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  • STRUCTURAL MECHANICS  (402)
  • 1985-1989  (402)
  • 1965-1969
  • 1950-1954
  • 1987  (402)
  • 1
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    Relative slope invariance of velocity-stress and strain-stress curves (1987)
    In:  CASI
    Details
    Publication Date: 2004-10-30
    Keywords: STRUCTURAL MECHANICS
    Type: NDE at NASA Langley. Advancing the State-of-the-Art and Providing a Quantitative Science Base for Materials Characterization; 4 p
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  • 2
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    Effective nonlinearity parameters of aluminum alloys as a function of volume fraction of second phase precipitates (1987)
    In:  CASI
    Details
    Publication Date: 2004-10-30
    Keywords: STRUCTURAL MECHANICS
    Type: NDE at NASA Langley. Advancing the State-of-the-Art and Providing a Quantitative Science Base for Materials Characterization; 10 p
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  • 3
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    Thermal strains and acoustic nonlinearity in crystalline solids (1987)
    In:  CASI
    Details
    Publication Date: 2004-10-30
    Keywords: STRUCTURAL MECHANICS
    Type: NDE at NASA Langley. Advancing the State-of-the-Art and Providing a Quantitative Science Base for Materials Characterization; 6 p
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  • 4
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    Optical probing of pulsed acoustic surface waves using wideband differential interferometry (1987)
    In:  CASI
    Details
    Publication Date: 2004-10-30
    Keywords: STRUCTURAL MECHANICS
    Type: NDE at NASA Langley. Advancing the State-of-the-Art and Providing a Quantitative Science Base for Materials Characterization; 4 p
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  • 5
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    Magnetoacoustic stress measurement in railroad rail steel (1987)
    In:  CASI
    Details
    Publication Date: 2004-10-30
    Keywords: STRUCTURAL MECHANICS
    Type: NDE at NASA Langley. Advancing the State-of-the-Art and Providing a Quantitative Science Base for Materials Characterization; 7 p
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  • 6
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    Remote determination of the two-dimensional diffusivity tensor in thin plates (1987)
    In:  CASI
    Details
    Publication Date: 2004-10-30
    Keywords: STRUCTURAL MECHANICS
    Type: NDE at NASA Langley. Advancing the State-of-the-Art and Providing a Quantitative Science Base for Materials Characterization; 4 p
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  • 7
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    Effects of transverse shearing on cylindrical bending, vibration, and buckling of laminated plates (1987)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA Journal (ISSN 0001-1452); 25; 123-129
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  • 8
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    Calculation of thermomechanical fatigue life based on isothermal behavior (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The isothermal and thermomechanical fatigue (TMF) crack initiation response of a hypothetical material was analyzed. Expected thermomechanical behavior was evaluated numerically based on simple, isothermal, cyclic stress-strain-time characteristics and on strainrange versus cyclic life relations that have been assigned to the material. The attempt was made to establish basic minimum requirements for the development of a physically accurate TMF life-prediction model. A worthy method must be able to deal with the simplest of conditions: that is, those for which thermal cycling, per se, introduces no damage mechanisms other than those found in isothermal behavior. Under these assumed conditions, the TMF life should be obtained uniquely from known isothermal behavior. The ramifications of making more complex assumptions will be dealt with in future studies. Although analyses are only in their early stages, considerable insight has been gained in understanding the characteristics of several existing high-temperature life-prediction methods. The present work indicates that the most viable damage parameter is based on the inelastic strainrange.
    Keywords: STRUCTURAL MECHANICS
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  • 9
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    Energy dissipation associated with crack extension in an elastic-plastic material (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Crack extension in elastic-plastic material involves energy dissipation through the creation of new crack surfaces and additional yielding around the crack front. An analytical procedure, using a two-dimensional elastic-plastic finite element method, was developed to calculate the energy dissipation components during a quasi-static crack extension. The fracture of an isotropic compact specimen was numerically simulated using the critical crack-tip-opening-displacement (CTOD) growth criterion. Two specimen sizes were analyzed for three values of critical CTOD. Results from the analysis showed that the total energy dissipation rate consisted of three components: the crack separation energy rate, the plastic energy dissipation rate, and the residual strain energy rate. All three energy dissipation components and the total energy dissipation rate initially increased with crack extension and finally reached constant values.
    Keywords: STRUCTURAL MECHANICS
    Type: Engineering Fracture Mechanics (ISSN 0013-7944); 28; 3, 19; 319-330
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  • 10
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    Compromise - An effective approach for the hierarchical design of structural systems (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The use of the compromise decision support problem in hierarchical design of structural systems is described. The mathematical template that supports the underlying precepts of hierarchical design in the context of the decision support problem technique is presented. A structural example that demonstrates the efficacy of the approach is included.
    Keywords: STRUCTURAL MECHANICS
    Type: Computers and Structures (ISSN 0045-7949); 26; 6, 19
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  • 11
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    Self-shadowing effects on the thermal-structural response of orbiting trusses (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Spacecraft and Rockets (ISSN 0022-4650); 24; 342-348
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  • 12
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    Stress ratio effect on cyclic debonding in adhesively bonded composite joints (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A study was conducted to investigate the stress ratio effect on cyclic debond growth behavior in adhesively bonded composite joints. The system studied consisted of graphite/epoxy adherends bonded with a toughened epoxy adhesive. This study showed that the strain energy release rate range was the driving factor for cyclic debonding of the tested bonded system when subjected to cyclic loads with different stress ratios for both mode I and mixed mode I-II loadings.
    Keywords: STRUCTURAL MECHANICS
    Type: Composite Structures (ISSN 0263-8223); 8; 1, 19; 31-45
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  • 13
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    A generalized hybrid transfinite element computational approach for nonlinear/linear unified thermal-structural analysis (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: STRUCTURAL MECHANICS
    Type: Computers and Structures (ISSN 0045-7949); 26; 4, 19; 655-665
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  • 14
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    Nonlinear beam kinematics for small strains and finite rotations (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A simple matrix expression is obtained for the strain components of a beam in which the magnitudes of neither beam displacements nor rotations are explicitly restricted. The only kinematical restrictions are that: (1) strains are small compared to unity and (2) components of local rotation, a newly identified kinematical quantity, are of the order of the strains to a fractional power equal to at least one half. Local rotations are defined as the change of orientation of material elements off the beam reference axis relative to those on the beam reference axis. Local rotations appear explicitly in the resulting strain expressions, facilitating the treatment of both open- and closed-section beams in applications of the theory. The resulting strain components are expressed in a local Cartesian coordinate system and can be calculated directly in that way. Thus, one can use a curvilinear coordinate system that is natural to the beam problem without the complications that usually surround such an approach. Examples show the simplicity and the generality of the present approach as well as why previously published results differ among themselves concerning tension-torsion coupling.
    Keywords: STRUCTURAL MECHANICS
    Type: Vertica (ISSN 0360-5450); 11; 3, 19
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  • 15
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    Non-linear analysis of symmetric structures with unsymmetric boundary conditions (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Two computational techniques are developed analytically to generate global approximation vectors for use in the nonlinear large-deflection analysis of symmetric structures with asymmetric boundary conditions. One method is based on linear combinations of FEM-generated symmetric and antisymmetric vector components, while the other employs a preconditioned-conjugate-gradient technique. The derivation of the procedures is explained in detail, and their effectiveness is evaluated in sample computations for an elliptic toroid and a cylindrical panel; the results are presented in tables and graphs and characterized.
    Keywords: STRUCTURAL MECHANICS
    Type: Engineering Computations (ISSN 0264-4401); 4; 161-171
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  • 16
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    Wave propagation in a plate after impact by a projectile (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The wave propagation in a circular plate after impact by a cylindrical projectile is studied. In the vicinity of impact, the pressure is computed numerically. An intense pressure pulse is generated that peaks 0.2 microns after impact, then drops sharply to a plateau. The response of the plate is determined adopting a modal solution of Mindlin's equations. Velocity and acceleration histories display both propagating and dispersive features.
    Keywords: STRUCTURAL MECHANICS
    Type: Acoustical Society of America, Journal (ISSN 0001-4966); 82; 498-505
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  • 17
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    Simplified composite micromechanics for predicting microstresses (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A unified set of composite micromechanics equations is summarized and described. This unified set is for predicting the ply microstresses when the ply stresses are known. The set consists of equations of simple form for predicting three-dimensional stresses (six each) in the matrix, fiber, and interface. Several numerical examples are included to illustrate use and computational effectiveness of the equations in this unified set. Numerical results from these examples are discussed with respect to their significance on microcrack formation and, therefore, damage initiation in fiber composites.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Reinforced Plastics and Composites (ISSN 0731-6844); 6; 268-284
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  • 18
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    The acoustic radiation damping of the modes of a rectangular panel (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The acoustic damping for single modes of a finite rectangular panel, simply supported in an infinite baffle, is theoretically determined from the ratio of the acoustic energy radiated per cycle to the vibratory energy of the panel. Asymptotic solutions for the low-frequency region are presented for a panel mode driven at an arbitrary frequency and for a panel mode vibrating at its natural frequency. Curves of acoustic damping for a panel mode vibrating at resonance, as a function of the panel thickness-to-length ratio, are presented for various panel aspect ratios. For panels vibrating below the critical frequency, the damping depends on the aspect ratio with square panels developing the smallest value. For panels vibrating above the critical frequency, the damping is nearly independent of the aspect ratio.
