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  • Chemical Engineering  (3,542)
  • Engineering General  (2,473)
  • STRUCTURAL MECHANICS  (1,910)
  • 1985-1989  (7,925)
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Years
Year
  • 1
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    Fatigue behavior of 5Ni-Cr-Mo-V steel weldments containing fabrication discontinuities (1988)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: The applicability of linear elastic fracture mechanics to characterize the fatigue behavior of high-strength steel weldments containing lack-of-penetration (LOP) and slag/lack-of-fusion (S/LOF) discontinuities is explored. Full penetration, double-V butt welds with reinforcements removed were tested under zero-to-tension axial loading. Various filler metals and welding techniques were used. Both sound welds and welds containing discontinuities were cycled to failure. Where possible, cycles to crack initiation were estimated by strain gage measurements. The fracture mechanics approach was successful in correlating the fatigue lifetimes of specimens containing single LOP discontinuities of varying size. However, the fatigue behavior of specimens containing multiple S/LOF discontinuities proved to be much more complex and difficult to analyze.
    Keywords: STRUCTURAL MECHANICS
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  • 2
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    Postbuckling behavior of fiber reinforced plates and curved panels (1987)
    In:  CASI
    Details
    Publication Date: 2019-08-28
    Description: Results obtained on the postbuckling behavior of plates and curved panels using the NOLIN computer program are reported. As an example, the postbuckling behavior of a flexible, isotropic and quadrangular plate is solved and the results are found to be accurate and relibale in comparison with those in the literature. The fatigue-deformation behavior of a rectangular CKL plate is measured, and the results are compared with those from NOLIN and other computer programs. A slightly curved panel with optimized layering is studied.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TT-20094 , NAS 1.77:20094
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  • 3
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    Design of Software for Design of Finite Element for Structural Analysis (1987)
    In:  CASI
    Details
    Publication Date: 2019-08-28
    Description: The concepts of software engineering which allow a user of the finite element method to describe a model, to collect and to check the model data in a data base as well as to form the matrices required for a finite element calculation are examined. Next the components of the model description are conceived including the mesh tree, the topology, the configuration, the kinematic boundary conditions, the data for each element, and the loads. The possibilities for description and review of the data are considered. The concept of the segments for the modularization of the programs follows the components of the model description. The significance of the mesh tree as a globular guiding structure will be understood in view of the principle of the unity of the model, the mesh tree, and the data base. The user-friendly aspects of the software system will be summarized: the principle of language communication, the data generators, error processing, and data security.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-88528 , NAS 1.15:88528
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  • 4
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    Tensile test of pressureless-sintered silicon nitride at elevated temperature (1985)
    In:  CASI
    Details
    Publication Date: 2019-08-28
    Description: Uniaxial tensile strength tests of pressureless sintered silicon nitride were carried out in air at temperatures ranging from room temperature up to 1600 C. Silicon nitrides containing Y2O3, Al2O3, Al2O3-MgO, or MgO-CeO2 additives were tested. The results show that the composition of the additive used influences the strength characteristics of the silicon nitride. The tensile strength rapidly decreased at temperatures above 1000 C for the materials containing MgO as the additive and above 1000 C for the material with Y2O3. When the temperature increased to as high as 1300 C, the strength decreased to about 10 percent of the room temperature strength in each case. Observations of the fracture origin and of the crack propagation on the fracture surfaces are discussed.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-77777 , NAS 1.15:77777 , NAL-TR-753
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  • 5
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    Mixed finite element models for free vibrations of thin-walled beams (1989)
    In:  CASI
    Details
    Publication Date: 2019-08-28
    Description: Simple, mixed finite element models are developed for the free vibration analysis of curved thin-walled beams with arbitrary open cross section. The analytical formulation is based on a Vlasov's type thin-walled beam theory with the effects of flexural-torsional coupling, transverse shear deformation and rotary inertia included. The fundamental unknowns consist of seven internal forces and seven generalized displacements of the beam. The element characteristic arrays are obtained by using a perturbed Lagrangian-mixed variational principle. Only C(sup o) continuity is required for the generalized displacements. The internal forces and the Lagrange multiplier are allowed to be discontinuous at interelement boundaries. Numerical results are presented to demonstrate the high accuracy and effectiveness of the elements developed. The standard of comparison is taken to be the solutions obtained by using 2-D plate/shell models for the beams.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TP-2868 , L-16506 , NAS 1.60:2868
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  • 6
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    On contact problems of elasticity theory (1986)
    In:  CASI
    Details
    Publication Date: 2019-08-27
    Description: Certain contact problems are reviewed in the two-dimensional theory of elasticity when round bodies touch without friction along most of the boundary and, therefore, Herz' hypothesis on the smallness of the contact area cannot be used. Fundamental equations were derived coinciding externally with the equation in the theory of a finite-span wing with unkown parameter. These equations are solved using Multhopp's well-known technique, and numerical calculations are performed in specific examples.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-88491 , NAS 1.15:88491
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  • 7
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    The mechanics of solids in the plastically-deformable state (1986)
    In:  CASI
    Details
    Publication Date: 2019-08-27
    Description: The mechanics of continua, which is based on the general stress model of Cauchy, up to the present has almost exclusively been applied to liquid and solid elastic bodies. Saint-Venant has developed a theory for the plastic or remaining form changes of solids, but it does not give the required number of equations for determining motion. A complete set of equations of motion for plastic deformable bodies is derived. This is done within the framework of Cauch mechanics. And it is supported by certain experimental facts which characterize the range of applications.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-88448 , NAS 1.15:88448
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  • 8
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    Overview of the NASA program in computational structural mechanics (1989)
    In:  CASI
    Details
    Publication Date: 2019-08-27
    Description: In order to meet the anticipated needs in modeling and analysis of advanced aerospace structures, NASA has developed a program focused on computational structural mechanics. The objective of this program is to advance the state-of-the-art in computational analysis to make accurate analysis of very large and complex structural problems routine. This will be accomplished by emphasizing two key areas: (1) the development of advanced analytical methods, extending beyond traditional approaches and, (2) the exploitation of the newest and most powerful parallel/multiprocessor computers available. Computational testbeds will be developed to serve as technology integrators and to promote/accelerate methodology research and development. An additional, and highly desirable, effect of the Computational Structural Mechanics (CSM) program would be to influence the design of future hardware and software systems to reflect the needs of structural analysis.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center, NASA Workshop on Computational Structural Mechanics 1987, Part 1; p 1-23
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  • 9
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    Fracture mechanics formulas on microcomputers (1985)
    In:  CASI
    Details
    Publication Date: 2019-08-27
    Description: An interactive fracture mechanics program was developed in BASIC minima on a CBM 4032 microcomputer. It furnishes stress intensity factors and the critical size of a flaw.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-77850 , NAS 1.15:77850
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  • 10
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    Thermoplasticity of coupled bodies in the case of stress-dependent heat transfer (1987)
    In:  CASI
    Details
    Publication Date: 2019-08-27
    Description: The problem of the thermal stresses in coupled deformable bodies is formulated for the case where the heat-transfer coefficient at the common boundary depends on the stress-strain state of the bodies (e.g., is a function of the normal pressure at the common boundary). Several one-dimensional problems are solved in this formulation. Among these problems is the determination of the thermal stresses in an n-layer plate and in a two-layer cylinder.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TT-20110 , NAS 1.77:20110
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  • 11
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    Station keeping of geostationary satellites by electric propulsion (1985)
    In:  CASI
    Details
    Publication Date: 2019-08-27
    Description: As various types of perturbations tend to drive a geostationary satellite away from its prescribed position, occasional orbit corrections have to be carried out by means of a suitable propulsion system. In future geostationary missions, low thrust electric propulsion is likely to be applied for station keeping because of considerable mass savings. In this paper a station keeping strategy for electric propulsion systems is developed. Both the unconstrained case and the case where thrust operation constraints are present are considered and tested by computer simulation of a realistic example.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-77820 , NAS 1.15:77820 , DGLR-PAPER-80-009 , Walter-Hohmann Symp. uber Raumflugmech.,; Mar 12, 1980 - Mar 13, 1980; Cologne; Germany
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  • 12
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    Structural Analysis Methods Development for Turbine Hot Section Components (1988)
    In:  CASI
    Details
    Publication Date: 2019-08-14
    Description: The structural analysis technologies and activities of the NASA Lewis Research Center's gas turbine engine Hot Section Technology (HOST) program are summarized. The technologies synergistically developed and validated include: time-varying thermal/mechanical load models; component-specific automated geometric modeling and solution strategy capabilities; advanced inelastic analysis methods; inelastic constitutive models; high-temperature experimental techniques and experiments; and nonlinear structural analysis codes. Features of the program that incorporate the new technologies and their application to hot section component analysis and design are described. Improved and, in some cases, first-time 3-D nonlinear structural analyses of hot section components of isotropic and anisotropic nickel-base superalloys are presented.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-100298 , E-3926 , NAS 1.15:100298
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  • 13
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    The 58th Shock and Vibration Symposium (1988)
    In:  CASI
    Details
    Publication Date: 2019-08-14
    Description: Dynamic analysis, dynamic testing, space shuttle main engine vibration, isolation and damping and analytical methods are among the topics discussed.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CP-2488-VOL-2 , M-572-VOL-2 , NAS 1.55:2488-VOL-2
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  • 14
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    The Shock and Vibration Bulletin. Part 1: Welcome, Keynote Address, Invited Papers, Nondevelopment Items Workshop and Pyrotechnic Shock Workshop (1987)
    In:  CASI
    Details
    Publication Date: 2019-08-14
    Description: The proceedings of the 57th Shock and Vibration Symposium are presented. In part 1 is presented the welcoming and the keynote address along with invited papers such as, Dynamic Testing - Seven Years Later. Papers from the Nondevelopment Items workshop such as, Guidelines for Qualifying Nondevelopment Equipment to Shock and Vibration, are presented. And from the Pyrotechnic Shock Workshop the paper entitled, Designing Electronics for Pyrotechnic Shock, is presented.
