boundary. Then the integral equation for the crack problem is derived. It is shown that the integral equation having the derivative of the crack surface displacement as the density function has a simple Cauchy type kernel. Hence, its solution and the stresses around the crack tips have the conventional square root singularity. The solution is given for various loading conditions. The results show that the effect of the Poisson's ratio and consequently that of the thickness constraint on the stress intensity factors are rather negligible.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: ASME PAPER 83-APM-35
    Format: text
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    Vibrations of blades with variable thickness and curvature by shell theory (1983)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: A procedure for analyzing the vibrations of rotating turbomachinery blades has been previously developed. This procedure is based upon shallow shell theory, and utilizes the Ritz method to determine frequencies and mode shapes. However, it has been limited heretofore to blades of uniform thickness, uniform curvature, and/or twist and rectangular planform. The present work shows how the procedure may be generalized to eliminate the aforementioned restrictions. Nonrectangular planforms are dealt with by a suitable coordinate transformation. This, as well as variable thickness, curvature and twist, require using numerical integration. The procedure is demonstrated on four examples of cantilevered blades for which theoretical and experimental data have been previously published: (1) flat plate with spanwise taper, (2) flat plate with chordwise taper, (3) twisted plate with chordwise taper, and (4) cylindrical shell with chordwise taper.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: ASME PAPER 83-GT-152
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  • 294
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    Internal and edge cracks in a plate of finite width under bending (1983)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: In this paper the title problem is studied by using Reissner's transverse shear theory. The main purpose of the paper is to investigate the effect of stress-free boundaries on the stress intensity factors in plates under bending. Among the results found particularly interesting are those relating to the limiting cases of the crack geometries. The numerical results are given for a single internal crack, two collinear cracks, and two edge cracks. Also studied is the effect of Poisson's ratio on the stress intensity factors.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: ASME, Transactions, Journal of Applied Mechanics (ISSN 0021-8936); 50; Sept
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    Integrated thermal-structural approach for shells of revolution (1983)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: Previously cited in issue 13, p. 2106, Accession no. A82-30094
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: (ISSN 0001-1452)
    Format: text
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    Damage tolerant design using collapse techniques (1983)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: Previously cited in issue 13, p. 2110, Accession no. A82-30168
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: (ISSN 0001-1452)
    Format: text
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    Robust penalty method for structural synthesis (1983)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: The Sequential Unconstrained Minimization Technique (SUMT) offers an easy way of solving nonlinearly constrained problems. However, this algorithm frequently suffers from the need to minimize an ill-conditioned penalty function. An ill-conditioned minimization problem can be solved very effectively by posing the problem as one of integrating a system of stiff differential equations utilizing concepts from singular perturbation theory. This paper evaluates the robustness and the reliability of such a singular perturbation based SUMT algorithm on two different problems of structural optimization of widely separated scales. The report concludes that whereas conventional SUMT can be bogged down by frequent ill-conditioning, especially in large scale problems, the singular perturbation SUMT has no such difficulty in converging to very accurate solutions.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: Journal of Engineering Mechanics (ISSN 0733-9399); 109; Aug. 198
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    Radiation exchange in large space structures and frames (1983)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: The analysis of radiation heat transfer is determined by the need to determine the geometrical quantity, F(ij), which is commonly called the view factor, and which represents the fraction of energy leaving surface i which strikes surface j. The present investigation shows that the use of a rotating plane to model a one-dimensional radiation element is both computationally efficient and accurate. Because of the reduced computational cost of this element, radiation view factors for complex structures can be calculated directly. Under some conditions, the characteristics of the one-dimensional element may lead to a loss in accuracy when it is used to model obstructing cylinders. In cases in which the element is too close to the radiating surfaces, curved surfaces must be represented by a collection of flat planes. However, it appears that as long as the one-dimensional element is more than 5 diameters from the other surfaces, its use is valid.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: AIAA PAPER 83-1462
    Format: text
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  • 299
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    Extrapolation of optimum design based on sensitivity derivatives (1983)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: In many applications, it is useful to have information regarding the effect of the perturbations of the design problem constants (parameters) on the optimum solution of the problem. Sobieszczanski-Sobieski et al. (1981) have, therefore, proposed to utilize an optimum sensitivity analysis as a structural design tool to assess the parameter perturbation effects by extrapolations based on optimum sensitivity derivatives. The present investigation is concerned with an example of optimum sensitivity analysis involving a composite panel. The case was selected in connection with the nonlinearity of the constraints and, the tendency for a set of active constraints to change when the parameters are disturbed. Under these adverse conditions, sensitivity derivatives are used in linear extrapolations to extend optimization information over a limited range of variation for a typical parameter.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: AIAA Journal (ISSN 0001-1452); 21; May 1983
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    Creep fatigue life prediction for engine hot section materials (isotropic) (1983)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: The activities performed during the first year of the NASA HOST Program, Creep Fatigue Life Prediction for Engine Hot Section Materials (Isotropic), being conducted by Pratt & Whitney Aircraft are summarized. The program is a 5 year, two part effort aimed at improving the high temperature crack initiation prediction technology for gas turbine hot section components. Significant results of the program produced thus far are discussed. Cast B1900 + Hf and wrought IN 718 were selected as the base and alternate materials, respectively. A single heat of B1900 + Hf was obtained and test specimens fabricated. The material was characterized with respect to grain size, gamma prime size, carbide distribution, and dislocation density. Monotonic tensile and creep testing has shown engineering properties within anticipated scatter for this material. Examination of the tensile tests has shown a transition from inhomogeneous planar slip within the grains at lower temperatures to more homogeneous matrix deformation. Examination of the creep tests has shown a transgranular failure mode at 1400 F and an intergranular failure mode at 1600 F and 1800 F.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA. Lewis Research Center Turbine Eng. Hot Sect. Technol. (HOST); p 209-210
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