    Keywords: STRUCTURAL MECHANICS
    Type: Acoustical Society of America, Journal (ISSN 0001-4966); 81; 1787-179
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  • 19
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    Advances and trends in computational structural mechanics (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The development status and applicational range of techniques in computational structural mechanics (CSM) are evaluated with a view to advances in computational models for material behavior, discrete-element technology, quality assessment, the control of numerical simulations of structural response, hybrid analysis techniques, techniques for large-scale optimization, and the impact of new computing systems on CSM. Primary pacers of CSM development encompass prediction and analysis of novel materials for structural components, computational strategies for large-scale structural calculations, and the assessment of response prediction reliability together with its adaptive improvement.
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA Journal (ISSN 0001-1452); 25; 977-995
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  • 20
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    Nonlinear/linear unified thermal stress formulations - Transfinite element approach (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A new unified computational approach for applicability to nonlinear/linear thermal-structural problems is presented. Basic concepts of the approach including applicability to nonlinear and linear thermal structural mechanics are first described via general formulations. Therein, the approach is demonstrated for thermal stress and thermal-structural dynamic applications. The proposed transfinite element approach focuses on providing a viable hybrid computational methodology by combining the modeling versatility of contemporary finite element schemes in conjunction with transform techniques and the classical Bubnov-Galerkin schemes. Comparative samples of numerical test cases highlight the capabilities of the proposed concepts.
    Keywords: STRUCTURAL MECHANICS
    Type: Computer Methods in Applied Mechanics and Engineering (ISSN 0045-7825); 64; 415-428
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  • 21
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    Sensitivity analysis and optimization of nodal point placement for vibration reduction (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A method is developed for sensitivity analysis and optimization of nodal point locations in connection with vibration reduction. A straightforward derivation of the expression for the derivative of nodal locations is given, and the role of the derivative in assessing design trends is demonstrated. An optimization process is developed which uses added lumped masses on the structure as design variables to move the node to a preselected location - for example, where low response amplitude is required or to a point which makes the mode shape nearly orthogonal to the force distribution, thereby minimizing the generalized force. The optimization formulation leads to values for added masses that adjust a nodal location while minimizing the total amount of added mass required to do so. As an example, the node of the second mode of a cantilever box beam is relocated to coincide with the centroid of a prescribed force distribution, thereby reducing the generalized force substantially without adding excessive mass. A comparison with an optimization formulation that directly minimizes the generalized force indicates that nodal placement gives essentially a minimum generalized force when the node is appropriately placed.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Sound and Vibration (ISSN 0022-460X); 119; 277-289
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  • 22
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    Stress analysis of the cracked-lap-shear specimen - An ASTM round-robin (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: This ASTM Round Robin was conducted to evaluate the state of the art in stress analysis of adhesively bonded joint specimens. Specifically, the participants were asked to calculate the strain-energy-release rate for two different geometry cracked lap shear (CLS) specimens at four different debond lengths. The various analytical techniques consisted of 2- and 3-dimensional finite element analysis, beam theory, plate theory, and a combination of beam theory and finite element analysis. The results were examined in terms of the total strain-energy-release rate and the mode I to mode II ratio as a function of debond length for each specimen geometry. These results basically clustered into two groups: geometric linear or geometric nonlinear analysis. The geometric nonlinear analysis is required to properly analyze the CLS specimens. The 3-D finite element analysis gave indications of edge closure plus some mode III loading. Each participant described his analytical technique and results. Nine laboratories participated.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Testing and Evaluation (ISSN 0090-3973); 15; 303-324
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  • 23
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    Verification of large beam-type space structures (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Spacecraft and Rockets (ISSN 0022-4650); 24; 469-473
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  • 24
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    An evaluation of higher-order modal methods for calculating transient structural response (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The present study evaluates a higher-order modal method proposed by Leung for transient structural analysis entitled the force-derivative method. This method repeatedly integrates by parts with respect to time the convolution-integral form of the structural response to produce successively better approximations to the contribution of the higher modes which are neglected in the modal summation. Comparisons are made of the force-derivative, the mode-displacement, and the mode-acceleration methods for several numerical example problems for various times, levels of damping, and forcing functions. The example problems include a tip-loaded cantilevered beam and a simply-supported multispan beam. The force-derivative method is shown to converge to an accurate solution in fewer modes than either the mode-displacement or the mode-acceleration methods. In addition, for problems in which there are a large number of closely-spaced frequencies whose mode shapes have a negligible contribution to the response, the force derivative method is very effective in representing the effect of the important, but otherwise neglected, higher modes.
    Keywords: STRUCTURAL MECHANICS
    Type: Computers and Structures (ISSN 0045-7949); 27; 1, 19
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  • 25
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    Finite rotation and nonlinear beam kinematics (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Standard means of representing finite rotation in rigid-body kinematics, including orientation angles, Euler parameters, and Rodrigues parameters, are reviewed and compared. General kinematical relations for a beam theory that treats arbitrarily large rotation are then presented. The standard methods of representing finite rotations are applied to these kinematical expressions, and comparison is made among the standard methods and additional methods found in the literature, such as quasi-coordinates and linear combinations of projection angles. The method of Rodrigues parameters is shown to stand out for both its simplicity and generality when applied to beam kinematics, a result that is really missing from the literature.
    Keywords: STRUCTURAL MECHANICS
    Type: Vertica (ISSN 0360-5450); 11; 1-2,
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  • 26
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    Model-size reduction for the analysis of symmetric structures with asymmetric boundary conditions (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A simple computational procedure is presented for reducing the size of the analysis model for a symmetric structure with asymmetric boundary conditions to that of the corresponding structure with symmetric boundary conditions. The procedure is based on approximating the asymmetric response of the structure by a linear combination of symmetric and antisymmetric global approximation vectors (or modes). The key elements of the procedure are (1) restructuring the governing finite-element equations to delineate the contributions to the symmetric and antisymmetric components of the asymmetric response, (2) successive application of the finite element method and the classical Rayleigh-Ritz technique. The finite-element method is first used to generate a few global approximation vectors (or modes). Then the amplitudes of these modes are computed by using the Rayleigh-Ritz technique. The effectiveness of the computational procedure is demonstrated by means of numerical examples of linear static problems of shells, and its potential for solving nonlinear problems is discussed.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal for Numerical Methods in Engineering (ISSN 0029-5981); 24; 913-926
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  • 27
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    Control of flexible structures by applied thermal gradients (1987)
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    Publication Date: 2011-08-19
    Description: Thermal, elastic, and feedback analyses are applied to the case of a beam with a distributed thermal actuator. The actuator is capable of producing a thermal gradient across the section of the beam. One candidate for such an actuator uses the Peltier effect, which appears in certain semiconductors. These devices act as heat pumps when a voltage is applied, causing a temperature gradient. It is shown that the thermal gradients can induce deflection in the beam. If the thermal gradients are applied in the proper sense to a vibrating beam, it is possible to increase the vibration damping exhibited by the structure. Experimental results are given for a cantilever beam, whose first vibrational mode damping ratio was increased from 0.81 to 7.4 percent with simple lead compensation.