    Keywords: STRUCTURAL MECHANICS
    Type: AD-A186748 , SVIC-BULL-57-PT-1
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  • 15
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    Elasticity Solution of an Adhesively Bonded Cover Plate of Various Geometries (1985)
    In:  CASI
    Details
    Publication Date: 2019-08-14
    Description: The plane strain of adhesively bonded structures consisting of two different isotropic adherends is considered. By expressing the x-y components of the displacements in terms of Fourier integrals and using the corresponding boundary and continuity conditions, the integral equations for the general problem are obtained and solved numerically by applying Gauss-Chebyshev integration scheme. The shear and the normal stresses in the adhesive are calculated for various geometries and material properties for a stiffened plate under uniaxial tension. Numerical results involving the stress intensity factors and the strain energy release rate are presented. The closed-form expressions for the Fredholm kernels are provided to obtain the solution for an arbitrary geometry and material properties. For the general geometry, the contribution of the normal stress is quite significant, while for symmetric geometries, the shear stress is dominant, the normal stress vanishes if the adherends are of the same material and the same thickness.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-177923 , NAS 1.26:177923
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  • 16
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    A loading system for creep testing under constant compressive stress (1987)
    In:  CASI
    Details
    Publication Date: 2019-08-13
    Description: A critical analysis is made of layouts assuring constant stress under creep, pointing out the difficulties of using these layouts for compressive testing. A new mechanical system to maintain stress during creep testing is proposed. Constant stress is achieved by a definite motion of the load. The proposed system can be used in tensile or compressive testing. Practical measurements reveal that the stress constancy error is not greater than plus or minus 1.5 percent up to relative deformation of 30 percent.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TT-20119 , NAS 1.77:20119 , (ISSN 0023-432X)
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  • 17
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    The 23rd Aerospace Mechanisms Symposium (1989)
    In:  CASI
    Details
    Publication Date: 2019-08-13
    Description: Technological areas covered include space lubrication, bearings, aerodynamic devices, spacecraft latches, deployment, positioning, and pointing. Devices for Space Station docking and manipulator and teleoperator mechanisms are also described.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CP-3032 , M-611 , NAS 1.55:3032 , May 03, 1989 - May 05, 1989; Huntsville, AL; United States
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  • 18
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    Characterization of structural connections using free and forced response test data (1989)
    In:  Other Sources
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    Publication Date: 2019-07-27
    Description: The accurate prediction of system dynamic response often has been limited by deficiencies in existing capabilities to characterize connections adequately. Connections between structural components often are complex mechanically, and difficult to accurately model analytically. Improved analytical models for connections are needed to improve system dynamic predictions. A procedure for identifying physical connection properties from free and forced response test data is developed, then verified utilizing a system having both a linear and nonlinear connection. Connection properties are computed in terms of physical parameters so that the physical characteristics of the connections can better be understood, in addition to providing improved input for the system model. The identification procedure is applicable to multi-degree of freedom systems, and does not require that the test data be measured directly at the connection locations.
    Keywords: STRUCTURAL MECHANICS
    Type: Biennial ASME Conference on Mechanical Vibration and Noise; Sept. 17-21, 1989; Montreal; Canada
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  • 19
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    Microstructural non-uniformity as related to unidirectional compression performance (1989)
    In:  Other Sources
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    Publication Date: 2019-07-27
    Description: The compression performance of unidirectional composite laminates (UDCLs) is related not only to intrinsic or local strength, but also to a sample's ability to resist propagaton of initial damage. This paper introduces a simple shear lag model which is applied to a compression loaded UDCL with initial damage. Among the information obtained are axial overload and matrix layer shear strain factors in the neighborhood of the damage zone. These factors indicate that propagation may occur with relatively little initial damage and emphasize the need for a more complete understanding of compression behavior than currently exists.
    Keywords: STRUCTURAL MECHANICS
    Type: International SAMPE Technical Conference; Sept. 25-28, 1989; Atlantic City, NJ; United States
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  • 20
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    On modelling the residual strength of impact damaged, compression loaded laminates (1989)
    In:  Other Sources
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    Publication Date: 2019-07-27
    Description: A methodology is presented to predict the residual compression strength of impact damaged composite laminates by considering the competing failure modes of local delamination buckling and compression failure. The minimum delamination buckling load and the location of the first local region to buckle are determined by a Rayleigh-Ritz analysis. The Rayleigh-Ritz analysis is formulated to account for the multiple delamination locations, Poisson's ratio mismatch between sublaminates and possible bending-stretching coupling behavior of the delaminated regions. The compression failure load is determined by a modified maximum strain criterion applied in the delaminated region. The minimum delamination buckling and compression failure loads may be compared to the global buckling load to predict initial failure. For non-catastrophic failures, failure sequences are predicted in an iterative manner. Analytical predictions for sequential failure modes and loads are shown to correlate well with experimental results. A comparative evaluation of various delamination buckling models and their accuracy in predicting experimental results is also presented.
    Keywords: STRUCTURAL MECHANICS
    Type: International SAMPE Technical Conference; Sept. 25-28, 1989; Atlantic City, NJ; United States
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  • 21
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    A model for compression after impact strength evaluation (1989)
    In:  Other Sources
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    Publication Date: 2019-07-27
    Description: One key property commonly used for evaluating composite material performance is compression after impact strength (CAI). Standarad CAI tests typically use a specific laminate stacking sequence, coupon geometry, and impact level. In order to understand what material factors affect CAI, evaluation of test results should include more than comparisons of the measured strength for different materials. This study considers the effects of characteristic impact damage state, specimen geometry, material toughness, ply group thickness, undamaged strength, and failure mode. The results of parametric studies, using an analysis model developed to predict CAI, are discussed. Experimental results used to verify the model are also presented. Finally, recommended pre- and post-test CAI evaluation schemes which help link material behavior to structural performance are summarized.
    Keywords: STRUCTURAL MECHANICS
    Type: International SAMPE Technical Conference; Sept. 25-28, 1989; Atlantic City, NJ; United States
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  • 22
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    Variable geometry trusses (1989)
    In:  Other Sources
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    Publication Date: 2019-07-27
    Description: Vibration control and kinematic control with variable-geometry trusses are covered. The analytical approach taken is to model each actuator with lumped masses and model a beam with finite elements, including in each model the generalized reaction forces from the beam on the actuator or vice versa. It is concluded that, from an operational standpoint, the variable-geometry truss actuator is more favorable than the inertia-type actuator. A spatial variable-geometry truss is used to test out rudimentary robotic tasks.
    Keywords: STRUCTURAL MECHANICS
    Type: U.S. Army Research Offoce Workshop on Smart Materials, Structures, and Mathematical Issues; Sept. 15-16, 1988; Blacksburg, VA; United States
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  • 23
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    Active control of buckling of flexible beams (1989)
    In:  Other Sources
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    Publication Date: 2019-07-27
    Description: Mathematical models are presented that simulate the dynamic characteristics of shape memory alloy actuators made of nickel-titanium alloy (Nitinol) controlling the buckling of compressive structural members. A closed-loop computer-controlled system has been designed, based on the proposed mathematical models, and has been implemented to control the buckling of simple beams. The performance of the computer-controlled system is evaluated experimentally and compared with the theoretical predictions to validate the developed models. The results emphasized the importance of buckling control and suggest the potential of shape memory alloy actuators as attractive means for controlling structural deformation in a simple and reliable way.
    Keywords: STRUCTURAL MECHANICS
    Type: Biennial Conference on Failure Prevention and Reliability - 1989; Sept. 17-21, 1989; Montreal; Canada
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  • 24
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    Fiber optic strain measurements in filament-wound graphite-epoxy tubes containing embedded fibers (1989)
    In:  Other Sources
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    Publication Date: 2019-07-27
    Description: Filament-wound graphite-epoxy tubes fabricated with embedded fiber optic sensors were tested at NASA Langley Research Center to evaluate the feasibility of monitoring stress with a fiber optic technique. Resistance strain gauges were attached to the tubes to measure strain at four locations along the tubes. Both static and dynamic strain measurements were made with an excellent agreement between the embedded fiber optic strain sensor and the strain gauges. The results indicate that fiber optic sensors embedded in composites may be useful as the sensing component of smart structures.
    Keywords: STRUCTURAL MECHANICS
    Type: Fiber Optic Smart Strutures and Skins; Sept. 8-9, 1988; Boston, MA; United States
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  • 25
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    Smooth indentation of a composite laminate (1988)
    In:  Other Sources
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    Publication Date: 2019-07-27
    Description: Finite difference method is used to analyze the problem of smooth contact between a rigid indenter and a laminated circular plate clamped at the edges. The plate consists of transversely isotropic layers. The interlaminar shear stresses in the contact region are found to be much different from the laminate plate theory solutions. It has been found that low-modulus interlayers cause significant reduction in the maximum interlaminar shear stresses.
    Keywords: STRUCTURAL MECHANICS
    Type: Technical Conference of the American Society for Composites; Sept. 25-29, 1988; Seattle, WA; United States
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  • 26
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    The natural frequencies of symmetric angle-ply laminates derived from eigensensitivity analysis (1988)
    In:  Other Sources
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    Publication Date: 2019-07-27
    Description: In this paper, a new closed-form approximate solution for the natural frequencies of symmetric rectangular angle-ply laminates simply supported on all four edges is derived. The solution, obtained from eigensensitivity analysis, is expressed as a truncated Fourier series in the ply angle. Results show that the prediction for the fundamental frequency is quite accurate for engineering applications, often within 1-2 percent of the true frequency.
