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  • General Chemistry  (9,374)
  • Cell & Developmental Biology  (3,632)
  • STRUCTURAL MECHANICS  (2,702)
  • ddc:330
  • 1980-1984  (8,498)
  • 1970-1974  (7,210)
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Keywords
Publisher
Years
Year
  • 101
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    Quasi-static solution algorithms for kinematically/materially nonlinear thermomechanical problems (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: This paper develops an algorithmic solution strategy which allows the handling of positive/indefinite stiffness characteristics associated with the pre- and post-buckling of structures subject to complex thermomechanical loading fields. The flexibility of the procedure is such that it can be applied to both finite difference and element-type simulations. Due to the generality of the algorithmic approach developed, both kinematic and thermal/mechanical type material nonlinearity including inelastic effects can be treated. This includes the possibility of handling completely general thermomechanical boundary conditions. To demonstrate the scheme, the results of several benchmark problems is presented.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Thermal Stresses (ISSN 0149-5739); 7; 3-4; 227-257
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  • 102
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    Analysis of large, non-isothermal elastic-visco-plastic deformations (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The development of a general mathematical model and solutions of test problems to analyze large nonisothermal elasto-visco-plastic deformatisms of structures is discussed. Geometric and material type nonlinearities of higher order are present in the development of the mathematical model and in the developed solution methodology.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-176220 , NAS 1.26:176220
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  • 103
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    Three-dimensional finite element and dynamic analysis of composite laminate subjected to impact (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A three dimensional finite element and dynamic analysis has been made for a layered fiber-reinforced composite laminate subjected to a given impact loading. Central difference method is employed in this analysis. The numerical results for the transient response of the laminate are presented.
    Keywords: STRUCTURAL MECHANICS
    Type: Computers and Structures (ISSN 0045-7949); 19; 5-6
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  • 104
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    Computation of eigenpairs of Ax = lambda Bx for vibrations of spinning deformable bodies (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: It is shown that, when linear theory is used, the general eigenvalue problem related with the free vibrations of spinning deformable bodies is of the type AX = lambda Bx, where A is Hermitian, and B is real positive definite. Since the order n of the matrices may be large, and A and B are banded or block banded, due to the economics of the numerical solution, one is interested in obtaining only those eigenvalues which fall within the frequency band of interest of the problem. The paper extends the well known method of bisections and iteration of R to the n power to n dimensional complex spaces, i.e., to C to the n power, so that it can be applied to the present problem.
    Keywords: STRUCTURAL MECHANICS
    Type: Computers and Structures (ISSN 0045-7949); 19; 5-6
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  • 105
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    Development and testing of stable, invariant, isoparametric curvilinear 2- and 3-D hybrid-stress elements (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Linear and quadratic Serendipity hybrid-stress elements are examined in respect of stability, coordinate invariance, and optimality. A formulation based upon symmetry group theory successfully addresses these issues in undistorted geometries and is fully detailed for plane elements. The resulting least-order stable invariant stress polynomials can be applied as astute approximations in distorted cases through a variety of tensor components and variational principles. A distortion sensitivity study for two- and three-dimensional elements provides favorable numerical comparisons with the assumed displacement method.
    Keywords: STRUCTURAL MECHANICS
    Type: Computer Methods in Applied Mechanics and Engineering (ISSN 0045-7825); 47; 331-356
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  • 106
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    Geometrically nonlinear analysis of laminated elastic structures (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Laminated composite plates and shells that can be used to model automobile bodies, aircraft wings and fuselages, and pressure vessels among many other were analyzed. The finite element method, a numerical technique for engineering analysis of structures, is used to model the geometry and approximate the solution. Various alternative formulations for analyzing laminated plates and shells are developed and their finite element models are tested for accuracy and economy in computation. These include the shear deformation laminate theory and degenerated 3-D elasticity theory for laminates.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-175609 , NAS 1.26:175609 , PB85-127173 , VPI-E-84-36
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  • 107
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    Structural sensitivity analysis: Methods, applications and needs (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Innovative techniques applicable to sensitivity analysis of discretized structural systems are reviewed. The techniques include a finite difference step size selection algorithm, a method for derivatives of iterative solutions, a Green's function technique for derivatives of transient response, simultaneous calculation of temperatures and their derivatives, derivatives with respect to shape, and derivatives of optimum designs with respect to problem parameters. Computerized implementations of sensitivity analysis and applications of sensitivity derivatives are also discussed. Some of the critical needs in the structural sensitivity area are indicated along with plans for dealing with some of those needs.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-85827 , NAS 1.15:85827 , Symp. on Recent Experiences in Multidisciplinary Analysis and Optimization; Hampton, VA; United States
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  • 108
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    On stress analysis of a crack-layer (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: This work considers the problem of elastic interaction of a macrocrack with an array of microcracks in the vicinity of the macrocrack tip. Using the double layer potential techniques, the solution to the problem within the framework of the plane problem of elastostatics has been obtained. Three particular problems of interest to fracture mechanics have been analyzed. It follows from analysis that microcrack array can either amplify or reduce the resulting stress field of the macrocrack-microcrack array system depending on the array's configuration. Using the obtained elastic solution the energy release rate associated with the translational motion of the macrocrack-microcrack array system has been evaluated.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-174774 , NAS 1.26:174774
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  • 109
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    Stability and Convergence of Underintegrated Finite Element Approximations (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The effects of underintegration on the numerical stability and convergence characteristics of certain classes of finite element approximations were analyzed. Particular attention is given to hourglassing instabilities that arise from underintegrating the stiffness matrix entries and checkerboard instabilities that arise from underintegrating constrain terms such as those arising from incompressibility conditions. A fundamental result reported here is the proof that the fully integrated stiffness is restored in some cases through a post-processing operation.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Lewis Research Center Nonlinear Struct. Anal.; p 95-103
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  • 110
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    Three-dimensional Stress Analysis Using the Boundary Element Method (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The boundary element method is to be extended (as part of the NASA Inelastic Analysis Methods program) to the three-dimensional stress analysis of gas turbine engine hot section components. The analytical basis of the method (as developed in elasticity) is outlined, its numerical implementation is summarized, and the approaches to be followed in extending the method to include inelastic material response indicated.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Lewis Research Center Nonlinear Struct. Anal.; p 149-160
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  • 111
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    Statistical failure prediction models for brittle materials (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Previously cited in issue 13, p. 2107, Accession no. A82-30104
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA Journal (ISSN 0001-1452); 22; 135-140
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  • 112
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    Experimental stress analysis of a thin walled pressurized torus loaded by contact with a plane (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Previously cited in issue 13, p. 2108, Accession no. A82-30114
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA Journal (ISSN 0001-1452); 22; 124-127
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  • 113
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    Slave finite elements: The temporal element approach to nonlinear analysis (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A formulation method for finite elements in space and time incorporating nonlinear geometric and material behavior is presented. The method uses interpolation polynomials for approximating the behavior of various quantities over the element domain, and only explicit integration over space and time. While applications are general, the plate and shell elements that are currently being programmed are appropriate to model turbine blades, vanes, and combustor liners.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Lewis Research Center Nonlinear Struct. Anal.; p 1-16
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  • 114
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    Cyclic torsion testing (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Torsional fatigue testing and data analysis procedures are described. Since there are no standards governing cyclic torsion testing that are generally accepted on a widespread basis by the technical community, the different approaches that dominate current experimental activity, and the ramifications of each are discussed. Particular attention is given to the theoretical and experimental difficulties that have paced refinement and general acceptance of test procedures. Finally, specific quantities and nomenclature modelled after analagous axial fatigue properties are suggested as an effective way to communicate torsional fatigue results until accepted standards are established.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-83756 , E-2232 , NAS 1.15:83756
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  • 115
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    Large deflections of circular isotropic membranes subjected to arbitrary axisymmetric loading (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Circular membranes with fixed peripheral edges, subjected to arbitrary axisymmetric loading are analyzed. A single governing differential equation in terms of radial stress is used. This nonlinear governing equation is solved using the finite difference method in conjunction with Newton-Raphson method. Three loading cases, namely (1) uniformly loaded membrane, (2) a membrane with uniform load over an inner portion, and (3) a membrane with ring load, are analyzed. Calculated central displacement and the central and edge radial stresses for uniformly loaded membrane, agree extremely well with the classical solution.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-86271 , NAS 1.15:86271
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  • 116
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    Nonlinear displacement analysis of advanced propeller structures using NASTRAN (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The steady state displacements of a rotating advanced turboprop are computed using the geometrically nonlinear capabilities of COSMIC NASTRAN Rigid Format 4 and MSC NASTRAN Solution 64. A description of the modified Newton-Raphson algorithm used by Solution 64 and the iterative scheme used by Rigid Format 4 is provided. A representative advanced turboprop, SR3, was used for the study. Displacements for SR3 are computed for rotational speeds up to 10,000 rpm. The results show Solution 64 to be superior for computating displacements of flexible rotating structures. This is attributed to its ability to update the displacement dependent centrifugal force during the solution process.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-83737 , E-2222 , NAS 1.15:83737
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  • 117
