Made available in DSpace on 2016-06-02T19:44:06Z (GMT). No. of bitstreams: 1 2963.pdf: 938446 bytes, checksum: 51bf8a04d7160d87fa142f9dc4d6c0c4 (MD5) Previous issue date: 2009-06-30 / Financiadora de Estudos e Projetos / The formation of equivalent stimuli classes is a psychological phenomenon that has important characteristics for the experimentation of processes involving symbolic behavior acquisition. This kind of behavior has been the target of a wide variety of contemporary studies which have also demonstrated the possibility of such approach to generate symbolic behavioral repertoires based only on the teaching of some relations between stimuli. It is vital to investigate the parameters that optimize the establishment of equivalent stimuli classes desired by the researcher when defining the behavior to be installed through the procedure of matching-to-sample (MTS). Studies in the area have widely shown that after training A1B1 and B1C1, there is an emergency of some relations, such as B1A1, C1B1, A1C1 and C1A1, which demonstrate, respectively, the properties of reflexivity, symmetry, transitivity and equivalence. One of the parameters that determine the effectiveness of a procedure on class formation is the type of control relation exercised by the comparison stimuli in MTS attempts. Therefore, the present study aimed to identify the role of specific types of training of conditional discriminations in the establishment of relations of control for selection and rejection. Study participants were two teenagers with Down syndrome. The training consisted on MTS sessions with and without mask in two training types: non-nodular and nodular. The former occurred by presenting stimuli which function was either model or comparison only, and the latter was characterized by presenting stimuli with dual function, i.e. model and comparison simultaneously. Verification testing of the control relations established at baseline was made after non-nodular training and after nodular training, and only then verification testing of behavioral emergency was made. Two stimuli sets involved attempts with mask, while other two consisted of attempts without a mask. The experiment was specifically designed in a way that the training of a stimuli set with mask has occurred almost simultaneously with the training of a stimuli set without mask. Thus, the influence of historical undesirable variables was avoided on deductions made from performance comparison of the two different attempts (with or without mask). Results demonstrated, generally, that the training procedure used was very effective in teaching and formation of classes, what made difficult even to compare the greater effectiveness of the procedures with or without use of mask in the training of conditional relations. It is suggested the replication of this study, with a larger number of participants of this same population, so that it is possible to evaluate the data generality. / A formação de classes de estímulos equivalentes é um fenômeno psicológico que possui características importantes para a experimentação de processos relacionados à aquisição do comportamento simbólico. Esse tipo de comportamento tem sido alvo de uma grande variedade de estudos contemporâneos que tem demonstrado, inclusive, a possibilidade desse tipo de abordagem em gerar repertórios comportamentais simbólicos com base no ensino de apenas algumas relações entre estímulos. É de fundamental importância investigar os parâmetros que aperfeiçoam o estabelecimento das classes de estímulos equivalentes desejadas pelo pesquisador, ao definirem o comportamento instalado por meio do procedimento de matching-to-sample (MTS). Estudos da área verificaram amplamente que, após o treino de A1B1 e B1C1, há emergência de algumas relações, tais como, B1A1, C1B1, A1C1 e C1A1, que demonstram, respectivamente, as propriedades de reflexividade, simetria, transitividade e equivalência. Um dos parâmetros que determinam a efetividade de um procedimento na formação de classes é o tipo de relação de controle exercido em tentativas de emparelhamento com o modelo. A partir disso, o presente estudo teve como objetivo identificar o papel de tipos específicos de treino de discriminações condicionais no estabelecimento de relações de controle por seleção e rejeição. Participaram do estudo dois jovens com síndrome de Down. O treino consistiu em sessões de MTS com e sem máscara, aonde houve treinos dos tipos não nodular, com um estímulo apresentando função única de modelo ou de comparação exclusivamente, e houve também treino do tipo nodular, caracterizado por estímulos com dupla função, ou seja, modelo e comparação simultaneamente. Os testes de verificação das relações de controle estabelecidas na linha de base foram feitos após o treino não nodular, em seguida, após o treino nodular, e só então os testes de verificação de emergência comportamental foi aplicado. Duas estruturas envolveram tentativas com máscara, enquanto as outras duas estruturas constituíram-se de tentativas sem máscara. O desenho experimental foi especificamente planejado para que, o treino de uma estrutura de treino com máscara ocorresse quase simultaneamente com o de uma estrutura sem máscara. Desse modo, evitou-se o papel de variáveis históricas indesejáveis para a inferência derivada da comparação do desempenho nos dois tipos diferentes de estruturas e tentativas. Os resultados mostraram, de um modo geral, que o procedimento de treino empregado foi bastante eficiente no ensino e formação de classes, o que dificultou, inclusive, a comparação da maior efetividade do procedimento com ou sem uso de máscara no treino das relações condicionais. Sugere-se que o estudo, embora extenso no que diz respeito ao ensino e teste de relações, considerando ainda o tipo de população envolvida, seja replicado com um número maior de participantes para que a generalidade dos dados seja avaliada.