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA Journal (ISSN 0001-1452); 25; 877-883
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  • 28
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    Nonlinear substructuring method for concurrent processing computers (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA Journal (ISSN 0001-1452); 25; 871-876
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  • 29
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    Nonlinear vibration and stability of rotating, pretwisted, preconed blades including Coriolis effects (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The coupled bending-bending-torsional equations of dynamic motion of rotating, linearly pretwisted blades are derived including large precone, second degree geometric nonlinearities and Coriolis effects. The equations are solved by the Galerkin method and a linear perturbation technique. Accuracy of the present method is verified by conparisons of predicted frequencies and steady state deflections with those from MSC/NASTRAN and from experiments. Parametric results are generated to establish where inclusion of only the second degree geometric nonlinearities is adequate. The nonlinear terms causing torsional divergence in thin blades are identified. The effects of Coriolis terms and several other structurally nonlinear terms are studied, and their relative importance is examined.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Aircraft (ISSN 0021-8669); 24; 342-352
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  • 30
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    Random loading fatigue crack growth: Crack closure considerations (1987)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The prediction of fatigue crack growth is an important element of effective fracture control for metallic structures and mechanical components, especially in the aerospace industry. The prediction techniques available and applied today are mostly based on fatigue crack growth measurements determined in constant amplitude testing. However, while many service loadings are constant amplitude, many more loadings are random amplitude. An investigation to determine which statistics of random loadings are relevant to fatigue crack closure was conducted. The fundamentals of random processes and crack closure are briefly reviewed, then the relevance of certain random process parameters to the crack closure calculation are discussed qualitatively. A course for further research is outlined.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Johnson Space Center, NASA(ASEE Summer Faculty Fellowship Program, 1987, Volume 2; 21 p
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  • 31
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    Active control of flexural vibrations in beams (1987)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: The feasibility of using piezoelectric actuators to control the flexural oscillations of large structures in space is investigated. Flexural oscillations are excited by impulsive loads. The vibratory response can degrade the pointing accuracy of cameras and antennae, and can cause high stresses at structural node points. Piezoelectric actuators have the advantage of exerting localized bending moments. In this way, vibration is controlled without exciting rigid body modes. The actuators are used in collocated sensor/driver pairs to form a feedback control system. The sensor produces a voltage that is proportional to the dynamic stress at the sensor location, and the driver produces a force that is proportional to the voltage applied to it. The analog control system amplifies and phase shifts the sensor signal to produce the voltage signal that is applied to the driver. The feedback control is demonstrated to increase the first mode damping in a cantilever beam by up to 100 percent, depending on the amplifier gain. The damping efficiency of the control system when the piezoelectrics are not optimally positioned at points of high stress in the beam is evaluated.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Johnson Space Center, NASA(ASEE Summer Faculty Fellowship Program, 1987, Volume 1; 20 p
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  • 32
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    An efficient frequency response solution for nonproportionally damped systems (1987)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: A method is presented to accurately and economically calculate steady state frequency responses based on the analysis of large finite element models with nonproportional damping effects. The new method is a hybrid of the traditional nonproportional and proportional damping solution methods. It captures the advantages of each computational approach without the burden of their respective shortcomings, as demonstrated with comparative analysis performed on a large finite element model.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-Marshall Space Flight Center, The 58th Shock and Vibration Symposium, Volume 1; p 389-394
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  • 33
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    A system identification technique based on the random decrement signatures. Part 2: Experimental results (1987)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: Identification of the system parameters of a randomly excited structure may be treated using a variety of statistical techniques. Of all these techniques, the Random Decrement is unique in that it provides the homogeneous component of the system response. Using this quality, a system identification technique was developed based on a least-squares fit of the signatures to estimate the mass, damping, and stiffness matrices of a linear randomly excited system. The results of an experiment conducted on an offshore platform scale model to verify the validity of the technique and to demonstrate its application in damage detection are presented.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-Marshall Space Flight Center, The 58th Shock and Vibration Symposium, Volume 1; p 275-287
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  • 34
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    On the glitches in the force transmitted by an electrodynamic exciter to a structure (1987)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Around resonance, the force transmitted by an exciter into a structure will be smaller or greater than a reference force generated by its coils due to electromechanical interaction. A simple analysis is presented which reveals how this phenomenon of force drop-off is controlled by three factors. The first factor, called Armature Mass Factor, describes a purely mechanical interaction between the structure and the exciter. The electromechanical energy conversion and its interaction with the structure yields two additional factors, called Electrical Resistance and Electrical Inductance Factors. They describe the effects of coil resistance, inductance and magnetic field strength relative to structural damping and stiffness. Present analysis indicates that, under proper circumstances, more than 90 percent of the force drop-off can be eliminated if armature-to-structure mass ratio is smaller or equal to half of modal loss factor.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-Marshall Space Flight Center, The 58th Shock and Vibration Symposium, Volume 1; p 245-255
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    Initial dynamic load estimates during configuration design (1987)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: This analysis includes the structural response to shock and vibration and evaluates the maximum deflections and material stresses and the potential for the occurrence of elastic instability, fatigue and fracture. The required computations are often performed by means of finite element analysis (FEA) computer programs in which the structure is simulated by a finite element model which may contain thousands of elements. The formulation of a finite element model can be time consuming, and substantial additional modeling effort may be necessary if the structure requires significant changes after initial analysis. Rapid methods for obtaining rough estimates of the structural response to shock and vibration are presented for the purpose of providing guidance during the initial mechanical design configuration stage.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-Marshall Space Flight Center, The 58th Shock and Vibration Symposium, Volume 1; p 203-223
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  • 36
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    Analysis of photopole data reduction models (1987)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: An analysis of the total impulse obtained from a buried explosive charge can be calculated from displacement versus time points taken from successive film frames of high speed motion pictures of the explosive event. The indicator of that motion is a pole and baseplate (photopole), which is placed on or within the soil overburden. Here, researchers are concerned with the precision of the impulse calculation and ways to improve that precision. Also examined here is the effect of each initial condition on the curve fitting process. It is shown that the zero initial velocity criteria should not be applied due to the linear acceleration versus time character of the cubic power series. The applicability of the new method to photopole data records whose early time motions are obscured is illustrated.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-Marshall Space Flight Center, The 58th Shock and Vibration Symposium, Volume 1; p 137-151
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  • 37
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    Structural analysis demonstration of constitutive and life models (1987)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: The overall objective of this program is to demonstrate the applicability of NASA-developed advanced constitutive and life damage models for calculating cyclic structural response and crack initiation in selected components of reusable space propulsion systems. The computer model resulting from this program will enable the user to produce an accurate life prediction of hot gas path, life limiting components of propulsion systems such as the space shuttle main engine (SSME). Previously developed computer models addressing constitutive modeling and life damage will be combined in an advanced finite element analysis to generate a sophisticated baseline life prediction program. A material data base will be established for the constitutive and life models parametrically involving temperature, strain range, strain rate, mean strain/stress, and dwell time. The verified computer program will be used to accomplish the life predictions of three SSME critical components as evidence of the model functionality.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Lewis Research Center Structural Integrity and Durability of Reusable Space Propulsion Systems; p 105-106
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  • 38
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    A new formulation of mean stress effects in fatigue (1987)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: A common method of treating the mean stress effect on fatigue life is to displace the elastic line on a Manson-Coffin-Basquin diagram while retaining the position of the plastic line. Manson and Halford pointed out that this procedure implies that mean stress significantly affects the cyclic stress-strain curve. Actually, however, they showed experimentally and by more general reasoning, that mean stress has little, if any, effect on the cyclic stress-strain curve. Thus, they concluded that it is necessary to displace the plastic line as well as the elastic line in order to keep the cyclic stress-strain curve unaltered. Another way to express the common displacement of the two lines is to keep the lines in place and change the horizontal coordinate to include a term relating to the displacement. Thus, instead of life, 2N sub f, as the horizontal coordinate, a new coordinate can become 2N sub f (1-sigma sub m/sigma sub f) superscript 1/b, thereby displacing both the elastic and plastic lines by an amount (1-sigma sub m/sigma sub f) superscript 1/b where sigma sub m is the mean stress and sigma sub f is the intercept of the elastic line at N sub f = 1/2 cycles and b is the slope of the elastic line.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Lewis Research Center Structural Integrity and Durability of Reusable Space Propulsion Systems; p 89-93
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  • 39
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    A TREETOPS simulation of the Hubble Space Telescope-High Gain Antenna interaction (1987)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Virtually any project dealing with the control of a Large Space Structure (LSS) will involve some level of verification by digital computer simulation. While the Hubble Space Telescope might not normally be included in a discussion of LSS, it is presented to highlight a recently developed simulation and analysis program named TREETOPS. TREETOPS provides digital simulation, linearization, and control system interaction of flexible, multibody spacecraft which admit to a point-connected tree topology. The HST application of TREETOPS is intended to familiarize the LSS community with TREETOPS by presenting a user perspective of its key features.
