Composite materials are increasingly used in aerospace, underwater, and automotive structures. Their use in structural applications is dictated by the outstanding strength and stiffness while being lightweight in addition to their flexibility in tailoring the desired performance in the design of structures. The present study focuses on the failure analysis and shape control of smart composite laminates under coupled hygrothermal, electric and mechanical stimuli. A linear thermo-electro-elastic constitutive model for transversely isotropic materials is used for each ply in the composite laminates. The first-ply failure and ultimate laminate failure criteria of composite laminates are used to predict the failure stress and mode of the composite laminate where we incorporate various commonly known macroscopic failure criteria including Tsai-Hill, Tsai Wu, maximum stress and maximum strain for each lamina. We study the use of piezoelectric materials such as lead zirconate titanate (PZT) and piezoelectric fiber composites as actuators for controlling deformation in composite laminates; this study focuses on bending deformation. The purpose is to minimize unwanted deformation, such as the one due to hygrothermal effect, by applying counter deformation to avoid failure in such composite laminates. In addition, analysis based on the Classical Laminate Theory (CLT) is performed for Carbon/Epoxy (AS4/3501-6) thin laminate with stacking sequence [90/45/-45/0]s under uniaxial and biaxial in-plane loading. One of the major types of failure in smart structures is caused by debonding of the actuator from the host structure which is caused by the high stress discontinuity between the interface of the host structure and the active part. By using embedded actuators, such that the active part is incorporated into one of the layers of the composite beam during the manufacturing process, the stress concentration effect can be reduced while obtaining similar actuation values. Moreover, a control algorithm is proposed that enables the composite laminate to overcome the failure load by using piezoelectric materials where a counter electric voltage could be applied which prevents failure from occurring. Furthermore, computer software called “Hyper Composite” was developed using Action Script® and Adobe Flash® in order to perform stress and failure analysis for general composite laminates. Several carpet plots were also generated to show the interacting behavior of two independent variables such as Young’s modulus, Poisson’s ratio, shear modulus and the coefficient of thermal and moisture expansion at different percentile constitutions for the laminate different plies. This computer software is useful for estimating overall properties of smart composite laminates in designing smart composite structures.

A simplified model is proposed to investigate the stress fields and the strain energy release rate (SERR) associated with cracks in bonded joints in wind turbine blades. The proposed two-dimensional model consists of nonparallel upper and lower shells with adhesive between the shells at the tapered end. Nonlinear finite element analysis (FEA) is performed in a systematic parametric study of material and geo- metric properties. Two failure modes and their locations are predicted at different combinations of parameters: yielding at the outside end of the adhesive and interface cracking at the inside end of the bondline. Effect of the shell curvature on the stress fields is also considered. Based on the classic beam theory and the beam-on-elastic-foundation (BOEF) assumption, stress and displacement fields of the adhesively-bonded joint were determined by a new theoretical model to support the results from the numerical computation. The failure analysis is continued by studying the effects of manufacturing defects in the adhesive bond. Single and multiple voids are embedded to simulate air bubble trapped in the interface. The numerical and analytical studies are conducted to investigate SERR associated with the voids and results are provided to illustrate the effects of void position and void size.

Xi-Cheng, Alan S. Willsky, George C. Verghese. / "March 1983" "Presented at the 1983 American Control Conference." / Bibliography: leaf 4. / "Grant N00014-77-C-0224" "Grant NGL-22-009-124"

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Orientador: Fernando de Azevedo Silva / Banca: Gustavo Aristides Santana Martinez / Banca: João Alberto de Oliveira / Resumo: Estudo de falha por fratura em eixo da laminadora de aros Leifeld, fabricado em aço de baixa liga e alta resistência, ABNT 4340, forjado, temperado e revenido, com dureza de 39 HRc, abordando aspectos de modelagem pelo método de elementos finitos, utilizando o programa Ansys e critérios de fadiga utilizando o diagrama de Goodman modificado como ferramenta de definição do limite de tensão alternada para fadiga e propostas de mudanças geométricas no eixo a fim de minimizar as tensões sobre a aba da árvore bem como eliminar a possibilidade de fratura por fadiga da mesma. O estudo procura mostrar de forma clara a montagem de um modelo sólido através de um software comercial e a interação com a realidade vivida na manutenção de fábrica, sendo que o estudo surgiu devido a falhas freqüentes e prematuras de árvores em máquinas de repuxamento de aros, de procedência alemã, usada para a fabricação de aros para pneu com câmara utilizados em caminhões e ônibus, máquina esta de propriedade da empresa Maxion Sistemas Automotivos S/A. / Abstract: This is a fracture failure analysis of a Leifeld flow forming machine spindle, manufactured in a low alloy and high resistance, ABNT 4340 steel, forged, quenched and tempered with hardness of 39 HRc, approaching modeling aspects in finite elements method using the program Ansys and also approaching fatigue criteria using the diagram of Goodman modified as a tool for definition criterion of fatigue alternate stress limit and proposed of geometric changes in the spindle in order to minimize the tensions on the brim of it as well as to eliminate the fracture possibility for fatigue of the same. The study tries to show the assembly of a solid model in a clear way through a commercial software and the interaction with the reality lived in the factory maintenance, the study was proposed due the frequent and premature spindles failures in the flow forming machine, made in Germany, used for the production of rim for tire with tube used in trucks and buses, this machine is property of Maxion Sistemas Automotivos S/A company. / Mestre

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-Utilisation de l’interaction non-linéaire entre des impulsions laser (proche infrarouge) ultracourtes et le silicium, en mode d’absorption multiphotonique ou de génération d’harmoniques optiques, pour la stimulation et le test photo-électrique. - Développement des méthodes d’imagerie statique et dynamique pour l’analyse de défaillance en appliquant les techniques d’optique femtoseconde sur circuits intégrés. - Modélisation de l’interaction laser-silicium avec la méthode FDTD (Rsoft). / Using the nonlinear interaction between ultra-short laser pulses (λ ~ 0.8μm to1.3μm) and silicon, with multi-photon absorption or optical harmonic generation, to achieve photoelectric stimulation and testing. Development of imaging methods for static and dynamic failure analysis techniques using femtosecond laser (TOBIC, 2pLADA) on integrated circuits.

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The ability to predict the failure rate of any military laser is very critical. In-field laser usage does not support the troubleshooting and repairing of a complex electro optical system. The only published laser failure rate model was last updated by the Department of Defense in 1975. Consequently, the failure rate predicted is inaccurate due to model deficiencies. This dissertation has developed a laser failure rate model for diode pumped lasers with improved failure rate prediction accuracy. The model has surpassed the capabilities of the Department of Defense model by the inclusion of key performance attributes that are currently not taken into account. The scope of work completed was based on a tailored Physics of Failure methodology. The research approach implemented was: 1. Integration of Failure Mode and Effects Analysis to evaluate deployed laser failure. 2. Beam simulation for alignment tolerance analysis. 3. Thermal and vibration effects analysis on laser performance. 4. Analysis and development of a methodology to represent a resonator failure rate model. A secondary contribution of this research effort is supporting the update of the current laser failure rate model. The success of revising the current model relies on leveraging the work of other organizations in the area of failure rate modeling and reliability predictions.