Three test methods were employed to characterize the response of unidirectional Boron/Aluminum metal matrix composite material under monotonic and cyclic loading conditions, namely: Iosipescu Shear, Off-Axis Tension and Compression. The characterization of the elastic and plastic response includes the elastic material properties, yielding and subsequent hardening of the unidirectional composite under different stress ratios in the material principal coordinate system. The elastic response is compared with the prediction of the transformation theory, based on the far field stress ōₓₓ, the Pagano-Halpin Model, and finite element analysis. Yield loci were generated for different stress ratios and were compared for the three different test methods, taking into account residual stresses and specimen geometry. The yield locus for in-plane shear was compared with the prediction of an analytical micromechanical model. The influence of the scatter in the experimental data on the predicted yield surface was also analyzed. Likewise the experimental material strength in tension and compression was compared with the Maximum Stress and the Tsai-Wu failure criterion. / M.S.

This investigation was aimed at understanding the global and local strain and deflection responses of stiffened skins. Global deformations of the stiffened skins, under load, produce high local stresses in the interface region between the stiffener and skin. Test panels were designed to study the stiffener and skin interactions using parameters typical of stiffened skins for aircraft fuselages. A total of six panels were tested. Two skin laminates, both 0.04 in. thick, and three stiffener configurations were studied. The panels, having clamped edge boundary conditions, were subjected to pressure loads of up to 14.5-14.8 psi. Out-of-plane deflections and longitudinal and transverse strains were measured in several locations. The deflection responses showed a strongly nonlinear behavior at pressure loads of less than 5 psi. In addition relatively severe gradients of both longitudinal and transverse strains were measured in the interface region of the stiffener and skin. Finite element models incorporating geometric nonlinearities were made of four of the panels. Results of these models substantiated the overall findings of the experimental measurements. / Master of Science / incomplete_metadata

M.S.

The objective of this study was to investigate, both experimentally and analytically, the stresses and deformations in angle-ply composite tubes subjected to axisymmetric thermal loading. For the theoretical portion, a generalized plane strain elasticity analysis was developed. The analysis included mechanical and thermal loading and temperature-dependent material properties. Using the elasticity analysis and a temperature range of 116 K to 450 K, stress levels were found to be high for the specific designs considered, compared to material failure levels. In addition, the use of temperature-dependent material properties was found to have a significant effect on the predicted stresses and deformations. The elasticity analysis was also used to study the effect of including a thin metallic coating on a graphite-epoxy tube. The stresses in the coatings were found to be quite high, exceeding the yield stress of aluminum. An important finding in the analytical studies was the fact that even tubes with a balanced-symmetric lamination sequence exhibited shear deformation or twist. The radial location of an off-axis ply was found to influence its effect on the overall torsional tube response. For the experimental portion, an apparatus was developed to measure torsional and axial response in the temperature range of 140 K to 360 K. Eighteen specimens were tested, combining three material systems, eight lamination sequences, and three off-axis ply orientation angles. For the twist response, agreement between analysis and experiment was found to be good. The axial response of the tubes tested was found to be greater than predicted by a factor of three. As a result of the study, it is recommended that the thermally-induced axial deformations be investigated further, both experimentally and analytically. / Master of Science

Results of an experimental and analytical study of the nonlinear response and failure characteristics of internally pressurized 4- to 16-ply-thick graphite-epoxy cylindrical panels are presented. Specimens with clamped boundaries simulating the skin between two frames and two stringers of a typical transport fuselage were tested to failure. Failure results of aluminum specimens are compared with the graphite-epoxy test results. The specimens failed at their edges where the local bending gradients and interlaminar stresses are maximum. STAGS nonlinear two-dimensional shell analysis computer code results are used to identify regions of the panels where the response is independent of the axial coordinate. A geometrically nonlinear one-dimensional cylindrical panel analysis was derived and used to determine panel response and interlaminar stresses. Inclusion of the geometric nonlinearity was essential for accurate prediction of panel response. Measurements of panel radius and edge circumferential displacements associated with specimen slipping were also required in the one-dimensional analysis for good correlation between analytical and experimental results. Some panels failed with significant damage in the form of tensile fiber breaks and ply delaminations preceding the ultimate pressure. Other panels failed suddenly without any apparent damage preceding the ultimate pressure. The failure usually occurred along one edge of the panel leaving the other edge intact. The damage on the panel surfaces and through-the-thickness were examined to determine the failure characteristics of the panels. Various failure criteria were applied to the stresses predicted from the one-dimensional analysis. The maximum stress failure criterion applied to the predicted tensile stress in the fiber direction agreed best with the experimentally determined first damage pressures. Results indicate that all panels tested would support applied internal pressures well above fuselage proof pressures. / Ph. D.

