Thin-walled beam structures are adopted as structural members in various fields of modem technology including aeronautical/aerospacial, naval, mechanical and civil ones. With the advent of advanced composite material systems, there is a vital need to reformulate the classical theory of thin-walled beams in a wider framework. This dissertation is intended to incorporate several essential effects which have a considerable importance for the rational design of composite thin-walled beam structures. These effects are the transverse shear deformation, the warping constraint, the secondary warping as well as the hygrothennal and the dynamic ones. The field equations of laminated composite thin-walled beams of either open or closed single and multicell cross-sections are derived through the application of Hamilton's variational principle. The Laplace Transform technique is used to obtain exact solutions. In this dissertation, the aero elastic divergence instability of aircraft wings modelled as thin-walled beams as well as the eigenfrequency problem of cantilevered composite thin-walled beams of closed cross-section are considered in the framework of a reformed theory incorporating non-classical effects. The numerical results reveal the great role played by non-classical effects as well as by the tailoring technique applied to the problems studied in this dissertation. / Ph. D.

An attempt is made to understand the phenomenon of aeroelasticity as applied to the helicopter rotors, specifically laminated composite rotor blades. Realizing the immense complexity of the problem, a beginning has been made by developing a structural model for a rotating composite beam. Present work has three objectives; 1) To carry out an extensive survey of research related to the aeroelastic analysis of rotor blades, 2) To expand an existing finite element model by introducing new degrees of freedom and validate the changes, 3) and, finally using this model to carry out a linear static and dynamic analysis for a rotating composite beam. It was found that the rotation and fiber orientations have a pronounced effect on the static deflections and the natural frequencies of vibration of the laminated beam. / Master of Science

Brittle materials are characterized by a wide scatter in their strength data and by size effects. In this work, size effects in brittle composite structures such as beams and plates with and without stress raisers are investigated experimentally and analytically. For structures with geometrical irregularities such as notches, holes or cut-outs, no analytical solutions exist and approximate numerical schemes have to be employed. For this purpose, the finite element method is extensively used. For stress analysis of isotropic beams under four point bending and composite plates under in-plane loading, a finite element analysis program F2DELAST based on two-dimensional elasticity theory was developed and verified with existing literature and also by a commercial finite element code ABAQUS. For composite beams under four-point bending, ABAQUS is used. For stress and failure analysis of laminated composite plates under transverse loading, a nonlinear finite element analysis program ENCOMPLIT which accounts for the geometrical nonlinearity in von Karman sense and transverse shear deformation was developed. Both the finite element programs written by the author and the ABAQUS were used for stress analysis as convenience dictates. For post-processing purposes, PATRAN and I-DEAS are used. Linear and nonlinear stress analyses were performed for the case of composite plates under transverse loading. A methodology for reliability analysis is developed for composite beams and plates with and without stress concentration under various loading conditions and various finite element reliability analysis programs were written. The materials used for the analysis are mainly carbon-carbon composites, however, where validation of finite element codes or comparison of the proposed failure criteria with other criteria are needed, graphite-epoxy composites, which are extensively used in the literature, are also used. The model is based on Weibull statistics. The Weibull model was extended to account for the three-dimensional stress field including interlaminar stresses. The effect of interlaminar stresses on the total reliability is investigated. Various failure theories for composite materials are reviewed. New failure criteria for bi-directional orthotropic lamina are developed and proposed. Failure analysis in the non-probabilistic sense (i.e. First-ply-failure analysis) is performed on carbon-carbon composite beams under 4-point bending and carbon-carbon composite plates under transverse loading using the existing failure criteria and the failure criteria proposed in this work. Comparisons are made with the existing failure criteria and also with experiments. An attempt was made to relate the (probabilistic) reliability analysis with (non-probabilistic) first-ply-failure analysis in terms of failure loads for composite beams under 4-point bending and square and rectangular composite plates under transverse loading. / Ph. D.

The goal of this investigation was to develop a two-dimensional model which describes the winding and curing processes of filament wound composite structures. The model was developed in two parts. The first part is the cure model which relates the cure temperature, applied at the boundaries of the composite, to the thermal, chemical, and physical processes occurring in the case during cure. For a specified cure cycle, the cure model can be used to calculate the temperature distribution, the degree of cure of the resin, and the resin viscosity inside the composite case. The second part is the layer tension loss and compaction model which relates the winding process variables (i.e., winding pattern, mandrel geometry, initial winding tension, and the properties of the fiber and resin system) to the instantaneous position and tension of the fibers in each layer of the case. A finite element computer code "FWCURE" was developed to obtain a numerical solution to the model. Verification of the cure sub-model was accomplished by measuring the temperature distributions in a 5.75 inch diameter graphite - epoxy test bottle and a 4 inch diameter graphite - epoxy tube during cure. The data were compared with the temperature distributions calculated using FWCURE. Differences between the measured and calculated temperatures was no more than 10 °C for both the test bottle and the cylindrical tube. A parametric study was performed by using FWCURE computer code. Results of the simulation illustrate the information that can be generated by the models and the importance of different processing and material parameters on the fabrication process. / Ph. D.

A comprehensive fabrication stress model was developed to compute fiber stresses in axisymmetric filament wound composite structures at any stage of the fabrication process, a prerequisite for the evaluation of the performance of the composite structures from fabrication process variables. The stress model uses an isoparametric axisymmetric finite element formulation and a double-layered composite element to model the mechanical behavior of the composite material in any cure state. An incremental finite element formulation was used to model the winding and mandrel removal stages. A thermo-mechanical formulation was used to model the curing stage. Also, all major physical phenomena occurring in the fabrication stages which significantly affect the fiber stresses are taken into account: instantaneous tension loss in winding, tension loss due to multiple circuit winding, tension loss due to fiber motion through the uncured resin, material cure transition, and fiber stiffness degradation in a compressive strain state. Two case studies were selected to evaluate and to illustrate the use of the fabrication stress model: the space shuttle booster Joint overwrap and a filament wound composite bottle. The analysis results of the overwrap case study show excellent agreement with experimental hoop strain data. The fabrication stresses from the analysis indicate that the overwrap should experience no strength degradation due to adverse fabrication stresses and strains. Very favorable residual stress results were also predicted by the model for the overwrap. The analysis results of the bottle case study, while having no experimental data to compare with, show very reasonable behaviors, which can be readily explained by a qualitative consideration of the actual winding problem. The stress and strain results from the case study show that the bottle would experience strength degradation when a sand/PVA mandrel is used, but it would retain maximum strength when a steel mandrel is used. / Ph. D.

Call number: LD2668 .T4 1979 E43 / Master of Science

Thesis. 1975. Ph.D.--Massachusetts Institute of Technology. Dept. of Mechanical Engineering. / Vita. / Includes bibliographical references. / by James Moore. / Ph.D.

No description available.

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 191-194). Available also in a digital version from Dissertation Abstracts.

Thesis (Ph. D.)--University of Alabama at Birmingham, 2009. / Title from PDF title page (viewed Feb. 8, 2010). Additional advisors: Uday Vaidya, Talat Salama, Wilbur Hitchcock, Ashraf Z. Al-Hamdan. Includes bibliographical references (p. 144-155).