    Keywords: STRUCTURAL MECHANICS
    Type: Structural Dynamics and Control Interaction of Flexible Structures; p 881-902
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  • 40
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    Vibration suppression by stiffness control (1987)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: The feasibility of using piezoelectric ceramics as both sensors and actuators for vibration suppression in a lightweight, flimsy structure was demonstrated. Multimode control was achieved using one sensor and actuator pair. The Positive Position Feedback control strategy requires only knowledge of the natural frequencies of the structure. Implementation of the Positive Position Feedback used only strain measurements to achieve damping, no velocities, or acceleration are needed. All spillover is stabilizing for sufficient small gains.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Marshall Space Flight Center Structural Dynamics and Control Interaction of Flexible Structures; p 693-758
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  • 41
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    Workshop on Structural Dynamics and Control Interaction of Flexible Structures (1987)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The Hubble Space Telescope features the most exacting line of sight jitter requirement thus far imposed on a spacecraft pointing system. Consideration of the fine pointing requirements prompted an attempt to isolate the telescope from the low level vibration disturbances generated by the attitude control system reaction wheels. The primary goal was to provide isolation from axial component of wheel disturbance without compromising the control system bandwidth. A passive isolation system employing metal springs in parallel with viscous fluid dampers was designed, fabricated, and space qualified. Stiffness and damping characteristics are deterministic, controlled independently, and were demonstrated to remain constant over at least five orders of input disturbance magnitude. The damping remained purely viscous even at the data collection threshold of .16 x .000001 in input displacement, a level much lower than the anticipated Hubble Space Telescope disturbance amplitude. Vibration attenuation goals were obtained and ground test of the vehicle has demonstrated the isolators are transparent to the attitude control system.
    Keywords: STRUCTURAL MECHANICS
    Type: Structural Dynamics and Control Interaction of Flexible Structures; p 669-690
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  • 42
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    Dynamic characteristics of a vibrating beam with periodic variation in bending stiffness (1987)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: A detailed dynamic analysis is performed of a vibrating beam with bending stiffness periodic in the spatial coordinate. Using a perturbation expansion technique the free vibration solution is obtained in a closed-form, and the effects of system parameters on beam response are explored. It is found that periodic stiffness acts to modulate the modal displacements from the characteristic shape of a simple sine wave. The results are verified by a finite element solution and through experimental testing.
    Keywords: STRUCTURAL MECHANICS
    Type: Structural Dynamics and Control Interaction of Flexible Structures; p 595-624
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  • 43
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    Structural dynamics system model reduction (1987)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: Loads analysis for structural dynamic systems is usually performed by finite element models. Because of the complexity of the structural system, the model contains large number of degree-of-freedom. The large model is necessary since details of the stress, loads and responses due to mission environments are computed. However, a simplified model is needed for other tasks such as pre-test analysis for modal testing, and control-structural interaction studies. A systematic method of model reduction for modal test analysis is presented. Perhaps it will be of some help in developing a simplified model for the control studies.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Marshall Space Flight Center Structural Dynamics and Control Interaction of Flexible Structures; p 625-668
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  • 44
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    Equivalent beam modeling using numerical reduction techniques (1987)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: Numerical procedures that can accomplish model reductions for space trusses were developed. Three techniques are presented that can be implemented using current capabilities within NASTRAN. The proposed techniques accomplish their model reductions numerically through use of NASTRAN structural analyses and as such are termed numerical in contrast to the previously developed analytical techniques. Numerical procedures are developed that permit reductions of large truss models containing full modeling detail of the truss and its joints. Three techniques are presented that accomplish these model reductions with various levels of structural accuracy. These numerical techniques are designated as equivalent beam, truss element reduction, and post-assembly reduction methods. These techniques are discussed in detail.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Marshall Space Flight Center Structural Dynamics and Control Interaction of Flexible Structures; p 567-594
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  • 45
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    Dynamics of trusses having nonlinear joints (1987)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: The transient analysis of trusses having nonlinear joints can be accomplished using the residual force technique. The technique was applied a two degree of freedom spring mass system, a four bay planar truss, and an actual ten bay deployable truss. Joints chosen for analysis were the nonlinear gap joints and the linear Voigt joints. Results from the nonlinear gap analyses generally indicate that coupling between the modes can display some interesting effects during free vibration. One particularly interesting effect was that the damping of the structure appeared to be higher than could be accounted for from modal damping alone. Energy transferral from the lower to the higher modes was found to exist as a result of the modal coupling. The apparently increased damping was due to the fact that the energy transferred to the higher modes is inherently dissipated more quickly. Another interesting phenomenon was that the lower modes could drive the higher modes even during free vibration and that these modes could display a rather large quasi-steady state behavior even when modal damping was present. Gaps were also found to increase the amplitude and period of the free vibration response as expected.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Marshall Space Flight Center Structural Dynamics and Control Interaction of Flexible Structures; p 539-566
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  • 46
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    An overview of controls research on the NASA Langley Research Center grid (1987)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: The NASA Langley Research Center has assembled a flexible grid on which control systems research can be accomplished on a two-dimensional structure that has many physically distributed sensors and actuators. The grid is a rectangular planar structure that is suspended by two cables attached to one edge so that out of plane vibrations are normal to gravity. There are six torque wheel actuators mounted to it so that torque is produced in the grid plane. Also, there are six rate gyros mounted to sense angular motion in the grid plane and eight accelerometers that measure linear acceleration normal to the grid plane. All components can be relocated to meet specific control system test requirements. Digital, analog, and hybrid control systems capability is provided in the apparatus. To date, research on this grid has been conducted in the areas of system and parameter identification, model estimation, distributed modal control, hierarchical adaptive control, and advanced redundancy management algorithms. The presentation overviews each technique and presents the most significant results generated for each area.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Marshall Space Flight Center Structural Dynamics and Control Interaction of Flexible Structures; p 435-456
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  • 47
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    Structural response of an advanced combustor liner: Test and analysis (1987)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: An advanced (segmented) combustor liner supplied by Pratt and Whitney Aircraft was tested in the structural component test rig at Lewis Research Center. It was found that the segmented liner operated at much lower temperatures than the conventional liner (about 400 F lower) for the same heat flux. At the lower temperatures and low thermal gradients, little distortion to the segments was observed. The operating conditions were not severe enough to distort or damage the segmented liner.
    Keywords: STRUCTURAL MECHANICS
    Type: Turbine Engine Hot Section Technology, 1987; p 349-356
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  • 48
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    Preliminary study of creep thresholds and thermomechanical response in Haynes 188 at temperatures in the range 649 to 871 C (1987)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The following conclusions were drawn from this study of creep thresholds and thermomechanical response: (1) creep threshold can be determined using the latest electrohydraulic test equipment, providing that test durations are short and relatively large accumulations of creep strain are used in defining the threshold; (2) significant creep strains were measured under monotonic loading as stress levels as low as 4 ksi at temperatures predicted for solar receiver service; and (3) the material exhibited creep ratchetting during simulated service cycles, a result not predicted by analysis using current constitutive models for Haynes 188.
    Keywords: STRUCTURAL MECHANICS
    Type: Turbine Engine Hot Section Technology, 1987; p 317-334
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  • 49
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    Use of inelastic strain as a basis for analyzing thermomechanical test data (1987)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: It was shown that the proposed data analysis method, based on inelastic strain-time response, can be used effectively to represent cyclic response at elevated temperatures for Hastelloy-X. A high level of confidence in this method was built by making comparisons of the experimental and fitted data in two forms. Because of this level of confidence, the analysis was taken one step further and inelastic strain rates were calculated from the derivatives of the fit equations.
    Keywords: STRUCTURAL MECHANICS
    Type: Turbine Engine Hot Section Technology, 1987; p 303-315
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  • 50
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    A continuum deformation theory for metal-matrix composites at high temperature (1987)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: A continuum theory is presented for representing the high temperature, time dependent, hereditary deformation behavior of metallic composites that can be idealized as pseudohomogeneous continua with locally definable directional characteristics. Homogenization of textured materials (molecular, granular, fibrous) and applicability of continuum mechanics in structural applications depends on characteristic body dimensions, the severity of gradients (stress, temperature, etc.) in the structure and the relative size of the internal structure (cell size) of the material. The point of view taken here is that the composite is a material in its own right, with its own properties that can be measured and specified for the composite as a whole.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA, Lewis Research Center, Turbine Engine Hot Section Technology, 1987; p 281-287
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    Constitutive modeling for isotropic materials (1987)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: The fourth and final year of the HOST project with the initial objective of developing a unified constitutive model for finite element structural analysis of turbine engine hot section components is discussed. The final year's work was primarily concerned with the study of nonisothermal problems and the potential for thermal history effects to occur explicitly in the constitutive equations.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA, Lewis Research Center, Turbine Engine Hot Section Technology, 1987; p 273-279
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  • 52
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    Total strain version of strainrange partitioning for thermomechanical fatigue at low strains (1987)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: A new method is proposed for characterizing and predicting the thermal fatigue behavior of materials. The method is based on three innovations in characterizing high temperature material behavior: (1) the bithermal concept of fatigue testing; (2) advanced, nonlinear, cyclic constitutive models; and (3) the total strain version of traditional strainrange partitioning.
