Short Fiber Metal Matrix Composites With Temperature Mechanical Behavior Of Macroscopic And Mesoscopic Numerical Study

At first, the thesis summarizes the studies on high temperature mechanic behavior of metal matrix composites in the recent 10 years world widely. Emphasis is placed on the accomplishments that have been achieved and questions that are needs to be solved from both theory and numerical simulation. Finally, some suggestions are put forward about the direction of this area in the future and the works to be carried out.The paper can be divided in five chapters:The first one: FEM (finite element method) is applied to study the stress and strain distribution of short fiber-reinforced MMC (metal matrix composites) DB(double shear specimens) at high temperature. The applicability of the DB to produce the multi-axial stress state is specially analyzed. The stress and strain distributions and the factors influencing the creep behavior of MMC have been obtained. In the first section, a comparison was carried on different kinds of multi-axial specimens used for isotropic materials. They cannot be used for the MMC, since MMC is anisotropic. A detail FEM model is developed for MMC DB. The distributions of stress and strain in the DB have been obtained, which show the DB can provide a relative uniform shear stress in the shear zone center. The influence of the orientation of the DB specimens on the fiber-existing plane on the behavior is depended on the orientations. When the angle- 9 between the applied shear stress direction and the fiber-existing plane is equal to 45?,the creep strain rate of DB specimens y is maximum. The homogeneous degree of stress distribution is improving with the angle 9 increasing.The second one: Based on the 3D unit cell model of short fiber enforced metal matrix composites, finite element method (FEM) is applied to analyze of the influence on the creep behavior. Special attention is put on the influence of the inter-phase properties and the direction of fiber axial direction to the loading direction. The study shows that the inter-phase properties suchas thickness, elastic and creep material properties have influence on the axial stress states andsteady creep rates of the composites. The loading direction relating to the fiber axial direction hasalso influences.The third one: the computation and analyses of thermal-mechanical cycle for MMC areconducted in this paper. At the first, the 3D unit cell model is founded. The simulation underseveral common cycle loading types are done. The emphasis is played on the residual axial stress,residual axial strain of fiber. A series of conclusions are arrived that the effect on axial stress, strainof fiber is different between symmetry and asymmetry.The fourth one: a new formula has been founded for predicting thermal conductivity rate. Bycomparison, it is more accurate to acquire thermal conductivity rate than methods usually adopted. The fifth one: the quantitative study is conducted on the stress redistribution in multi-fibersystem after single fiber fractured. Based on the detailed analysis, not only fiber space but alsofiber array in the matrix has an effect on the load redistribution among the surrounding fibers.Finally, the tendency of crack was modeled by adopting Gurson model after single fiber fractured;the fiber space can affect the extending of crack in the matrix directly.