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  • STRUCTURAL MECHANICS  (441)
  • 1990-1994  (441)
  • 1965-1969
  • 1991  (441)
  • 1
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    NASA airframe structural integrity program (1991)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: NASA has initiated a research program with the long-term objective of supporting the aerospace industry in addressing issues related to the aging commercial transport fleet. The interdisciplinary program combines advanced fatigue crack growth prediction methodology with innovative nondestructive examination technology with the focus on multi-site damage (MSD) at riveted connections. A fracture mechanics evaluation of the concept of pressure proof testing the fuselage to screen for MSD has been completed. Also, a successful laboratory demonstration of the ability of the thermal flux method to detect disbonds at riveted lap splice joints has been conducted. All long-term program elements have been initiated and the plans for the methodology verification program are being coordinated with the airframe manufacturers.
    Keywords: STRUCTURAL MECHANICS
    Type: In: Structural integrity of aging airplanes (A93-45772 19-01); p. 141-152.
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  • 2
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    An unconditionally stable staggered algorithm for transient finite element analysis of coupled thermoelastic problems (1991)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: An unconditionally stable second order accurate implicit-implicit staggered procedure for the finite element solution of fully coupled thermoelasticity transient problems is proposed. The procedure is stabilized with a semi-algebraic augmentation technique. A comparative cost analysis reveals the superiority of the proposed computational strategy to other conventional staggered procedures. Numerical examples of one- and two-dimensional thermomechanical coupled problems demonstrate the accuracy of the proposed numerical solution algorithm.
    Keywords: STRUCTURAL MECHANICS
    Type: Computer Methods in Applied Mechanics and Engineering (ISSN 0045-7825); 85; 3 Fe; 349-365
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  • 3
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    Analytical modelling of laminated composites (1991)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: This paper presents a unique approach to the analysis of thick laminated composites by presenting two simple finite element methods. The first uses the predictor corrector technique to extend the simple Mindlin-type element to achieve greater accuracy, and the second develops a new least squares element which can approximate a C(1) continuous element. The least squares element has the capability to incorporate a simplified higher-order basis into a piecewise continuous displacement field creating an accurate, yet computationally simple, element. These two methods have the potential to significantly upgrade analysis methods with little additional computational cost.
    Keywords: STRUCTURAL MECHANICS
    Type: International Conference on Composite Materials (ICCM/8); Jul 15, 1991 - Jul 19, 1991; Honolulu, HI; United States
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  • 4
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    Deformation and stress response of composite laminated shells under internal pressure (1991)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: This paper presents a theoretical study of the response of filament wound composite shells under internal pressure. Each layer of the material is generally cylindrically anisotropic. By using cylindrically anisotropic elasticity field equations and Lekhnitskii's stress functions, a system of sixth-order ordinary differential equations is obtained. The general expressions for the stresses and displacements in the laminated composite shells under internal pressure are discussed. Two composite systems, graphite/epoxy and glass/epoxy, are selected to demonstrate the influence of degree of material anisotropy and fiber orientations on the axial and induced twisting deformation. Stress distributions of (45/-45)s symmetric angle-ply fiber-reinforced laminated shells are shown to illustrate the effect of radius-to-thickness ratio.
    Keywords: STRUCTURAL MECHANICS
    Type: International Conference on Composite Materials (ICCM/8); Jul 15, 1991 - Jul 19, 1991; Honolulu, HI; United States
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  • 5
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    Transient motion of thick anisotropic plates (1991)
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    Publication Date: 2019-08-28
    Description: Analyses are developed for the response of anisotropic plate strips to a transient load. The load is taken in the form of a line load of normal stress on the surface or within the body of the strip. The characteristic free vibrational modes of the strip are derived and used to derive the secular equation for this case in closed form and to isolate the mathematical conditions for symmetric and antisymmetric wave mode propagation in completely separate terms. The applied loads are expanded in terms of these normal modes and the response of the plate is obtained by superposition of the appropriate components. Material systems of higher symmetry are contained implicitly in the analysis.
