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Articles 121 - 126 of 126
Full-Text Articles in Structures and Materials
Development Of A Stratified Plate Model For Composite Panels, Alan L. Lesmerises
Development Of A Stratified Plate Model For Composite Panels, Alan L. Lesmerises
Theses and Dissertations
A new model for composites represents a composite panel as an alternating stack of isotropic matrix and orthotropic fiber-dominated layers. An energy approach results in a set of partial differential equations and boundary conditions where the mechanical properties of the matrix and fibers appear separately. Two solution methods are developed. The first, called Strata Theory is developed for general applications, while the second, called the Exact Stratified Plate, is used as a benchmark for comparison to Strata Theory. Both solutions assume zero gradients of displacement through the thickness of a fiber layer. They are compared for an isotropic material and …
Sensitivity Analysis For The Selection Of Linear Quadratic Regulator Weighing Parameters Q And R For Active Vibration Suppression Of A Cantilevered Beam, Steven L. Story
Sensitivity Analysis For The Selection Of Linear Quadratic Regulator Weighing Parameters Q And R For Active Vibration Suppression Of A Cantilevered Beam, Steven L. Story
Theses and Dissertations
There has been much interest during the past decade to develop and launch large space structures. The high cost of launching material into orbit will require that these structures be assembled in space using light weight elements which are vulnerable to dynamic excitations. Active control may be necessary to rapidly attenuate large amplitude vibrations. The active vibration control system is usually designed after the structure has been optimized. The integrated design of the control system and the structure may provide additional weight savings. This thesis presents a sensitivity analysis of the structure/ control optimization problem. The structure used is an …
Finite Element Investigation Into The Dynamic Instability Characteristics Of Laminated Composite Panels, Walter W. Taylor Jr.
Finite Element Investigation Into The Dynamic Instability Characteristics Of Laminated Composite Panels, Walter W. Taylor Jr.
Theses and Dissertations
Dynamic instability of a laminated composite panel subjected to a transverse load is studied. Up to cubic variations in the thickness coordinate are included in the inplane displacement field, and only the constant component is kept in the transverse displacement. The transverse shear strains retain only linear displacement terms and vary parabolically through the thickness. The complete quadratic displacement functions are included in the inplane strains. A 36 degree of freedom shell element is used to obtain numerical results. The static snap through load vs displacement curve, as well as the critical collapse load, is examined by invoking the Riks …
Material Properties Of Silicon Carbide Fibers With Continuously Applied Sol-Gel Alumina Coatings, Christian C. Daehnick
Material Properties Of Silicon Carbide Fibers With Continuously Applied Sol-Gel Alumina Coatings, Christian C. Daehnick
Theses and Dissertations
An investigation was conducted to determine the effect of non-alpha- alumina coatings applied under varying conditions on some of the properties of silicon carbide fibers. Limited characterization of the coating by optical, scanning electron, and transmitted electron microscopy as well as energy- dispersive x-ray analysis was performed. Tensile tests were used to determine changes in elastic modulus, ultimate strength, and strain to failure of the coated fibers relative to uncoated fibers. The coatings were found to lower the mean value of the measured properties as their thickness increased, but the measurements were not accurate enough to determine if this corresponded …
Investigation Of Direct And Indirect Optimization Algorithms For Aerospace Structures, Harry Hopkins Iii
Investigation Of Direct And Indirect Optimization Algorithms For Aerospace Structures, Harry Hopkins Iii
Theses and Dissertations
This thesis investigated the performance of two direct and two indirect methods of structural optimization. A gradient calculator and overall design system was created with the finite element code FRAME. Three of the methods were employed using this system with the fourth being a commercial available code. The algorithms were applied to two different sized trusses using static constraints and were measured for accuracy, reliability, and efficiency. Results for the problems tested showed the Direct methods were sensitive to starting designs and their performance depended on the proper selection of internal parameters. They were also shown to have a high …
Solution To Eigenvalue Problems Of Antisymmetric Cross-Ply And Antisymmetric Angle-Ply Laminated Plates Using Affine Transformations, Zaffir A. Chaudry
Solution To Eigenvalue Problems Of Antisymmetric Cross-Ply And Antisymmetric Angle-Ply Laminated Plates Using Affine Transformations, Zaffir A. Chaudry
Theses and Dissertations
Using affine transformations and suitably recasting the buckling vibration differential equations, the eigenvalue problem of anti-symmetric cross-ply and antisymmetric angle-ply laminated rectangular plates has been reduced to a function of two strong material constants, the generalized rigidity ratio, whose range is in the closed interval from 0 to 1, and the ratio of principal lamina stiffness. With the reduction in number of constants an exhaustive parameter study of buckling and vibration solution trends, is possible. The buckling coefficients decrease with decreasing value of generalized rigidity ratio for both antisymmetric cross-ply and antisymmetric angle-ply laminates. For a given aspect ratio, and …