Simulation of Materials Damage in the Field of Internal Stresses

Abstract

Internal stresses occur within a material in the presence of non-uniform deformation. The main types of the internal stresses are the thermal and residual ones and fields of structural defects as well. These stresses have an essential effect on the diffusion processes kinetics. In this case change of the strength material properties takes place. The properties degradation is accompanied by damaging and failing the material. The physical mechanisms underlying changes of properties include, for example, decreasing of surface fracture energy, stress corrosion cracking, and hydrogen embrittlement. The diffusion process is described by a non-stationary equation of a parabolic type under both initial and boundary conditions. The purpose of this paper is simulating the material damage as a result of running the diffusion processes. Triple grain boundaries are considered as structural defects. They serve as stress concentrators under dynamic and temperature loadings. This is caused by the orientation dependence of elastic and thermophysical characteristics of the contiguous grain material. The dilatation field of considered defects depends logarithmically on the radial coordinate. Such a dependence enables one to obtain an exact analytical solution for the task on hydrogen segregation kinetics. Analytical relations for the field of atomic hydrogen concentration near the triple grain boundaries are given. If the concentration of hydrogen atoms exceeds the solubility limit at a given temperature, hydride phases are formed in some metals (e.g., Zr). Hydride growth kinetics in the stress field of structural defects under study is considered. The changes of the volume hydride are accompanied by microcrack formation along the grain boundaries. The results of theoretical analysis are employed to explain the hydrogen embrittlement of metals.