    Keywords: STRUCTURAL MECHANICS
    Type: Turbine Engine Hot Section Technology, 1987; p 435-458
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  • 53
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    Thermal barrier coating life prediction model (1987)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: The objectives of this research were to determine the predominant modes of degradation of a plasma sprayed thermal barrier coating (TBC) system, and then to develop and verify life prediction models accounting for these degradation modes. The TBC system consists of a low pressure plasma sprayed (LPPS) bond coat layer of Ni-22Cr-10Al-O.3Y, an air plasma sprayed (APS) yttria partially stabilized zirconia (ZrO sub 2-8Y sub 2 O sub 3) top coat on a conventionally cast Rene 80 (Ni base) substrate. Thermal cycle testing of TBCs was employed to evaluate the effect of coating edges, bond coat oxidation, bond coat creep, top coat thickness, and bond coat thickness.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA, Lewis Research Center, Turbine Engine Hot Section Technology, 1987; p 377-393
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    Thermal expansion mismatch and plasticity in thermal barrier coating (1987)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: The basic objective of this investigation is the quantitative determination of stress states in a model thermal barrier coating (TBC) as it cools in the air to 600 C from an assumed stress-free state at 700 C. This model is intended to represent a thin plasma-sprayed zirconia-yttria ceramic layer with a nickel chromium-aluminum-yttrium bond coat on a cylindrical substrate made of nickel-based superalloys typically found in gas turbines.
    Keywords: STRUCTURAL MECHANICS
    Type: Turbine Engine Hot Section Technology, 1987; p 357-368
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  • 55
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    Finite element implementation of viscoplastic models (1987)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: A brief description of the implementation in MARK, the general purpose finite element structural analysis code, of two viscoplastic models developed by Robinson is given. One model is for isotropic materials and the other is for metal matrix composites. Also presented are analytical results obtained for hot section components using these models.
    Keywords: STRUCTURAL MECHANICS
    Type: Turbine Engine Hot Section Technology, 1987; p 335-348
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  • 56
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    Component specific modeling (1987)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: The objective was to develop and verify a series of interdisciplinary modeling and analysis techniques specialized to address hot section components. These techniques incorporate data as well as theoretical methods from many diverse areas, including cycle and performance analysis, heat transfer analysis, linear and nonlinear stress analysis, and mission analysis.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA, Lewis Research Center, Turbine Engine Hot Section Technology, 1987; p 259-265
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  • 57
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    Response characteristics of MHOST (MARC Hot-Section Technology) for 3-D inelastic analysis of hot-section components (1987)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The advantages of a newly developed code are demonstrated by comparisons of the analysis with existing theoretical data as well as with other available finite element programs. The new program shows promise to significantly reduce the computer time. It also permits accurate and efficient structural analysis of engine hot section components.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA, Lewis Research Center, Turbine Engine Hot Section Technology, 1987; p 249-254
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  • 58
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    Mechanics of materials model (1987)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: The Mechanics of Materials Model (MOMM) is a three-dimensional inelastic structural analysis code for use as an early design stage tool for hot section components. MOMM is a stiffness method finite element code that uses a network of beams to characterize component behavior. The MOMM contains three material models to account for inelastic material behavior. These include the simplified material model, which assumes a bilinear stress-strain response; the state-of-the-art model, which utilizes the classical elastic-plastic-creep strain decomposition; and Walker's viscoplastic model, which accounts for the interaction between creep and plasticity that occurs under cyclic loading conditions.
    Keywords: STRUCTURAL MECHANICS
    Type: Turbine Engine Hot Section Technology, 1987; p 255-257
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  • 59
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    Shape optimization of damping layers (1987)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: Shape optimization of unconstrained and constrained damping layers is completed. The specific problem analyzed is a cantilever beam loaded at its tip by a harmonic force. Finite element modeling and mathematical programming techniques are used to obtain the solution. Performance measures are taken to be reduction of maximum diplacement and increase in fatigue lifetime. Results include the improvement, over the uniform treatment case, of these measures when the profile of the damping layer is optimized.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-Marshall Space Flight Center, The 58th Shock and Vibration Symposium, Volume; p 395-409
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  • 60
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    Optimal shock isolation with minimum settling time (1987)
    In:  CASI
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    Description: It is shown how unique isolator forces and corresponding forces can be chosen by superimposing a minimum settling time onto the limiting performance of the shock isolation system. Basically, this means that the system which has reached the peak value of the performance index is settled to rest in minimum time.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-Marshall Space Flight Center, The 58th Shock and Vibration Symposium, Volume 1; p 379-388
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  • 61
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    Structural frequency functions for an impulsive, distributed forcing function (1987)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: The response of a penetrator structure to a spatially distributed mechanical impulse with a magnitude approaching field test force levels (1-2 Mlb) were measured. The frequency response function calculated from the response to this unique forcing function is compared to frequency response functions calculated from response to point forces of about 2000 pounds. The results show that the strain gages installed on the penetrator case respond similiarly to a point, axial force and to a spatially distributed, axial force. This result suggests that the distributed axial force generated in a penetration event may be reconstructed as a point axial force when the penetrator behaves in linear manner.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-Marshall Space Flight Center, The 58th Shock and Vibration Symposium, Volume 1; p 291-319
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  • 62
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    Advanced joining concepts for passive vibration control (1987)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: A comprehensive parametric study was carried out to establish design guidelines for favorable tradeoffs between damping benefits and the associated stiffness, strength and weight penalties in a rhombic joint. The results are compared with the corresponding tradeoffs for a double-lap joint made of the same materials.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-Marshall Space Flight Center, The 58th Shock and Vibration Symposium, Volume 1; p 459-471
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    A passive vibration-cancelling isolation mount (1987)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: An analysis of an idealized passive vibration-cancelling two-terminal mount with one degree of freedom at each mechanical terminal isolating a nonrigid machine from a nonrigid foundation is presented. To evaluate a vibration-cancelling (VC) mount, its effectiveness as a function of frequency is compared with the effectiveness of both conventional and compound mounts isolating a rigid machine from a nonrigid foundation. The comparisons indicate that a carefully designed and manufactured VC mount should provide substantially greater vibration reduction at its cancellation frequency than either a conventional or compound mount having the same low frequency stiffness, i.e., stiffness at the natural frequency of the machine mount system.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-Marshall Space Flight Center, The 58th Shock and Vibration Symposium, Volume 1; p 411-439
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    Exact finite element method analysis of viscoelastic tapered structures to transient loads (1987)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: A general method is presented for determining the dynamic torsional/axial response of linear structures composed of either tapered bars or shafts to transient excitations. The method consists of formulating and solving the dynamic problem in the Laplace transform domain by the finite element method and obtaining the response by a numerical inversion of the transformed solution. The derivation of the torsional and axial stiffness matrices is based on the exact solution of the transformed governing equation of motion, and it consequently leads to the exact solution of the problem. The solution permits treatment of the most practical cases of linear tapered bars and shafts, and employs modeling of structures with only one element per member which reduces the number of degrees of freedom involved. The effects of external viscous or internal viscoelastic damping are also taken into account.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-Marshall Space Flight Center, The 58th Shock and Vibration Symposium, Volume 1; p 361-375
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    Verification of large beam-type space structures (1987)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The verification approach of large beam type space structures is verified. The proposed verification approach consists of two parts. The first part is to remove the gravity effect on the tested substructure and to identify the on-orbit dynamic characteristics of the substructure by using the measurements of the ground test. A scaling law is also established to define the critical length of the structure which can be tested in 1-g field without incurring a buckling problem. The second part is to develop an adequate scaling law to extrapolate the dynamic characteristics of the prototype structure by using results from the substructure. The verification approaches are demonstrated on two typical structural configurations, the feed support structure of a wrap-rip antenna and a candidate shuttle flight experiment. The results indicate that it is practical to verify the on-orbit dynamic characteristics of these structures by using the proposed approach.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Marshall Space Flight Center Structural Dynamics and Control Interaction of Flexible Structures; p 247-254
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    NESSUS/expert and NESSUS/FPI in the Probabilistic Structural Analysis Methods (PSAM) program (1987)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The Numerical Evaluation of Stochastic Structures under Stress (NESSUS) is the primary computer code being developed in the NASA Probabilistic Structural Analysis Methods (PSAM) project. It consists of four modules NESSUS/EXPERT, NESSUS/FPI, NESSUS/PRE and NESSUS/FEM. This presentation concentrates on EXPERT and FPI. To provide an effective interface between NESSUS and the user, an expert system module called NESSUS/EXPERT is being developed. That system uses the CLIPS artificial intelligence code developed to NASA-JSC. The code is compatible with FORTRAN, the standard language for codes in PSAM. The user interacts with the CLIPS inference engine, which is linked to the knowledge database. The perturbation database generated by NESSUS/FEM and managed in EXPERT is used to develop the so-called response or performance model in the random variables. Two independent probabilistic methods are available in PSAM for the computation of the probabilistic structural response. These are the Fast Probability Integration (FPI) method and Monte Carlo simulation. FPI is classified as an advanced reliability method and has been developed over the past ten years by researchers addressing the reliability of civil engineering structures. Monte Carlo is a well-established technique for computing probabilities by conducting a number of deterministic analyses with specified input distributional information.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Lewis Research Center Structural Integrity and Durability of Reusable Space Propulsion Systems; p 139-143
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    Nonlinear heat transfer and structural analyses of SSME turbine blades (1987)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Three-dimensional nonlinear finite-element heat transfer and structural analyses were performed for the first stage high-pressure fuel turbopump blade of the space shuttle main engine (SSME). Directionally solidified (DS) MAR-M 246 material properties were considered for the analyses. Analytical conditions were based on a typical test stand engine cycle. Blade temperature and stress-strain histories were calculated using MARC finite-element computer code. The study was undertaken to assess the structural response of an SSME turbine blade and to gain greater understanding of blade damage mechanisms, convective cooling effects, and the thermal-mechanical effects.