    Keywords: STRUCTURAL MECHANICS
    Type: Technical Conference of the American Society for Composites; Sept. 25-29, 1988; Seattle, WA; United States
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  • 27
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    Effect of adhesive debond on stress-intensity factors in bonded composite panels (1988)
    In:  Other Sources
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    Publication Date: 2019-07-27
    Description: Stress-intensity factors are calculated for a cracked infinite sheet adhesively bonded to a stringer, and debonding of the adhesive layer is predicted. The stringer is modeled as a semiinfinite sheet. Adhesive nonlinearity is also included. Both the sheet and stringer are treated as homogeneous, orthotropic materials, a set of integral equations is formulated and solved to obtain the adhesive shear stresses and crack-tip stress-intensity factors. Adhesive debonding is predicted using a rupture criterion based on the combined adhesive stresses. A through-the-thickness crack is located in the infinite sheet perpendicular to the edge of the stringer. When the crack is not under the stringer, the debond extends along the edge of the stringer. When the crack tip is beneath the stringer, the debond extends to the crack tip, then along the edge of the stringer. Stress levels required for debond initiation decrease as the crack tip is moved beneath the stringer. With a nonlinear adhesive, the debond initiates at higher applied stress levels than in linear adhesive cases. Compared with the linear adhesive solution, modeling a nonlinear adhesive causes the stress-intensity factor to decrease when debonding is included.
    Keywords: STRUCTURAL MECHANICS
    Type: International Symposium on Adhesively Bonded Joints; Testing, Analysis, and Design; Sept. 10-12, 1986; Baltimore, MD; United States
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  • 28
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    A comparison of pure mode I and mixed mode I-III cracking of an adhesive containing an open knit cloth carrier (1988)
    In:  Other Sources
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    Publication Date: 2019-07-27
    Description: Static and fatigue tests were carried out on two commercial modified epoxy film adhesives with a wide open knit polyester carrier in order to compare crack resistance in mode I and mixed mode I-III loading. The carrier cloth is found to have a significant influence on the cracking behavior of the adhesives. The open air net carrier used in this study separates from the adhesive in mode I cracking but shreds during mixed-mode crack extension. This decreases the opening mode toughness but increases the mixed-mode toughness as compared with results obtained earlier using a heavier knit carrier. The results suggest that the type of carrier may have a far larger influence on crack resistance than is generally recognized.
    Keywords: STRUCTURAL MECHANICS
    Type: International Symposium on Adhesively Bonded Joints; Testing, Analysis, and Design; Sept. 10-12, 1986; Baltimore, MD; United States
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  • 29
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    Factors influencing elastic stresses in double cantilever beam specimens (1988)
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    Publication Date: 2019-07-27
    Description: An elastic stress analysis was conducted for a double cantilever beam (DCB) specimen using finite-element methods. The purpose of this study was to identify the important parameters that influence stresses ahead of the delamination front. The study focused on an aluminum DCB specimen, typical of adhesively-bonded joints, and on a graphite/epoxy specimen representing a cocured composite. Opening mode sigma sub y stresses ahead of the crack tip were calculated and compared with those for a monolithic reference specimen. Beyond the singularity-dominated region very near the crack tip, the sigma sub y distribution was elevated compared to the monolithic case. Both the adhesive thickness and the adherend transverse (thickness-direction) stiffness were found to influence the elevation of sigma sub y. In contrast, adherend thickness and longitudinal stiffness has very little effect on this stress distribution. Estimates for adhesive yielding beyond the aluminum DCB crack tip showed that both the area and height of the plastic zone increased to a peak value for increasing adhesive thicknesses. Results from this study would provide insight for comparing data from different DCB specimens and for designing new DCB specimens.
    Keywords: STRUCTURAL MECHANICS
    Type: International Symposium on Adhesively Bonded Joints; Testing, Analysis, and Design; Sept. 10-12, 1986; Baltimore, MD; United States
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  • 30
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    Deformations and strains in a thick adherend lap joint (1988)
    In:  Other Sources
    Details
    Publication Date: 2019-07-27
    Description: Displacement fields in a thick adherend lap joint were measured by high-sensitivity moire interferometry. Contour maps of in-plane U and V displacements were obtained across adhesive and adherend surfaces. Loads ranged from a modest load to a near-failure load. Quantitative results are given for displacements and strains in the adhesive and along the adhesive/adherend boundary lines. The results show nearly constant shear strain in the adhesive, nonlinear strains as a function of load or average shear stress, and viscoelastic or time-dependent response. Longitudinal normal strains in the adhesive are nearly two orders of magnitude less than the shear strains. With its subwavelength displacement resolution and high spatial resolution, moire interferometry is especially well suited for deformation studies of adhesive joints.
    Keywords: STRUCTURAL MECHANICS
    Type: International Symposium on Adhesively Bonded Joints; Testing, Analysis, and Design; Sept. 10-12, 1986; Baltimore, MD; United States
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    Adhesively bonded joints: Testing, analysis, and design; Proceedings of the International Symposium, Baltimore, MD, Sept. 10-12, 1986 (1988)
    In:  Other Sources
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    Publication Date: 2019-07-27
    Description: The papers contained in this volume provide an overview of the state of the art of testing, analysis, and design of adhesively bonded joints. The papers are grouped in the following sections: mechanical testing, stress analysis, failure mechanisms, and design and durability. Specific topics discussed include determination and verification of elastic parameters for adhesives; factors influencing elastic stresses in double cantilever beam specimens; special mixed finite elements for interfacial stress analysis of adhesively bonded joints; debonding characteristics of adhesively bonded woven Kevlar composites; and environmental durability of adhesively bonded joints.
    Keywords: STRUCTURAL MECHANICS
    Type: International Symposium on Adhesively Bonded Joints; Testing, Analysis, and Design; Sept. 10-12, 1986; Baltimore, MD; United States
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    Fatigue crack growth with single overload - Measurement and modeling (1987)
    In:  Other Sources
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    Publication Date: 2019-07-27
    Description: This paper compares experiments with an analytical model of fatigue crack growth under variable amplitude. The stereoimaging technique was used to measure displacements near the tips of fatigue cracks undergoing simple variations in load amplitude-single overloads and overload/underload combinations. Measured displacements were used to compute strains, and stresses were determined from the strains. Local values of crack driving force (Delta-K effective) were determined using both locally measured opening loads and crack tip opening displacements. Experimental results were compared with simulations made for the same load variation conditions using Newman's FAST-2 model. Residual stresses caused by overloads, crack opening loads, and growth retardation periods were compared.
    Keywords: STRUCTURAL MECHANICS
    Type: Effects of load and thermal histories on mechanical behavior of materials; Feb. 25, 26, 1987; Denver, CO; United States
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    Nondestructive construction error detection in large space structures (1988)
    In:  Other Sources
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    Publication Date: 2019-07-27
    Description: Continuum modeling of large space structures is extended to the problem of detecting construction errors in large space structures such as the proposed space station. First-order dynamic sensitivity equations for structures involving eigenfrequencies, modal masses, modal stiffnesses, and modal damping are presented. Matrix equations relating changes in element parameters to dynamic sensitivities are summarized. The sensitivity equations for the entire dynamical system are rearranged as a system of algebraic equations with unknowns of stiffness losses at selected locations. The feasibility of the formulation is numerically demonstrated on a simply-supported Euler-Bernouilli beam with simulated construction defects. The method is next extended to large space structures modelled as equivalent continua with simulated construction defects.
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA PAPER 88-2460 , AIAA SDM Issues of the International Space Station, Conference; Apr. 21, 22, 1988; Williamsburg, VA; United States
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    Effect of axial impact on the static flexure of graphite/epoxy beams (1987)
    In:  Other Sources
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    Publication Date: 2019-07-27
    Description: Graphite-epoxy beams were subjected to an eccentric axial impact load in a drop tower test fixture in order to study their large displacement flexural behavior. The time history of the transient axial load exhibited a large magnitude occurring just after impact, which was many times greater than the static failure load. The damage caused by this peak dynamic load was measured by the reduction in energy absorption of the impacted beam relative to a virgin beam in static tests. For the thirty-ply specimens, the amount of damage increased with increasing axial stiffness.
    Keywords: STRUCTURAL MECHANICS
    Type: American Society for Composites, Technical Conference; Sept. 23-25, 1987; Newark, DE; United States
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    Identification of structural interface characteristics using component mode synthesis (1987)
    In:  Other Sources
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    Publication Date: 2019-07-27
    Description: The inability to adequately model connections has limited the ability to predict overall system dynamic response. Connections between structural components are often mechanically complex and difficult to accurately model analytically. Improved analytical models for connections are needed to improve system dynamic predictions. This study explores combining Component Mode synthesis methods for coupling structural components with Parameter Identification procedures for improving the analytical modeling of the connections. Improvements in the connection properties are computed in terms of physical parameters so the physical characteristics of the connections can be better understood, in addition to providing improved input for the system model. Two sample problems, one utilizing simulated data, the other using experimental data from a rotor dynamic test rig, are presented.
    Keywords: STRUCTURAL MECHANICS
    Type: Modal testing and analysis; Sept. 27-30, 1987; Boston, MA; United States
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    Prediction and experimental observation of damage dependent damping in laminated composite beams (1987)
    In:  Other Sources
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    Publication Date: 2019-07-27
    Description: The equations of motion are developed for laminated composite beams with load-induced matrix cracking. The damage is accounted for by utilizing internal state variables. The net result of these variables on the field equations is the introduction of both enhanced damping, and degraded stiffness. Both quantities are history dependent and spatially variable, thus resulting in nonlinear equations of motion. It is explained briefly how these equations may be quasi-linearized for laminated polymeric composites under certain types of structural loading. The coupled heat conduction equation is developed, and it is shown that an enhanced Zener damping effect is produced by the introduction of microstructural damage. The resulting equations are utilized to demonstrate how damage dependent material properties may be obtained from dynamic experiments. Finaly, experimental results are compared to model predictions for several composite layups.
