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  • Inorganic Chemistry  (11,285)
  • General Chemistry  (11,218)
  • STRUCTURAL MECHANICS  (1,510)
  • 1970-1974  (10,115)
  • 1930-1934  (7,544)
  • 1910-1914
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Year
  • 101
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    Nonlinear analysis of the forced response of structural elements (1974)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: A general procedure is presented for the nonlinear analysis of the forced response of structural elements to harmonic excitations. Internal resonances (i.e., modal interactions) are taken into account. All excitations are considered, with special consideration given to resonant excitations. The general procedure is applied to clamped-hinged beams. The results reveal that exciting a higher mode may lead to a larger response in a lower interacting mode, contrary to the results of linear analyses.
    Keywords: STRUCTURAL MECHANICS
    Type: Acoustical Society of America; vol. 55
    Format: text
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  • 102
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    Finite elasto-plastic deformation. I - Theory and numerical examples (1974)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: It is demonstrated that the problem of elasto-plastic finite deformation is governed by a quasi-linear model irrespective of deformation magnitude. This feature follows from the adoption of a rate viewpoint toward finite deformation analysis in an Eulerian reference frame. Objectivity of the formulation is preserved by introduction of a frame-invariant stress rate. Equations for piece-wise linear incremental finite element analysis are developed by application of the Galerkin method to the instantaneously linear governing differential equations of the quasi-linear model. Numerical solution capability has been established for problems of plane strain and plane stress. The accuracy of the numerical analysis is demonstrated by consideration of a number of problems of homogeneous finite deformation admitting comparative analytic solution. It is shown that accurate, objective numerical solutions can be obtained for problems involving dimensional changes of an order of magnitude and rotations of a full radian.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal of Solids and Structures; 10; Mar. 197
    Format: text
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  • 103
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    A method for detecting structural deterioration in bridges (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The problem of detecting deterioration in bridge structures is studied with the use of Randomdec analysis. Randomdec signatures, derived from the ambient bridge vibrations in the acoustic range, were obtained for a girder bridge over a period of a year to show the insensitivity of the signatures to environmental changes. A laboratory study was also conducted to show the sensitivity of signatures to fatigue cracks on the order of a centimeter in length in steel beams.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-137548 , NEAR-TR-71
    Format: application/pdf
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  • 104
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    Effects of proof loads and combined mode loadings on fracture and flaw growth characteristics of aerospace alloys (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: This experimental program was undertaken to determine the effects of (1) combined tensile and bending loadings, (2) combined tensile and shear loadings, and (3) proof overloads on fracture and flaw growth characteristics of aerospace alloys. Tests were performed on four alloys: 2219-T87 aluminum, 5Al-2.5Sn (ELl) titanium, 6Al-4V beta STA titanium and high strength 4340 steel. Tests were conducted in room air, gaseous nitrogen at -200F (144K), liquid nitrogen and liquid hydrogen. Flat center cracked and surface flawed specimens, cracked tube specimens, circumferentially notched round bar and surface flawed cylindrical specimens were tested. The three-dimensional photoelastic technique of stress freezing and slicing was used to determine stress intensity factors for surface flawed cylindrical specimens subjected to tension or torsion. Results showed that proof load/temperature histories used in the tests have a small beneficial effect or no effect on subsequent fracture strength and flaw growth rates.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-134611 , D180-17997-1
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  • 105
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    Analysis of twist and lean of tall towers (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A method for analytically determining the amount of twist and lean of a tall tower of equilateral triangular cross section is described. This method is also applicable to tall structures of other shapes and cross-sectional areas. A BASIC computer program that determines the angle of twist and amount of lean is provided.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-X-70113 , KSC-TR-297-REV-1
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  • 106
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    Users manual: Dynamics of two bodies connected by an elastic tether, six degrees of freedom forebody and five degrees of freedom decelerator (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The equations of motion and a computer program for the dynamics of a six degree of freedom body joined to a five degree of freedom body by a quasilinear elastic tether are presented. The forebody is assumed to be a completely general rigid body with six degrees of freedom; the decelerator is also assumed to be rigid, but with only five degrees of freedom (symmetric about its longitudinal axis). The tether is represented by a spring and dashpot in parallel, where the spring constant is a function of tether elongation. Lagrange's equation is used to derive the equations of motion with the Lagrange multiplier technique used to express the constraint provided by the tether. A computer program is included which provides a time history of the dynamics of both bodies and the tension in the tether.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-120261 , GER-16047
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  • 107
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    Attitude dynamics simulation subroutines for systems of hinge-connected rigid bodies (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Several computer subroutines are designed to provide the solution to minimum-dimension sets of discrete-coordinate equations of motion for systems consisting of an arbitrary number of hinge-connected rigid bodies assembled in a tree topology. In particular, these routines may be applied to: (1) the case of completely unrestricted hinge rotations, (2) the totally linearized case (all system rotations are small), and (3) the mixed, or partially linearized, case. The use of the programs in each case is demonstrated using a five-body spacecraft and attitude control system configuration. The ability of the subroutines to accommodate prescribed motions of system bodies is also demonstrated. Complete listings and user instructions are included for these routines (written in FORTRAN V) which are intended as multi- and general-purpose tools in the simulation of spacecraft and other complex electromechanical systems.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-138819 , JPL-TR-32-1592
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  • 108
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    Finite element formulations for problems of large elastic-plastic deformation (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: An Eulerian finite element formulation is presented for problems of large elastic-plastic flow. The method is based on Hill's variational principle for incremental deformations, and is suited to isotropically hardening Prandtl-Reuss materials. The formulation is given in a manner which allows any conventional finite element program, for "small strain" elasticplastic analysis, to be simply and rigorously adapted to problems involving arbitrary amounts of deformation and arbitrary levels of stress in comparison to plastic deformation moduli. The method is applied to a necking bifurcation analysis of a bar in plane-strain tension. A unified general formulation of finite element equations, both Lagrangian and Eulerian, for large deformations, with arbitrary choice of the conjugate stress and strain measures, and a discussion is given of other proposed formulations for elastic-plastic finite element analysis at large strain.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-138820
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  • 109
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    On numerically accurate finite element (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A general criterion for testing a mesh with topologically similar repeat units is given, and the analysis shows that only a few conventional element types and arrangements are, or can be made suitable for computations in the fully plastic range. Further, a new variational principle, which can easily and simply be incorporated into an existing finite element program, is presented. This allows accurate computations to be made even for element designs that would not normally be suitable. Numerical results are given for three plane strain problems, namely pure bending of a beam, a thick-walled tube under pressure, and a deep double edge cracked tensile specimen. The effects of various element designs and of the new variational procedure are illustrated. Elastic-plastic computation at finite strain are discussed.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-138821
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  • 110
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    Plastic flow around rigid spherical inclusions (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The extent of plastic flow in a spherical solid (assumed to be homogeneous and elastically and plastically isotropic), surrounding a concentric rigid sphere was calculated as a function of applied external pressure. The applied pressure necessary to cause plastic deformation throughout the solid was obtained.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-142596 , REPT-2278
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  • 111
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    Substantiation Data for Advanced Beaded and Tubular Structural Panels. Volume 3: Testing (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The test program is described, which was conducted to provide the necessary experimental data to verify the design and analysis methods developed for beaded and tubular panels. Test results are summarized and presented for all local buckling and full size panel tests. Selected representative test data from each of these tests is presented in detail. The results of this program established a valid analysis and design procedure for circular tube panels. Test results from three other configurations show deformational modes which are not adequately accounted for in the present analyses.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-132515
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  • 112