    Keywords: STRUCTURAL MECHANICS
    Type: Structural Integrity and Durability of Reusable Space Propulsion Systems; p 95-104
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    Experimental characterization of deployable trusses and joints (1987)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: The structural dynamic properties of trusses are strongly affected by the characteristics of joints connecting the individual beam elements. Joints are particularly significant in that they are often the source of nonlinearities and energy dissipation. While the joints themselves may be physically simple, direct measurement is often necessary to obtain a mathematical description suitable for inclusion in a system model. Force state mapping is a flexible, practical test method for obtaining such a description, particularly when significant nonlinear effects are present. It involves measurement of the relationship, nonlinear or linear, between force transmitted through a joint and the relative displacement and velocity across it. An apparatus and procedure for force state mapping are described. Results are presented from tests of joints used in a lightweight, composite, deployable truss built by the Boeing Aerospace Company. The results from the joint tests are used to develop a model of a full 4-bay truss segment. The truss segment was statically and dynamically tested. The results of the truss tests are presented and compared with the analytical predictions from the model.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Marshall Space Flight Center Structural Dynamics and Control Interaction of Flexible Structures; p 1271-1288
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    On the control of structures by applied thermal gradients (1987)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: Some preliminary results of research on control of flexible structures performed at the Jet Propulsion Laboratory are presented. It was shown that the thermoelectric device is a feasible actuator and may effectively be used to control structures, provided the structure has a relatively low thermal inertia. The control law only depends on the open-loop system natural frequency.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Marshall Space Flight Center Structural Dynamics and Control Interaction of Flexible Structures; p 1214-1250
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    Finite element models of wire rope for vibration analysis (1987)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: The usefulness of wire rope in shock and vibration isolation is briefly reviewed and its modeling for the purpose of vibration analysis is addressed. A model of a nominally straight segment of wire rope is described in which the rope structure is represented by a maiden, or central, strand of wire with one (or more) strand(s) wrapped around it in a helix (helices). The individual strands are modeled using finite elements and MSC NASTRAN. Small linear segments of each wire are modeled mathematically by dividing them lengthwise into triangular prisms representing each prism by a solid NASTRAN element. To model pretensioning and allow for extraction of internal force information from the NASTRAN model, the wound strands are connected to the maiden strand and each other using spring (scalar elastic) elements. Mode shapes for a length of wire rope with one and fixed to a moving base and the other attached to a point mass, are presented. The use of the NASTRAN derived mode shapes to approximate internal normal forces in equations of motion for vibration analyses is considered.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Marshall Space Flight Center Structural Dynamics and Control Interaction of Flexible Structures; p 1251-1270
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    Notes on implementation of Coulomb friction in coupled dynamical simulations (1987)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: A coupled dynamical system is defined as an assembly of rigid/flexible bodies that may be coupled by kinematic connections. The interfaces between bodies are modeled using hinges having 0 to 6 degrees of freedom. The equations of motion are presented for a mechanical system of n flexible bodies in a topological tree configuration. The Lagrange form of the D'Alembert principle was employed to derive the equations. The equations of motion are augmented by the kinematic constraint equations. This augmentation is accomplished via the method of singular value decomposition.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Marshall Space Flight Center Structural Dynamics and Control Interaction of Flexible Structures; p 1197-1213
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    Creep and fatigue research efforts on advanced materials (1987)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: Two of the more important materials problems encountered in turbine blades of aircraft engines are creep and fatigue. To withstand these high-temperature phenomena modern engines utilize single-crystal, nickel-based superalloys as the material of choice in critical applications. Recent research activities at Lewis on single-crystal blading material as well as future research initiatives on metal matrix composites related to creep and fatigue are discussed. The goal of these research efforts is improving the understanding of microstructure-property relationships and thereby guide material development.
    Keywords: STRUCTURAL MECHANICS
    Type: Aeropropulsion '87. Session 1: Aeropropulsion Materials Research; 18 p
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    Evaluate the application of modal test and analysis processes to structural fault detection in MSFC - STS project elements (1987)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The Space Transportation System (STS) is a complex and expensive flight system intended to carry unique payloads into low Earth orbit and return. A catastrophic failure, such as STS 51-L, resulted in the loss of both human life as well as expensive and unique hardware. The impact of this incident reaffirms the need to do everything possible to ensure the integrity and reliability of STS. One means of achieving this goal is to expand the number of inspection technologies available. Reported here is the evaluation of the use of modal analysis and test techniques for the purpose of assessing the structural integrity of STS components for which Marshall Space Flight Center has responsibility. This entailed reviewing existing literature and developing a low-level experimental program determine the feasibility of using this technology for structural fault detection.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Marshall Space Flight Center, Research Reports: 1987 NASA(ASEE Summer Faculty Fellowship Program; 25 p
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    An investigation of oblique hypervelocity impact (1987)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: This report describes the results of an investigation of phenomena associated with the oblique hypervelocity impact of spherical projectiles on multi-sheet aluminum structures. A model to be employed in the design of meteoroid and space debris protection systems for space structures is developed. The model consists of equations relating crater and perforation damage of a multi-sheet structure to parameters such as projectile size, impact velocity, and trajectory obliquity. The equations are obtained through a regression analysis of oblique hypervelocity impact test data. This data shows that the response of a multi-sheet structure to oblique impact is significantly different from its response to normal hypervelocity impact. It was found that obliquely incident projectiles produce ricochet debris that can severely damage panels or instrumentation located on the exterior of a space structure. Obliquity effects of high-speed impact must, therefore, be considered in the design of any structure exposed to the hazardous meteoroid and space debris environment.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Marshall Space Flight Center, Research Reports: 1987 NASA(ASEE Summer Faculty Fellowship Program; 30 p
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    Verification of FANTASTIC integrated code (1987)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: FANTASTIC is an acronym for Failure Analysis Nonlinear Thermal and Structural Integrated Code. This program was developed by Failure Analysis Associates, Palo Alto, Calif., for MSFC to improve the accuracy of solid rocket motor nozzle analysis. FANTASTIC has three modules: FACT - thermochemical analysis; FAHT - heat transfer analysis; and FAST - structural analysis. All modules have keywords for data input. Work is in progress for the verification of the FAHT module, which is done by using data for various problems with known solutions as inputs to the FAHT module. The information obtained is used to identify problem areas of the code and passed on to the developer for debugging purposes. Failure Analysis Associates have revised the first version of the FANTASTIC code and a new improved version has been released to the Thermal Systems Branch.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Marshall Space Flight Center, Research Reports: 1987 NASA(ASEE Summer Faculty Fellowship Program; 13 p
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    Passive isolation/damping system for the Hubble space telescope reaction wheels (1987)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: NASA's Hubble Space Telescope contain large, diffraction limited optics with extraordinary resolution and performance for surpassing existing observatories. The need to reduce structural borne vibration and resultant optical jitter from critical Pointing Control System components, Reaction Wheels, prompted the feasibility investigation and eventual development of a passive isolation system. Alternative design concepts considered were required to meet a host of stringent specifications and pass rigid tests to be successfully verified and integrated into the already built flight vehicle. The final design employs multiple arrays of fluid damped springs that attenuate over a wide spectrum, while confining newly introduced resonances to benign regions of vehicle dynamic response. Overall jitter improvement of roughly a factor of 2 to 3 is attained with this system. The basis, evolution, and performance of the isolation system, specifically discussing design concepts considered, optimization studies, development lessons learned, innovative features, and analytical and ground test verified results are presented.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-Lyndon B. Johnson Space Center, The 21st Aerospace Mechanisms Symposium; p 211-226
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    Dynamic characteristics of single crystal SSME blades (1987)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The Space Shuttle Main Engine (SSME) High Pressure Fuel Turbopump (HPFTP) blades are currently manufactured using a directionally solidified (DS) material, MAR-M-246+Hf. However, a necessity to reduce the occurrence of fatigue cracking within the DS blades has lead to an interest in the use of a single crystal (SC) material, PWA-1480. A study was initiated to determine the dynamic characteristics of the HPFTP blades made of SC material and find possible critical engine order excitations. This study examined both the first and second stage drive turbine blades of the HPFTP. The dynamic characterization was done analytically as well as experimentally. The analytical study examined the SC first stage HPFTP blade dynamic characteristics under typical operating conditions. The blades were analyzed using MSC/NASTRAN and a finite element model. Two operating conditions, 27500 RPM and 35000 RPM, were investigated.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Lewis Research Center Structural Integrity and Durability of Reusable Space Propulsion Systems; p 211-214