    Keywords: STRUCTURAL MECHANICS
    Type: The role of damping in vibration and noise control; Sept. 27-30, 1987; Boston, MA; United States
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  • 37
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    Problems and progress in aeroelasticity for interdisciplinary design (1987)
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    Publication Date: 2019-07-27
    Description: Some problems and progress in the development of aerodynamic and aeroelastic computational capabilities are reviewed with emphasis on needs for use in current interdisciplinary design procedures as well as for stand-alone analyses. The primary focus is on integral-equation methods which are well suited for general, accurate, efficient, and unified treatment of flow around vehicles having arbitrary shapes, motions, and deformations at subsonic, transonic, and supersonic speeds up to high angles of attack. Computational methods for potential flows and viscous flows are discussed, and some applications are shown. Calculation of steady and unsteady aeroelastic characteristics of aircraft with nonlinear aerodynamic behavior is also addressed briefly.
    Keywords: STRUCTURAL MECHANICS
    Type: Recent trends in aeroelasticity, structures, and structural dynamics; Feb. 6, 7, 1986; Gainesville, FL; United States
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  • 38
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    A substructure technique for dynamics of flexible mechanical systems with contact-impact (1987)
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    Publication Date: 2019-07-27
    Description: A substructure synthesis method is proposed to account for contact-impact effects in flexible components of mechanical systems. Components that may come into contact is divided into substructures, on each of which local deformation modes are defined to described deformation fields of components. Constraint modes and fixed interface normal modes are used to account for elastic deformation within each substructure. A constraint addition-deletion technique is used to account for contact between impacting bodies. Lagrange multipliers associated with the constraints, which represent constraint forces, are used to determine separation of contacting nodes. Use of the method is illustrated on problems of longitudinal and transverse impact of bodies.
    Keywords: STRUCTURAL MECHANICS
    Type: Advances in design automation - 1987; Sept. 27-30, 1987; Boston, MA; United States
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  • 39
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    Finite element methodology for integrated flow-thermal-structural analysis (1988)
    In:  CASI
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    Publication Date: 2019-07-20
    Description: Papers entitled, An Adaptive Finite Element Procedure for Compressible Flows and Strong Viscous-Inviscid Interactions, and An Adaptive Remeshing Method for Finite Element Thermal Analysis, were presented at the June 27 to 29, 1988, meeting of the AIAA Thermophysics, Plasma Dynamics and Lasers Conference, San Antonio, Texas. The papers describe research work supported under NASA/Langley Research Grant NsG-1321, and are submitted in fulfillment of the progress report requirement on the grant for the period ending February 29, 1988.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-183144 , NAS 1.26:183144
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  • 40
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    Passive damping concepts for free and forced member and grillage vibration (1988)
    In:  CASI
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    Publication Date: 2019-07-20
    Description: The performance of potential passive damping concepts is investigted for a long tubular aluminum alloy member, and a two-bar grillage structure. The members are restrained partially at the ends and are of the type being considered by NASA for possible use in the construction of a future space station. Four different passive damping concepts are studied and include nylon brush, wool swab, copper brush, and silly putty in chamber dampers. Both free and forced vibration tests are conducted. It is found that the silly putty in chamber damper concept provides considerably greater passive damping as compared to that of the other three concepts. For the grillage natural vibration, a five wool swab damper configuration provides greater damping than the five silly putty dampers in chamber configuration. Due to the constrained motion imposed by the vibrator used in the tests, the effectiveness of the passive dampers could not be adequately evaluated for the individual member. However, it is found that for the grillage under forced vibration, the five silly putty dampers in chamber damper configuration provides very effective passive damping although only at and around the resonant frequency. At resonance, these dampers provide a 51 percent reduction in the dynamic magnification factor for this case.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-183114 , NAS 1.26:183114
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    Experimental and theoretical investigation of passive damping concepts for member forced and free vibration (1987)
    In:  CASI
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    Publication Date: 2019-07-20
    Description: Potential passive damping concepts for use in space structures are identified. The effectiveness of copper brush, wool swab, and silly putty in chamber dampers is investigated through natural vibration tests on a tubular aluminum member. The member ends have zero translation and possess partial rotational restraints. The silly putty in chamber dampers provide the maximum passive damping efficiency. Forced vibration tests are then conducted with one, two, and three damper chambers containing silly putty. Owing to the limitation of the vibrator used, the performance of these dampers could not be evaluated experimentally until the forcing function was disengaged. Nevertheless, their performance is evaluated through a forced dynamic finite element analysis conducted as a part of this investigation. The theoretical results based on experimentally obtained damping ratios indicate that the passive dampers are considerably more effective under member natural vibration than during forced vibration. Also, the maximum damping under forced vibration occurs at or near resonance.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-183082 , NAS 1.26:183082
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    A hybrid-stress finite element approach for stress and vibration analysis in linear anisotropic elasticity (1987)
    In:  CASI
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    Publication Date: 2019-07-20
    Description: A hybrid stress finite element method is developed for accurate stress and vibration analysis of problems in linear anisotropic elasticity. A modified form of the Hellinger-Reissner principle is formulated for dynamic analysis and an algorithm for the determination of the anisotropic elastic and compliance constants from experimental data is developed. These schemes were implemented in a finite element program for static and dynamic analysis of linear anisotropic two dimensional elasticity problems. Specific numerical examples are considered to verify the accuracy of the hybrid stress approach and compare it with that of the standard displacement method, especially for highly anisotropic materials. It is that the hybrid stress approach gives much better results than the displacement method. Preliminary work on extensions of this method to three dimensional elasticity is discussed, and the stress shape functions necessary for this extension are included.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-179311 , NAS 1.26:179311 , TR-87-05
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  • 43
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    Component mode synthesis and large deflection vibration of complex structures. Volume 3: Multiple-mode nonlinear free and forced vibrations of beams using finite element method (1987)
    In:  CASI
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    Publication Date: 2019-07-20
    Description: Multiple-mode nonlinear forced vibration of a beam was analyzed by the finite element method. Inplane (longitudinal) displacement and inertia (IDI) are considered in the formulation. By combining the finite element method and nonlinear theory, more realistic models of structural response are obtained more easily and faster.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-181292 , NAS 1.26:181292
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    Component mode synthesis and large deflection vibration of complex structures. Volume 1: Examples of NASTRAN modal synthesis capability (1987)
    In:  CASI
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    Publication Date: 2019-07-20
    Description: The use of NASTRAN model synthesis capability is illustrated. A classical truss problem is examined and the results are compared to results from other methods to test for accuracy. The problem is examined using both fixed interface modes and free interface modes. The solution is carried out for an applied dynamic load as far as recovery of forces in individual members as a function of time. Another small beam problem is used to compare different means of combining substructures.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-181290 , NAS 1.26:181290
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  • 45
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    Component mode synthesis and large deflection vibration of complex structures. Volume 2: Single-mode large deflection vibrations of beams and plates using finite element method (1987)
    In:  CASI
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    Publication Date: 2019-07-20
    Description: A finite element method is presented for the large amplitude vibrations of complex structures that can be modelled with beam and rectangular plate elements subjected to harmonic excitation. Both inplane deformation and inertia are considered in the formulation. Derivation of the harmonic force and nonlinear stiffness matrices for a beam and a rectangular plate element are presented. Solution procedures and convergence characteristics of the finite element method are described. Nonlinear response to uniform and concentrated harmonic loadings and improved nonlinear free vibration results are presented for beams and rectangular plates of various boundary conditions.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-181291 , NAS 1.26:181291
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  • 46
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    Two-dimensional finite element analysis of rectangular panel with hole using NICE/SPAR (1987)
    In:  CASI
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    Publication Date: 2019-07-20
    Description: A panel 30 in. long, 11.5 in. wide, with a 2.0 in. diameter hole at the center is analyzed. Since a two-dimensional analysis is conducted, the thickness of the panel is taken as unity. Owing to the symmetry, it is sufficient to analyze only one fourth of the panel with appropriate boundary conditions.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-180630 , NAS 1.26:180630
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    Substructure analysis using NICE/SPAR and applications of force to linear and nonlinear structures (1987)
    In:  CASI
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    Publication Date: 2019-07-20
    Description: Parallel computing studies are presented for a variety of structural analysis problems. Included are the substructure planar analysis of rectangular panels with and without a hole, the static analysis of space mast, using NICE/SPAR and FORCE, and substructure analysis of plane rigid-jointed frames using FORCE. The computations are carried out on the Flex/32 MultiComputer using one to eighteen processors. The NICE/SPAR runstream samples are documented for the panel problem. For the substructure analysis of plane frames, a computer program is developed to demonstrate the effectiveness of a substructuring technique when FORCE is enforced. Ongoing research activities for an elasto-plastic stability analysis problem using FORCE, and stability analysis of the focus problem using NICE/SPAR are briefly summarized. Speedup curves for the panel, the mast, and the frame problems provide a basic understanding of the effectiveness of parallel computing procedures utilized or developed, within the domain of the parameters considered. Although the speedup curves obtained exhibit various levels of computational efficiency, they clearly demonstrate the excellent promise which parallel computing holds for the structural analysis problem. Source code is given for the elasto-plastic stability problem and the FORCE program.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-180317 , NAS 1.26:180317
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    Multiple-mode nonlinear free and forced vibrations of beams using finite element method (1987)
    In:  CASI
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    Publication Date: 2019-07-20
    Description: Multiple-mode nonlinear free and forced vibration of a beam is analyzed by the finite element method. The geometric nonlinearity is investigated. Inplane displacement and inertia (IDI) are also considered in the formulation. Harmonic force matrix is derived and explained. Nonlinear free vibration can be simply treated as a special case of the general forced vibration by setting the harmonic force matrix equal to zero. The effect of the higher modes is more pronouced for the clamped supported beam than the simply supported one. Beams without IDI yield more effect of the higher modes than the one with IDI. The effects of IDI are to reduce nonlinearity. For beams with end supports restrained from axial movement (immovable cases), only the hardening type nonlinearity is observed. However, beams of small slenderness ratio (L/R = 20) with movable end supports, the softening type nonlinearity is found. The concentrated force case yields a more severe response than the uniformly distributed force case. Finite element results are in good agreement with the solution of simple elliptic response, harmonic balance method, and Runge-Kutte method and experiment.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-180538 , NAS 1.26:180538
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    Passive damping concepts for slender columns in space structures (1985)
    In:  CASI
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    Publication Date: 2019-07-20
    Description: Research into the identification of potential passive damping concepts for use in very slender structural members was continued. The following damping concepts are under investigation: mass-string dampers; bright zinc chain; polyethylene tubing; external viscoelastic tape; brushes for electrostatic and frictional damping; suspended chambers with oil and discs; and hybrid concepts. Each of these concepts are briefly discussed.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-179807 , NAS 1.26:179807
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    A Taylor-Galerkin finite element algorithm for transient nonlinear thermal-structural analysis (1986)
    In:  CASI
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    Publication Date: 2019-07-20
    Description: A Taylor-Galerkin finite element method for solving large, nonlinear thermal-structural problems is presented. The algorithm is formulated for coupled transient and uncoupled quasistatic thermal-structural problems. Vectorizing strategies ensure computational efficiency. Two applications demonstrate the validity of the approach for analyzing transient and quasistatic thermal-structural problems.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-177064 , NAS 1.26:177064
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    Bending rate damping in elastic systems (1989)
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    Publication Date: 2019-07-13
    Description: Preliminary results of an investigation of the bending rate damping model for elastic structures are presented. A model for which the internal damping term is physically plausible and which can accomodate cantilevered boundary conditions is discussed. The model formulation and mathematical foundations are given, and numerical results are discussed.
