In this paper, an integrated numerical model is proposed to investigate the effects of particulate size and volume fraction on the deformation, damage, and failure behaviors of particulate-reinforced metal matrix composites (PRMMCs). In the framework of a random microstructure-based finite element modelling, the plastic deformation and ductile cracking of the matrix are, respectively, modelled using Johnson–Cook constitutive relation and Johnson–Cook ductile fracture model. The matrix-particle interface decohesion is simulated by employing the surface-based-cohesive zone method, while the particulate fracture is manipulated by the elastic–brittle cracking model, in which the damage evolution criterion depends on the fracture energy cracking criterion. A 2D nonlinear finite element model was developed using ABAQUS/Explicit commercial program for modelling and analyzing damage mechanisms of silicon carbide reinforced aluminum matrix composites. The predicted results have shown a good agreement with the experimental data in the forms of true stress–strain curves and failure shape. Unlike the existing models, the influence of the volume fraction and size of SiC particles on the deformation, damage mechanism, failure consequences, and stress–strain curve of A359/SiC particulate composites is investigated accounting for the different possible modes of failure simultaneously.
ii À memória de minha mãe À minha esposa Aos meus familiares eu dedico este trabalho. "... sem Mim nada podeis fazer" (João 15:5) iii Agradecimentos À Deus pela presença constante. Ao meu orientador Dr. Jesualdo Luiz Rossi, por ter acreditado no meu trabalho e pela valiosa participação em todas as etapas do mesmo. Ao CNPq pela concessão da bolsa de estudos. Ao Dr. Luís Felipe C. P. de Lima, pelas orientações e apoio iniciais. Ao Dr. Arnaldo H. P. de Andrade, pelas discussões e sugestões na elaboração dos textos. Ao meu irmão Eng. Edson Souza de Jesus Filho pelo auxílio constante. Aos colegas do MM e IEO que direta ou indiretamente participaram da elaboração deste trabalho. Escola Politécnica da USP, na pessoa da Srta. Márcia Ribeiro pela utilização de equipamentos e auxílio na preparação de amostras. A todo o pessoal da biblioteca do Ipen e à Politécnica da USP, pela colaboração e paciência dispensadas. À minha esposa Valéria Tomi K. de Moraes Jesus pela compreensão, apoio e incentivo constantes e fundamentais para mais esta conquista. adição de partículas de reforço mostrou ser eficiente na melhoria da resistência ao desgaste de todos os materiais compósitos em relação ao material sem reforço. v OBTAINMENT, ABSTRACT The aim of this investigation was the obtainment of metal matrix composites (MMC) by the route of powder metallurgy, and the valuation of these materials with relation to their machining and wear characteristics. Firstly, were obtained pure comercial aluminium matrix composites materials, with 5, 10 and 15% volumectric fraction of silicon carbide particles. Was also obtained a material without reinforcement particles in order to verify by comparison, the influence of adittion of reinforcement particles. The obtained materials were characterized physics (hidrostatic density), mechanics (hardness and tensile tests) and microstructurally (optical microscopy and scanning electron microscopy). The results showed a homogeneous distribution of reinforcement particles in the composite, and improvement in the mechanical properties, mainly tensile strength (UTS) in comparison to the unreinforced material. After, tests were made to verify the materials behavior during machining and to check the performance of several tool materials (cemented carbide, ceramics and polycrystalline diamond). In these tests, values of the cutting force were measured by instrumented tool-holders. Phenomena such as tool wear, built-up edge formation and mechanism of chip formation were also observed and evaluated. The results from the cemented carbide tool tests, were utilisated for the machinability index determination of each material. These results were applied to the Taylor equation and the equation constants for each material and test conditions were determinated. The results showed that the inclusion of silicon carbide particles made extremely difficult the machining of the composites, and only with diamond tool, satisfactory results were obtained. At last, wear tests were performed to verify the influence of the reinforcement...
The tribological aspects of contact are greatly affected by the friction throughout the contact interface. Generally, contact of deformable bodies is a nonlinear problem. Introduction of the friction with its irreversible character makes the contact problem more difficult. Furthermore, when one or more of the contacting bodies is made of a viscoelastic material, the problem becomes more complicated. A nonlinear time-dependent contact problem is addressed. The objective of the present work is to develop a computational procedure capable of handling quasistatic viscoelastic frictional contact problems. The contact problem as a convex programming model is solved by using an adaptive incremental procedure. The contact constraints are incorporated into the model by using the Lagrange multiplier method. In addition, a local-nonlinear nonclassical friction model is adopted to model the friction at the contact interface. This eliminates the difficulties that arise with the application of the classical Coulomb’s law. On the other hand, the Wiechert model, as an effective model capable of describing both creep and relaxation phenomena, is adopted to simulate the linear behavior of viscoelastic materials. The resulting constitutive integral equations are linearized; therefore, complications that arise during the integration of these equations, especially with contact problems, are avoided. Two examples are presented to demonstrate the applicability of the proposed method.
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