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    The design and use of an error correction information system for NASTRAN (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Error Correction Information System (ECIS) is a system for a two-way transmittal of NASTRAN maintenance information via a data base stored on a nationwide accessible computer. ECIS consists of two data bases. The first data base is used for comments, reporting NASTRAN Software Problem Reports (SPR's) and bookkeeping information which can be updated by the user or the NASTRAN Office. The second data base is used by the NSMO to store all SPR information and updates. The hardware needed by an accessing user is any desktop computer terminal and a telephone to communicate with the central computer. The instruction format is an engineering oriented language and requires less than an hour to obtain a working knowledge of its functions.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-X-72651
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  • 113
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    Design and fabrication of a boron reinforced intertank skirt (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Analytical and experimental studies were performed to evaluate the structural efficiency of a boron reinforced shell, where the medium of reinforcement consists of hollow aluminum extrusions infiltrated with boron epoxy. Studies were completed for the design of a one-half scale minimum weight shell using boron reinforced stringers and boron reinforced rings. Parametric and iterative studies were completed for the design of minimum weight stringers, rings, shells without rings and shells with rings. Computer studies were completed for the final evaluation of a minimum weight shell using highly buckled minimum gage skin. The detail design is described of a practical minimum weight test shell which demonstrates a weight savings of 30% as compared to an all aluminum longitudinal stiffened shell. Sub-element tests were conducted on representative segments of the compression surface at maximum stress and also on segments of the load transfer joint. A 10 foot long, 77 inch diameter shell was fabricated from the design and delivered for further testing.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-132448
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  • 114
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    Graphite-polyimide composite for application to aircraft engines (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A combined experimental and theoretical investigation was performed in order to (1) demonstrate that high quality angleplied laminates can be made from HT-S/PMR-RI (PMR in situ polymerization of monomeric reactants), (2) characterize the PMR-PI material and to determine the HT-S unidirectional composite properties required for composite micro and macromechanics and laminate analyses, and (3) select HT-S/PMR-PI laminate configurations to meet the general design requirements for high-tip-speed compressor blades. The results of the investigation showed that HT-S/PMR laminate configurations can be fabricated which satisfy the high-tip-speed compressor blade design requirements when operating within the temperature capability of the polymide matrix.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TN-D-7698 , E-7700
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  • 115
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    User's guide for analysis of finite elastoplastic deformation: The FIPDEF and FIPAX programs for the CDC 6600 (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Computer programs are presented which provide incremental finite-element analysis capability for problems of quasi-static, finite, elastoplastic deformation in two spatial dimensions (plane strain, plane stress, axisymmetric). Monotonic or cyclic loading of isotropic hardening materials is considered. The only restriction on the form of the stress-strain curve is that the rate of work hardening exceed some small positive value. The user's guide assumes familiarity with both finite-element analysis and FORTRAN IV programming for the CDC 6600. Sufficient information is provided to support problem solving ultization of the programs.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-X-2998 , E-7610
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  • 116
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    Application of optimality criteria in structural synthesis (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The rational use of optimality criteria was investigated for a class of structural synthesis problems where materials, configuration and applied load conditions are specified, and the minimum weight design is to be determined. The potential of hybrid methods of structural optimization for dealing with relatively large design problems involving practical complexity was explored. The reduced basis concept in design space was used to decrease the number of generalized design variables dealt with by the mathematical programming algorithm. Optimality criteria methods for obtaining design vectors associated with displacement, system buckling and natural frequency constraints are presented. A stress ratio method was used to generate a basis design vector representing the stress constraints. The finite element displacement method was used as the basic structural analysis tool. Results for several examples of truss systems subject to stress, displacement and minimum size constraints are presented. An assessment of these results indicates the effectiveness of the hybrid method developed.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-138612 , UCLA-ENG-7446
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  • 117
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    Transonic flutter study of a 50.5 deg cropped-delta wing with two rearward-mounted nacelles (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Transonic flutter characteristics of three geometrically similar delta-wing models were experimentally determined in the Langley transonic dynamics tunnel at Mach numbers from about 0.6 to 1.2. The models were designed to be simplified versions of an early supersonic transport wing design. The model was an aspect-ratio-1.28 cropped-delta wing with a leadingedge sweep of 50.5 deg. The flutter characteristics obtained for this wing configuration indicated a minimum flutter-speed index near a Mach number of 0.92 and a transonic compressibility dip amounting to about a 27-percent decrease in the flutter-speed index relative to the value at a Mach number of 0.6. Analytical studies were performed for one wing model at Mach numbers of 0.6, 0.7, 0.8, and 0.9 by using both doublet-lattice and lifting-surface (kernel-function) unsteady aerodynamic theory. A comparison of the analytical and experimental flutter results showed good agreement at all Mach numbers investigated.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TN-D-7544 , L-9348
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  • 118
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    Elastic stability of laminated, flat and curved, long rectangular plates subjected to combined inplane loads (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A method is presented to predict theoretical buckling loads of long, rectangular flat and curved laminated plates with arbitrary orientation of orthotropic axes each lamina. The plate is subjected to combined inplane normal and shear loads. Arbitrary boundary conditions may be stipulated along the longitudinal sides of the plate. In the absence of inplane shear loads and extensional-shear coupling, the analysis is also applicable to finite length plates. Numerical results are presented for curved laminated composite plates with boundary conditions and subjected to various loadings. These results indicate some of the complexities involved in the numerical solution of the analysis for general laminates. The results also show that the reduced bending stiffness approximation when applied to buckling problems could lead to considerable error in some cases and therefore must be used with caution.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-2330 , D6-60227
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  • 119
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    The use of COD and plastic instability in crack propagation and arrest in shells (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The initiation, growth, and possible arrest of fracture in cylindrical shells containing initial defects are dealt with. For those defects which may be approximated by a part-through semi-elliptic surface crack which is sufficiently shallow so that part of the net ligament in the plane of the crack is still elastic, the existing flat plate solution is modified to take into account the shell curvature effect as well as the effect of the thickness and the small scale plastic deformations. The problem of large defects is then considered under the assumptions that the defect may be approximated by a relatively deep meridional part-through surface crack and the net ligament through the shell wall is fully yielded. The results given are based on an 8th order bending theory of shallow shells using a conventional plastic strip model to account for the plastic deformations around the crack border.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-132472 , PAPER-6
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  • 120
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    Three-dimensional crack problems (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Methods for solving three dimensional crack problems are discussed. The stress intensity factor for the case of uniform pressure on the surface crack is analysis. An analysis of concentrated forces acting on the crack faces parallel to the crack front of a half-plane crack was made. Two dimensional calculations were made using the exact solution for the stress field around an elliptical hole in a uniformly stretched plate. The strain energy density was computed in the neighborhood of the ends of narrow, but sharp, ellipses.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-138652
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  • 121
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    Application of boundary integral method to elastoplastic analysis of V-notched beams (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The boundary integral equation method was applied in the solution of the plane elastoplastic problem. The use of this method was illustrated by obtaining stress and strain distributions for a number of specimens with a single-edge notch and subjected to pure bending. The boundary integral equation method reduced the inhomogeneous biharmonic equation to two coupled Fredholm-type integral equations. These integral equations were replaced by a system of simultaneous algebraic equations and solved numerically in conjunction with a method of successive elastic solutions.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TN-D-7637 , E-7658
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  • 122
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    Differential phase shift keyed communication system (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A communication system using differential phase-shift-keying (DPSK) transmits and receives binary data without requiring timing or phase reference signals. The system encodes and modulates the data at the transmitter, and decodes and demodulates the data at the receiver, without ambiguity as to the data content.