    Keywords: STRUCTURAL MECHANICS
    Type: IEEE Conference on Decision and Control; Dec 13, 1989 - Dec 15, 1989; Tampa, FL; United States
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    Eigensolution of finite element problems in a completely connected parallel architecture (1989)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: A parallel algorithm for the solution of the generalized eigenproblem in linear elastic finite element analysis, (K)(phi)=(M)(phi)(omega), where (K) and (M) are of order N, and (omega) is of order q is presented. The parallel algorithm is based on a completely connected parallel architecture in which each processor is allowed to communicate with all other processors. The algorithm has been successfully implemented on a tightly coupled multiple-instruction-multiple-data (MIMD) parallel processing computer, Cray X-MP. A finite element model is divided into m domains each of which is assumed to process n elements. Each domain is then assigned to a processor, or to a logical processor (task) if the number of domains exceeds the number of physical processors. The macro-tasking library routines are used in mapping each domain to a user task. Computational speed-up and efficiency are used to determine the effectiveness of the algorithm. The effect of the number of domains, the number of degrees-of-freedom located along the global fronts and the dimension of the subspace on the performance of the algorithm are investigated. For a 64-element rectangular plate, speed-ups of 1.86, 3.13, 3.18 and 3.61 are achieved on two, four, six and eight processors, respectively.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-102450 , E-5235 , ICOMP-89-31 , NAS 1.15:102450 , AIAA PAPER 89-1395 , Structures,Structural Dynamics, and Materials Conference; Apr 03, 1989 - Apr 05, 1989; Mobile, AL; United States
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    Force prediction using singular-value decomposition (1988)
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    Publication Date: 2019-07-13
    Description: Results of a preliminary investigation into a method which can be used to improve the results of an experimental force prediction analysis is presented. The method uses a singular value decomposition technique to reduce measurement noise present in the measured input data matrix. The fundamental theory for the method along with an experimental example is shown. The method is shown to provide encouraging force prediction improvements when the input data matrix contains high levels of measurement noise.
    Keywords: STRUCTURAL MECHANICS
    Type: International Modal Analysis Conference; Feb 01, 1988 - Feb 04, 1988; Kissimmee, FL; United States
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    Estimation of distributed acoustic lasers (1988)
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    Publication Date: 2019-07-13
    Description: The purpose of this paper is to present the results of a preliminary investigation of an indirect method which can be used to generate a set of equivalent point loads approximating an applied distributed acoustic load. The method combines the source information with the structure's modal characteristics and forces which give the same response as the applied acoustic load. The technique is demonstrated by predicting a set of point forces acting on a thin aluminum panel which simulate a normally-incident random pressure. The technique is verified by comparing measured strain autospectrums with estimated strain autospectrums generated using the predicting forces. Strain errors within 5 dB were achieved. A limited amount of information about the acoustic load could be deduced using the predicted force autospectrums and phase differences between these forces.
    Keywords: STRUCTURAL MECHANICS
    Type: International Modal Analysis Conference; Feb 01, 1988 - Feb 04, 1988; Kissimmee, FL; United States
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    Some applicatiaons of Lanczos vectors in structural dynamics (1988)
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    Publication Date: 2019-07-13
    Description: This paper summarizes several applications of Lanczos vectors and Krylov vectors. Lanczos vectors or Krylov vectors for use in component synthesis, Lanczos vectors for systems with unsymmetric damping (unsymmetric Block-Lanczos method), and the use of Lanczos vectors to obtain reduced-order models for control of flexible structures. For each of the above applications the theoretical background is briefly summarized and a numerical example is given.
    Keywords: STRUCTURAL MECHANICS
    Type: International Modal Analysis Conference; Feb 01, 1988 - Feb 04, 1988; Kissimmee, FL; United States
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    Remote structural damage detection via substructuring (1988)
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    Publication Date: 2019-07-13
    Description: An approach to structural damage detection which utilizes the concept of a substructure transfer function matrix is proposed. The major advantage of this approach is that structural changes localized within a small volume can be detected by studying the changes in the transfer function for a relatively small substructure containing the damaged portion.
    Keywords: STRUCTURAL MECHANICS
    Type: International Modal Analysis Conference; Feb 01, 1988 - Feb 04, 1988; Kissimmee, FL; United States
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    Power flow in a beam using a 5-accelerometer probe (1988)
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    Publication Date: 2019-07-13
    Description: A method to determine structure-borne power flow is examined which uses central finite differences to approximate the field variables required to calculate the shear and bending components of flexural vibration. An experimental study using a beam driven by a shaker was performed with the aim of comparing estimates using this proposed five-accelerometer method and the conventional two-accelerometer, free-field method. The advantages and disadvantages of the new method are pointed out.
    Keywords: STRUCTURAL MECHANICS
    Type: NOISE-CON 88; Jun 20, 1988 - Jun 22, 1988; West Lafayette, IN; United States
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    Application of unsteady aerodynamic methods for transonic aeroelastic analysis (1988)
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    Publication Date: 2019-07-13
    Description: Aerodynamic methods for aeroelastic analysis are applied to various flow problems. These methods include those that solve the three-dimensional transonic small disturbance (TSD) potential equation, the two-dimensional full potential (FP) equation, and the thin-layer Navier-Stokes equations. Flutter analysis performed using TSD aerodynamics shows that such methods can be used to analyze some aeroelastic phenomena. For thicker bodies and larger amplitude motions a nonisentropic full potential method is presented.
    Keywords: STRUCTURAL MECHANICS
    Type: ICAS Congress; Aug 28, 1988; Jerusalem; Israel
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    Application of integrated fluid-thermal structural analysis methods (1988)
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    Publication Date: 2019-07-13
    Description: Hypersonic vehicles operate in a hostile aerothermal environment which has a significant impact on their aerothermostructural performance. Significant coupling occurs between the aerodynamic flow field, structural heat transfer, and structural response creating a multidisciplinary interaction. Interfacing state-of-the-art disciplinary analysis methods are not efficient, hence interdisciplinary analysis methods integrated into a single aerothermostructural analyzer are needed. The NASA Langley Research Center is developing such methods in an analyzer called LIFTS (Langley Integrated Fluid-Thermal-Structural) analyzer. The evolution and status of LIFTS is reviewed and illustrated through applications.
    Keywords: STRUCTURAL MECHANICS
    Type: ICAS Congress; Aug 28, 1988; Jerusalem; Israel
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    A geometrically nonlinear theory of shear deformable laminated composite plates and its use in the postbuckling analysis (1988)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: This paper is devoted to the formulation of a higher-order, geometrically nonlinear theory of anisotropic symmetrically-laminated composite plates and to the analysis, in this context, of their postbuckling behavior. Special attention is given to the postbuckling analysis of plates made of transversely isotropic layers for which case, the influence played by the degree of transversal-isotropy of the layers as well as by the goemetrical parameters of the panel is investigated. Finally, the results obtained within the present higher-order theory are compared with their first order transverse shear deformation as well as with their classical (Kirchhoff) counterparts and a number of conclusions concerning their range of applicability and the influence of various parameters are presented.
    Keywords: STRUCTURAL MECHANICS
    Type: ICAS Congress; Aug 28, 1988; Jerusalem; Israel
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    Optimum vibration control of flexible beams by piezo-electric actuators (1988)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: The utilization of piezoelectric actuators in controlling the structural vibrations of flexible beams is examined. A Modified Independent Modal Space Control (MIMSC) method is devised to enable the selection of the optimal location, control gains and excitation voltage of the piezoelectric actuators in a way that would minimize the amplitudes of vibrations of beams to which these actuators are bonded, as well as the input control energy necessary to suppress these vibrations. The developed method accounts for the effects that the piezoelectric actuators have on changing the elastic and inertial properties of the flexible beams. Numerical examples are presented to illustrate the application of the developed MIMSC method in minimizing the structural vibrations of beams of different materials when subjected to different loading and end conditions using ceramic or polymeric piezoelectric actuators. The obtained results emphasize the importance of the devised method in designing more realistic active control systems for flexible beams, in particular, and large flexible structures in general.
    Keywords: STRUCTURAL MECHANICS
    Type: VPI&SU/AIAA Symposium; Jun 29, 1987 - Jul 01, 1987; Blacksburg, VA; United States
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  • 62
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    Fatigue behavior of axial and pressure cycled butt and girth welds containing defects (1988)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: This paper presents the results of a study directed at developing a data base for establishing fitness-for-purpose defect acceptance criteria for welds with defects. The study focused on A106 Grade B steel pipe. Data are presented for flat plate, wall segment, and vessel specimens and actual pipe sections containing either artificial or natural planar or volumetric defects. Defect acceptance criteria developed from the test data are discussed.