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    Fatigue and Fracture Branch: A compendium of recently completed and on-going research projects (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: This compendium of recently completed and ongoing research projects from the Fatigue and Fracture Branch at NASA Langley Research Center provides technical descriptions and key results of all such projects expected to lead to publication of significant findings. The common thread to all these studies is the application of fracture mechanics analyses to engineering problems in metals and composites, with particular emphasis on airframe structural materials. References to recent publications are included where appropriate.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-85825 , NAS 1.15:85825
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  • 118
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    Methods for analysis of cracks in three-dimensional solids (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Various analytical and numerical methods used to evaluate the stress intensity factors for cracks in three-dimensional (3-D) solids are reviewed. Classical exact solutions and many of the approximate methods used in 3-D analyses of cracks are reviewed. The exact solutions for embedded elliptic cracks in infinite solids are discussed. The approximate methods reviewed are the finite element methods, the boundary integral equation (BIE) method, the mixed methods (superposition of analytical and finite element method, stress difference method, discretization-error method, alternating method, finite element-alternating method), and the line-spring model. The finite element method with singularity elements is the most widely used method. The BIE method only needs modeling of the surfaces of the solid and so is gaining popularity. The line-spring model appears to be the quickest way to obtain good estimates of the stress intensity factors. The finite element-alternating method appears to yield the most accurate solution at the minimum cost.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-86266 , NAS 1.15:86266
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  • 119
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    Support structures for large infrared telescopes (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: An infrared telescope requires an accuracy of its reflecting surfaces of less than a micrometer. Future missions may require such accuracy from telescopes that are 20 meters or larger in diameter. The structure for supporting such a telescope will most probably take the form of a deep truss. Various approaches for constructing the primary mirror in space are illustrated. One that employs automated deployment of interconnected reflector-structure modules was described in detail. Estimates were made of the precision obtainable with properly configured truss structures and the required ability of active control systems for achieving the desired accuracy.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-3800 , NAS 1.26:3800 , ARC-TN-1121
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  • 120
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    The effect of thickness on fatigue crack propagation in 7475-T731 aluminum alloy sheet (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Tests were conducted on three thicknesses of 7475-T731 aluminum alloy sheet to investigate the effect of thickness on fatigue crack propagation under constant amplitude loading conditions and on retardation following a single peak overload. Constant amplitude loading tests were performed at stress ratios of 0.05 and 0.75 to obtain data for conditions with crack closure and without crack closure, respectively. At both stress ratios a thickness effect was clearly evident, with thicker specimens exhibiting higher growth rates in the transition from plane strain to plane stress region. The effect of thickness for a stress ratio of 0.05 corresponded well with the fracturing mode transitions observed on the specimens. A model based on the strain energy release rate which accounted for the fracture mode transition was found to correlate the thickness effects well. The specimens tested at the stress ratio of 0.75 did not make the transition from tensile mode to shear mode, indicating that another mechanism besides crack closure or fracture mode transition was active.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-172367 , NAS 1.26:172367
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  • 121
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    Three-dimensional finite-element analysis of chevron-notched fracture specimens (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Stress-intensity factors and load-line displacements were calculated for chevron-notched bar and rod fracture specimens using a three-dimensional finite-element analysis. Both specimens were subjected to simulated wedge loading (either uniform applied displacement or uniform applied load). The chevron-notch sides and crack front were assumed to be straight. Crack-length-to-specimen width ratios (a/w) ranged from 0.4 to 0.7. The width-to-thickness ratio (w/B) was 1.45 or 2. The bar specimens had a height-to-width ratio of 0.435 or 0.5. Finite-element models were composed of singularity elements around the crack front and 8-noded isoparametric elements elsewhere. The models had about 11,000 degrees of freedom. Stress-intensity factors were calculated by using a nodal-force method for distribution along the crack front and by using a compliance method for average values. The stress intensity factors and load-line displacements are presented and compared with experimental solutions from the literature. The stress intensity factors and load-line displacements were about 2.5 and 5 percent lower than the reported experimental values, respectively.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-85798 , NAS 1.15:85798
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  • 122
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    The ASTRO-1 preliminary design review coupled load analysis (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Results of the ASTRO-1 preliminary design review coupled loads analysis are presented. The M6.0Y Generic Shuttle mathematical models were used. Internal accelerations, interface forces, relative displacements, and net e.g., accelerations were recovered for two ASTRO-1 payloads in a tandem configuration. Twenty-seven load cases were computed and summarized. Load exceedences were found and recommendations made.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-82587 , NAS 1.15:82587
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  • 123
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    A computer program for predicting nonlinear uniaxial material responses using viscoplastic models (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A computer program was developed for predicting nonlinear uniaxial material responses using viscoplastic constitutive models. Four specific models, i.e., those due to Miller, Walker, Krieg-Swearengen-Rhode, and Robinson, are included. Any other unified model is easily implemented into the program in the form of subroutines. Analysis features include stress-strain cycling, creep response, stress relaxation, thermomechanical fatigue loop, or any combination of these responses. An outline is given on the theoretical background of uniaxial constitutive models, analysis procedure, and numerical integration methods for solving the nonlinear constitutive equations. In addition, a discussion on the computer program implementation is also given. Finally, seven numerical examples are included to demonstrate the versatility of the computer program developed.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-83675 , E-2120 , NAS 1.15:83675
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  • 124
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    Structures and Dynamics Division research and technology plans for FY 1894 and accomplishments for FY 1982 (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The Objectives, Expected Results, Approach, and Fiscal Year FY 1984 Milestones for the Structures and Dynamics Division's research programs are examined. The FY 1983 Accomplishments are presented where applicable.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-85828 , NAS 1.15:85828
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  • 125
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    Spartan Release Engagement Mechanism (REM) stress and fracture analysis (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The revised stress and fracture analysis of the Spartan REM hardware for current load conditions and mass properties is presented. The stress analysis was performed using a NASTRAN math model of the Spartan REM adapter, base, and payload. Appendix A contains the material properties, loads, and stress analysis of the hardware. The computer output and model description are in Appendix B. Factors of safety used in the stress analysis were 1.4 on tested items and 2.0 on all other items. Fracture analysis of the items considered fracture critical was accomplished using the MSFC Crack Growth Analysis code. Loads and stresses were obtaind from the stress analysis. The fracture analysis notes are located in Appendix A and the computer output in Appendix B. All items analyzed met design and fracture criteria.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-171091 , NAS 1.26:171091 , LMSC-HREC-TR-D951498
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  • 126
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    An investigation into the probabilistic combination of quasi-static and random accelerations (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The development of design load factors are investigated for aerospace and aircraft components and experiment support structures, which are subject to a simultaneous vehicle dynamic vibration and acoustically generated random vibration. The characteristics of the combined acceleration probability density function is determined, and an appropriate percentile level for the combined acceleration is selected. This mechanism is developed and graphical data is provided to select combined accelerations for most popular percentile levels.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-82584 , NAS 1.15:82584
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  • 127
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    VIBRA: An interactive computer program for steady-state vibration response analysis of linear damped structures (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: An interactive steady state frequency response computer program with graphics is documented. Single or multiple forces may be applied to the structure using a modal superposition approach to calculate response. The method can be reapplied to linear, proportionally damped structures in which the damping may be viscous or structural. The theoretical approach and program organization are described. Example problems, user instructions, and a sample interactive session are given to demonstate the program's capability in solving a variety of problems.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-85789-REV , L-15771-REV , NAS 1.15:85789-REV , AVSCOM-TM-84-B-1-REV
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  • 128
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    Pyrotechnic shock: A literature survey of the Linear Shaped Charge (LSC) (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Linear shaped charge (LSC) literature for the past 20 years is reviewed. The following topics are discussed: (1) LSC configuration; (2) LSC usage; (3) LSC induced pyroshock; (4) simulated pyrotechnic testing; (5) actual pyrotechnic testing; (6) data collection methods; (7) data analysis techniques; (8) shock reduction methods; and (9) design criteria. Although no new discoveries have been made in LSC research, charge shapes are improved to allow better cutting performance, testing instrumentation is refined, and some new explosives, for use in LSC, are formulated.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-82583 , NAS 1.15:82583
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  • 129
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    Finite element thermal-structural analysis of cable-stiffened space structues (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Finite element thermal-structural analyses of large, cable-stiffened space structures are presented. A computational scheme for the calculation of prestresses in the cable-stiffened structures is also described. The determination of thermal loads on orbiting space structures due to environment heating is discussed briefly. Three finite element structural analysis techniques are presented for the analysis of prestressed structures. Linear, stress stiffening, and large displacement analysis techniques were investigated. These three techniques were employed for analysis of prestressed cable structures at different prestress levels. The analyses produced similar results at small prestress, but at higher prestress, differences between the results became significant. For the cable-stiffened structures studied, the linear analysis technique may not provide acceptable results. The stress stiffening analysis technique may yield results of acceptable accuracy depending upon the level of prestress. The large displacement analysis technique produced accurate results over a wide range of prestress and is recommended as a general analysis technique for thermal-structural analysis of cable-stiffened space structures.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-173709 , NAS 1.26:173709
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  • 130