    Keywords: STRUCTURAL MECHANICS
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  • 123
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    Shear-stress intensity factors for elastic sheets with cover plates (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Shear stress intensity factors are calculated for three problems concerning inextensible cover plates either bonded to or embedded in an elastic sheet which is under uniaxial tension. The stress intensity factors are small when the ratio of sheet thickness to cover plate length is small and, as the ratio increase, rapidly approach their asymptotic values for infinite sheet thickness. In the problem of the embedded cover plate, the stress intensity factor also depends on the Poisson's ratio of the sheet material. The dependence on Poisson's ratio, however, is significant only when the ratio of sheet thickness to cover plate length is small. Some possible implications of the present results for debonding of reinforced sheets under cyclic loading are briefly discussed.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TN-D-7473 , L-8882
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  • 124
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    A recurrence matrix method for the analysis of longitudinal and torsional vibrations in non-uniform multibranch beams with variable boundary conditions (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: An approximate method for calculating the longitudinal and torsional natural frequencies and associated modal data of a beamlike, variable cross section multibranch structure is presented. The procedure described is the numerical integration of the first order differential equations that characterize the beam element in longitudinal motion and that satisfy the appropriate boundary conditions.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-X-71973
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  • 125
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    NASTRAN variance analysis and plotting of HBDY elements (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The NASTRAN Thermal Analyzer has been intended to do variance analysis and plot the thermal boundary elements. The objective of the variance analysis addition is to assess the sensitivity of temperature variances resulting from uncertainties inherent in input parameters for heat conduction analysis. The plotting capability provides the ability to check the geometry (location, size and orientation) of the boundary elements of a model in relation to the conduction elements. Variance analysis is the study of uncertainties of the computed results as a function of uncertainties of the input data. To study this problem using NASTRAN, a solution is made for both the expected values of all inputs, plus another solution for each uncertain variable. A variance analysis module subtracts the results to form derivatives, and then can determine the expected deviations of output quantities.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-139007 , EC-245
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  • 126
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    Effect of outdoor exposure at ambient and elevated temperatures on fatigue life of Ti-6Al-4V titanium alloy sheet in the annealed and the solution treated and aged condition (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Specimens of Ti-6Al-4V titanium alloy sheet in the annealed and the solution-treated and aged heat-treatment condition were exposed outdoors at ambient and 560 K (550 F) temperatures to determine the effect of outdoor exposure on fatigue life. Effects of exposure were determined by comparing fatigue lives of exposed specimens to those of unexpected specimens. Two procedures for fatigue testing the exposed specimens were evaluated: (1) fatigue tests conducted outdoors by applying 1200 load cycles per week until failure occurred and (2) conventional fatigue tests (continuous cycling until failure occurred) conducted indoors after outdoor exposure under static load. The exposure period ranged from 9 to 28 months for the outdoor fatigue-test group and was 24 months for the static-load group. All fatigue tests were constant-amplitude bending of specimens containing a drilled hole (stress concentration factor of 1.6). The results of the tests indicate that the fatigue lives of solution-treated and aged specimens were significantly reduced by the outdoor exposure at 560 K but not by the exposure at ambient temperature. Fatigue lives of the annealed specimens were essentially unaffected by the outdoor exposure at either temperature. The two test procedures - outdoor fatigue test and indoor fatigue test after outdoor exposure - led to the same conclusions about exposure effects.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TN-D-7540 , L-9374
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  • 127
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    Transient Response of Shells of Revolution by Direct Integration and Modal Superposition Methods (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The results of an analytical effort to obtain and evaluate transient response data for a cylindrical and a conical shell by use of two different approaches: direct integration and modal superposition are described. The inclusion of nonlinear terms is more important than the inclusion of secondary linear effects (transverse shear deformation and rotary inertia) although there are thin-shell structures where these secondary effects are important. The advantages of the direct integration approach are that geometric nonlinear and secondary effects are easy to include and high-frequency response may be calculated. In comparison to the modal superposition technique the computer storage requirements are smaller. The advantages of the modal superposition approach are that the solution is independent of the previous time history and that once the modal data are obtained, the response for repeated cases may be efficiently computed. Also, any admissible set of initial conditions can be applied.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-X-2916 , L-9216
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  • 128
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    Experimental and analytical determination of vibration characteristics of corrugated, flexibly supported, heat-shield panels (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Experimental and analytical natural frequencies, nodal patterns, and typical modal displacements for a corrugated, flexibly supported, heat-shield panel are discussed. Good correlation was found between the experimental data and NASTRAN analytical results for the corrugated panel over a relatively wide frequency spectrum covered in the investigation. Of the two experimental techniques used for mode shape and displacement measurements (a noncontacting displacement sensor system and a holographic technique using a helium-neon, continuous-wave laser), the holographic technique was found, in the present investigation, to be faster and better suited for determining a large number of complex nodal patterns of the corrugated panel.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TN-D-7562 , L-9364
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  • 129
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    High efficiency multifrequency feed (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Antenna systems and particularly compact and simple antenna feeds which can transmit and receive simultaneously in at least three frequency bands, each with high efficiency and polarization diversity are described. The feed system is applicable for frequency bands having nominal frequency bands with the ratio 1:4:6. By way of example, satellite communications telemetry bands operate in frequency bands 0.8 - 1.0 GHz, 3.7 - 4.2 GHz and 5.9 - 6.4 GHz. In addition, the antenna system of the invention has monopulse capability for reception with circular or diverse polarization at frequency band 1.
    Keywords: STRUCTURAL MECHANICS
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  • 130
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    Turnstile slot antenna (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A turnstile slot antenna is disclosed, the antenna being for and integral with a spacecraft having a substantially cylindrical body portion. The antenna comprises a circumferential slot about the periphery of the spacecraft body portion with an annular wave guide cavity defining a radial transmission line disposed within the spacecraft body portion behind and in communication with the circumferential slot. Feed stubs and associated transmission apparatus are provided to excite the annular cavity in quadrature phase such that an omnidirectional, circularly polarized, rotating radiation pattern is generated. The antenna of the instant invention has utility both as a transmitting and receiving device, and ensures continuous telemetry and command coverage with the spacecraft.
    Keywords: STRUCTURAL MECHANICS
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  • 131
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    Rotating raster generator (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A rotating raster generator is provided which enables display of a television raster at any arbitrary roll angle. The generator includes four integrator circuits each of which receives a first voltage input corresponding to the sine or cosine of the desired roll angle and a second input comprising conventional horizontal or vertical sync pulses. The integrator circuits each comprise an operational amplifier and a capacitor connected for producing a ramp output having a rate of change proportional to the roll angle input, an electronic switch responsive to the sync input for resetting the integrator, and a summer that adds the ramp output of the integrator to the roll angle input so as to provide a zero-centered deflection control voltage.
    Keywords: STRUCTURAL MECHANICS
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  • 132
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    Pulse code modulated signal synchronizer (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A bit synchronizer for a split phase PCM transmission is reported that includes three loop circuits which receive incoming phase coded PCM signals. In the first loop, called a Q-loop, a generated, phase coded, PCM signal is multiplied with the incoming signals, and the frequency and phase of the generated signal are nulled to that of the incoming subcarrier signal. In the second loop, called a B-loop, a circuit multiplies a generated signal with incoming signals to null the phase of the generated signal in a bit phase locked relationship to the incoming signal. In a third loop, called the I-loop, a phase coded PCM signal is multiplied with the incoming signals for decoding the bit information from the PCM signal. A counter means is used for timing of the generated signals and timing of sample intervals for each bit period.
    Keywords: STRUCTURAL MECHANICS
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  • 133
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    Decision feedback loop for tracking a polyphase modulated carrier (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A multiple phase modulated carrier tracking loop for use in a frequency shift keying system is described in which carrier tracking efficiency is improved by making use of the decision signals made on the data phase transmitted in each T-second interval. The decision signal is used to produce a pair of decision-feedback quadrature signals for enhancing the loop's performance in developing a loop phase error signal.
    Keywords: STRUCTURAL MECHANICS
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  • 134
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    Effect of inertia properties on attitude stability of nonrigid spin-stabilized spacecraft (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The phenomenon of energy dissipation in spinning spacecraft is discussed with particular reference to its dependence on spacecraft inertia properties. Specific dissipation mechanisms are identified. The effect of external environmental factors on spin stability is also discussed. Generalized curves are presented relating system stability to the principal inertia ratio for various forms of energy dissipation. Dual-spin systems and the effect of lateral inertia asymmetry are also reviewed.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TN-D-7468 , G-7359
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  • 135
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    Integral flange design program (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: An automated interactive flange design program utilizing an electronic desk top calculator is presented. The program calculates the operating and seating stresses for circular flanges of the integral or optional type subjected to internal pressure. The required input information is documented. The program provides an automated procedure for computing stresses in selected flange geometries for comparison to the allowable code values.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-X-71933
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  • 136
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    An improved exceedance theory for combined random stresses (1974)
    In:  CASI
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    Publication Date: 2019-06-27
    Description: An extension is presented of Rice's classic solution for the exceedances of a constant level by a single random process to its counterpart for an n-dimensional vector process. An interaction boundary, analogous to the constant level considered by Rice for the one-dimensional case, is assumed in the form of a hypersurface. The theory for the numbers of boundary exceedances is developed by using a joint statistical approach which fully accounts for all cross-correlation effects. An exact expression is derived for the n-dimensional exceedance density function, which is valid for an arbitrary interaction boundary. For application to biaxial states of combined random stress, the general theory is reduced to the two-dimensional case. An elliptical stress interaction boundary is assumed and the exact expression for the density function is presented. The equations are expressed in a format which facilitates calculating the exceedances by numerically evaluating a line integral. The behavior of the density function for the two-dimensional case is briefly discussed.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TR-R-418 , L-9120
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  • 137
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    Computer program for supersonic Kernel-function flutter analysis of thin lifting surfaces (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: This report describes a computer program (program D2180) that has been prepared to implement the analysis described in (N71-10866) for calculating the aerodynamic forces on a class of harmonically oscillating planar lifting surfaces in supersonic potential flow. The planforms treated are the delta and modified-delta (arrowhead) planforms with subsonic leading and supersonic trailing edges, and (essentially) pointed tips. The resulting aerodynamic forces are applied in a Galerkin modal flutter analysis. The required input data are the flow and planform parameters including deflection-mode data, modal frequencies, and generalized masses.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-X-2913 , L-9126
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  • 138
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    Nonlinear analysis of structures (1974)
    In:  CASI
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    Publication Date: 2019-06-27
    Description: The development of nonlinear analysis techniques within the framework of the finite-element method is reported. Although the emphasis is concerned with those nonlinearities associated with material behavior, a general treatment of geometric nonlinearity, alone or in combination with plasticity is included, and applications presented for a class of problems categorized as axisymmetric shells of revolution. The scope of the nonlinear analysis capabilities includes: (1) a membrane stress analysis, (2) bending and membrane stress analysis, (3) analysis of thick and thin axisymmetric bodies of revolution, (4) a general three dimensional analysis, and (5) analysis of laminated composites. Applications of the methods are made to a number of sample structures. Correlation with available analytic or experimental data range from good to excellent.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-2351 , RE-454
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  • 139
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    Analysis and design of advanced composite bounded joints (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Advances in the analysis of adhesive-bonded joints are presented with particular emphasis on advanced composite structures. The joints analyzed are of double-lap, single-lap, scarf, stepped-lap and tapered-lap configurations. Tensile, compressive, and in-plane shear loads are covered. In addition to the usual geometric variables, the theory accounts for the strength increases attributable to adhesive plasticity (in terms of the elastic-plastic adhesive model) and the joint strength reductions imposed by imbalances between the adherends. The solutions are largely closed-form analytical results, employing iterative solutions on a digital computer for the more complicated joint configurations. In assessing the joint efficiency, three potential failure modes are considered. These are adherend failure outside the joint, adhesive failure in shear, and adherend interlaminar tension failure (or adhesive failure in peel). Each mode is governed by a distinct mathematical analysis and each prevails throughout different ranges of geometric sizes and proportions.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-2218
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  • 140
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    Automatic frequency control for FM transmitter (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: An automatic frequency control circuit for an FM television transmitter is described. The frequency of the transmitter is sampled during what is termed the back porch portion of the horizontal synchronizing pulse which occurs during the retrace interval, the frequency sample compared with the frequency of a reference oscillator, and a correction applied to the frequency of the transmitter during this portion of the retrace interval.