    Keywords: STRUCTURAL MECHANICS
    Type: Natl. Symposium on Fracture Mechanics; Jun 30, 1986 - Jul 02, 1986; San Antonio, TX; United States
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  • 63
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    Line spring model and its applications to part-through crack problems in plates and shells (1988)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: The line spring model is described and extended to cover the problem of interaction of multiple internal and surface cracks in plates and shells. The shape functions for various related crack geometries obtained from the plane strain solution and the results of some multiple crack problems are presented. The problems considered include coplanar surface cracks on the same or opposite sides of a plate, nonsymmetrically located coplanar internal elliptic cracks, and in a very limited way the surface and corner cracks in a plate of finite width and a surface crack in a cylindrical shell with fixed end.
    Keywords: STRUCTURAL MECHANICS
    Type: Natl. Symposium on Fracture Mechanics; Jun 30, 1986 - Jul 02, 1986; San Antonio, TX; United States
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    Stress-intensity factors for corner cracks in rectangular bars (1988)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Stress intensity factors are presented for a wide range of quarter-elliptical corner cracks in a rectangular bar. The bars were subjected to remote tension, out-of-plane bending, or in-plane bending loading, and the stress intensity factors were calculated from a three-dimensional finite element analysis using the nodal-force method. For all loadings considered, smaller width bars produce higher normalized stress intensity factors than the larger width bars. For tensile loading, quarter-circular corner cracks give higher stress intensity factors near the free surfaces and lower values in the interior. The results are compared with data in the literature for remote tensile loading.
    Keywords: STRUCTURAL MECHANICS
    Type: Natl. Symposium on Fracture Mechanics; Jun 30, 1986 - Jul 02, 1986; San Antonio, TX; United States
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    NASA Workshop on Computational Structural Mechanics 1987, part 3 (1989)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: Computational Structural Mechanics (CSM) topics are explored. Algorithms and software for nonlinear structural dynamics, concurrent algorithms for transient finite element analysis, computational methods and software systems for dynamics and control of large space structures, and the use of multi-grid for structural analysis are discussed.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CP-10012-PT-3 , NAS 1.55:10012-PT-3 , Nov 18, 1987 - Nov 20, 1987; Hampton, VA; United States
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  • 66
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    Refinements in a viscoplastic model (1989)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: A thermodynamically admissible theory of viscoplasticity with two internal variables (a back stress and a drag strength) is presented. Six material functions characterize a specific viscoplastic model. In the pursuit of compromise between accuracy and simplicity, a model is developed that is a hybrid of two existing viscoplastic models. A limited number of applications of the model to Al, Cu, and Ni are presented. A novel implicit integration method is also discussed. Applications are made to obtain solutions using this viscoplastic model.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-102338 , E-4988 , NAS 1.15:102338 , Winter Annual Meeting of the American Society of Mechanical Engineers; Dec 10, 1989 - Dec 15, 1989; San Francisco, CA; United States
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    On the state estimation of structures with second order observers (1989)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: The use of Linear Quadratic Regulator (LQR) control synthesis techniques implies the availability of full state feedback. For vibration control of structures, usually only a limited number of states are measured from which an observer model reconstructs the full state. It is shown that using second order observers is a viable technique for reconstructing the unmeasured states of structures under mildly restrictive conditions. Moreover, the computational advantages of the second order observer as compared to a first order observer indicate that significantly larger observer models may be utilized. Numerical examples are used to demonstrate the performance of second order observers. The implications of second order observers in the development of Controls-Structures Interaction (CSI) technology is discussed.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-101602 , NAS 1.15:101602 , AIAA, ASME, et al., 30th Structures, Structural Dynamics and Materials Conference; Apr 03, 1989 - Apr 05, 1989; Mobile, AL; United States
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  • 68
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    Global/local stress analysis of composite panels (1989)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: A method for performing a global/local stress analysis is described, and its capabilities are demonstrated. The method employs spline interpolation functions which satisfy the linear plate bending equation to determine displacements and rotations from a global model which are used as boundary conditions for the local model. Then, the local model is analyzed independent of the global model of the structure. This approach can be used to determine local, detailed stress states for specific structural regions using independent, refined local models which exploit information from less-refined global models. The method presented is not restricted to having a priori knowledge of the location of the regions requiring local detailed stress analysis. This approach also reduces the computational effort necessary to obtain the detailed stress state. Criteria for applying the method are developed. The effectiveness of the method is demonstrated using a classical stress concentration problem and a graphite-epoxy blade-stiffened panel with a discontinuous stiffener.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-101622 , NAS 1.15:101622 , Joint ASCE/ASME Mechanics Conference; Jul 09, 1989 - Jul 12, 1989; Santa Barbara, CA; United States
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    Computational Methods for Structural Mechanics and Dynamics, part 1 (1989)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: The structural analysis methods research has several goals. One goal is to develop analysis methods that are general. This goal of generality leads naturally to finite-element methods, but the research will also include other structural analysis methods. Another goal is that the methods be amenable to error analysis; that is, given a physical problem and a mathematical model of that problem, an analyst would like to know the probable error in predicting a given response quantity. The ultimate objective is to specify the error tolerances and to use automated logic to adjust the mathematical model or solution strategy to obtain that accuracy. A third goal is to develop structural analysis methods that can exploit parallel processing computers. The structural analysis methods research will focus initially on three types of problems: local/global nonlinear stress analysis, nonlinear transient dynamics, and tire modeling.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CP-3034-PT-1 , L-16560-PT-1 , NAS 1.55:3034-PT-1 , Jun 19, 1985 - Jun 21, 1985; Hampton, VA; United States
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    Seventeenth NASTRAN (R) Users' Colloquium (1989)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: General application of finite element methodology and the specific application of the NASA Structural Analysis System, NASTRAN, to a variety of static and dynamic structural problems were reviewed.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CP-3029 , NAS 1.55:3029 , AD-A226755 , Apr 24, 1989 - Apr 28, 1989; San Antonio, TX; United States
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    Characterization of structural connections using free and forced response test data (1989)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: The accurate prediction of system dynamic response often has been limited by deficiencies in existing capabilities to characterize connections adequately. Connections between structural components often are complex mechanically, and difficult to accurately model analytically. Improved analytical models for connections are needed to improve system dynamic preditions. A procedure for identifying physical connection properties from free and forced response test data is developed, then verified utilizing a system having both a linear and nonlinear connection. Connection properties are computed in terms of physical parameters so that the physical characteristics of the connections can better be understood, in addition to providing improved input for the system model. The identification procedure is applicable to multi-degree of freedom systems, and does not require that the test data be measured directly at the connection locations.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-101991 , E-4695 , NAS 1.15:101991 , Biennial Conference on Mechanical Vibration and Noise; Sep 17, 1989 - Sep 20, 1989; Montreal, Quebec; Canada
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  • 72
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    Turbine Engine Hot Section Technology, 1987 (1987)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: Presentations were made concerning the development of design analysis tools for combustor liners, turbine vanes, and turbine blades. Presentations were divided into six sections: instrumentation, combustion, turbine heat transfer, structural analysis, fatigue and fracture, surface protective coatings, constitutive behavior of materials, stress-strain response and life prediction methods.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CP-2493 , E-3745 , NAS 1.55:2493 , Oct 20, 1987 - Oct 21, 1987; Cleveland, OH; United States
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    Free-vibration characteristics and correlation of a space station split-blanket solar array (1989)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: Two methods for studying the free-vibration characteristics of a large split-blanket solar array in a zero-g cantilevered configuration are presented. The zero-g configuration corrresponds to an on-orbit configuration of the Space Station solar array. The first method applies the equations of continuum mechanics to determine the natural frequencies of the array; the second uses the finite element method program, MSC/NASTRAN. The stiffness matrix from the NASTRAN solution was found to be erroneously grounded. The results from the two methods are compared. It is concluded that the grounding does not seriously compromise the solution to the elastic modes of the solar array. However, the correct rigid body modes need to be included to obtain the correct dynamic model.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-101452 , E-4563 , NAS 1.15:101452 , Structures, Structural Dynamics and Materials Conference; Apr 03, 1989 - Apr 05, 1989; Mobile, AL; United States
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    Noninteractive macroscopic reliability model for ceramic matrix composites with orthotropic material symmetry (1989)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: A macroscopic noninteractive reliability model for ceramic matrix composites is presented. The model is multiaxial and applicable to composites that can be characterized as orthotropic. Tensorial invariant theory is used to create an integrity basis with invariants that correspond to physical mechanisms related to fracture. This integrity basis is then used to construct a failure function per unit volume (or area) of material. It is assumed that the overall strength of the composite is governed by weakest link theory. This leads to a Weibull type model similar in nature to the principle of independent action (PIA) model for isotropic monolithic ceramics. An experimental program to obtain model parameters is briefly discussed. In addition, qualitative features of the model are illustrated by presenting reliability surfaces for various model parameters.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-101414 , E-4512 , NAS 1.15:101414 , International Gas Turbine and Aeroengine Congress and Exposition; Jun 04, 1989 - Jun 08, 1989; Toronto, Ontario; Canada
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    A review of failure models for unidirectional ceramic matrix composites under monotonic loads (1989)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: Ceramic matrix composites offer significant potential for improving the performance of turbine engines. In order to achieve their potential, however, improvements in design methodology are needed. In the past most components using structural ceramic matrix composites were designed by trial and error since the emphasis of feasibility demonstration minimized the development of mathematical models. To understand the key parameters controlling response and the mechanics of failure, the development of structural failure models is required. A review of short term failure models with potential for ceramic matrix composite laminates under monotonic loads is presented. Phenomenological, semi-empirical, shear-lag, fracture mechanics, damage mechanics, and statistical models for the fast fracture analysis of continuous fiber unidirectional ceramic matrix composites under monotonic loads are surveyed.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-101421 , E-4520 , NAS 1.15:101421 , International Gas Turbine and Aeroengine Congress and Exposition; Jun 04, 1989 - Jun 08, 1989; Toronto, Ontario; Canada
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    Parametric studies of advanced turboprops (1988)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: The effects of geometric variables (sweep and twist) on the structural performance of advanced turboprops are investigated. The investigation is limited to aerodynamically efficient turboprops using an acceptable design configuration as a baseline. The baseline configuration is modified using a seven by seven array of independently varying sweep and twist parameters while maintaining acceptable aerodynamic efficiency. The turboprop structural performance is evaluated in terms of critical speeds, tip displacements, and vibration frequencies where geometric nonlinearities are included. The results obtained are presented in such a manner as to highlight the effects of sweep and twist on the structural performance of aerodynamically efficient turboprop configurations.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-101389 , E-4451 , NAS 1.15:101389 , Structures, Structural Dynamics and Materials Conference,; Apr 18, 1988 - Apr 20, 1988; Williamsburg, VA; United States
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  • 77
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    Local-global analysis of crack growth in continuously reinforced ceramic matrix composites (1988)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: The development is described of a mathematical model for predicting the strength and micromechanical failure characteristics of continuously reinforced ceramic matrix composites. The local-globe analysis models the vicinity of a propagating crack tip as a local heterogeneous region (LHR) consisting of spring like representation of the matrix, fibers and interfaces. This region is embedded in an anisotropic continuum (representing the bulk composite) which is modeled by conventional finite elements. Parametric studies are conducted to investigate the effects of LHR size, component properties, interface conditions, etc. on the strength and sequence of the failure processes in the unidirectional composite system. The results are compared with those predicted by the models developed by Marshall et al. (1985) and by Budiansky et al. (1986).
