The stress characteristics near to the grain boundaries of bicrystal and tricrystal specimens

The stress characteristics in the anisotroipic bicrystal and tricrystal specimens have been analyzed by the anisotropic elastic model, orthotropic Hill's model and rate dependent crystallographic model. The finite element analysis results show that non-uniform stresses are induced by the grain boundary. For bicrystal specimens in different crystallographic orientations, there are stress concentrations and high stress gradients near the boundaries. The activation and slip of slip systems a re dependent on the crystallographic orientations of the grains, and also on the relative crystallographic orientations of the two adjunctive grains. For the tricrystal specimens, there is not always stress concentration in the triple junction, and the concentration degree depends on the relative crystallographic orientations of the three grains. Different to the bicrystal specimens, there may be or may be no stress concentration near grain boundaries in the tricrystal specimens, depending on the relative crystallographic orientations of the three grains. The stress concentration near the grain boundaries and triple junction can be high enough for the local plastic deformation, damage and voiding or cracking even the whole specimen is still in the elastic state. Further it can be concluded that homogenous assumption for polycrystalline materials is not suitable to study the meso or micro mechanisms of the damage and fracture as well as their detail processing.