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    An aeroelastician's perspective of wind tunnel and flight experiences with active control of structural response and stability (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Active controls technology is assessed based on a review of most of the wind-tunnel and flight tests and actual applications of active control concepts since the late sixties. The distinction is made between so-called ""rigid-body'' active control functions and those that involve significant modification of structural elastic response or stability. Both areas are reviewed although the focus is on the latter area. The basic goals and major results of the various studies or applications are summarized, and the anticipated use of active controls on current and near-future research and demonstration aircraft is discussed. Some of the ""holes'' remaining in the feasbility/benefits demonstration of active controls technology are examined.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-85761 , NAS 1.15:85761
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  • 131
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    Prediction of fatigue crack-growth patterns and lives in three-dimensional cracked bodies (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Fatigue crack growth patterns and lives for surface cracks, surface cracks at holes, and corner cracks at holes in three dimensional bodies were predicted using linear-elastic fracture mechanics concepts that were modified to account for crack-closure behavior. The predictions were made by using stress intensity factor equations for these crack configurations and the fatigue crack-growth (delta K against rate) relationship for the material of interest. The crack configurations were subjected to constant-amplitude fatigue loading under either remote tension or bending loads. The predicted crack growth patterns and crack growth lives for aluminum alloys agreed well with test data from the literature.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-85787 , NAS 1.15:85787
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    Mixed Models and Reduction Techniques for Large-Rotation, Nonlinear Analysis of Shells of Revolution with Application to Tires (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: An effective computational strategy is presented for the large-rotation, nonlinear axisymmetric analysis of shells of revolution. The three key elements of the computational strategy are: (1) use of mixed finite-element models with discontinuous stress resultants at the element interfaces; (2) substantial reduction in the total number of degrees of freedom through the use of a multiple-parameter reduction technique; and (3) reduction in the size of the analysis model through the decomposition of asymmetric loads into symmetric and antisymmetric components coupled with the use of the multiple-parameter reduction technique. The potential of the proposed computational strategy is discussed. Numerical results are presented to demonstrate the high accuracy of the mixed models developed and to show the potential of using the proposed computational strategy for the analysis of tires.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TP-2343 , L-15802 , NAS 1.60:2343
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  • 133
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    Periodic control of the individual-blade-control helicopter rotor (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Results of an investigation into methods of controller design for an individual helicopter rotor blade in the high forward-flight speed regime are described. This operating condition poses a unique control problem in that the perturbation equations of motion are linear with coefficients that vary periodically with time. The design of a control law was based on extensions to modern multivariate synthesis techniques and incorporated a novel approach to the reconstruction of the missing system state variables. The controller was tested on both an electronic analog computer simulation of the out-of-plane flapping dynamics, and on a four foot diameter single-bladed model helicopter rotor in the M.I.T. 5x7 subsonic wind tunnel at high levels of advance ratio. It is shown that modal control using the IBC concept is possible over a large range of advance ratios with only a modest amount of computational power required.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-166607 , NAS 1.26:166607
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  • 134
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    A review of chevron-notched fracture specimens (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The historical development of chevron notched fracture specimens is reviewed. Stress intensity factors and load line displacement solutions proposed for some of these specimens are compared. The original bend bar configurations up to the present day short rod and bar specimens are reviewed. The results of an analytical round robin that was conducted on chevron-notched specimens are presented. In the round robin, stress-intensity factors for either the chevron notched round rod or square bar specimens were calculated. The consensus stress intensity factor (compliance) solution for these specimens is assessed. The stress intensity factor solutions proposed for three and four point bend chevron notched specimens are reviewed.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-85797 , NAS 1.15:85797
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  • 135
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    Nonlinear Finite Element Analysis of Shells with Large Aspect Ratio (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A higher order degenerated shell element with nine nodes was selected for large deformation and post-buckling analysis of thick or thin shells. Elastic-plastic material properties are also included. The post-buckling analysis algorithm is given. Using a square plate, it was demonstrated that the none-node element does not have shear locking effect even if its aspect ratio was increased to the order 10 to the 8th power. Two sample problems are given to illustrate the analysis capability of the shell element.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Lewis Research Center Nonlinear Struct. Anal.; p 45-54
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  • 136
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    Analysis of lateral and torsional vibration characteristics of beams and shafts with end located rotational masses (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Partial differential equations are derived for free lateral and torsional vibration of a uniform free-free beam with a rotational mass attached to each extremity. For appropriate boundary conditions, nonlinear algebraic equations are obtained using a symbolic manipulation computer program, the solutions of which enable the computation of the neutral frequencies and mode-shapes. The mode-shapes are linear combinations of trigonometric and hyperbolic sine and cosine functions. A computer program is written for the numerical solution of the algebraic equations mentioned above, which can compute the natural frequencies, mode-shapes, and node points for any given set of parameters, for any given number of modes.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-84593 , NAS 1.15:84593
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  • 137
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    Survey of NASA research on crash dynamics (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Ten years of structural crash dynamics research activities conducted on general aviation aircraft by the National Aeronautics and Space Administration (NASA) are described. Thirty-two full-scale crash tests were performed at Langley Research Center, and pertinent data on airframe and seat behavior were obtained. Concurrent with the experimental program, analytical methods were developed to help predict structural behavior during impact. The effects of flight parameters at impact on cabin deceleration pulses at the seat/occupant interface, experimental and analytical correlation of data on load-limiting subfloor and seat configurations, airplane section test results for computer modeling validation, and data from emergency-locator-transmitter (ELT) investigations to determine probable cause of false alarms and nonactivations are assessed. Computer programs which provide designers with analytical methods for predicting accelerations, velocities, and displacements of collapsing structures are also discussed.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TP-2298 , L-15757 , NAS 1.60:2298
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  • 138
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    Contact stresses in pin-loaded orthotropic plates (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The effects of pin elasticity, friction, and clearance on the stresses near the hole in a pin-loaded orthotropic plate are described. The problem is modeled as a contact elasticity problem using complex variable theory, the pin and the plate being two elastic bodies interacting through contact. This modeling is in contrast to previous works which assumed that the pin is rigid or that it exerts a known cosinusoidal radial traction on the hole boundary. Neither of these approaches explicitly involves a pin. A collocation procedure and iteration were used to obtain numerical results for a variety of plate and pin elastic properties and various levels of friction and clearance. Collocation was used to enforce the boundary and iteration was used to find the contact and no-slip regions on the boundary. Details of the numerical scheme are discussed.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-173475 , NAS 1.26:173475 , CCMS-84-02 , VPI-E-84-14
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  • 139
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    Static and dynamic structural-sensitivity derivative calculations in the finite-element-based Engineering Analysis Language (EAL) system (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The implementation of static and dynamic structural-sensitivity derivative calculations in a general purpose, finite-element computer program denoted the Engineering Analysis Language (EAL) System is described. Derivatives are calculated with respect to structural parameters, specifically, member sectional properties including thicknesses, cross-sectional areas, and moments of inertia. Derivatives are obtained for displacements, stresses, vibration frequencies and mode shapes, and buckling loads and mode shapes. Three methods for calculating derivatives are implemented (analytical, semianalytical, and finite differences), and comparisons of computer time and accuracy are made. Results are presented for four examples: a swept wing, a box beam, a stiffened cylinder with a cutout, and a space radiometer-antenna truss.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-85743 , L-15659 , NAS 1.15:85743
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  • 140
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    Stress intensity factors in a reinforced thick-walled cylinder (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: An elastic thick-walled cylinder containing a radial crack is considered. It is assumed that the cylinder is reinforced by an elastic membrane on its inner surface. The model is intended to simulate pressure vessels with cladding. The formulation of the problem is reduced to a singular integral equation. Various special cases including that of a crack terminating at the cylinder-reinforcement interface are investigated and numerical examples are given. Results indicate that in the case of the crack touching the interface the crack surface displacement derivative is finite and consequently the stress state around the corresponding crack tip is bounded; and generally, for realistic values of the stiffness parameter, the effect of the reinforcement is not very significant.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-172307 , NAS 1.26:172307
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  • 141
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    Surface cracks in a plate of finite width under tension or bending (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The problem of a finite plate containing collinear surface cracks is considered and solved by using the line spring model with plane elasticity and Reissner's plate theory. The main focus is on the effect of interaction between two cracks or between cracks and stress-free plate boundaries on the stress intensity factors in an effort to provide extensive numerical results which may be useful in applications. Some sample results are obtained and are compared with the existing finite element results. Then the problem is solved for a single (internal) crack, two collinear cracks, and two corner cracks for wide range of relative dimensions. Particularly in corner cracks, the agreement with the finite element solution is surprisingly very good. The results are obtained for semi-elliptic and rectangular crack profiles which may, in practice, correspond to two limiting cases of the actual profile of a subcritically growing surface crack.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-172309 , NAS 1.26:172309
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  • 142
