The use of composite materials in industrial applications such as aeronautical, aerospace or wind energy production has greatly increased in recent decades. Due to their inherent properties, these materials allow lighter, larger and more resistant structures. However, the use of composite materials for components or structures with highly stringent requirements, is hampered by the lack of knowledge of their reliability. In this thesis, some fundamental aspects about the use of fibre Bragg grating (FBG) sensors for internal strain measurements in composite laminates are discussed. In addition, a highly accurate method for locating the crack tip position in mixed-mode delamination growth has been presented. Finally, an experimental application of FBGs to dynamic measurements in mode I fatigue test has been performed / L’ús de materials compostos en aplicacions de caràcter industrial com per exemple l’aeronàutica, aeroespacial o la de producció d’energia eòlica, ha crescut exponencialment durant les últimes dècades. Degut a les seves extraordinàries propietats, l’ús d’aquests materials permet la construcció d’estructures més lleugeres, grans i resistents, tot i que el seu ús en components d’alta responsabilitat estructural està limitat per la manca de coneixement en relació a la seva fiabilitat estructural. En aquesta tesi es discuteixen alguns aspectes significants sobre l’ús de FBGs per a mesurar camps de deformació en l’interior de laminats de material compòsit, s’ha analitzat també la capacitat de localització de la punta d’una esquerda en creixement de mode mixt i per últim s’ha desenvolupat una aplicació pràctica dels FBG en temps real en assaigs a fatiga en mode I

This work presents a study and implementation of the simulation of residual stresses in castings. The objects of study are a cast iron truck Hub part (provided by the company Volvo 3P) and an optimized version of the Hub resulting from the application of a topology optimization process. The models are solved through an uncoupled thermo-mechanical solidification analysis, performed both in the FE commercial software Abaqus and the FD commercial software Magmasoft and the results are compared. First, a thermal analysis is carried out where the casting is cooled down from a super-heated temperature to room temperature. The thermal history obtained, is then used as an external force to calculate the residual stresses by means of a quasi-static mechanical analysis, using a J2-plasticity model. The simulation procedures are explained through a simplified model of the Hub and then applied to the geometries of interest. A results comparison between the original Hub and its optimized version is also presented. The theoretical base is given in this work as well as detailed implementation procedures. The results shows that the part subjected to the topology optimization process develop less residual stresses than its original version.

<p>This work presents a study and implementation of the simulation of residual stresses in castings. The objects of study are a cast iron truck Hub part (provided by the company Volvo 3P) and an optimized version of the Hub resulting from the application of a topology optimization process. The models are solved through an uncoupled thermo-mechanical solidification analysis, performed both in the FE commercial software Abaqus and the FD commercial software Magmasoft and the results are compared. First, a thermal analysis is carried out where the casting is cooled down from a super-heated temperature to room temperature. The thermal history obtained, is then used as an external force to calculate the residual stresses by means of a quasi-static mechanical analysis, using a J2-plasticity model. The simulation procedures are explained through a simplified model of the Hub and then applied to the geometries of interest. A results comparison between the original Hub and its optimized version is also presented. The theoretical base is given in this work as well as detailed implementation procedures. The results shows that the part subjected to the topology optimization process develop less residual stresses than its original version.</p>

The relationship between crack path and test method was examined by comparing the performance of adhesive-adherend combinations (six) in quasi-static fracture, mixed-mode fatigue, and creep crack growth. Crack paths in creep and quasi-static fracture were similar due to similar crack-tip plastic zone sizes in the epoxy adhesive even though the crack growth rates in creep were much smaller. Under condensed moisture and mixed-mode, creep and threshold fatigue tests produced interfacial failure. Under room-temperature dry environment, near threshold mixed-mode fatigue was interfacial, but was not in creep or quasi-static fracture. Smaller plastic zone size and crack path proximity to the interface that followed increased the sensitivity of near threshold, mixed-mode fatigue to surface properties. Therefore, the interfacial or cohesive failure of an adhesive system, which may judge the quality of the bond, can be a function of the test being conducted and may not be an absolute indicator of joint quality.

The relationship between crack path and test method was examined by comparing the performance of adhesive-adherend combinations (six) in quasi-static fracture, mixed-mode fatigue, and creep crack growth. Crack paths in creep and quasi-static fracture were similar due to similar crack-tip plastic zone sizes in the epoxy adhesive even though the crack growth rates in creep were much smaller. Under condensed moisture and mixed-mode, creep and threshold fatigue tests produced interfacial failure. Under room-temperature dry environment, near threshold mixed-mode fatigue was interfacial, but was not in creep or quasi-static fracture. Smaller plastic zone size and crack path proximity to the interface that followed increased the sensitivity of near threshold, mixed-mode fatigue to surface properties. Therefore, the interfacial or cohesive failure of an adhesive system, which may judge the quality of the bond, can be a function of the test being conducted and may not be an absolute indicator of joint quality.