    Keywords: STRUCTURAL MECHANICS
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  • 141
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    Gated compressor, distortionless signal limiter (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A distortionless gated compressor for limiting the amplitude of a signal so as not to produce undesired signal levels responsive thereto is disclosed. The gated compressor includes a distortionless multiplier which multiplies an AC signal from a factor defined by a DC control signal. The compressor includes a plurality of channels each responsive to a signal produced in response to the multiplier's output. When the signal supplied to any channel exceeds a prescribed level, the level of the DC control signal is reduced to reduce the multiplier's output level and thereby prevent the signal applied to any channel from exceeding its prescribed level.
    Keywords: STRUCTURAL MECHANICS
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  • 142
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    New triangular and quadrilateral plate-bending finite elements (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A nonconforming plate-bending finite element of triangular shape and associated quadrilateral elements are developed. The transverse displacement is approximated within the element by a quintic polynomial. The formulation takes into account the effects of transverse shear deformation. Results of the static and dynamic analysis of a square plate, with edges simply supported or clamped, are compared with exact solutions. Good accuracy is obtained in all calculations.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TN-D-7407 , L-9180
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  • 143
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    Thin-metal lined PRD 49-III composite vessels (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Filament wound pressure vessels of various configurations were evaluated for burst strength and fatigue performance. The dimensions and characteristics of the vessels are described. The types of tests conducted are explained. It was determined that all vessels leaked in a relatively few cycles (20 to 60 cycles) with failure occurring in all cases in the metallic liner. The thin liner would de-bond from the composite and buckling took place during depressurization. No composite failures or indications of impeding composite failures were obtained in the metal-lined vessels.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-134555 , ASG-2-5540
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  • 144
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    Cyclic-stress analysis of notches for supersonic transport conditions (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The feasibility of using the finite element method to account for the effects of cyclic load and temperature on local stresses and strains at a notch was demonstrated. The behavior of a notched titanium panel was studied under variable loads and temperatures representative of flight conditions for the lower wing surface of a Supersonic Transport (SST). The analysis was performed with the use of the BOPACE finite-element computer program which provides capability to determine high temperature and large viscoplastic effects caused by cyclic thermal and mechanical loads. The analysis involves the development of the finite-element model as well as determination of the structural behavior of the notched panel. Results are presented for twelve SST flights comprised of five different load-temperature cycles. The results show the approach is feasible, but material response to cyclic loads, temperatures, and hold times requires improved understanding to allow proper modeling of the material.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-132387
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  • 145
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    Stress intensity factors for deep cracks emanating from the corner formed by a hole intersecting a plate surface (1974)
    In:  CASI
    Details
    Publication Date: 2019-07-20
    Description: A technique consisting of a marriage between stress freezing photoelasticity and a numerical method was used to obtain stress intensity factors for natural cracks emanating from the corner at which a hole intersects a plate surface. Geometrics studied were: crack depth to thickness ratios of approximately 0.2, 0.5, and 0.75; crack depth to crack length ratios of approximately 1.0 to 2.0. All final crack geometries were grown under monotonic loading and growth was not self similar with most of the growth occurring through the thickness under remote extension. Stress intensity plate surface K sub s factors were determined at the intersection of the flaw border with the plate surface K sub s and with the edge of the hole K sub h. Results showed that for the relatively shallow flaws K sub h approximately equal to 1.5 K sub s, for the moderately deep flaws K sub h approximately equal to K sub s, and for the deep flaws K sub h approximately equal to 0.5 K sub s, revealing a severe sensitivity of K to flaw geometry.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-136930 , VPI-E-74-1
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  • 146
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    A procedure for verifying the structural integrity of an existing pressurized wind tunnel (1974)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: The present work describes the approach employed in verifying the structural integrity at maximum operating pressure of a low turbulence pressurized wind tunnel built in 1939-1940. The approach utilized existing ASME Code guidelines and fracture mechanics techniques in combination with the latest nondestructive examination methods to validate the desired life of the facility while minimizing reconstruction or major modifications. Detailed stress analyses using a finite element computer program and a numerical integration program were performed on critical areas of the tunnel. Critical vessel areas were evaluated for remaining fatigue life. Fracture mechanics analyses of the shell were performed at various regions, and critical flaw sizes at each location were determined. Analysis of the test data permitted the remaining useful life of the tunnel to be estimated at 8 to 10 years.
    Keywords: STRUCTURAL MECHANICS
    Type: ASME PAPER 74-MAT-12 , Pressure Vessels and Piping Conference; Jun 24, 1974 - Jun 28, 1974; Miami Beach, FL
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  • 147
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    Investigation of pyrotechnic shock (1974)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Review of comparative pyrotechnic shock outputs of various electro-explosive release devices that have been obtained in tests of an instrumented spacecraft structure. This research uses pyrotechnic shock spectra levels as an indicator of shock environment severity in support of a program of pyrotechnic device analysis and redesign intended to reduce shock generation.
    Keywords: STRUCTURAL MECHANICS
    Type: International Instrumentation Symposium; May 21, 1974 - May 23, 1974; Albuquerque, NM
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  • 148
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    Hingeless rotor theory and experiment on vibration reduction by periodic variation of conventional controls (1974)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: A preliminary evaluation is made of the concept of vibration reduction by properly selected oscillatory collective and cyclic control applications. The investigations are based on experimental frequency response data covering advance ratios from approximately 0.2 to 0.85. Because there was no instrumentation for the measurement of the pitch and roll vibrations, these values were obtained by properly adding up the flap-bending moments at 3.3 in. Any other quantity representing pitch/roll vibrations can be compensated for in the same fashion. The calculated control inputs required for vibration reduction stay within acceptable limits. For four of the five conditions tested they are smaller than the values used for the frequency response tests. As to be expected, the compensating controls greatly affect the blade loads, i.e., torsion, flap- and chordwise bending.
    Keywords: STRUCTURAL MECHANICS
    Type: Specialists Meeting on Rotorcraft Dynamics; Feb 13, 1974 - Feb 15, 1974; Moffett Field, CA
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  • 149
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    Skylab vibroacoustic test program (1974)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Vibroacoustic testing was performed on the orbital workshop dynamic test article and the payload assembly, the two major elements of the Skylab payload. The testing was conducted on each of the Skylab elements separately in the reverberation chamber at the Johnson Space Center. The two test configurations were high fidelity flight article simulations. The testing was conducted in two phases; in the first phase, acoustic tests were performed at levels simulating the lift-off and atmospheric flight acoustic criteria. In the second phase, low frequency sinusoidal vibration tests were conducted to obtain modal response data. The objectives of the Skylab vibroacoustic test program were to: verify the vibration design and test criteria; qualify selected flight components to the vibroacoustic criteria; and verify analytical models used for dynamic load analyses. This paper describes the vibroacoustic testing and discusses the results.
    Keywords: STRUCTURAL MECHANICS
    Type: AAS PAPER 74-106 , Annual Meeting; Aug 20, 1974 - Aug 22, 1974; Los Angeles, CA
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  • 150
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    Estimation of material properties of a nonlinearly elastic bar (1974)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: A method of determining certain characteristic flexural rigidities and elastic properties of nonlinearly elastic materials is presented. An estimation method utilizing perturbation methods and a least squares fitting technique is used to solve the nonlinear differential equation derived from the moment curvature relation, subject to boundary values representing deflections of the bar at discrete points. Deflection data from numerical simulations of a nonlinearly elastic, prismatic bar are used to demonstrate the estimation method. Numerical experiments relating the accuracy of the identification to the number and accuracy of the boundary values are presented. Conclusions based on the numerical experiments are included.