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-182231 , E-4537 , NAS 1.26:182231 , International Gas Turbine and Aeroengine Congress and Exposition; Jun 04, 1989 - Jun 08, 1989; Toronto, Ontario; Canada
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    Hierarchic plate and shell models based on p-extension (1988)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: Formulations of finite element models for beams, arches, plates and shells based on the principle of virtual work was studied. The focus is on computer implementation of hierarchic sequences of finite element models suitable for numerical solution of a large variety of practical problems which may concurrently contain thin and thick plates and shells, stiffeners, and regions where three dimensional representation is required. The approximate solutions corresponding to the hierarchic sequence of models converge to the exact solution of the fully three dimensional model. The stopping criterion is based on: (1) estimation of the relative error in energy norm; (2) equilibrium tests, and (3) observation of the convergence of quantities of interest.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-4203 , NAS 1.26:4203 , WU/CCM-87/5 , Conference on The Impact of Mathematical Analysis on the Numerical Solution of Engineering Problems; Sep 17, 1986 - Sep 19, 1986; College Park, MD; United States
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    Prediction of stresses in aircraft panels subjected to acoustic forces (1988)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: Summarized are the progress and accomplishments performed under NASA/Langley Research Center Master Agreement NAS1-17993, Task Assignment No. 22, entitled Prediction of Stresses in Aircraft Panels Subjected to Acoustic Forces, for the period October 1, 1985 to December 15, 1987. The primary effort of this task is the development of analytical methods for prediction of stresses in aircraft panels subjected to acoustic forces. The progress and accomplishments of various activities are discussed first. Then, publications, presentations and thesis are presented.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-182513 , NAS 1.26:182513
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    Calculation of Weibull strength parameters and Batdorf flow-density constants for volume- and surface-flaw-induced fracture in ceramics (1988)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: The calculation of shape and scale parameters of the two-parameter Weibull distribution is described using the least-squares analysis and maximum likelihood methods for volume- and surface-flaw-induced fracture in ceramics with complete and censored samples. Detailed procedures are given for evaluating 90 percent confidence intervals for maximum likelihood estimates of shape and scale parameters, the unbiased estimates of the shape parameters, and the Weibull mean values and corresponding standard deviations. Furthermore, the necessary steps are described for detecting outliers and for calculating the Kolmogorov-Smirnov and the Anderson-Darling goodness-of-fit statistics and 90 percent confidence bands about the Weibull distribution. It also shows how to calculate the Batdorf flaw-density constants by uing the Weibull distribution statistical parameters. The techniques described were verified with several example problems, from the open literature, and were coded. The techniques described were verified with several example problems from the open literature, and were coded in the Structural Ceramics Analysis and Reliability Evaluation (SCARE) design program.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-100890 , E-4128 , NAS 1.15:100890 , International Symposium on Ceramic Materials and Components for Engines; Nov 27, 1988 - Nov 30, 1988; Las Vegas, NV; United States
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    Turbine Engine Hot Section Technology 1986 (1986)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: The Turbine Engine Hot Section Technology (HOST) Project of the NASA Lewis Research Center sponsored a workshop to discuss current research pertinent to turbine engine durability problems. Presentations were made concerning the hot section environment and the behavior of combustion liners, turbine blades, and turbine vanes. The presentations were divided into six sessions: Instrumentation, Combustion, Turbine Heat Transfer, Structural Analysis, Fatigue and Fracture, and Surface Protection. Topics discussed included modeling of thermal and fluid-flow phenomena, structural analysis, fatigue and fracture, surface protective coatings, constitutive behavior of materials, stress-strain response, and life-prediction methods. Researchers from industry, academia, and government presented results of their work sponsored by the HOST project.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CP-2444 , E-3205 , NAS 1.55:2444 , Oct 21, 1986 - Oct 22, 1986; Cleveland, OH; United States
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    Recent developments in structural sensitivity analysis (1988)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: Recent developments are reviewed in two major areas of structural sensitivity analysis: sensitivity of static and transient response; and sensitivity of vibration and buckling eigenproblems. Recent developments from the standpoint of computational cost, accuracy, and ease of implementation are presented. In the area of static response, current interest is focused on sensitivity to shape variation and sensitivity of nonlinear response. Two general approaches are used for computing sensitivities: differentiation of the continuum equations followed by discretization, and the reverse approach of discretization followed by differentiation. It is shown that the choice of methods has important accuracy and implementation implications. In the area of eigenproblem sensitivity, there is a great deal of interest and significant progress in sensitivity of problems with repeated eigenvalues. In addition to reviewing recent contributions in this area, the paper raises the issue of differentiability and continuity associated with the occurrence of repeated eigenvalues.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-100668 , NAS 1.15:100668 , ISPE International Conference on CAD/CAM, Robotics, and Factories of the Future; Aug 14, 1988 - Aug 17, 1988; Southfield, MI; United States
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  • 83
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    Analytical approach to peel stresses in bonded composite stiffened panels (1987)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: A closed-form solution was obtained for the stresses and displacements of two bonded beams. A system of two fourth-order and two second-order differential equations with the associated boundary equations was determined using a variational work approach. A FORTRAN computer program was devised to solve for the eigenvalues and eigenvectors of this system and to calculate the coefficients from the boundary conditions. The results were then compared with NASTRAN finite-element solutions and shown to agree closely.
    Keywords: STRUCTURAL MECHANICS
    Type: Developments in Mechanics. Volume 14(c) - Midwestern Mechanics Conference; Aug 31, 1987; West Lafayette, IN; United States
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    A simple method to model truss-beams as equivalent continua (1987)
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    Publication Date: 2019-07-13
    Description: A new method is presented for obtaining stiffness constants for structures modeled as three-dimensional linear elastic beams. The three-dimensional lattice is comprised of multiple two-dimensional lattices. Matrix manipulation is used to determine the contribution of each two-dimensional substructure to the complete three dimensional lattice.
    Keywords: STRUCTURAL MECHANICS
    Type: Developments in Mechanics. Volume 14(a) - Midwestern Mechanics Conference; Aug 31, 1987; West Lafayette, IN; United States
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    A nonlinear viscoelastic constitutive equation - Yield predictions in multiaxial deformations (1987)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Yield stress predictions of a nonlinear viscoelastic constitutive equation for amorphous polymer solids have been obtained and are compared with the phenomenological von Mises yield criterion. Linear viscoelasticity theory has been extended to include finite strains and a material timescale that depends on the instantaneous temperature, volume, and pressure. Results are presented for yield and the correct temperature and strain-rate dependence in a variety of multiaxial deformations. The present nonlinear viscoelastic constitutive equation can be formulated in terms of either a Cauchy or second Piola-Kirchhoff stress tensor, and in terms of either atmospheric or hydrostatic pressure.
    Keywords: STRUCTURAL MECHANICS
    Type: Developments in Mechanics. Volume 14(b) - Midwestern Mechanics Conference; Aug 31, 1987; West Lafayette, IN; United States
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    Structural analysis methods development for turbine hot section components (1988)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: The structural analysis technologies and activities of the NASA Lewis Research Center's gas turbine engine Hot Section Technology (HOST) Program are summarized. The technologies synergistically developed and validated include: time-varying thermal/mechanical load models; component-specific automated geometric modeling and solution strategy capabilities; advanced inelastic analysis methods; inelastic constitutive models; high-temperature experimental techniques and experiments; and nonlinear structural analysis codes. Features of the program that incorporate the new technologies and their application to hot section component analysis and design are described. Improved and, in some cases, first-time 3-D nonlinear structural analyses of hot section components of isotropic and anisotropic nickel-base superalloys are presented.
    Keywords: STRUCTURAL MECHANICS
    Type: Toward improved durability in advanced aircraft engine hot sections; Jun 05, 1988 - Jun 09, 1988; Amsterdam; Netherlands
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    Fatigue life prediction modeling for turbine hot section materials (1988)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: A major objective of the fatigue and fracture efforts under the Hot Section Technology (HOST) program was to significantly improve the analytic life prediction tools used by the aeronautical gas turbine engine industry. This was achieved in the areas of high-temperature thermal and mechanical fatigue of bare and coated high-temperature superalloys. The cyclic crack initiation and propagation resistance of nominally isotropic polycrystalline and highly anisotropic single crystal alloys were addressed. Life prediction modeling efforts were devoted to creep-fatigue interaction, oxidation, coatings interactions, multiaxiality of stress-strain states, mean stress effects, cumulative damage, and thermomechanical fatigue. The fatigue crack initiation life models developed to date include the Cyclic Damage Accumulation (CDA) and the Total Strain Version of Strainrange Partitioning (TS-SRP) for nominally isotropic materials, and the Tensile Hysteretic Energy Model for anisotropic superalloys. A fatigue model is being developed based upon the concepts of Path-Independent Integrals (PII) for describing cyclic crack growth under complex nonlinear response at the crack tip due to thermomechanical loading conditions. A micromechanistic oxidation crack extension model was derived. The models are described and discussed.