DC resistance and AC conductance and capacitance have been measured under various conditions in an effort to electrically characterize and make electrical-mechanical correlations for 15 carbon black filled rubber samples. Resistance, conductance and capacitance have been monitored as functions of uniaxial compressive stress, time, temperature, and mechanical and thermal history. Capacitance and conductance have also been monitored as functions of frequency under various degrees of compressive loading and before and after specific heat treatments. A direct relationship has been found between sample • conductance and capacitance under any thermal and/or mechanical condition. This is in agreement with previous theories of conduction network formation and percolation. Various conduction mechanisms have been enumerated and an equivalent circuit of a network of lumped R-C "microelements'' has been qualitatively described. Stress, relaxation, frequency, and temperature dependences of the macroscopic parameters measured ( conductivity and capacitance) are discussed in terms of this model. / M.S.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / O emprego de materiais compósitos de matriz polimérica como reparo e reforço em estruturas nas indústrias do petróleo tem se tornado uma prática industrial comum. O uso destes reforços compreende desde o recobrimento de superfícies com defeitos, passantes ou não, até o reforço estrutural. Na última década, muitos estudos foram feitos para o desenvolvimento de uma metodologia alternativa para reforço e reparo de dutos com materiais compósitos. Recentemente, em 2006, o sistema ISO de normas técnicas apresentou a primeira especificação técnica de "Reparo em Compósitos para dutos das indústrias de Petróleo, Petroquímica e de Gás Natural Qualificação, projeto, instalação, testes e inspeção" ISO/PDTS 24817. O presente trabalho tem como objetivo o desenvolvimento de um sistema de reparo, utilizando materiais compósitos de matriz polimérica para o reparo e reforço estrutural de dutos e tubulações industriais, em conformidade com a Norma ISO 24817:2006. Foram desenvolvidos procedimentos para a confecção de corpos de prova destinados a ensaios mecânicos, e para aplicação do sistema de reparo. O sistema de reparo é destinado a defeitos tais como perda de espessura, amassamentos e danos transpassantes. Foi construída, em paralelo, toda a infraestrutura para a montagem de um laboratório destinado ao estudo de materiais compósitos, no Laboratório de Adesão e Aderência. São apresentados resultados de parte dos ensaios mecânicos necessários, comparação dos resultados obtidos com modelos teóricos e testes hidrostáticos. / The use of polymer matrix composites to repair and strengthen structures in the oil industry has become a common industry practice. The use of these reinforcements extends from covering surfaces with defects, through wall or not, to structural reinforcement. In the last decade, many studies have been done to develop an alternative approach to the strengthening and repairing of pipelines with composite materials. Recently, in 2006, the ISO system of technical standards presented the document technical support "Petroleum, petrochemical and natural gas industries Composite repairs for pipework Qualification, design, installation, testing and inspection" ISO/PDTS 24817. This study aims to develop a repair system using polymer matrix composite materials for repair and reinforcement of piping and pipelines in accordance with ISO 24817:2006. Procedures where developed for the confection of test specimens for mechanical testing, and application of the repair. The system is intended to repair defects such as thickness loss, gouges, and damage through wall or not. In parallel, an entire infrastructure was built for the conception of a laboratory for the study of composite materials at the Laboratory of Adhesion and Adherence. Here are presented the results of the required mechanical tests, the comparison results with theoretical models, and the hydrostatic testing.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / O emprego de materiais compósitos de matriz polimérica como reparo e reforço em estruturas nas indústrias do petróleo tem se tornado uma prática industrial comum. O uso destes reforços compreende desde o recobrimento de superfícies com defeitos, passantes ou não, até o reforço estrutural. Na última década, muitos estudos foram feitos para o desenvolvimento de uma metodologia alternativa para reforço e reparo de dutos com materiais compósitos. Recentemente, em 2006, o sistema ISO de normas técnicas apresentou a primeira especificação técnica de "Reparo em Compósitos para dutos das indústrias de Petróleo, Petroquímica e de Gás Natural Qualificação, projeto, instalação, testes e inspeção" ISO/PDTS 24817. O presente trabalho tem como objetivo o desenvolvimento de um sistema de reparo, utilizando materiais compósitos de matriz polimérica para o reparo e reforço estrutural de dutos e tubulações industriais, em conformidade com a Norma ISO 24817:2006. Foram desenvolvidos procedimentos para a confecção de corpos de prova destinados a ensaios mecânicos, e para aplicação do sistema de reparo. O sistema de reparo é destinado a defeitos tais como perda de espessura, amassamentos e danos transpassantes. Foi construída, em paralelo, toda a infraestrutura para a montagem de um laboratório destinado ao estudo de materiais compósitos, no Laboratório de Adesão e Aderência. São apresentados resultados de parte dos ensaios mecânicos necessários, comparação dos resultados obtidos com modelos teóricos e testes hidrostáticos. / The use of polymer matrix composites to repair and strengthen structures in the oil industry has become a common industry practice. The use of these reinforcements extends from covering surfaces with defects, through wall or not, to structural reinforcement. In the last decade, many studies have been done to develop an alternative approach to the strengthening and repairing of pipelines with composite materials. Recently, in 2006, the ISO system of technical standards presented the document technical support "Petroleum, petrochemical and natural gas industries Composite repairs for pipework Qualification, design, installation, testing and inspection" ISO/PDTS 24817. This study aims to develop a repair system using polymer matrix composite materials for repair and reinforcement of piping and pipelines in accordance with ISO 24817:2006. Procedures where developed for the confection of test specimens for mechanical testing, and application of the repair. The system is intended to repair defects such as thickness loss, gouges, and damage through wall or not. In parallel, an entire infrastructure was built for the conception of a laboratory for the study of composite materials at the Laboratory of Adhesion and Adherence. Here are presented the results of the required mechanical tests, the comparison results with theoretical models, and the hydrostatic testing.