    Keywords: STRUCTURAL MECHANICS
    Type: Southeastern Conference on Theoretical and Applied Mechanics; Mar 21, 1974 - Mar 22, 1974; Washington, DC
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  • 151
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    Viscoelastic structures (1974)
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    Publication Date: 2019-07-13
    Description: Numerical analysis of viscoelastic problems may be achieved by either a step-by-step solution procedure or by the integral transform approach. However, for complicated loading and material property relationships, the latter method proves ineffective. Programs specifically developed for the analysis of viscoelastic structures are considered along with multipurpose programs with specific viscoelastic analysis capabilities.
    Keywords: STRUCTURAL MECHANICS
    Type: Symposium on Structural mechanics computer programs: Surveys, assessments, and availability; Jun 12, 1974 - Jun 14, 1974; College Park, MD
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  • 152
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    High-tip-speed fiber composite compressor blades - Vibration and strength analyses (1974)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: An analytical procedure is described which couples composite mechanics computer codes with NASTRAN. This procedure was used to perform a detailed analysis of a high-tip-speed fiber composite compressor fan blade. The results indicate that the various vibration modes of this blade are highly coupled. Mechanical load ply stresses are well below the corresponding room temperature strengths. Lamination residual stresses are likely to cause transply cracks and interply delamination. Transply cracks and relaxation of root fixity decrease the vibrational frequencies whereas centrifugal stiffening increases them. Comparisons of results for various parameters are presented in tabular and graphical form.
    Keywords: STRUCTURAL MECHANICS
    Type: Conference on Fibrous Composites in Flight Vehicle Design; May 22, 1974 - May 24, 1974; Dayton, OH
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  • 153
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    Combined bending-torsion fatigue reliability of AISI 4340 steel shafting with K sub t = 2.34 (1974)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Results generated by three, unique fatigue reliability research machines which can apply reversed bending loads combined with steady torque are presented. Six-inch long, AISI 4340 steel, grooved specimens with a stress concentration factor of 2.34 and R sub C 35/40 hardness were subjected to various combinations of these loads and cycled to failure. The generated cycles-to-failure and stress-to-failure data are statistically analyzed to develop distributional S-N and Goodman diagrams. Various failure theories are investigated to determine which one represents the data best. The effect of the groove and of the various combined bending-torsion loads on the S-N and Goodman diagrams are determined. Three design applications are presented. The third one illustrates the weight savings that may be achieved by designing for reliability.
    Keywords: STRUCTURAL MECHANICS
    Type: ASME PAPER 74-WA/DE-12 , American Society of Mechanical Engineers, Winter Annual Meeting; Nov 17, 1974 - Nov 22, 1974; New York, NY
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  • 154
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    Stress analysis of the compact specimen including the effects of pin loading (1974)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: An improved method of boundary collocation was applied to the two-dimensional stress analysis of the compact specimen. The effects of the pin-loaded holes on stress-intensity factors and crack-opening displacements were investigated for various crack-length-to-specimen-width ratios, hole locations, and internal loadings. The stress-intensity factors for the 'standard' compact specimen under plane-stress or plane-strain conditions were found to be within 1 percent of the stress-intensity factors reported in the ASTM Test for Plane-Strain Fracture Toughness of Metallic Materials (E 399-72) over a range of crack-length-to-specimen-width ratios of 0.4 to 0.7. However, for crack-length-to-specimen-width ratios less than 0.4, the pin-load holes (which were not previously accounted for) had a significant effect on stress intensity and crack-opening displacements.
    Keywords: STRUCTURAL MECHANICS
    Type: Fracture Analysis; National Symposium on Fracture Mechanics; Aug 27, 1973 - Aug 29, 1973; College Park, MD
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  • 155
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    Theory to test comparisons for selected aerospace multishell structures and their interfaces under thermomechanical loadings (1974)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Guidelines for structural shell analyses were obtained on the basis of theory-to-test comparisons made on two large-scale aerospace structures subject to thermomechanical loads. The first structural test was the cylindrical aluminum skin-stringer-ring construction of the S-IC forward skirt and S-II interstage. The second structural test included the truncated, cone-shaped, bonded honeycomb sandwich shell of the Spacecraft Lunar Module Adapter; the cylindrical bonded aluminum honeycomb sandwich construction of the Instrument Unit; and the skin-stringer construction with rings and intercostals of the S-IVB forward skirt. Analyses were made for loadings simulating the flight environment. Elementary shear lag theory was superimposed on shell analysis for interface junctions between stages to obtain favorable theory-to-test stress comparisons.
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA PAPER 74-1270 , Canadian Aeronautics and Space Institute and American Institute of Aeronautics and Astronautics, Joint Meeting, Toronto; Oct 30, 1974 - Oct 31, 1974; Toronto; Canada
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  • 156
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    Automated structural design with aeroelastic constraints - A review and assessment of the state of the art (1974)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: A review and assessment of the state of the art in automated aeroelastic design is presented. Most of the aeroelastic design studies appearing in the literature deal with flutter, and, therefore, this paper also concentrates on flutter. The flutter design problem is divided into three cases: as isolated flutter mode, neighboring flutter modes, and a hump mode which can rise and cause a sudden, discontinuous change in the flutter velocity. Synthesis procedures are presented in terms of techniques that are appropriate for problems of various levels of difficulty. Current trends, which should result in more efficient, powerful and versatile design codes, are discussed. Approximate analysis procedures and the need for simultaneous consideration of multiple design requirements are emphasized.
    Keywords: STRUCTURAL MECHANICS
    Type: Structural Optimization Symposium; Nov 17, 1974 - Nov 21, 1974; New York, NY
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  • 157
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    Fracture Testing with Surface Crack Specimens (1974)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: Recommendations are given for the design, preparation, and static fracture testing of surface crack specimens. The recommendations are preceded by background information including discussions of stress intensity factors, crack opening displacements, and fracture toughness values associated with surface crack specimens. Cyclic load and sustained load tests are discussed briefly.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-X-71772 , E-8274 , Natl. Symp. on Fracture Mech.; Aug 25, 1975 - Aug 27, 1975; Pittsburgh, PA; united States
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  • 158
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    A review of surface-crack fracture testing (1974)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: A brief historical review of surface-crack testing and analysis is given together with some examples of service failures due to surface cracks. The factors which complicate the analysis and interpretation of surface-crack fracture data are discussed. Current efforts to develop consensus recommendations for tensile testing of surface-crack specimens are summarized.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-X-71629 , E-8163 , Mater. Eng. Ann. Meeting of the Am. Soc. for Metals; Oct 21, 1974 - Oct 24, 1974; Detroit, MI; United States
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  • 159
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    Nonlinear finite-element analysis of laminated composite shells (1974)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Two aspects of the geometrically nonlinear analysis of laminated composite shells are considered in this paper. The first pertains to the simplifications and computational advantages resulting from the use of group-theoretic methods in conjunction with computerized symbolic (algebraic) manipulation in the element development. The second aspect pertains to the combined effects of shear deformation and nonlinearity on the accuracy and convergence of two-dimensional, shear-flexible stiffness finite element models.
    Keywords: STRUCTURAL MECHANICS
    Type: Computational methods in nonlinear mechanics; International Conference; Sep 23, 1974 - Sep 25, 1974; Austin, TX
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  • 160
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    A review of surface-crack fracture testing (1974)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: A brief historical review of surface-crack testing and analysis is given together with some examples of service failures due to surface cracks. The factors which complicate the analysis and interpretation of surface-crack fracture data are discussed. Current efforts to develop consensus recommendations for tensile testing of surface-crack specimens are summarized.
    Keywords: STRUCTURAL MECHANICS
    Type: American Society for Metals, Materials Engineering Annual Meeting; Oct 21, 1974 - Oct 24, 1974; Detroit, MI
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  • 161
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    Contact problem for an elastic reinforcement bonded to an elastic plate (1974)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: The contact problem for a thin elastic reinforcement bonded to an elastic plate is considered. The stiffening layer is treated as an elastic membrane and the base plate is assumed to be an elastic continuum. The bonding between the two materials is assumed to be either one of direct adhesion or through a thin adhesive layer which is treated as a shear spring. The solution for the simple case in which both the stiffener and the base plate are treated as membranes is also given. The contact stress is obtained for a series of numerical examples. In the direct adhesion case the contact stress becomes infinite at the stiffener ends with a typical square root singularity for the continuum model and behaving as a delta function for the membrane model. In the case of bonding through an adhesive layer the contact stress becomes finite and continuous along the entire contact area.