    Keywords: STRUCTURAL MECHANICS
    Type: Toward improved durability in advanced aircraft engine hot sections; Jun 05, 1988 - Jun 09, 1988; Amsterdam; Netherlands
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  • 88
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    The effect of modal truncation on modal modification (1987)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Several investigators have shown that the ability of modal modification routines to accurately predict dynamic structural changes is highly dependent on the completeness of the original modal database of the structure-modal truncation. This paper more closely examines the effects of modal truncation on modal modifications. The results of this study show the modified modal vector to be a weighted linear sum of the original modal vectors. Due to this weighted linear sum process, modal truncation might affect almost any mode in a modification process. Therefore, the quality of a modal modification is not necessarily dependent on the number of modes present in a database, but more importantly on which modes are present.
    Keywords: STRUCTURAL MECHANICS
    Type: International Modal Analysis Conference; Apr 06, 1987 - Apr 09, 1987; London
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  • 89
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    A preliminary investigation of finite-element modeling for composite rotor blades (1988)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: The results from an initial phase of an in-house study aimed at improving the dynamic and aerodynamic characteristics of composite rotor blades through the use of elastic couplings are presented. Large degree of freedom shell finite element models of an extension twist coupled composite tube were developed and analyzed using MSC/NASTRAN. An analysis employing a simplified beam finite element representation of the specimen with the equivalent engineering stiffness was additionally performed. Results from the shell finite element normal modes and frequency analysis were compared to those obtained experimentally, showing an agreement within 13 percent. There was appreciable degradation in the frequency prediction for the torsional mode, which is elastically coupled. This was due to the absence of off-diagonal coupling terms in the formulation of the equivalent engineering stiffness. Parametric studies of frequency variation due to small changes in ply orientation angle and ply thickness were also performed. Results showed linear frequency variations less than 2 percent per 1 degree variation in the ply orientation angle, and 1 percent per 0.0001 inch variation in the ply thickness.
    Keywords: STRUCTURAL MECHANICS
    Type: International Conference on Rotorcraft Basic Research; Feb 16, 1988 - Feb 18, 1988; College Park, MD; United States
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  • 90
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    A comparative overview of modal testing and system identification for control of structures (1987)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: This paper presents a comparative overview of the disciplines of modal testing used in structural engineering and system identification used in control theory. A list of representative references from both areas is given and the basic methods are briefly described. Recent progress on the interaction of modal testing and control disciplines is discussed. It is concluded that combined efforts of researchers in both disciplines are required for unification of modal testing and system identification methods for control of flexible structures.
    Keywords: STRUCTURAL MECHANICS
    Type: 1987 SEM Spring Conference on Experimental Mechanics; Jun 14, 1987 - Jun 19, 1987; Houston, TX; United States
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  • 91
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    Vibration frequencies of tapered bars with nonclassical boundary conditions (1988)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: The goals for this research were revised and clarified. The goals are restated along with an evaluation of the accomplishment of the goal. All of the cases of the truncated-cone beams that were originally proposed to be solved were solved. A summary of these solutions is presented. Some cases of beams with unequal tapers were solved and are discussed.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-183059 , NAS 1.26:183059
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  • 92
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    The integration of a mesh reflector to a 15-foot box truss structure. Task 3: Box truss analysis and technology development (1987)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: To demonstrate the design and integration of a reflective mesh surface to a deployable truss structure, a mesh reflector was installed on a 15 foot box truss cube. The specific features demonstrated include: (1) sewing seams in reflective mesh; (2) mesh stretching to desired preload; (3) installation of surface tie cords; (4) installation of reflective surface on truss; (5) setting of reflective surface; (6) verification of surface shape/accuracy; (7) storage and deployment; (8) repeatability of reflector surface; and (9) comparison of surface with predicted shape using analytical methods developed under a previous task.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-178228 , NAS 1.26:178228 , MCR-86-669-TASK-3
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  • 93
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    Design sensitivity analysis and optimization of built-up structures (1987)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: Developments during the course of the research in design sensitivity analysis and optimization of built-up structures, with both sizing and shape design variables, show clearly that a unified variational approach to design sensitivity analysis can yield derivatives of structural response with respect to design. Rigorous and practically computable results for structural components and built-up structures have been demonstrated and used to solve design optimization problems.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-180973 , NAS 1.26:180973
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  • 94
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    Stress effects in multilayers (1987)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: Calculations of interfacial stress in abrupt junctions and its effect on the defect state of the interface are examined.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-181172 , NAS 1.26:181172
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  • 95
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    Closure measurements on short fatigue cracks (1985)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Single-edged notched specimens, 2.3 mm thick, of 2024-T3 aluminum were cyclicly loaded at R-ratios of 0.5, 0.0, -1.0 and -2.0. The notch roots were periodically inspected with an optical microscope to locate the initiation of very short cracks. Acetate replicas were also taken. The loads were selected to produce fatigue lives of 500,000 cycles or less. Crack opening displacements were measured at single positions across cracks as short as 0.035 mm and as long as the full thickness of the specimen. The opening load ratios for the short cracks are somewhat smaller than for long cracks at positive R-ratios, but are considerably smaller for negative R-ratios.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-180315 , NAS 1.26:180315
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  • 96
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    On 3-D inelastic analysis methods for hot section components. Volume 1: Special finite element models (1987)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: This Annual Status Report presents the results of work performed during the third year of the 3-D Inelastic Analysis Methods for Hot Section Components program (NASA Contract NAS3-23697). The objective of the program is to produce a series of new computer codes that permit more accurate and efficient three-dimensional analysis of selected hot section components, i.e., combustor liners, turbine blades, and turbine vanes. The computer codes embody a progression of mathematical models and are streamlined to take advantage of geometrical features, loading conditions, and forms of material response that distinguish each group of selected components. This report is presented in two volumes. Volume 1 describes effort performed under Task 4B, Special Finite Element Special Function Models, while Volume 2 concentrates on Task 4C, Advanced Special Functions Models.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-179494 , NAS 1.26:179494 , PWA-5940-46-VOL-1 , ASR-3
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  • 97
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    Simulation studies for surfaces and materials strength (1987)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Three different investigations based on computer simulations were carried out. Simulation calculations were performed using model potentials with two- and three-body interactions which were represented by the Mie and the Axilrod-Teller potentials, respectively. In the first part, to analyze stability criteria for simple crystals, a parametrical investigation was performed and stability regions for five different crystalline structures were determined with respect to potential energy parameters. To simulate some of the basic surface processes such as diffusion and nucleation, in the second and third parts, silicon surfaces were considered as a specific example. In these studies diffusion of adatoms on stepped surfaces were simulated and energetics associated with the formation of kink sites were calculated.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-180539 , NAS 1.26:180539
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  • 98
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    Nonlinear rotordynamics analysis (1986)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: Three analytic consequences of the nonlinear Jeffcott equations are examined. The primary application of these analyses is directed toward understanding the excessive vibrations recorded in the Liquid Oxygen (LOX) pump of the Space Shuttle Main Engine (SSME) during hot firing ground testing. The first task is to provide bounds on the coefficients of the equations which delimit the two cases of numerical solution as a circle or an annulus. The second task examines the mathematical generalization to multiple forcing functions, which includes the special problems of mass imbalance, side force, rubbing, and combination of these forces. Finally, stability and boundedness of the steady-state solutions is discussed and related to the corresponding linear problem.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-178931 , NAS 1.26:178931
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  • 99
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    Fracture analysis of radial scientific instrument module registration fittings of the space telescope (1986)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Various pieces of the registration fittings for the Radial Scientific instrument (SI) module of the Space Telescope were examined from a fracture mechanics point of view and deemed to be fail-safe or else have had maximum allowable flaw sizes specified for them. The results of these analyses are summarized in tabular form. In many instances the applied stress levels were so low that the threshold stress intensity factor range was never reached. In most of the others the allowable flaw sizes were large enough to be detected by visual inspection. However, for some parts, such as the flexures connecting the aluminum cover to the ball retainer in the fitting at point A, the flaw sizes were rather small. Eddy current tests are capable of detecting flaws of this size (0.022 inches x 0.1 inches), so for those which have been so tested these small flaws should represent no danger of going undetected. In every instance approximations were made to err on the conservative side. These were pointed out in the discussions of the analyses for each fitting. One conservative approximation that was not mentioned, however, is the fact that retardation was not included in the crack propagation computations.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-178932 , NAS 1.26:178932
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  • 100
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    Large Deformation Dynamic Bending of Composite Beams (1986)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: Studies were conducted on the large deformation response of composite beams subjected to a dynamic axial load. The beams were loaded with a moderate eccentricity to promote bending. The study was primarily experimental but some finite element results were obtained. Both the deformation and the failure of the beams were of interest. The static response of the beams was also studied to determine potential differences between the static and dynamic failure. Twelve different laminate types were tested. The beams were loaded dynamically with a gravity driven impactor traveling at 19.6 ft/sec and quasi-static tests were conducted on identical beams in a displacement controlled manner. For laminates of practical interest, the failure modes under static and dynamic loadings were identical. Failure in most of the laminate types occurred in a single event involving 40% to 50% of the plies. However, failure in laminates with 30 deg or 15 deg off-axis plies occured in several events. All laminates exhibited bimodular elastic properties. Using empirically determined flexural properties, a finite element analysis was reasonably accurate in predicting the static and dynamic deformation response.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-4006 , NAS 1.26:4006
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