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    Stochastic and hybrid-stress plate/shell finite elements for hot-section components (1987)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The research effort in the Center for the Advancement of Computational Mechanics at Georgia Tech has two main thrusts. The first of these is the development of special approaches for the numerical stress analysis of solids and structures whose material and geometric properties are uncertain. The second seeks to develop and implement high-efficiency plate and shell elements. The stochastic element method, currently being implemented, will be able to more accurately portray the probabilistic nature of stress, strain, and displacement in actual structures. Current research has provided a hybrid-stress shell element whose behavior is acceptable for aspect ratios as high as 30 to 1. Thus, substantially more complex analyses will be practicable as soon as this element is fully implemented. An additional advantage of the hybrid approach is that it permits more accurate stress-recovery at the upper and lower surfaces of the shell, an important consideration in high thickness-gradient applications. The software associated with the above research is being implemented in the form of extensions to the Nessus code. The hybrid shell element has been successfully tested in several small-deformation elastic analyses. The theoretical formulation of the stochastic elements is essentially complete; its implementation is just beginning.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Lewis Research Center Structural Integrity and Durability of Reusable Space Propulsion Systems; p 151-152
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    Probabilistic structural analysis verification studies (1987)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: The basic objective of this verification effort is to apply probabilistic structural analysis methods developed and implemented in the Numerical Evaluation of Stochastic Structures Under Stress (NESSUS) code to typical space propulsion components. The chosen typical components are turbine blade, high pressure duct, Lox post, and transfer tube liners. Since analysis options of increasing levels of sophistication are implemented in NESSUS incrementally, the verification efforts are also tailored to have increasing levels of sophistication during the progression of the contract. The current released version of the code is limited to linear structural analysis.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Lewis Research Center Structural Integrity and Durability of Reusable Space Propulsion Systems; p 133-137
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    Sensitivity analysis for large-scale problems (1987)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: The development of efficient techniques for calculating sensitivity derivatives is studied. The objective is to present a computational procedure for calculating sensitivity derivatives as part of performing structural reanalysis for large-scale problems. The scope is limited to framed type structures. Both linear static analysis and free-vibration eigenvalue problems are considered.
    Keywords: STRUCTURAL MECHANICS
    Type: Sensitivity Analysis in Engineering; p 357-374
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    Accuracy of the domain method for the material derivative approach to shape design sensitivities (1987)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: Numerical accuracy for the boundary and domain methods of the material derivative approach to shape design sensitivities is investigated through the use of mesh refinement. The results show that the domain method is generally more accurate than the boundary method, using the finite element technique. It is also shown that the domain method is equivalent, under certain assumptions, to the implicit differentiation approach not only theoretically but also numerically.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center Sensitivity Analysis in Engineering; p 347-356
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    Application of design sensitivity analysis for greater improvement on machine structural dynamics (1987)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: Methodologies are presented for greatly improving machine structural dynamics by using design sensitivity analyses and evaluative parameters. First, design sensitivity coefficients and evaluative parameters of structural dynamics are described. Next, the relations between the design sensitivity coefficients and the evaluative parameters are clarified. Then, design improvement procedures of structural dynamics are proposed for the following three cases: (1) addition of elastic structural members, (2) addition of mass elements, and (3) substantial charges of joint design variables. Cases (1) and (2) correspond to the changes of the initial framework or configuration, and (3) corresponds to the alteration of poor initial design variables. Finally, numerical examples are given for demonstrating the availability of the methods proposed.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Reserach Center Sensitivity Analysis in Engineering; p 285-298
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    Design sensitivity analysis of rotorcraft airframe structures for vibration reduction (1987)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Optimization of rotorcraft structures for vibration reduction was studied. The objective of this study is to develop practical computational procedures for structural optimization of airframes subject to steady-state vibration response constraints. One of the key elements of any such computational procedure is design sensitivity analysis. A method for design sensitivity analysis of airframes under vibration response constraints is presented. The mathematical formulation of the method and its implementation as a new solution sequence in MSC/NASTRAN are described. The results of the application of the method to a simple finite element stick model of the AH-1G helicopter airframe are presented and discussed. Selection of design variables that are most likely to bring about changes in the response at specified locations in the airframe is based on consideration of forced response strain energy. Sensitivity coefficients are determined for the selected design variable set. Constraints on the natural frequencies are also included in addition to the constraints on the steady-state response. Sensitivity coefficients for these constraints are determined. Results of the analysis and insights gained in applying the method to the airframe model are discussed. The general nature of future work to be conducted is described.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center Sensitivity Analysis in Engineering; p 299-318
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    Application of a system modification technique to dynamic tuning of a spinning rotor blade (1987)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: An important consideration in the development of modern helicopters is the vibratory response of the main rotor blade. One way to minimize vibration levels is to ensure that natural frequencies of the spinning main rotor blade are well removed from integer multiples of the rotor speed. A technique for dynamically tuning a finite-element model of a rotor blade to accomplish that end is demonstrated. A brief overview is given of the general purpose finite element system known as Engineering Analysis Language (EAL) which was used in this work. A description of the EAL System Modification (SM) processor is then given along with an explanation of special algorithms developed to be used in conjunction with SM. Finally, this technique is demonstrated by dynamically tuning a model of an advanced composite rotor blade.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center Sensitivity Analysis in Engineering; p 247-261
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    On computing eigensolution sensitivity data using free vibration solutions (1987)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: A simplified method of computing eigensolution sensitivity derivatives in structural dynamics is developed. It is shown that if the elements of stiffness and mass matrices associated with a design variable are homogeneous functions of that design variable, then eigenvalue derivatives can be computed from element strain and kinetic energies. Furthermore, if cross-mode energies are known, eigensolution derivatives of modified systems can be computed approximately using assume mode reanalysis formulation. A ten bar truss example is used to illustrate the present formulations.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center Sensitivity Analysis in Engineering; p 233-245
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    Modal sensitivity for structural systems with repeated frequencies (1987)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: Repeated or closely packed modal frequencies are common physical occurrences for vibrating structures which are complex or possess multi-planes of symmetry. The computation of the sensitivity to structural modifications for these frequencies and mode shapes is made difficult by the fact that the mode shapes are not unique, since any linear combination of eigenvectors corresponding to a repeated eigenvalue is also an eigenvector. The work of Chen and Pan is extended, who used modal expansion techniques for accommodating the sensitivity analysis of structures with repeated eigenvalues. Starting with a discussion of the physical significance of sensitivity analysis for repeated frequency modes, a derivation is presented of the governing equations for the derivatives of a repeated eigenvalue. This is followed with a small example to illustrate the results. An efficient computation procedure, based upon an expansion of Nelson's ideas for large banded systems, is then proposed for systems with repeated or closely spaced eigenvalues.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center Sensitivity Analysis in Engineering; p 197-213
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    Sensitivity derivatives and optimization of nodal point locations for vibration reduction (1987)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: A method is developed for sensitivity analysis and optimization of nodal point locations in connection with vibration reduction. A straightforward derivation of the expression for the derivative of nodal locations is given, and the role of the derivative in assessing design trends is demonstrated. An optimization process is developed which uses added lumped masses on the structure as design variables to move the node to a preselected location; for example, where low response amplitude is required or to a point which makes the mode shape nearly orthogonal to the force distribution, thereby minimizing the generalized force. The optimization formulation leads to values for added masses that adjust a nodal location while minimizing the total amount of added mass required to do so. As an example, the node of the second mode of a cantilever box beam is relocated to coincide with the centroid of a prescribed force distribution, thereby reducing the generalized force substantially without adding excessive mass. A comparison with an optimization formulation that directly minimizes the generalized force indicates that nodal placement gives essentially a minimum generalized force when the node is appropriately placed.