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    The crack-inclusion interaction problem (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The general plane elastostatic problem of interaction between a crack and an inclusion is considered. The Green's functions for a pair of dislocations and a pair of concentrated body forces are used to generate the crack and the inclusion. Integral equations are obtained for a line crack and an elastic line inclusion having an arbitrary relative orientation and size. The nature of stress singularity around the end points of rigid and elastic inclusions is described and three special cases of this intersection problem are studied. The problem is solved for an arbitrary uniform stress state away from the crack-inclusion region. The nonintersecting crack-inclusion problem is considered for various relative size, orientation, and stiffness parameters, and the stress intensity factors at the ends of the inclusion and the crack are calculated. For the crack-inclusion intersection case, special stress intensity factors are defined and are calculated for various values of the parameters defining the relative size and orientation of the crack and the inclusion and the stiffness of the inclusion.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-172308 , NAS 1.26:172308
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  • 143
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    Creep-rupture reliability analysis (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A probabilistic approach to the correlation and extrapolation of creep-rupture data is presented. Time temperature parameters (TTP) are used to correlate the data, and an analytical expression for the master curve is developed. The expression provides a simple model for the statistical distribution of strength and fits neatly into a probabilistic design format. The analysis focuses on the Larson-Miller and on the Manson-Haferd parameters, but it can be applied to any of the TTP's. A method is developed for evaluating material dependent constants for TTP's. It is shown that optimized constants can provide a significant improvement in the correlation of the data, thereby reducing modelling error. Attempts were made to quantify the performance of the proposed method in predicting long term behavior. Uncertainty in predicting long term behavior from short term tests was derived for several sets of data. Examples are presented which illustrate the theory and demonstrate the application of state of the art reliability methods to the design of components under creep.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-3790 , E-1982 , NAS 1.26:3790
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  • 144
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    Effect of creep in titanium alloy Ti-6Al-4V at elevated temperature on aircraft design and flight test (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Short-term compressive creep tests were conducted on three titanium alloy Ti-6Al-4V coupons at three different stress levels at a temperature of 714 K (825 F). The test data were compared to several creep laws developed from tensile creep tests of available literature. The short-term creep test data did not correlate well with any of the creep laws obtained from available literature. The creep laws themselves did not correlate well with each other. Short-term creep does not appear to be very predictable for titanium alloy Ti-6Al-4V. Aircraft events that result in extreme, but short-term temperature and stress excursions for this alloy should be approached cautiously. Extrapolations of test data and creep laws suggest a convergence toward predictability in the longer-term situation.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-86033 , H-1228 , NAS 1.15:86033
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  • 145
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    POSTOP: Postbuckled open-stiffener optimum panels, user's manual (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The computer program POSTOP developed to serve as an aid in the analysis and sizing of stiffened composite panels that may be loaded in the postbuckling regime, is intended for the preliminary design of metal or composite panels with open-section stiffeners, subjected to multiple combined biaxial compression (or tension), shear and normal pressure load cases. Longitudinal compression, however, is assumed to be the dominant loading. Temperature, initial bow eccentricity and load eccentricity effects are included. The panel geometry is assumed to be repetitive over several bays in the longitudinal (stiffener) direction as well as in the transverse direction. Analytical routines are included to compute panel stiffnesses, strains, local and panel buckling loads, and skin/stiffener interface stresses. The resulting program is applicable to stiffened panels as commonly used in fuselage, wing, or empennage structures. The capabilities and limitations of the code are described. Instructions required to use the program and several example problems are included.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-172260 , NAS 1.26:172260
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  • 146
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    Skin-stiffener interface stresses in composite stiffened panels (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A model and solution method for determining the normal and shear stresses in the interface between the skin and the stiffener attached flange were developed. An efficient, analytical solution procedure was developed and incorporated in a sizing code for stiffened panels. The analysis procedure described provides a means to study the effects of material and geometric design parameters on the interface stresses. These stresses include the normal stress, and the shear stresses in both the longitudinal and the transverse directions. The tendency toward skin/stiffener separation may therefore be minimized by choosing appropriate values for the design variables. The most important design variables include the relative bending stiffnesses of the skin and stiffener attached flange, the bending stiffness of the stiffener web, and the flange width. The longitudinal compressive loads in the flange and skin have significant effects on the interface stresses.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-172261 , NAS 1.26:172261
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  • 147
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    POSTOP: Postbuckled open-stiffener optimum panels-theory and capability (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The computer program POSTOP was developed to serve as an aid in the analysis and sizing of stiffened composite panels that are loaded in the postbuckling regime. A comprehensive set of analysis routines was coupled to a widely used optimization program to produce this sizing code. POSTOP is intended for the preliminary design of metal or composite panels with open-section stiffeners, subjected to multiple combined biaxial compression (or tension), shear and normal pressure load cases. Longitudinal compression, however, is assumed to be the dominant loading. Temperature, initial bow eccentricity and load eccentricity effects are included. The panel geometry is assumed to be repetitive over several bays in the longitudinal (stiffener) direction as well as in the transverse direction. Analytical routines are included to compute panel stiffnesses, strains, local and panel buckling loads, and skin/stiffener interface stresses. The resulting program is applicable to stiffened panels as commonly used in fuselage, wing, or empennage structures. The analysis procedures and rationale for the assumptions used therein are described in detail.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-172259 , NAS 1.26:172259
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  • 148
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    Structural efficiency studies of corrugated compression panels with curved caps and beaded webs (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Curved cross-sectional elements are employed in structural concepts for minimum-mass compression panels. Corrugated panel concepts with curved caps and beaded webs are optimized by using a nonlinear mathematical programming procedure and a rigorous buckling analysis. These panel geometries are shown to have superior structural efficiencies compared with known concepts published in the literature. Fabrication of these efficient corrugation concepts became possible by advances made in the art of superplastically forming of metals. Results of the mass optimization studies of the concepts are presented as structural efficiency charts for axial compression.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TP-2272 , L-15703 , NAS 1.60:2272
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  • 149
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    A finite difference scheme for the equilibrium equations of elastic bodies (1984)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: A compact difference scheme is described for treating the first-order system of partial differential equations which describe the equilibrium equations of an elastic body. An algebraic simplification enables the solution to be obtained by standard direct or iterative techniques.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-172293 , ICASE-84-2 , NAS 1.26:172293
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  • 150
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    Development of a thermal and structural model for a NASTRAN finite-element analysis of a hypersonic wing test structure (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The development of a thermal and structural model for a hypersonic wing test structure using the NASTRAN finite-element method as its primary analytical tool is described. A detailed analysis was defined to obtain the temperature and thermal stress distribution in the whole wing as well as the five upper and lower root panels. During the development of the models, it was found that the thermal application of NASTRAN and the VIEW program, used for the generation of the radiation exchange coefficients, were definicent. Although for most of these deficiencies solutions could be found, the existence of one particular deficiency in the current thermal model prevented the final computation of the temperature distributions. A SPAR analysis of a single bay of the wing, using data converted from the original NASTRAN model, indicates that local temperature-time distributions can be obtained with good agreement with the test data. The conversion of the NASTRAN thermal model into a SPAR model is recommended to meet the immediate goal of obtaining an accurate thermal stress distribution.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-170413 , NAS 1.26:170413 , H-1219
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  • 151
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    Three-dimensional measurements of fatigue crack closure (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Three dimensional fatigue crack opening profiles in transparent polymer test specimens were determined. The load required to separate crack faces was measured along the crack profile at various positions through the specimens thickness. Crack opening loads at the specimen surface (under plane stress conditions) were compared with measurements made under plane strain conditions the specimen interior. The fatigue crack opening load was correlated with fatigue crack retardation behavior caused by peak overloads, and the results discussed in terms of three dimensional aspects of the fatigue crack closure mechanism for fatigue crack retardation.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-175366 , NAS 1.26:175366
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  • 152
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    Effect of structural flexibility on the design of vibration-isolating mounts for aircraft engines (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Previous analyses of the design of vibration-isolating mounts for a rear-mounted engine to decouple linear and rotational oscillations are extended to take into account flexibility of the engine-mount structure. Equations and curves are presented to allow the design of mount systems and to illustrate the results for a range of design conditions.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-85725 , L-15704 , NAS 1.15:85725
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  • 153
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    Hinge specification for a square-faceted tetrahedral truss (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A square-faceted tetrahedral truss is geometrically analyzed. Expressions are developed for single degree of freedom hinges which allow packaging of the structure into a configuration in which all members are parallel and closely packed in a square pattern. Deployment is sequential, thus providing control over the structure during deployment.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-172272 , NAS 1.26:172272 , ARC-TN-1123
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  • 154
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    Bending fatigue of electron-beam-welded foils. Application to a hydrodynamic air bearing in the Chrysler/DOE upgraded automotive gas tubine engine (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A hydrodynamic air bearing with a compliment surface is used in the gas generator of an upgraded automotive gas turbine engine. In the prototype design, the compliant surface is a thin foil spot welded at one end to the bearing cartridge. During operation, the foil failed along the line of spot welds which acted as a series of stress concentrators. Because of its higher degree of geometric uniformity, electron beam welding of the foil was selected as an alternative to spot welding. Room temperature bending fatigue tests were conducted to determine the fatigue resistance of the electron beam welded foils. Equations were determined relating cycles to crack initiation and cycles to failure to nominal total strain range. A scaling procedure is presented for estimating the reduction in cyclic life when the foil is at its normal operating temperature of 260 C (500 F).