Made available in DSpace on 2015-05-08T14:59:58Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 8451295 bytes, checksum: 74544bf6e3d65bb8e6eb7bec81fffac1 (MD5) Previous issue date: 2014-07-16 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / This study examined the influence of hydrogen in quasi-static toughness of dissimilar welded joint, consisting of base metals steel AISI 8630M and ASTM A36, HSLA steels classified as (High Strength Low Alloy). As a metal filler wire AWS-ERNiCrMo 3ARBL was used both in the buttering 8630M steel sheet as the welding filling. This is a welded joint similar to one of the most used joints in the oil sector that, by the last decade have shown some fractures by circumferential cracking, is being studied worldwide in order to identify the causes and safer solutions for your application. As parameter of fracture toughness is studied the CTOD (Crack Top Open Displecement) using type specimens SE(B) subjected to three point bending. The assays were performed in air after pre-doping cathodic hydrogen into water at 0°C synthetic sea, having to main references the standards ISO 12135: 2002 and ISO 15653: 2010 The results showed a significant susceptibility of the steel 8630M to retained hydrogen, reaching a embrittlement via CTOD around 25%. In turn, the dissimilar welding joint CTOD values present twice that of the base metal (steel 8630M), under the conditions with and without hydrogenation, had virtually no susceptibility to the cathodic hydrogen retained in their microstructure / O presente trabalho analisou a influencia do hidrogênio na tenacidade quase estática de uma junta soldada dissimilar constituída dos metais de base aços AISI 8630M e ASTM A36, classificados como aços ARBL (Alta Resistência e Baixa Liga). Como metal de adição utilizou-se o arame AWS ERNiCrMo-3 (comercialmente conhecido como INCONEL 625) tanto no amanteigamento da chapa de aço 8630M, quanto no enchimento da solda. Trata-se de uma junta soldada similar a junta AISI 8630M-Inconel 625-API X65, bastante utilizada no setor petrolífero que, por ter apresentado na última década algumas fraturas por trincamento circunferencial, vem sendo mundialmente estudada com o intuito de se identificar as causas e soluções mais seguras para sua aplicação. Como parâmetro de tenacidade à fratura estudou-se o deslocamento de abertura da ponta da trinca, do inglês CTOD (Crack Top Open Displecement), utilizando-se espécimes tipo SE(B) submetido à flexão em três pontos. Os ensaios foram realizados ao ar após pré- dopagem por hidrogênio catódico em água do mar sintética a 0ºC, tendo como principais referencias as Normas ISO 12135: 2002 e ISO 15653: 2010. Os resultados apresentaram uma significativa susceptibilidade do aço 8630M ao hidrogênio retido, apresentando uma queda na tenacidade (CTOD) em torno de 25%. Por sua vez, a junta soldada dissimilar além de apresentar valores de CTOD duas vezes superior ao do metal de base (aço 8630M), nas condições com e sem hidrogenação, praticamente não apresentou susceptibilidade ao hidrogênio retido em sua microestrutura

Neste trabalho buscou-se propor e implementar um modelo de material capaz de prever o comportamento mecânico de estruturas em compósitos poliméricos reforçados (CPR). Inicialmente fez-se um levantamento bibliográfico sobre os modos de danificação intralaminar e falhas interlaminares bem como sobre formas de abordagem (analítica e numérica) para tratar esses problemas. Em seguida, foram apresentadas em detalhes as etapas experimentais executadas, descrevendo todo o procedimento de fabricação dos corpos-de-prova e os resultados obtidos a partir dos ensaios quase-estáticos de tração, compressão, cisalhamento e flexão. Com base nesses resultados e em informações provenientes da literatura, propõem-se alguns modelos de material que foram implementados em sub-rotinas FORTRAN. Tais modelos são posteriormente compilados em conjunto com um programa de elementos finitos (ABAQUS®) a fim de serem avaliados e terem seus parâmetros calibrados. Numa primeira fase, através de simulações computacionais dos ensaios de tração e compressão avaliou-se os modelos de material implementados. Numa segunda fase, os parâmetros foram calibrados tomando como base três estudos de caso (flexão, endentação e teste de impacto) envolvendo seqüências de empilhamento distintas. Após a simulação computacional desses estudos, apresentou-se a proposta de uma metodologia para avaliar problemas de impacto a baixa velocidade em estruturas laminadas. Conclui-se assim que o presente projeto de pesquisa traz contribuições inovadoras, mas também apresenta várias perspectivas de trabalhos futuros. / In this work, material models were proposed to predict the mechanical behavior of composite structures. First of all, it was done a study about damage intra-ply and inter-ply (delamination) on composite materials and about analytical and numerical approaches to solve problems of progressive damage on composite structures was performed. After, many specimens were manufactured and experimental tests (tensile, compression, shear and flexural tests) were carried out. Experimental results and information from literature were used to develop some material models, which were implemented using FORTRAN compiler. These material models were compiled with a commercial finite element program (ABAQUS®) in order to evaluate and calibrate parameters of the models. In the first step, computational simulations of tensile and compression test were carried out to evaluate material models implemented. In the second step, the parameters of the material models were calibrated using three case studies (flexural, indentation and impact test) with some staking sequences. After that, a methodology was proposed to evaluate impact problems on composite structures under low velocity. Therefore, this research project not only shows new contributions but also suggests many future investigations.