    Keywords: STRUCTURAL MECHANICS
    Type: ASME PAPER 74-WA/APM-20 , American Society of Mechanical Engineers, Winter Annual Meeting; Nov 17, 1974 - Nov 22, 1974; New York, NY
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  • 162
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    The problem of edge cracks in an infinite strip (1974)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: The elastostatic plane problem of an infinite strip containing two symmetrically located internal cracks perpendicular to the boundary is formulated in terms of a singular integral equation with the derivative of the crack surface displacement as the density function. The solution of the problem is obtained for various crack geometries and for uniaxial tension applied to the strip away from the crack region. The limiting case of the edge cracks is then considered in some detail. The fundamental function of the integral equation is obtained and a numerical technique for solving the singular integral equations with this particular type of fundamental function which is characteristic of the edge cracks is described. The stress-intensity factor for the complete range of net ligament-to-width ratio is calculated. The results also include the solution of the edge crack problem in an elastic half plane.
    Keywords: STRUCTURAL MECHANICS
    Type: ASME PAPER 74-WA/APM-12 , American Society of Mechanical Engineers, Winter Annual Meeting; Nov 17, 1974 - Nov 22, 1974; New York, NY
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  • 163
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    Utilization survey of prototype structural test article (1974)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: A survey was conducted of six aerospace companies and two NASA agencies to determine how prototype structural test articles are used in flight operations. The prototype structures are airframes and similar devices which are used for testing and generally are not flown. The survey indicated the following: (1) prototype test articles are not being discarded after development testing is complete, but are used for other purposes, (2) only two cases of prototypes being refurbished and flown were identified, (3) protective devices and inspection techniques are available to prevent or minimize test article damage, (4) substitute programs from design verification are availabel in lieu of using prototype structural articles, and (5) there is a trend away from dedicated test articles. Four options based on these study results were identified to reduce test and hardware costs without compromising reliability of the flight program.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-120543 , D180-18424-1
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  • 164
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    A method to determine the stored energy function of compressible rubberlike materials (1974)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Keywords: STRUCTURAL MECHANICS
    Type: Mechanical behavior of materials; Symposium; Aug 21, 1974 - Aug 24, 1974; Kyoto; Japan
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  • 165
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    Finite-element analysis of vibration and flutter of cantilever anisotropic plates (1974)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: The hybrid stress finite element method is used to study the effects of filament angle and orthotropicity parameter on the vibration and flutter characteristics of cantilevered anisotropic plates. The results indicate a generally strong lack of monotonic dependence on filament angle. Also, the natural frequency in certain cases involving the first few modes, can become relatively insensitive to both filament angle and orthotropicity parameter for a range of filament angle beyond 70 deg. Values of critical dynamic pressure are obtained by a modal approach, in which the mode shapes are obtained by the hybrid stress method. Convergence of the modal method is rather rapid for the configurations analyzed, and a comparison of the method with an exact solution for the case of an isotropic simply supported plate shows that use of six modes gives excellent agreement.
    Keywords: STRUCTURAL MECHANICS
    Type: ASME PAPER 74-WA/APM-15 , American Society of Mechanical Engineers, Winter Annual Meeting; Nov 17, 1974 - Nov 22, 1974; New York, NY
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  • 166
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    Small-scale yielding analysis of mixed mode plane-strain crack problems (1974)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: The small-scale yielding analysis of an elastic-plastic body with a line crack under plane-strain conditions subject to combinations of Mode I and II loadings is examined. The analysis of the near-tip field follows the works of Hutchinson and Rice and Rosengren. Dominant singularity solutions governing the asymptotic behavior of the stresses and strains at the crack tip are obtained for the complete range of loadings between Mode I and II. The results of an accurate finite element technique, which imbeds the dominant singularity solutions, directly relates the near-tip behavior to the elastic stress intensity factors K(I) and K(II). Implications of this study to mixed mode fracture mechanics is also discussed, particularly with respect to the direction of crack initiation and the relation of fracture toughness under mixed modes to that in Mode I. Details of the mixed mode plastic zone sizes and shapes are also given.
    Keywords: STRUCTURAL MECHANICS
    Type: Fracture Analysis; National Symposium on Fracture Mechanics; Aug 27, 1973 - Aug 29, 1973; College Park, MD
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  • 167
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    Some approximation concepts for structural synthesis (1974)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: An efficient automated minimum weight design procedure is presented which is applicable to sizing structural systems that can be idealized by truss, shear panel, and constant strain triangles. Static stress and displacement constraints under alternative loading conditions are considered. The optimization algorithm is an adaptation of the method of inscribed hyperspheres and high efficiency is achieved by using several approximation concepts including temporary deletion of noncritical constraints, design variable linking, and Taylor series expansions for response variables in terms of design variables. Optimum designs for several planar and space truss examples problems are presented. The results reported support the contention that the innovative use of approximation concepts in structural synthesis can produce significant improvements in efficiency.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-140937 , PAPER-73-341 , AIAA/ASME/SAE 14th Struct.; Mar 20, 1973 - Mar 22, 1973; Williamsburg, VA; United States|AGARD Structural Optimization; 8 p
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  • 168
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    The prediction of structural response to buffet flow: A state-of-the-art review (1974)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Certain aspects of the dynamic system being discussed are reviewed and important structural and aerodynamic quantities of the system are discussed. A theoretical model is presented which relates these quantities to each other. These quantities are then each, in turn, considered in terms of the state of the art of determining the quantities and in terms of areas where further research is needed. The similarity laws and scaling relationships applicable to determining buffet structural response are then discussed, and areas where simplification is required or may be permissible are mentioned. Finally, the various types of model tests pertinent to predicting response of the aircraft structure to buffet flow are discussed.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-X-72627 , L-9820 , 39th AGARD Structural and Mater. Meeting,; Oct 07, 1974 - Oct 12, 1974; Munich
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  • 169
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    Analysis of edge impact stresses in composite plates (1974)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: The in-plane edge impact of composite plates, with or without a protection strip, is investigated. A computational analysis based on the Fast Fourier Transform technique is presented. The particular application of the present method is in the understanding of the foreign object damage problem of composite fan blades. The method is completely general and may be applied to the study of other stress wave propagation problems in a half space. Results indicate that for the protective strip to be effective in reducing impact stresses in the composite the thickness must be equal or greater than the impact contact dimension. Large interface shear stresses at the strip - composite boundary can be induced under impact.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-134720 , AMS-1141
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  • 170
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    Synthesis of stiffened shells of revolution (1974)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: Computer programs for the synthesis of shells of various configurations were developed. The conditions considered are: (1) uniform shells (mainly cones) using a membrane buckling analysis, (2) completely uniform shells (cones, spheres, toroidal segments) using linear bending prebuckling analysis, and (3) revision of second design process to reduce the number of design variables to about 30 by considering piecewise uniform designs. A perturbation formula was derived and this allows exact derivatives of the general buckling load to be computed with little additional computer time.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-138839
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  • 171
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    The circumferentially notched cylindrical bar as a fracture toughness test specimen (1974)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: A brief review is given of the application of the notched cylinder as a screening specimen for use in sorting materials in respect to their relative levels of plane strain fracture toughness and a discussion of fracture mechanics applications including Irwin's important contributions in this area. In addition, practical problems encountered in application of this specimen will be presented.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-X-71551 , E-7933 , Symp. on Linear Fracture Mech.; Jul 29, 1974 - Jul 30, 1974; Bethlehem, PA; United States
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  • 172
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    Debond propagation in composite reinforced metals (1974)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: Strain energy release rates were used to correlate cyclic debonding between metal sheets and composite reinforcement. An expression for the strain energy release rate was derived and applied to fatigue test results for three material systems: graphite bonded to aluminum with both a room temperature and an elevated temperature curing adhesive, and S-glass bonded to aluminum with an elevated temperature curing adhesive. For each material system, several thicknesses were tested with a range of fatigue loads. Cyclic debonding was monitored using a photoelastic technique. A close correlation was found between the observed debond rates and the calculated strain energy release rates for each material system.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-X-71948 , ASTM Symp. on Fatigue of Composite Mater.; Dec 02, 1973 - Dec 07, 1973; Bal Harbour, FL; United States
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  • 173
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    Application of boundary integral method to elastoplastic analysis of v-notched beams (1974)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: The boundary integral equation method was applied in the solution of the plane elastoplastic problems. The use of this method was illustrated by obtaining stress and strain distributions for a number of specimens with a single edge notch and subjected to pure bending. The boundary integral equation method reduced the non-homogeneous biharmonic equation to two coupled Fredholm-type integral equations. These integral equations were replaced by a system of simultaneous algebraic equations and solved numerically in conjunction with the method of successive elastic solutions.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-X-71472 , E-7658 , US Natl. Congr. of Appl. Mech.; Jun 03, 1974 - Jun 07, 1974; Boulder, CO; United States