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-83539 , DOE/NASA/51040-51 , E-1910 , NAS 1.15:83539
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  • 155
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    Buckling loads of stiffened panels subjected to combined longitudinal compression and shear: Results obtained with PASCO, EAL, and STAGS computer programs (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Buckling analyses used in PASCO are summarized with emphasis placed on the shear buckling analyses. The PASCO buckling analyses include the basic VIPASA analysis, which is essentially exact for longitudinal and transverse loads, and a smeared stiffener solution, which treats a stiffened panel as an orthotropic plate. Buckling results are then presented for seven stiffened panels loaded by combinations of longitudinal compression and shear. The buckling results were obtained with the PASCO, EAL, and STAGS computer programs. The EAL and STAGS solutions were obtained with a fine finite element mesh and are very accurate. These finite element solutions together with the PASCO results for pure longitudinal compression provide benchmark calculations to evaluate other analysis procedures.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TP-2215 , NAS 1.60:2215 , L-15630
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  • 156
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    Heat generation in aircraft tires under braked rolling conditions (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: An analytical model was developed to approximate the internal temperature distribution in an aircraft tire operating under conditions of unyawed braked rolling. The model employs an array of elements to represent the tire cross section and considers the heat generated within the tire to be caused by the change in strain energy associated with cyclic tire deflection. The additional heating due to tire slip and stresses induced by braking are superimposed on the previously developed free rolling model. An extensive experimental program was conducted to verify temperatures predicted from the analytical model. Data from these tests were compared with calculations over a range of operating conditions. The model results were in reasonably good agreement with measured values.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-3768 , NAS 1.26:3768
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  • 157
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    Sensitivity analysis of discrete structural systems: A survey (1984)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: Methods for calculating sensitivity derivatives for discrete structural systems are surveyed, primarily covering literature published during the past two decades. Methods are described for calculating derivatives of static displacements and stresses, eigenvalues and eigenvectors, transient structural response, and derivatives of optimum structural designs with respect to problem parameters. The survey is focused on publications addressed to structural analysis, but also includes a number of methods developed in nonstructural fields such as electronics, controls, and physical chemistry which are directly applicable to structural problems. Most notable among the nonstructural-based methods are the adjoint variable technique from control theory, and the Green's function and FAST methods from physical chemistry.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-86333 , NAS 1.15:86333
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  • 158
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    Interactive buckling of thin-walled structural components under static and dynamic loads (1984)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: Recent advances in the study of interactive buckling of thin walled structural components achieved with the aid of finite strip technique used in conjunction with the theory of mode interaction are summarized. The interaction of the primary local mode with Euler buckling (in columns) and flexural torsional buckling (in columns and beams) is of primary interest. The interaction of two companion local modes with the overall mode is also considered briefly for the columns with doubly symmetric cross sections. The effect of dynamic loads in the form of suddenly applied and compression is also investigated.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center Res. in Struct. and Dyn., 1984; p 219-236
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  • 159
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    Non-Gaussian approach for parametric random vibration of non-linear structures (1984)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: The dynamic response of a nonlinear, single degree of freedom structural system subjected to a physically white noise parametric excitation is investigated. The Ito stochastic calculus is employed to derive a general differential equation for the moments of the response coordinates. The differential equations of moments of any order are found to be coupled with higher order moments. A non-Gaussian closure scheme is developed to truncate the moment equations up to fourth order. The statistical of the stationary response are computed numerically and compared with analytical solutions predicted by a Gaussian closure scheme and the stochastic averaging method. It is found that the computed results exhibit the jump phenomenon which is typical of the characteristics of deterministic nonlinear systems. In addition, the numerical algorithm leads to multiple solutions all of which give positive mean squares. However, two of these solutions are found to violate the properties of high order moments. One solution preserves the moments properties and demonstrates that the system achieves a stationary response.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center Res. in Struct. and Dyn., 1984; p 269-287
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    Shear deformation plate continua of large double-layered space structures (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The energy equivalence to construct equivalent continua for the actual lattice structure is described. An energy equivalent continuum is defined as that which has the same amount of strain and kinetic energies stored in it as the original lattice structure when both are subjected to the same loading conditions. The equivalent continuum is characterized by its strain and kinetic energies from which the constitutive relations and the equations of motion can be derived. A simple method to model large rigid jointed lattices as continuous media with couple stresses is presented. The transition from the discrete system to the continuous medium is achieved by expanding the displacements and the rotations of the nodal points in a Taylor series about a suitable chosen origin. Basic kinematic assumptions are introduced to insure that the assumptions used in deriving the governing equations of the modeled continuum are satisfied. The number of terms retained in the Taylor series expansion will depend upon the properties to be evaluated. This implies that the kind of continuum needed to model from the discrete lattice, before the actual properties are derived was to predetermined.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center Res. in Struct. and Dyn., 1984; p 197-217
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    Approximation methods for inverse problems involving the vibration of beams with tip bodies (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Two cubic spline based approximation schemes for the estimation of structural parameters associated with the transverse vibration of flexible beams with tip appendages are outlined. The identification problem is formulated as a least squares fit to data subject to the system dynamics which are given by a hybrid system of coupled ordinary and partial differential equations. The first approximation scheme is based upon an abstract semigroup formulation of the state equation while a weak/variational form is the basis for the second. Cubic spline based subspaces together with a Rayleigh-Ritz-Galerkin approach were used to construct sequences of easily solved finite dimensional approximating identification problems. Convergence results are briefly discussed and a numerical example demonstrating the feasibility of the schemes and exhibiting their relative performance for purposes of comparison is provided.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-172468 , NAS 1.26:172468 , ICASE-84-51
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    Reliability considerations for the total strain range version of strainrange partitioning (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A proposed total strainrange version of strainrange partitioning (SRP) to enhance the manner in which SRP is applied to life prediction is considered with emphasis on how advanced reliability technology can be applied to perform risk analysis and to derive safety check expressions. Uncertainties existing in the design factors associated with life prediction of a component which experiences the combined effects of creep and fatigue can be identified. Examples illustrate how reliability analyses of such a component can be performed when all design factors in the SRP model are random variables reflecting these uncertainties. The Rackwitz-Fiessler and Wu algorithms are used and estimates of the safety index and the probablity of failure are demonstrated for a SRP problem. Methods of analysis of creep-fatigue data with emphasis on procedures for producing synoptic statistics are presented. An attempt to demonstrate the importance of the contribution of the uncertainties associated with small sample sizes (fatique data) to risk estimates is discussed. The procedure for deriving a safety check expression for possible use in a design criteria document is presented.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-174757 , NAS 1.26:174757
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    Computer models and output, Spartan REM: Appendix B (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A computer model of the Spartan Release Engagement Mechanism (REM) is presented in a series of numerical charts and engineering drawings. A crack growth analysis code is used to predict the fracture mechanics of critical components.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-171093 , NAS 1.26:171093 , LMSC-HREC-PR-D951498-B
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    STARS: A general-purpose finite element computer program for analysis of engineering structures (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: STARS (Structural Analysis Routines) is primarily an interactive, graphics-oriented, finite-element computer program for analyzing the static, stability, free vibration, and dynamic responses of damped and undamped structures, including rotating systems. The element library consists of one-dimensional (1-D) line elements, two-dimensional (2-D) triangular and quadrilateral shell elements, and three-dimensional (3-D) tetrahedral and hexahedral solid elements. These elements enable the solution of structural problems that include truss, beam, space frame, plane, plate, shell, and solid structures, or any combination thereof. Zero, finite, and interdependent deflection boundary conditions can be implemented by the program. The associated dynamic response analysis capability provides for initial deformation and velocity inputs, whereas the transient excitation may be either forces or accelerations. An effective in-core or out-of-core solution strategy is automatically employed by the program, depending on the size of the problem. Data input may be at random within a data set, and the program offers certain automatic data-generation features. Input data are formatted as an optimal combination of free and fixed formats. Interactive graphics capabilities enable convenient display of nodal deformations, mode shapes, and element stresses.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-RP-1129 , H-1224 , NAS 1.61:1129
