THE EVOLUTION OF INTRAGRANULAR MICROCRACKS INDUCED BY STRESS-, ELECTRO- AND THERMO-MIGRATIONS

Based on the classical theory of surface diffusion and its weak statement,a finite element analysis is conducted for the evolution of intragranular microcracks in metal materials due to the curvature,stress field,electric field and thermal gradient. The effects of the aspect ratio,the magnitude of the stress,the electric field and the thermal stress field induced by the electric current on the evolution are investigated in detail. The results show that the evolution of microcracks depends on the competition of surface energy,strain energy and electric energy. There exists a critical value of electric filed and stress filed for a given aspect ratio . When and,the microcrack will evolve into a cylinder directly. When or,the microcrack will be divided into two right-and-left or lower-and-upper microcracks. The thermal stress caused by the electric current could decrease the value of,which is conducive to the microcrack splitting. Besides,thermal stress can increase the drift speed and decrease the splitting time of the microcrack