Le terme élastographie désigne les techniques d'imagerie dédiées à l'étude des propriétés mécaniques des tissus biologiques in vivo. Au cours de cette thèse, nous nous sommes intéressés à deux de ces techniques. La première est l'élastographie quasi-statique par ultrasons permettant de mesurer les déformations locales induites dans un tissu sous l'action d'une contrainte globale. La seconde est l'élastographie par résonance magnétique (ERM) permettant d'accéder localement à une estimation du module de cisaillement. Pour cette dernière technique, une onde de cisaillement est générée au sein du milieu puis imagée a l'aide d'une séquence IRM spécifique. Les images d'ondes acquises permettent la reconstruction du module de cisaillement local. Dans le cadre de ces travaux, une nouvelle technique d'acquisition de l'image d'onde de cisaillement a été proposée, ainsi qu'une méthode de reconstruction du module de cisaillement basée sur l'estimation locale de fréquence par rapport de filtres. Un autre axe de recherche a consisté en l'étude de l'effet d'une précontrainte appliquée à un milieu sur son module de cisaillement mesuré par ERM. Cet effet a tout d'abord été étudié sur des milieux homogènes puis avec des milieux test hétérogènes. Dans ce dernier cas, l'utilisation de l'élastographie quasi-statique par ultrasons s'avère nécessaire pour accéder à la déformation locale du milieu. Cette dernière information a été combinée avec les informations obtenues en ERM pour extraire pour chaque région d'intérêt une courbe déformation/module de cisaillement / The term elastography refers to imaging techniques dedicated to the in vivo investigation of the mechanical properties of biological tissues. During this thesis, we focused on two elastography techniques. The first one is quasi-static ultrasound elastography, able to locally estimate tissue strain induced by a global deformation of a medium. The second one is Magnetic Resonance Elastography (MRE), able to measure the local shear modulus. In MRE, a shear wave is generated within the medium and imaged using a specific MRI sequence. The resulting wave images are then processed to estimate the local shear modulus. A new acquisition scheme of the shear wave images was proposed during this thesis. A method, based on local frequency estimation, was also developed for the estimation of the local shear modulus using the properties of a ratio of filters. Another research axis was the study of the effect of a prestrain application on the measured shear modulus. This effect was first studied with homogeneous media and then with heterogeneous test objects. In this last case, the use of quasi-static ultrasound elastography was necessary to locally access to the medium strain. This information was then combined with the information obtained using MRE to extract, for each region of interest, a strain/shear modulus curve

This master’s thesis deals with creation and modification of several numerical rat’s brain models which are subsequently used in electromagnetic software CST Studio Suite 2014. The first part of the thesis is focused to insertion of exciting source to the model which depends on the used approach. These sources produce signals on the surface of the rat’s brain model which are then analysed. The experimental part of the thesis dealt with three different procedures of cooking agar jelly, which were used for creation of five plate capacitors, which subsequently served for measure electric properties of phantom. The conclusion of this master’s thesis is focused on comparison between results from simulations and experimental parts with a subsequent analysis of the deviations of results and their possible causes.

In this work is proposed the generalized powertrain of the parallel hybrid car. The powertrain is composed from the sub-models of the power sources. Each sub-model is described by the quasi-static modeling. For given routes is computed the power demand. Based on the derived power demand, three energy management systems are tested. First system is based on heuristic rules. The second one use more sophisticated control algorithms - the optimization method. Main idea is based on minimum principle, when the control algorithm tries to minimize the cost function (fuel use, emission). The last one is based on the equivalent consumption minimization strategy.