In the present thesis, fatigue behavior of nodular cast iron (NCI) is investigated using micromechanical simulations. An elastic-plastic porous material experiences an increase in a void volume fraction with each cycle of loading. This is called void ratchetting. The hypothesis of this thesis is to explain the fatigue failure of NCI using void ratchetting mechanism. The strain-life, stress-life, notch support effect, and fatigue crack growth are studied using the micromechanical simulations. In all these studies, matrix material is defined as an elastic-plastic with isotropic/kinematic hardening. No damage law is used to define material degradation. The axisymmetric cell model is developed to study strain-life and stress-life approaches for fatigue. The cell model is subjected to cyclic loading and cycle by cycle simulations are carried out until failure. The failure of the cell model is defined based on the drop in the macroscopic response of the cell model. The notch support effect is investigated using a 2D plane strain model within stress-life concept. From the simulation results, strain-life and stress-life curves are extracted, and they are in qualitative and quantitative agreement with experimental data collected from literature. The fatigue crack growth is studied using a micromechanical cell model under small scale yielding conditions. The graphite particles are considered as voids, and they are resolved discretely in fracture process zone. The region outside of the fracture process zone is considered as a homogenized medium. When positive alternating loads are applied, ligaments in the fracture process zone show ratchetting behavior, which is responsible for an effective fatigue crack growth. This mechanism is relevant for the fatigue crack growth in NCI. The 2D plane strain boundary layer model is able to predict the effect of load ratio on threshold for the fatigue crack growth and the fatigue crack growth rate. The fatigue crack growth rate curves obtained from the simulations are compared with experimental data. It is essential to note that the void ratchetting (plastic collapse of the intervoid ligaments) is a crucial mechanism in NCI and more focus should be given to this mechanism as it is simple to implement and gives satisfying simulation results.

Ce mémoire présente une méthode mise au point pour caractériser et analyser des fissures de fatigue présentant un fort caractère tridimensionnel dans des matériaux métalliques opaques. L'analyse consiste à déterminer avec précision la position du front de la fissure étudiée et à mesurer des valeurs de facteurs d'intensité des contraintes le long du front par projection sur les séries de Williams du champ de déplacement issu de la corrélation numérique d'images 3D obtenues par tomographie aux rayons X. La corrélation d'images 3D numériques est utilisée afin de mesurer le champ de déplacement en volume lors de la mise sous chargement d'une éprouvette fissurée fatiguée. La corrélation d'images nécessitant un mouchetis, le matériau retenu pour les expériences est la fonte à graphite sphéroïdal car il présente un mouchetis 3D naturel (les nodules de graphites) parfaitement imagé par tomographie aux rayons X. Le cyclage est appliqué à l'aide d'une machine de fatigue in situ permettant d'alterner des phases de propagation de la fissure avec des acquisitions tomographiques sous différentes charges. L'introduction d'un défaut artificiel (une entaille obtenue par usinage laser) permet de maîtriser l'amorçage et la propagation de la fissure in situ. La méthode de corrélation d'images 3D numériques employée dans ces travaux étant basée sur des éléments finis, nous avons cherché à tirer profit de différents outils développés dans le cadre de cette méthode. Les surfaces libres sont spécifiées afin de bien conditionner le maillage et un enrichissement dans l'esprit des X-FEM permet de renseigner la fissure dont la position est repérée grâce à la trace laissée dans le résidu de corrélation entre l'image avant cyclage et la dernière image acquise. Une régularisation mécanique est également introduite dans le calcul sous forme d'un filtre de longueur d'onde choisie. Le champ de déplacement mesuré avec précision est ensuite projeté sur les séries de Williams augmentées des termes correctifs de Leblond et Torlai qui prennent en compte la courbure du front de la fissure. L'annulation du terme super-singulier d'ordre -1 des séries de Williams est utilisée pour détecter la position du front de la fissure. Une procédure itérative a été mise en place afin de concilier l'enrichissement et la courbure du front avec la projection sur les séries de Williams. Une fois la position du front 3D de la fissure déterminée et les valeurs des facteurs d'intensité des contraintes associées calculées, les résultats obtenus sont confrontés à la littérature. / This manuscript describes a methodology used to compute Stress Intensity Factor values along the curved front of a fatigue crack inside a nodular cast iron. An artificial defect is introduced at the surface of a small sample. The initiation and growth of a fatigue crack from this defect during constant amplitude cycling is monitored in situ by laboratory x-ray tomography. The method for processing the 3D images in order to compute SIF values is described in detail. The results obtained show variations of the stress intensity factor values along the crack front.

The diploma thesis is concerned with evaluation of actual production technology of part “hydraulics cover” and with design of new, progressive variation machining of this part. Solution is focused at first on rationalization of cutting tools and choice of suitable cutting tools. An effort is to achieve shorter production time and decrease costs on production of component. With this problem is related alteration of technological documentation and technical economic evaluation for determination return rate of investments into progressive cutting tools.