    Keywords: STRUCTURAL MECHANICS
    Type: Annual Review of Progress in Quantitative Nondestructive Evaluation; Jul 15, 1990 - Jul 20, 1990; La Jolla, CA; United States
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  • 6
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    Lamb wave scattering by a surface-breaking crack in a plate (1991)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: An NDE method based on finite-element representation and modal expansion has been developed for solving the scattering of Lamb waves in an elastic plate waveguide. This method is very powerful for handling discontinuities of arbitrary shape, weldments of different orientations, canted cracks, etc. The advantage of the method is that it can be used to study the scattering of Lamb waves in anisotropic elastic plates and in multilayered plates as well.
    Keywords: STRUCTURAL MECHANICS
    Type: Annual Review of Progress in Quantitative Nondestructive Evaluation; Jul 15, 1990 - Jul 20, 1990; La Jolla, CA; United States
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  • 7
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    Formulation of full state feedback for infinite order structural systems (1991)
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    Publication Date: 2019-08-28
    Description: The estimation of exact displacement and displacement rate feedback kernels from finite dimensional control solutions based on finite element structural models is discussed. These kernels are then transformed to equivalent curvature and curvature rate feedback kernels. These curvature kernels are augmented with single point displacement and rotation feedback to account for rigid body motions. A growing class of sensors known as area-averaging sensors is used to measure the curvature and curvature rate state functions. The output of area-averaging sensors equals the convolution of all structural curvature states with the spatial sensitivity function of the sensors. Transforming the discrete feedback gains into continuous feedback kernels and employing area-averaging sensors make it possible to implement full state feedback for infinite order structural systems.
    Keywords: STRUCTURAL MECHANICS
    Type: Joint U.S./Japan Conference on Adaptive Structures; Nov 13, 1990 - Nov 15, 1990; Maui, HI; United States
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  • 8
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    Effect of interlaminar normal stresses on the uniaxial zero-to-tension fatigue behavior of graphite/epoxy tubes (1991)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: Fatigue tests conducted with and without internal pressure have been found to possess approximately the same fatigue life as (+/-45)s graphite/epoxy tubes for zero-to-tension axial load-controlled conditions on an axial torsion servohydraulic apparatus. These tests therefore cannot be considered as confirmations of the suspected detrimental effect of interlaminar tensile stresses on the fatigue performance of thin-walled tubes. The addition of 90-deg plies on both the inside and the outside is found to significantly improve the tubes' static and fatigue strengths.
    Keywords: STRUCTURAL MECHANICS
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  • 9
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    Discrete piezoelectric sensors and actuators for active control of two-dimensional spacecraft components (1991)
    In:  Other Sources
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    Publication Date: 2019-08-27
    Description: This paper describes research into the use of discrete piezoelectric sensors and actuators for active modal control of flexible two-dimensional structures such as might be used as components for spacecraft. A dynamic coupling term is defined between the sensor/actuator and the structure in terms of structural model shapes, location and piezoelectric behavior. The relative size of the coupling term determines sensor/actuator placement. Results are shown for a clamped square plate and for a large antenna. An experiment was performed on a thin foot-square plate clamped on all sides. Sizable vibration control was achieved for first, second/third (degenerate) and fourth modes.
    Keywords: STRUCTURAL MECHANICS
    Type: In: Sensors and sensor integration; Proceedings of the Meeting, Orlando, FL, Apr. 4, 1991 (A93-21961 07-35); p. 102-114.
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  • 10
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    A continuum model for damage evolution in laminated composites (1991)
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    Publication Date: 2019-08-27
    Description: The accumulation of matrix cracking is examined using continuum damage mechanics lamination theory. A phenomenologically based damage evolutionary relationship is proposed for matrix cracking in continuous fiber reinforced laminated composites. The use of material dependent properties and damage dependent laminate averaged ply stresses in this evolutionary relationship permits its application independently of the laminate stacking sequence. Several load histories are applied to crossply laminates using this model, and the results are compared to published experimental data. The stress redistribution among the plies during the accumulation of matrix damage is also examined. It is concluded that characteristics of the stress redistribution process could assist in the analysis of the progressive failure process in laminated composites.
    Keywords: STRUCTURAL MECHANICS
    Type: IUTAM Symposium; May 29, 1990 - Jun 01, 1990; Troy, NY; United States
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