Meso-mechanical Cyclic Constitutive Study For The Ratchetting Of Particulate Reinforced Metal Matrix Composites

Particle-reinforced metal matrix composites (PRMMCs) are being widely used in the areas of military industry, aerospace, automotive industry and sporting goods (eg. link of satellite, lightweight composite armor, engine piston and cylinder of cars and head of Golf clubs) due to their good performances in lightweight, high strength, good thermal stability, lower production cost and macro isotropy. In these areas, the structure components are often subjected to cyclic loading and sometimes to high temperature and heavy pressure. It is well known that during the asymmetrical cyclic stressing, a cyclic accumulation of inelastic deformation will occur in the structure, which is called as ratchetting. Since the ratchetting behaviour may reduce the fatigue life or cause unacceptable plastic deformation for the structures, it is one of the important issues which must be concerned in engineering application. In the last two decades, a lot of experimental and theoretical studies have been performed on the ratchetting of the metal materials. The elasto-plastic and visco-plastic cyclic constitutive models for the ratchetting of monolithic metal materials have been achieved to great extent. However, for heterogeneous materials such as composites, the existed studies are mainly focused on the cyclic stress-strain responses presented under the strain-controlled cyclic loading condition; the cyclic constitutive model for the ratchetting of composites is still a challenge work. So detailed experimental observation and finite element simulation are necessary to reveal the ratchetting of composites and then to establish a meso-mechanical cyclic constitutive model which can reasonably describe the ratchetting of composites. The work will make an important breakthrough in the cyclic constitutive models, and will promote the development of solid mechanics on the aspect of heterogeneous materials. The research is also of tremendous application value for the prediction of fatigue life and reliability design for the engineering structures made from the composites.In order to carry out a study on the ratchetting of the PRMMCs, the following issues have been addressed in this thesis:1. Detailed finite element simulations were carried out for the ratchetting of SiCp/6061A1alloy composites (volume fractions of14%and21%) at room temperature. In the simulations, the influence of the particle volume fractions, shapes and distribution on the ratchetting of the composites were discussed, and some significant results were obtained for the construction of meso-mechanical constitutive models for the PRMMCs. Moreover, based on the finite element simulation, the evolution of plastic deformation in the matrix alloy and its distribution features were observed, which will supply significant information for the studies of meso-mechanisms of the early damage and failure in the PRMMCs.2. Base on the Hill’s incremental and Eshelby equivalent inclusion theory, the Mori-Tanaka homogenization formulations were extended, and a new meso-mechanical cyclic elasto-plastic constitutive model was proposed to predict the time-independent ratchetting of PRMMCs by considering the corresponding experiments. The reasonability and accuracy of the proposed model to describe the ratchetting of the composites were verified by comparing the predicted results with the corresponding experimental ones.3. Base on the framework of unified visco-plasticity, Eshelby equivalent inclusion theory, and the generalized incremental affine linearization formulation, the Mori-Tanaka homogenization approach was extended into its visco-plastic version. A new meso-mechanical cyclic visco-plastic constitutive model was then proposed to predict the time-dependent ratchetting of PRMMCs. Finally, the time-dependent ratchetting of the composites was simulated by the proposed model at room and high temperature, and the simulated results were verified by comparing with the corresponding experiments.4. The multiaxial ratchetting of the PRMMCs was simulated by the newly developed meso-mechanical cyclic elasto-plastic and visco-plastic constitutive models, and the simulated results were verified by the comparisons with the corresponding finite element simulations.