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    Materials properties, loads, and stress analysis, Spartan REM: Appendix A (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The mechanical properties, load tests, and stress analysis of the Spartan Release Engagement Mechanism (REM) is presented. The fracture properties of the components of the unit are also discussed. Detailed engineering drawings are included.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-171092 , NAS 1.26:171092 , LMSC-HREC-PR-D951498-A
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    A buckling analysis for rectangular orthotropic plates with centrally located cutouts (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: An analysis to obtain the buckling loads of a rectangular orthotropic plate with a centrally located cutout is described. Cutout shapes can be elliptical, circular, rectangular, or square. The boundary conditions considered in the analysis are simply supported unloaded edges and either clamped or simply supported loaded edges. The plate is loaded in uniaxial compression by either uniform edge displacement or uniform edge stress. A computer program that implements this analysis is described, and the program use is demonstrated by sample problems.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-86263 , L-15784 , NAS 1.15:86263
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    Full-scale crash-test evaluation of two load-limiting subfloors for general aviation airframes (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Three six place, low wing, twin engine general aviation airplane test specimens were crash tested at the Langley Impact Dynamics Research Facility under controlled free flight conditions. One structurally unmodified airplane was the base line specimen for the test series. The other two airplanes were structurally modified to incorporate load limiting (energy absorbing) subfloor concepts into the structure for full scale crash test evaluation and for comparison with the unmodified airplane test results. Typically, the lowest floor accelerations, the lowest anthropomorphic dummy responses, and the least seat crushing of standard and load limiting seats occurred in the airplanes modified with load limiting subfloors, wherein the greatest structural crushing of the subfloor took place. The better performing of the two load limiting subfloor concepts reduced the peak airplane floor accelerations to -25g to -30g as compared with approximately -40g to -55g for the unmodified airplane structure.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TP-2380 , L-15764 , NAS 1.60:2380
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  • 168
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    Nondestructive evaluation of residual stress in low-carbon steel (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The effects of the preferred orientation on the temperature dependence of ultrasonic velocity in low carbon steels are investigated. The sensitivity of the acousto-elastic constant to changes in microstructure is assessed as well as the possibility of determining some mechanical properties of a material by measuring the acousto-elastic constant.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-174157 , NAS 1.26:174157
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    Investigation of the HPFTP first stage impeller crack (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The occurrence of a crack in the HPFTP first stage impeller of pump 2608 R2 during test 750-245 prompted this analysis to examine possible causes of the failure. Preliminary analysis, using an existing NASTRAN model of the impeller, showed a deficiency in the model's ability to reliably calculate stress in the area of concern (outboard edge of the impeller shroud). A new NASTRAN model was constructed to better define the stress state in the area of crack initiations. Static stress analysis and normal models analysis were performed on the new model. Results are presented.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-171281 , NAS 1.26:171281 , LMSC-HREC-TN-D951725
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    Crack problems for bonded nonhomogeneous materials under antiplane shear loading (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The singular nature of the crack tip stress field in a nonhomogeneous medium with a shear modulus with a discontinuous derivative was investigated. The simplest possible loading and geometry, the antiplane shear loading of two bonded half spaces in which the crack is perpendicular to the interface is considered. It is shown that the square root singularity of the crack tip stress field is unaffected by the discontinuity in the derivative of the shear modulus. The problem is solved for a finite crack and results for the stress intensity factors are presented.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-173892 , NAS 1.26:173892
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    Opening of an interface flaw in a layered elastic half-plane under compressive loading (1984)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: A static analysis is given of the problem of an elastic layer perfectly bonded, except for a frictionless interface crack, to a dissimilar elastic half-plane. The free surface of the layer is loaded by a finite pressure distribution directly over the crack. The problem is formulated using the two dimensional linear elasticity equations. Using Fourier transforms, the governing equations are converted to a pair of coupled singular integral equations. The integral equations are reduced to a set of simultaneous algebraic equations by expanding the unknown functions in a series of Jacobi polynomials and then evaluating the singular Cauchy-type integrals. The resulting equations are found to be ill-conditioned and, consequently, are solved in the least-squares sense. Results from the analysis show that, under a normal pressure distribution on the free surface of the layer and depending on the combination of geometric and material parameters, the ends of the crack can open. The resulting stresses at the crack-tips are singular, implying that crack growth is possible. The extent of the opening and the crack-top stress intensity factors depend on the width of the pressure distribution zone, the layer thickness, and the relative material properties of the layer and half-plane.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-86282 , NAS 1.15:86282
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    Automatic finite element generators (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The design and implementation of a software system for generating finite elements and related computations are described. Exact symbolic computational techniques are employed to derive strain-displacement matrices and element stiffness matrices. Methods for dealing with the excessive growth of symbolic expressions are discussed. Automatic FORTRAN code generation is described with emphasis on improving the efficiency of the resultant code.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Lewis Research Center Nonlinear Struct. Anal.; p 85-94
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    Inelastic and Dynamic Fracture and Stress Analyses (1984)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: Large deformation inelastic stress analysis and inelastic and dynamic crack propagation research work is summarized. The salient topics of interest in engine structure analysis that are discussed herein include: (1) a path-independent integral (T) in inelastic fracture mechanics, (2) analysis of dynamic crack propagation, (3) generalization of constitutive relations of inelasticity for finite deformations , (4) complementary energy approaches in inelastic analyses, and (5) objectivity of time integration schemes in inelastic stress analysis.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Lewis Research Center Nonlinear Struct. Anal.; p 105-118
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    Element-by-element Solution Procedures for Nonlinear Structural Analysis (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Element-by-element approximate factorization procedures are proposed for solving the large finite element equation systems which arise in nonlinear structural mechanics. Architectural and data base advantages of the present algorithms over traditional direct elimination schemes are noted. Results of calculations suggest considerable potential for the methods described.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Lewis Research Center Nonlinear Struct. Anal.; p 65-84
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    New Variational Formulations of Hybrid Stress Elements (1984)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: In the variational formulations of finite elements by the Hu-Washizu and Hellinger-Reissner principles the stress equilibrium condition is maintained by the inclusion of internal displacements which function as the Lagrange multipliers for the constraints. These versions permit the use of natural coordinates and the relaxation of the equilibrium conditions and render considerable improvements in the assumed stress hybrid elements. These include the derivation of invariant hybrid elements which possess the ideal qualities such as minimum sensitivity to geometric distortions, minimum number of independent stress parameters, rank sufficient, and ability to represent constant strain states and bending moments. Another application is the formulation of semiLoof thin shell elements which can yield excellent results for many severe test cases because the rigid body nodes, the momentless membrane strains, and the inextensional bending modes are all represented.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Lewis Research Center Nonlinear Struct. Anal.; p 17-29
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    Stress-intensity factor equations for cracks in three-dimensional finite bodies subjected to tension and bending loads (1984)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: Stress intensity factor equations are presented for an embedded elliptical crack, a semielliptical surface crack, a quarter elliptical corner crack, a semielliptical surface crack along the bore of a circular hole, and a quarter elliptical corner crack at the edge of a circular hole in finite plates. The plates were subjected to either remote tension or bending loads. The stress intensity factors used to develop these equations were obtained from previous three dimensional finite element analyses of these crack configurations. The equations give stress intensity factors as a function of parametric angle, crack depth, crack length, plate thickness, and, where applicable, hole radius. The ratio of crack depth to plate thickness ranged from 0 to 1, the ratio of crack depth to crack length ranged from 0.2 to 2, and the ratio of hole radius to plate thickness ranged from 0.5 to 2. The effects of plate width on stress intensity variation along the crack front were also included.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-85793 , NAS 1.15:85793
