3-D Finite Element Analysis For Ratcheting Of Particle Reinforced Metal Matrix Composites

A cyclic accumulation of plastic deformation(i.e.,ratcheting) will occur in the material when an asymmetrical cyclic stress is applied. Ratcheting effect is important for the safety design and life assessment of engineering structures, which was extensively studied. From the existing researches on the particulate reinforced metal matrix composites (PRMMCs), it is seen that the mechanical behavior of PRMMCs is remarkably affected by the size, shape and distribution of the particulates, as well as interfacial bonding states. However, only the monotonic tensile behavior of the composites was emphasized in the existing work, and the mono-particle unit cell employed is too small to reflect more microstructure features of the composites. It is necessary to carry out the numerical simulation on the ratcheting behavior of the composites using 3-D multi-particle unit cells.The thesis mainly concerns the following issues:(1) Based on the 2-D analysis of the monotonic tensile and ratcheting behaviors of SiC_p/6061Al composites, the effects of interfacial thickness and bonding states on the mechanical properties of the composites were discussed by employing a new cyclic ratcheting constitutive model. Some microscopic deformation features in the matrix and the interface, and their evolution rules were analyzed. The results show that the model with thinner interface approaches more nearly to perfect interface; the better the interfacial bonding is, i.e., the higher Young's modulus, yield strength and hardening modulus are, and then the smaller the ratcheting strain.(2) The effect of particulate arrangement on the ratcheting is also discussed by using 3-D multi-particle unit cell. The microscopic features, such as the particulate shape, numbers and size as well as the arrangement, were concerned in the numerical simulation of the ratcheting using a 3-D multi-particle unit cell generated by Random Sequential Adsorption(RSA) method. It is concluded that increasing the particulate numbers contained in the unit cell and ensuring the uniform arrangement and size of particles can enhance the reinforcement of the particles.(3) The time-dependent ratcheting behavior of SiC_p/6061Al composites was numerically analyzed at room and high temperatures using a 3-D multi-particulate unit cell with certain arrangement of particles and a suitable choice of interfacial parameters. In the prediction, an advanced cyclic visco-plastic constitutive model which can describe reasonably the time-dependent ratcheting behavior of the matrix material is employed. The capability of the model to predict the ratcheting was addressed by comparing the simulated results with the experimental ones. It is shown that the weak interface model with suitable interfacial parameters provides more reasonable simulation to the time-dependent ratcheting of the composites than the perfect interface model does.