    Keywords: STRUCTURAL MECHANICS
    Type: Sensitivity Analysis in Engineering; p 215-231
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    Optimal control concepts in design sensitivity analysis (1987)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: A close link is established between open loop optimal control theory and optimal design by noting certain similarities in the gradient calculations. The resulting benefits include a unified approach, together with physical insights in design sensitivity analysis, and an efficient approach for simultaneous optimal control and design. Both matrix displacement and matrix force methods are considered, and results are presented for dynamic systems, structures, and elasticity problems.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center Sensitivity Analysis in Engineering; p 133-145
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    Design sensitivity analysis of nonlinear structural response (1987)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: A unified theory is described of design sensitivity analysis of linear and nonlinear structures for shape, nonshape and material selection problems. The concepts of reference volume and adjoint structure are used to develop the unified viewpoint. A general formula for design sensitivity analysis is derived. Simple analytical linear and nonlinear examples are used to interpret various terms of the formula and demonstrate its use.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center Sensitivity Analysis in Engineering; p 113-132
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    Sensitivity and optimization of composite structures using MSC/NASTRAN (1987)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: Design sensitivity analysis for composites will soon be available in MSC/NASTRAN. The design variables for composites can be lamina thicknesses, orientation angles, material properties or a combination of all three. With the increasing use of composites in aerospace and automotive industries, this general capability can be used in its own right for carrying out sensitivity analysis of complicated real-life structures. As part of a research effort, the sensitivity analysis was coupled with a general purpose optimizer. This preliminary version of the optimizer is capable of dealing with minimum weight structural design with a rather general design variable linking capability at the element level or system level. Only sizing type of design variables (i.e., lamina thicknesses) can be handled by the optimizer. Test cases were run and validated by comparison with independent finite element packages. The linking of design sensitivity capability for composites in MSC/NASTRAN with an optimizer would give designers a powerful automated tool to carry out practical opitmization design of real-life complicated composite structures.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center Sensitivity Analysis in Engineering; p 147-166
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    Sensitivity of overall vehicle stiffness to local joint stiffness (1987)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: How overall vehicle stiffness is affected by local joint stiffness is discussed. By using the principle of virtual work and the minimum strain energy theorem, a closed form expression for the sensitivity coefficient was derived. The insensitivity of the vehicle stiffness to a particular joint, when its stiffness exceeds a certain value (or threshold value), was proven mathematically. In order to investigate the sensitivity of the structure to the joint stiffness, a so-called stick model was created, and the modeling technique is briefly described. Some data on joint stiffness of tested vehicles are also presented.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center Sensitivity Analysis in Engineering; p 97-112
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    Sensitivity method for integrated structure/active control law design (1987)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The development is described of an integrated structure/active control law design methodology for aeroelastic aircraft applications. A short motivating introduction to aeroservoelasticity is given along with the need for integrated structures/controls design algorithms. Three alternative approaches to development of an integrated design method are briefly discussed with regards to complexity, coordination and tradeoff strategies, and the nature of the resulting solutions. This leads to the formulation of the proposed approach which is based on the concepts of sensitivity of optimum solutions and multi-level decompositions. The concept of sensitivity of optimum is explained in more detail and compared with traditional sensitivity concepts of classical control theory. The analytical sensitivity expressions for the solution of the linear, quadratic cost, Gaussian (LQG) control problem are summarized in terms of the linear regulator solution and the Kalman Filter solution. Numerical results for a state space aeroelastic model of the DAST ARW-II vehicle are given, showing the changes in aircraft responses to variations of a structural parameter, in this case first wing bending natural frequency.
    Keywords: STRUCTURAL MECHANICS
    Type: Sensitivity Analysis in Engineering; p 59-75
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  • 93
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    Behavior sensitivities for control augmented structures (1987)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: During the past few years it has been recognized that combining passive structural design methods with active control techniques offers the prospect of being able to find substantially improved designs. These developments have stimulated interest in augmenting structural synthesis by adding active control system design variables to those usually considered in structural optimization. An essential step in extending the approximation concepts approach to control augmented structural synthesis is the development of a behavior sensitivity analysis capability for determining rates of change of dynamic response quantities with respect to changes in structural and control system design variables. Behavior sensitivity information is also useful for man-machine interactive design as well as in the context of system identification studies. Behavior sensitivity formulations for both steady state and transient response are presented and the quality of the resulting derivative information is evaluated.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center Sensitivity Analysis in Engineering; p 33-57
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  • 94
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    Preconditioned conjugate gradient technique for the analysis of symmetric anisotropic structures (1987)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: An efficient preconditioned conjugate gradient (PCG) technique and a computational procedure are presented for the analysis of symmetric anisotropic structures. The technique is based on selecting the preconditioning matrix as the orthotropic part of the global stiffness matrix of the structure, with all the nonorthotropic terms set equal to zero. This particular choice of the preconditioning matrix results in reducing the size of the analysis model of the anisotropic structure to that of the corresponding orthotropic structure. The similarities between the proposed PCG technique and a reduction technique previously presented by the authors are identified and exploited to generate from the PCG technique direct measures for the sensitivity of the different response quantities to the nonorthotropic (anisotropic) material coefficients of the structure. The effectiveness of the PCG technique is demonstrated by means of a numerical example of an anisotropic cylindrical panel.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal for Numerical Methods in Engineering (ISSN 0029-5981); 24; 2057-207
    Format: text
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  • 95
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    Viscoelastic/damage modeling of filament-wound spherical pressure vessels (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A model of the viscoelastic/damage response of a filament-wound spherical vessel used for long-term pressure containment is developed. The matrix material of the composite system is assumed to be linearly viscoelastic. Internal accumulated damage based upon a quadratic relationship between transverse modulus and maximum circumferential strain is postulated. The resulting nonlinear problem is solved by an iterative routine. The elastic-viscoelastic correspondence is employed to produce, in the Laplace domain, the associated elastic solution for the maximum circumferential strain which is inverted by the method of collocation to yield the time-dependent solution. Results obtained with the model are compared to experimental observations.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Reinforced Plastics and Composites (ISSN 0731-6844); 6; 126-137
    Format: text
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  • 96
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    Structural sizing by generalized, multilevel optimization (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA Journal (ISSN 0001-1452); 25; 139-145
    Format: text
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  • 97
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    Fatigue Criterion to System Design, Life, and Reliability (1987)
    In:  Other Sources
    Details
    Publication Date: 2013-06-04
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Propulsion and Power (ISSN 0748-4658); 3; 76-83
    Format: text
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  • 98
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    Fracture study of windshield glass panes (1987)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The major stresses which cause crack propagation in windshield glass panes are induced by bending moments which result from the pressure differentials across the panes. Hence the stress intensity factors for the finite plate with the semi-elliptical surface flaw and edge crack under the bending moments are examined. The results show that the crack growth will be upperbound if it is computed by using the stress intensity factor for the finite plate with the edge crack subjected to pure bending moments. Furthermore, if the ratio of crack depth to plate thickness, a/t, is within 0.3, the stress intensity factor can be conservatively assumed to be constant at the value of a/t equal to zero. A simplified equation to predict the structural life of glass panes is derived based on constant stress intensity factor. The accuracy of structural life is mainly dependent on how close the empirical parameter, m, can be estimated.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Johnson Space Center, NASA(ASEE Summer Faculty Fellowship Program, 1987, Volume 2; 20 p
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  • 99
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    Experimental studies on the tripping behavior of narrow T-stiffened flat plates subjected to hydrostatic pressure and underwater shock (1987)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: An experimental investigation was conducted to determine the static and dynamic responses of a specific stiffened flat plate design. The air-backed rectangular flat plates of 6061-T6 aluminum with an externally machined longitudinal narrow-flanged T-stiffener and clamped boundary conditions were subjected to static loading by water hydropump pressure and shock loading from an eight pound TNT charge detonated underwater. The dynamic test plate was instrumented to measure transient strains and free field pressure. The static test plate was instrumented to measure transient strains, plate deflection, and pressure. Emphasis was placed upon forcing static and dynamic stiffener tripping, obtaining relevant strain and pressure data, and studying the associated plate-stiffener behavior.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-Marshall Space Flight Center, The 58th Shock and Vibration Symposium, Volume 1; p 61-95
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  • 100
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    Viscous damped space structure for reduced jitter (1987)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: A technique to provide modal vibration damping in high performance space structures was developed which uses less than one once of incompressible fluid. Up to 50 percent damping can be achieved which can reduce the settling times of the lowest structural mode by as much as 50 to 1. This concept allows the designers to reduce the weight of the structure while improving its dynamic performance. Damping by this technique is purely viscous and has been shown by test to be linear over 5 orders of input magnitude. Amplitudes as low as 0.2 microinch were demonstrated. Damping in the system is independent of stiffness and relatively insensitive to temperature.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-Marshall Space Flight Center, The 58th Shock and Vibration Symposium, Volume 1; p 233-243
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