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    Analytical results for postbuckling behavior of plates in compression and shear (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The postbuckling behavior of long rectangular isotropic and orthotropic plates is determined. By assuming trigonometric functions in one direction, the nonlinear partial differential equations of von Karman large deflection plate theory are converted into nonlinear ordinary differential equations. The ordinary differential equations are solved numerically using an available boundary value problem solver which makes use of Newton's method. Results for longitudinal compression show different postbuckling behavior between isotropic and orthotropic plates. Results for shear show that change in inplane edge constraints can cause large change in postbuckling stiffness.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-85766 , NAS 1.15:85766
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    Crack layer theory (1984)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: A damage parameter is introduced in addition to conventional parameters of continuum mechanics and consider a crack surrounded by an array of microdefects within the continuum mechanics framework. A system consisting of the main crack and surrounding damage is called crack layer (CL). Crack layer propagation is an irreversible process. The general framework of the thermodynamics of irreversible processes are employed to identify the driving forces (causes) and to derive the constitutive equation of CL propagation, that is, the relationship between the rates of the crack growth and damage dissemination from one side and the conjugated thermodynamic forces from another. The proposed law of CL propagation is in good agreement with the experimental data on fatigue CL propagation in various materials. The theory also elaborates material toughness characterization.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-174634 , NAS 1.26:174634
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    Algorithms for elasto-plastic-creep postbuckling (1984)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: This paper considers the development of an improved constrained time stepping scheme which can efficiently and stably handle the pre-post-buckling behavior of general structure subject to high temperature environments. Due to the generality of the scheme, the combined influence of elastic-plastic behavior can be handled in addition to time dependent creep effects. This includes structural problems exhibiting indefinite tangent properties. To illustrate the capability of the procedure, several benchmark problems employing finite element analyses are presented. These demonstrate the numerical efficiency and stability of the scheme. Additionally, the potential influence of complex creep histories on the buckling characteristics is considered.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Engineering Mechanics (ISSN 0733-9399); 110; 911-929
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    Flutter analysis of advanced turbopropellers (1984)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Previously cited in issue 12, p. 1742, Accession no. A83-29824
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA Journal (ISSN 0001-1452); 22; 801
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    Self-adaptive Solution Strategies (1984)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: The development of enhancements to current generation nonlinear finite element algorithms of the incremental Newton-Raphson type was overviewed. Work was introduced on alternative formulations which lead to improve algorithms that avoid the need for global level updating and inversion. To quantify the enhanced Newton-Raphson scheme and the new alternative algorithm, the results of several benchmarks are presented.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Lewis Research Center Nonlinear Struct. Anal.; p 55-63
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    Stress decay in an orthotropic half-plane under self-equilibrating sinusoidal loading (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: An elastic orthotropic half-plane subjected to sinusoidal normal loading along an entire straight edge is analyzed. Stresses are calculated for material property combinations which are representative of some unidirectional fiber reinforced composites and of (+ or - 45) (subs) laminates made from the same unidirectional materials. Plots of the stresses as functions of the distance from the loaded boundary show that they can differ greatly from their counterparts in the isotropic half-plane under the same loading. How the results impact the question of the applicability of St. Venant's principle to orthotropic materials is briefly discussed.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-85791 , NAS 1.15:85791
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    Effect of preforming adherends on static and fatigue strength of bonded composite single-lap joints (1984)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: An analytical and experimental investigation was conducted on bonded composite single-lap joints with the adherends performed to reduce the angle between the line of action of the applied in-plane force and the bondline. A classical closed-form solution was used to analyze the composite joints with various preform angles and overlap lengths. The adherends of the test specimens were preformed before bonding, during the layup and curing process. Static tests were conducted for preform angles of 0, 5, 10, and 15 deg and overlap lengths of 0.75, 1.75, 2.75, and 3.75 in. A limited fatigue study was conducted for specimens with a 2.75-in. overlap and a preform angle of 5 deg. Results of the analysis showed that preforming the adherends of bonded composite single-lap joints significantly reduced the shear and peel stress concentrations in the adhesive. Experimental results showed that preforming the adherends significantly increased their static and fatigue strength and thus increased the load level for which bonded composite single-lap joints can be designed.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TP-2324 , L-15780 , NAS 1.60:2324
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    Finite element analysis of wrinkling membranes (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The development of a nonlinear numerical algorithm for the analysis of stresses and displacements in partly wrinkled flat membranes, and its implementation on the SAP VII finite-element code are described. A comparison of numerical results with exact solutions of two benchmark problems reveals excellent agreement, with good convergence of the required iterative procedure. An exact solution of a problem involving axisymmetric deformations of a partly wrinkled shallow curved membrane is also reported.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-172325 , NAS 1.26:172325 , USC-CE-83-05
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    Simultaneous analysis and design (1984)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: Optimization techniques are increasingly being used for performing nonlinear structural analysis. The development of element by element (EBE) preconditioned conjugate gradient (CG) techniques is expected to extend this trend to linear analysis. Under these circumstances the structural design problem can be viewed as a nested optimization problem. There are computational benefits to treating this nested problem as a large single optimization problem. The response variables (such as displacements) and the structural parameters are all treated as design variables in a unified formulation which performs simultaneously the design and analysis. Two examples are used for demonstration. A seventy-two bar truss is optimized subject to linear stress constraints and a wing box structure is optimized subject to nonlinear collapse constraints. Both examples show substantial computational savings with the unified approach as compared to the traditional nested approach.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-172334 , NAS 1.26:172334
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    Hygrothermal influence on delamination behavior of graphite/epoxy laminates (1984)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: The hygrothermal effect on the fracture behavior of graphite-epoxy laminates was investigated to develop a methodology for damage tolerance predictions in advanced composite materials. Several T300/934 laminates were tested using a number of specimen configurations to evaluate the effects of temperature and humidity on delamination fracture toughness under mode 1 and mode 2 loading. It is indicated that moisture has a slightly beneficial influence on fracture toughness or critical strain energy release rate during mode 1 delamination, but has a slightly deleterious effect on mode 2 delamination and mode 1 transverse cracking. The failed specimens are examined by SEM and topographical differences due to fracture modes are identified. It is concluded that the effect of moisture on fracture topography can not be distinguished.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-85935 , A-9705 , NAS 1.15:85935
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    Finite element analysis of steadily moving contact fields (1984)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: By introducing a moving updated Lagrangian observer, this paper develops traveling finite elements with the capacity to handle the global response resulting from steadily moving contact fields. The generality of the results is such that large deformation kinematics and kinetics as well as the full compliment of inertial fields can be handled. To streamline the handling of nonlinear behavior, an elliptically constrained solution algorithm is also developed. Employing this algorithm, the results of several numerical benchmarking studies are presented which illustrate the capacity of the moving updated Lagrangian formulation as well as the potential effects of nonlinearity.
    Keywords: STRUCTURAL MECHANICS
    Type: Computers and Structures (ISSN 0045-7949); 18; 2 19; 1984
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    Methods for analysis of cracks in three-dimensional solids (1984)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Analytical and numerical methods evaluating the stress-intensity factors for three-dimensional cracks in solids are presented, with reference to fatigue failure in aerospace structures. The exact solutions for embedded elliptical and circular cracks in infinite solids, and the approximate methods, including the finite-element, the boundary-integral equation, the line-spring models, and the mixed methods are discussed. Among the mixed methods, the superposition of analytical and finite element methods, the stress-difference, the discretization-error, the alternating, and the finite element-alternating methods are reviewed. Comparison of the stress-intensity factor solutions for some three-dimensional crack configurations showed good agreement. Thus, the choice of a particular method in evaluating the stress-intensity factor is limited only to the availability of resources and computer programs.