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  • 174
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    Three-dimensional elastic stress and displacement analysis of finite geometry solids containing cracks (1974)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: The line method of analysis is applied to the Navier-Cauchy equations of elastic equilibrium to calculate the displacement distributions in various bodies containing cracks. The application of this method to these equations leads to coupled sets of simultaneous ordinary differential equations whose solutions are obtained along sets of lines in a discretized region. When decoupling the equations and their boundary conditions is not possible, the use of a successive approximation procedure permits the analytical solution of the resulting ordinary differential equations. The results obtained show a considerable potential for using this method in the three-dimensional analysis of finite geometry solids and suggest a possible extension of this technique to nonlinear material behavior.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-X-71467 , E-7170 , US Natl. Congr. of Applied Mechanics; Jun 03, 1974 - Jun 07, 1974; Boulder, CO; United States
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  • 175
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    Programmers manual for static and dynamic reusable surface insulation stresses (resist) (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Programming information for the RESIST program for the dynamic and thermal stress analysis of the space shuttle surface insulation is presented. The overall flow chart of the program, overlay chart, data set allocation, and subprogram calling sequence are given along with a brief description of the individual subprograms and typical subprogram output.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-132607
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  • 176
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    Advanced beaded and tubular structural panels. Volume 1: Design and analysis (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A study was conducted to exploit the efficiency of curved elements in the design of lightweight structural panels under combined loads of axial compression, inplane shear, and bending. Data cover analytical procedures for optimum panel design, static strength analyses, results of panel design studies, and correlation of theory with test results.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-132460
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  • 177
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    A Study of the Effect of Adhesive and Matrix Stiffnesses on the Axial, Normal, and Shear Stress Distributions of a Boron-epoxy Reinforced Composite Joint (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The mechanical properties of a symmetrical, eight-step, titanium-boron-epoxy joint are discussed. A study of the effect of adhesive and matrix stiffnesses on the axial, normal, and shear stress distributions was made using the finite element method. The NASA Structural Analysis Program (NASTRAN) was used for the analysis. The elastic modulus of the adhesive was varied from 345 MPa to 3100 MPa with the nominal value of 1030 MPa as a standard. The nominal values were used to analyze the stability of the joint. The elastic moduli were varied to determine their effect on the stresses in the joint.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-141311
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  • 178
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    Development of the program SPECEL: A special element for elasto-plastic crack tip analysis (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Theory is stated in terms of increments of displacement and stress, and of instantaneous or accumulated values of stress. The equilibrium equations, in the absence of body forces, are written, along with constitutive relations for plane strain.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-140895 , SM-74-10
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  • 179
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    Development of solution techniques for nonlinear structural analysis (1974)
    In:  CASI
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    Publication Date: 2019-06-27
    Description: Nonlinear structural solution methods in the current research literature are classified according to order of the solution scheme, and it is shown that the analytical tools for these methods are uniformly derivable by perturbation techniques. A new perturbation formulation is developed for treating an arbitrary nonlinear material, in terms of a finite-difference generated stress-strain expansion. Nonlinear geometric effects are included in an explicit manner by appropriate definition of an applicable strain tensor. A new finite-element pilot computer program PANES (Program for Analysis of Nonlinear Equilibrium and Stability) is presented for treatment of problems involving material and geometric nonlinearities, as well as certain forms on nonconservative loading.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-120525 , D180-18325-1
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  • 180
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    Minimum-weight designs for hat-stiffened composite panels under uniaxial compression (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Optimum hat-stiffened compression panel designs are determined by a structural synthesis technique. The effects of simplifying assumptions made in the buckling analysis for the optimization program are investigated by a linked plate element program. Optimization results for hat-stiffened graphite-epoxy panels show a 50-percent weight savings over optimized aluminum panels. Composite panels are shown to possess a variety of proportions at nearly constant weight.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TN-D-7779 , L-9739
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  • 181
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    SPAR demonstration problems (1974)
    In:  CASI
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    Publication Date: 2019-06-27
    Description: A series of examples are presented to indicate some of the principal functions of the SPAR system and to illustrate SPAR's control card-data card structure. Information in the following categories is given: (1) a description of the problem and, in most cases, comparisons with analytical solutions; (2) a list of the input cards; (3) a printout of the table of contents of the direct access library into which all SPAR output was directed; and (4) a few representative plots.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-120505 , LMSC-D403169
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  • 182
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    SPAR reference manual (1974)
    In:  CASI
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    Publication Date: 2019-06-27
    Description: SPAR is a system of related programs which may be operated either in batch or demand (teletype) mode. Information exchange between programs is automatically accomplished through one or more direct access libraries, known collectively as the data complex. Card input is command-oriented, in free-field form. Capabilities available in the first production release of the system are fully documented, and include linear stress analysis, linear bifurcation buckling analysis, and linear vibrational analysis.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-120504 , LMSC-D403168
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  • 183
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    WINDOWAC (Wing Design Optimization With Aeroelastic Constraints): Program manual (1974)
    In:  CASI
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    Publication Date: 2019-06-27
    Description: User and programer documentation for the WIDOWAC programs is given. WIDOWAC may be used for the design of minimum mass wing structures subjected to flutter, strength, and minimum gage constraints. The wing structure is modeled by finite elements, flutter conditions may be both subsonic and supersonic, and mathematical programing methods are used for the optimization procedure. The user documentation gives general directions on how the programs may be used and describes their limitations; in addition, program input and output are described, and example problems are presented. A discussion of computational algorithms and flow charts of the WIDOWAC programs and major subroutines is also given.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-X-3071 , L-9195
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  • 184
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    A computer program for plotting stress-strain data from compression, tension, and torsion tests of materials (1974)
    In:  CASI
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    Publication Date: 2019-06-27
    Description: A computer program for plotting stress-strain curves obtained from compression and tension tests on rectangular (flat) specimens and circular-cross-section specimens (rods and tubes) and both stress-strain and torque-twist curves obtained from torsion tests on tubes is presented in detail. The program is written in FORTRAN 4 language for the Control Data 6000 series digital computer with the SCOPE 3.0 operating system and requires approximately 110000 octal locations of core storage. The program has the capability of plotting individual strain-gage outputs and/or the average output of several strain gages and the capability of computing the slope of a straight line which provides a least-squares fit to a specified section of the plotted curve. In addition, the program can compute the slope of the stress-strain curve at any point along the curve. The computer program input and output for three sample problems are presented.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-X-3091 , L-9384
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  • 185
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    Analysis of longitudinal thickness-shear stiffness of a monolayer filamentary composite (1974)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: The longitudinal thickness-shear behavior of a rectangular cross-section prism containing circular cross-section fibers embedded in a matrix is analyzed. The problem is formulated as a Saint-Venant flexure problem modeled by a tip-loaded cantilever composite beam and solution is obtained by the boundary-point least-squares method. It is shown that the longitudinal thickness-shear modulus is much greater than the in-plane shear modulus for a monofilament composite and therefore an independent analysis is necessary to predict the longitudinal thickness-shear behavior of the composite. Numerical results are presented in graphical form for various values of fiber volume fraction and material parameters typical of modern advanced composites.
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA Journal; 12; Oct. 197
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  • 186
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    On numerically accurate finite element solutions in the fully plastic range (1974)
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    Description: A general criterion for testing a mesh with topologically similar repeat units is given, and it is shown that only a few conventional element types and arrangements are suitable for computations in the fully plastic range. Further, a new variational principle, which can easily be incorporated into an existing finite element program, is presented. This makes it possible to perform accurate computations even for element designs that would not normally be suitable. An appendix extends the discussion to elastic-plastic computation at finite strain.