    Keywords: STRUCTURAL MECHANICS
    Type: Aeronautical Society of India, Journal (ISSN 0001-9267); 36; 153-172
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    Plasticity, viscoplasticity, and creep of solids by mechanical subelement models (1984)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: This paper discusses the modelling by mechanical subelements, the general plasticity, the viscoplasticity, and the creep behavior of solids under multiaxial loading conditions. The formulation of a time-independent elastic-plastic analysis is based on the viscoplasticity theory and the assumed stress finite element method. An example of an in-plane stress problem is included.
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    Evolution of assumed stress hybrid finite element (1984)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Early versions of the assumed stress hybrid finite elements were based on the a priori satisifaction of stress equilibrium conditions. In the new version such conditions are relaxed but are introduced through additional internal displacement functions as Lagrange multipliers. A rational procedure is to choose the displacement terms such that the resulting strains are now of complete polynomials up to the same degree as that of the assumed stresses. Several example problems indicate that optimal element properties are resulted by this method.
    Keywords: STRUCTURAL MECHANICS
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  • 191
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    A refined nonlinear theory of plates with transverse shear deformation (1984)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A higher-order shear deformation theory of plates accounting for the von Karman strains is presented. The theory contains the same dependent unknowns as in the Hencky-Mindlin type first-order shear deformation theory and accounts for parabolic distribution of the transverse shear strains through the thickness of the plate. Exact solutions of simply supported plates are obtained using the linear theory and the results are compared with the exact solutions of three-dimensional elasticity theory, the first order shear deformation theory, and the classical plate theory. The present theory predicts the deflections, stresses, and frequencies more accurately when compared to the first-order theory and the classical plate theory.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal of Solids and Structures (ISSN 0020-7683); 20; 9-10
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  • 192
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    Statistics and thermodynamics of fracture (1984)
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    Publication Date: 2019-06-28
    Description: A probabilistic model of the fracture processes unifying the phenomenological study of long term strength of materials, fracture mechanics and statistical approaches to fracture is briefly outlined. The general framework of irreversible thermodynamics is employed to model the deterministic side of the failure phenomenon. The stochastic calculus is used to account for thg failure mechanisms controlled by chance; particularly, the random roughness of fracture surfaces.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal of Engineering Science (ISSN 0020-7225); 22; 8-10
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  • 193
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    A history dependent damage model for low cycle fatigue (1984)
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    Publication Date: 2019-06-28
    Description: This paper examines damage assessment and accumulation. A nonlinear damage postulate is advanced that embodies the dependence of the damage rate on cycle-dependent changes in the bulk microstructure and the surface topography. The postulate is analytically formulated in terms of the deformation history dependence of the bulk behavior. This formulation is used in conjunction with baseline data in accordance with the damage postulate to predict the low cycle fatigue resistance of OFE copper. Close comparison of the predictions with observed behavior suggests the postulate offers a viable basis for nonlinear damage analysis.
    Keywords: STRUCTURAL MECHANICS
    Type: ASME PAPER 84-PVP-112
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  • 194
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    Composite laminates with negative through-the-thickness Poisson's ratios (1984)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A simple analysis using two-dimensional lamination theory combined with the appropriate three-dimensional anisotropic constitutive equation is presented to show some rather surprising results for the range of values of the through-the-thickness effective Poisson's ratio nu sub xz for angle ply laminates. Results for graphite-epoxy show that the through-the-thickness effective Poisson's ratio can range from a high of 0.49 for a 90 laminate to a low of -0.21 for a + or - 25s laminate. It is shown that negative values of nu sub xz are also possible for other laminates.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Composite Materials (ISSN 0021-9983); 18; 447-455
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  • 195
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    Isopachic contouring of opaque plates (1984)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Contour maps of change of thickness of opaque plates subjected to external loads are obtained using holographic interferometry in conjunction with the moire effect. A simple holographic-interferometry arrangement is used first to obtain contour maps of the out-of-plane displacements of the two sides of the object. Carrier patterns of equal magnitude but opposite signs are added to these contours. Superposition of the reconstructed holograms of the two sides produces a pattern of additive-moire fringes, which are contours of change of thickness. Effects of midplane warpage of the loaded specimen are cancelled. Sensitivity is lambda/2 per fringe order, contrast of the isopachic-fringe pattern is excellent, and the process is compatible with a mechanical-testing-machine environment.
    Keywords: STRUCTURAL MECHANICS
    Type: Experimental Mechanics (ISSN 0014-4851); 24; 169-176
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  • 196
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    Analysis of hourglass instabilities and control in underintegrated finite element methods (1984)
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    Publication Date: 2019-06-28
    Description: Belytschko et al. (1981, 1984) has developed stabilization methods for the treatment of underintegrated FEM problems; these methods involve the computation of an underintegrated stiffness matrix, which is rank-deficient, and the addition of a stabilization matrix which effectively eliminates the spurious modes. An attempt is presently made to give this a priori stabilization method a mathematical means of support. Attention is also given to an a posteriority stabilization method for hourglass control, in which an approximate solution of the underintegrated system is obtained and then subjected to a special projection in order to eliminate the hourglass modes. A proof is obtained for the convergence of this stabilized underintegrated approximation to the exact solution of a model problem at almost the same rate (as the mesh is refined) as the fully integrated solutions.
    Keywords: STRUCTURAL MECHANICS
    Type: Computer Methods in Applied Mechanics and Engineering (ISSN 0045-7825); 44; 339-363
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  • 197
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    Fracture of composite-adhesive-composite systems (1984)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: This program was undertaken to initiate the development of a test method for testing adhesive joints in metal-adhesive-composite systems. The uniform double cantilever beam (UDCB) and the width tapered beam (WTB) specimen geometries were evaluated for measuring Mode I fracture toughness in these systems. The WTB specimen is the preferred geometry in spite of the fact that it is more costly to machine than the UDCB specimen. The use of loading tabs attached to thin sheets of composites proved to be experimentally unsatisfactory. Consequently, a new system was developed to load thin sheets of adherends. This system allows for the direct measurement of displacement along the load line. In well made joints separation occurred between the plies rather than in the adhesive.
    Keywords: STRUCTURAL MECHANICS
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  • 198
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    On stress field near a stationary crack tip (1984)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: It is well known that the stress and elastic-plastic deformation fields near a crack tip have important roles in the corresponding fracture process. For elastic-perfectly-plastic solids, different solutions are given in the literature. In this work several of these solutions are examined and compared for Mode I (tension), Mode II (shear), and mixed Modes I and II loading conditions in plane strain. By consideration of the dynamic solution, it is shown that the assumption that the material is yielding all around a crack tip may not be reasonable in all cases. By admitting the existence of some elastic sectors, continuous stress fields are obtained even for mixed Modes I and II.
    Keywords: STRUCTURAL MECHANICS
    Type: AD-A152863 , Mechanics of Materials (ISSN 0167-6636); 3; 235-243
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  • 199
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    Surface cracks in a plate of finite width under extension or bending (1984)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: In this paper the problem of a finite plate containing collinear surface cracks is considered. The problem is solved by using the line spring model with plane elasticity and Reissner's plate theory. The main purpose of the study is to investigate the effect of interaction between two cracks or between cracks and stress-free plate boundaries on the stress intensity factors and to provide extensive numerical results which may be useful in applications. First, some sample results are obtained and are compared with the existing finite element results. Then the problem is solved for a single (internal) crack, two collinear cracks and two corner cracks for wide range of relative dimensions. Particularly in corner cracks the agreement with the finite element solution is surprisingly very good. The results are obtained for semielliptic and rectangular crack profiles which may, in practice, correspond to two limiting cases of the actual profile of a subcritically growing surface crack.
    Keywords: STRUCTURAL MECHANICS
    Type: Theoretical and Applied Fracture Mechanics (ISSN 0167-8442); 2; 197-216
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  • 200
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    Stability and accuracy analysis of some fully-discrete algorithms for the one-dimensional second-order wave equation (1984)
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    Publication Date: 2019-06-28
    Description: The present investigation is concerned with some basic results for a predictor-multicorrector algorithm applied to the one-dimensional wave equation, giving particular attention to so-called 2-pass explicit schemes in which both lumped and coupled mass matrices are employed. In an assessment of the accuracy and stability properties of the algorithms, use is made of the one-dimensional, second-order wave equation. The maximum stable time step of the lumped right-hand-side mass, 2-pass explicit algorithm is twice that of the 1-pass explicit algorithm. Improved accuracy is obtained by employing higher-order, or consistent, right-hand-side, mass.
    Keywords: STRUCTURAL MECHANICS
    Type: Computers and Structures (ISSN 0045-7949); 19; 4 19
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