    Keywords: STRUCTURAL MECHANICS
    Type: Computer Methods in Applied Mechanics and Engineering; 4; Sept
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  • 187
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    Optimization of mechanical vibration isolation systems with multi-degrees of freedom (1974)
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    Publication Date: 2019-06-27
    Description: The main objective was to optimize the steady response of lumped parameter vibration systems with multi-degrees of freedom subject to one or several harmonic excitations. Since the steady-state response varies with the resonant frequencies of the systems, the dampers introduced in the system are optimized in such a way that the most critical response is reduced to a minimum. A discussion is included of the techniques of optimization, and a report is given of the results of tests performed for supporting the technique adopted.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Sound and Vibration; 36; Sept. 8
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  • 188
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    Vibration analysis of a completely free elliptical plate (1974)
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    Publication Date: 2019-06-27
    Description: The Ritz method is applied to the variation analysis of a completely free elliptical plate as an efficient alternative to a procedure using a truncated series of regular and modified Mathieu functions. It is shown that a solution as accurate as desired can be obtained with the Ritz method in solving thin plate vibration problems with difficult geometries.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Sound and Vibration; 34; June 8
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  • 189
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    Antiplane shear crack terminating at and going through a bimaterial interface (1974)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: The antiplane shear problem of two bonded elastic half-planes containing a crack perpendicular to the interface is considered. The cases of a semiinfinite crack terminating at the interface, a finite crack away from and terminating at the interface, two cracks one on each side of the interface, and a finite crack crossing the interface are separately investigated. The nature of the stress singularity for the crack terminating at and going through the interface is studied, and it is shown that at the irregular point on the interface, for the former the power of singularity is not -1/2 and for the latter the stresses are bounded. For a material pair of aluminum-epoxy some numerical results giving the stress intensity factors, the density functions, and the crack opening displacements are presented.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal of Fracture; 10; June 197
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  • 190
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    The tensile failure modes of metal-matrix composite materials (1974)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: The strengths of individual boron fibers extracted from various as-received and thermally fatigued aluminum alloy matrix materials were measured. The results are described in terms of a Weibull distribution, and strengths of composites fabricated from these fibers are calculated in terms of lower and upper bounds. Tests conducted on composite specimens indicated that strengths approaching the upper bounds can be achieved in composites fabricated by normal diffusion bonding techniques. Cyclic temperature changes effectively reduced the strength values toward the lower bounds. It was concluded that this effect resulted from the degradation of the strength of the fiber-matrix bond.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of the Mechanics and Physics of Solids; 22; May 1974
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  • 191
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    Inelastic, nonlinear analysis of stiffened shells of revolution by numerical integration (1974)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: This paper describes the latest addition to the STARS system of computer programs, STARS-2P, for the plastic, large deflection analysis of axisymmetrically loaded shells of revolution. The STARS system uses a numerical integration scheme to solve the governing differential equations. Several unique features for shell of revolution programs that are included in the STARS-2P program are described. These include orthotropic nonlinear kinematic hardening theory, a variety of shell wall cross sections and discrete ring stiffeners, cyclic and nonproportional mechanical and thermal loading capability, the coupled axisymmetric large deflection elasto-plastic torsion problem, an extensive restart option, arbitrary branching capability, and the provision for the inelastic treatment of smeared stiffeners, isogrid, and waffle wall constructions. To affirm the validity of the results, comparisons with available theoretical and experimental data are presented.
    Keywords: STRUCTURAL MECHANICS
    Type: ASME PAPER 74-PVP-35
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  • 192
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    Large deflection elastic-plastic dynamic response of stiffened shells of revolution (1974)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: This paper presents the formulation and check-out problems for a computer code DYNAPLAS, which analyzes the large deflection elastic-plastic dynamic response of stiffened shells of revolution. The formulation for spacial discretization is by the finite element method with finite differences being used for the evaluation of the pseudo forces due to material and geometric nonlinearities. Time integration is by the Houbolt method or central differences. The stiffeners may be due to concentrated or distributed eccentric rings and spring supports at arbitrary angles around the circumference of the elements. Check-out problems include the comparison of solutions from DYNAPLAS with experimental and other computer solutions for rings and conical and cylindrical shells. A hypothetical submarine including stiffeners and missile tube is studied under a combination of hydrostatic and dynamically applied asymmetrical pressure loadings.
    Keywords: STRUCTURAL MECHANICS
    Type: ASME PAPER 74-PVP-3
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  • 193
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    The response of rotating machinery to external random vibration (1974)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: A high-speed turbogenerator employing gas-lubricated hydrodynamic journal and thrust bearings was subjected to external random vibrations for the purpose of assessing bearing performance in a dynamic environment. The pivoted-pad type journal bearings and the step-sector thrust bearing supported a turbine-driven rotor weighing approximately twenty-one pounds at a nominal operating speed of 36,000 rpm. The response amplitudes of both the rigid-supported and flexible-supported bearing pads, the gimballed thrust bearing, and the rotor relative to the machine casing were measured with capacitance type displacement probes. Random vibrations were applied by means of a large electrodynamic shaker at input levels ranging between 0.5 g (rms) and 1.5 g (rms). Vibrations were applied both along and perpendicular to the rotor axis. Response measurements were analyzed for amplitude distribution and power spectral density. Experimental results compare well with calculations of amplitude power spectral density made for the case where the vibrations were applied along the rotor axis. In this case, the rotor-bearing system was treated as a linear, three-mass model.
    Keywords: STRUCTURAL MECHANICS
    Type: ASME PAPER 73-DET-110
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  • 194
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    Interaction between parallel cracks in layered composites (1974)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: The plane strain problem of a millilayered composite with parallel cracks is considered. The main objective is to study the interaction between parallel and collinear cracks. The problem is formulated in terms of a set of simultaneous singular integral equations which are solved numerically. The effect of material properties on the interaction between cracks is also demonstrated.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal of Solids and Structures; 10; July 197
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  • 195
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    A penny-shaped crack in a filament-reinforced matrix. I - The filament model. II - The crack problem (1974)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: The study deals with the elastostatic problem of a penny-shaped crack in an elastic matrix which is reinforced by filaments or fibers perpendicular to the plane of the crack. An elastic filament model is first developed, followed by consideration of the application of the model to the penny-shaped crack problem in which the filaments of finite length are asymmetrically distributed around the crack. Since the primary interest is in the application of the results to studies relating to the fracture of fiber or filament-reinforced composites and reinforced concrete, the main emphasis of the study is on the evaluation of the stress intensity factor along the periphery of the crack, the stresses in the filaments or fibers, and the interface shear between the matrix and the filaments or fibers. Using the filament model developed, the elastostatic interaction problem between a penny-shaped crack and a slender inclusion or filament in an elastic matrix is formulated.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal of Solids and Structures; 10; July 197
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  • 196
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    A plate with a crack, stiffened by a partially debonded stringer (1974)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: The effect of a partially debonded infinite stringer on the stress intensity factor at the crack tip is investigated. It is assumed that the stringer is bonded to an isotropic plate through an adhesive, along a line perpendicular to the crack. Due to the high stress concentration around the crack tip and on the adhesive, partial debonding is assumed to develop between the stringer and the plate. The integral equation, obtained from the continuity of displacements along the line where the stringer and the plate are bonded, is solved numerically to give the shear stress distribution between the plate and the stringer and the stress intensity factors at both crack tips.
    Keywords: STRUCTURAL MECHANICS
    Type: Engineering Fracture Mechanics; 6; Mar. 197
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  • 197
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    An approximate method of analysis for notched unidirectional composites (1974)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: An approximate method is proposed for the analysis of unidirectional, filamentary composite materials having slit notches perpendicular to the fibers and subjected to tension parallel to the fibers. The approach is based on an engineering model which incorporates important effects of material heterogeneity by considering average extensional stresses in the fibers and average shear stresses in the matrix. Effects of interfacial failure and matrix plasticity at the root of the notch are considered. Predictions of the analysis are in reasonably good agreement with previous analytical models and experimental data for graphite/epoxy.
    Keywords: STRUCTURAL MECHANICS
    Type: Engineering Fracture Mechanics; 6; Mar. 197
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  • 198
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    Bonded half planes containing an arbitrarily oriented crack (1974)
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    Publication Date: 2019-06-27
    Description: The plane elastostatic problem for two bonded half planes containing an arbitrarily oriented crack in the neighborhood of the interface is considered. Using Mellin Transforms the problem is formulated as a system of singular integral equations. The equations are solved for various crack orientations, material combinations, and external loads. The numerical results given in the paper include the stress intensity factors, the strain energy release rates, and the probable clevage angles giving the direction of crack propagation.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal of Solids and Structures; 10; June 197
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  • 199
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    Bifurcation analysis of the onset of necking in an elastic/plastic cylinder under uniaxial tension (1974)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: The bifurcation problem governing the onset of axisymmetric necking in a circular cylindrical specimen in uniaxial tension is analysed. The specimen is made of an incompressible elastic/plastic material. One end is subject to a prescribed uniform axial displacement relative to the other and both ends are shear free. The true stress at bifurcation is greater than the stress at which the maximum load is attained by an amount which depends on (a) the radius to length ratio of the specimen, (b) the ratio of the elastic shear modulus to the tangent modulus, and (c) the derivative of the tangent modulus with respect to the stress. Bifurcation takes place immediately following attainment of the maximum load when the specimen is sufficiently slender.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of the Mechanics and Physics of Solids; 22; Jan. 197
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  • 200
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    Limitations to the small scale yielding approximation for crack tip plasticity (1974)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: Recent finite-element results by S. G. Larsson and A. J. Carlsson suggest a limited range of validity to the 'small scale yielding approximation,' whereby small crack tip plastic zones are correlated in terms of the elastic stress intensity factor. It is shown with the help of a model for plane strain yielding that their results may be explained by considering the non-singular stress, acting parallel to the crack at its tip, which accompanies the inverse square-root elastic singularity. Further implications of the non-singular stress term for crack tip deformations and fracturing are examined. It is suggested that its effect on crack tip parameters, such as the opening displacement and J-integral, is less pronounced than its effect on the yield zone size.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of the Mechanics and Physics of Solids; 22; Jan. 197
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