MICROSTRUCTURAL MODEL OF INTERGRANULAR FRACTURE DURING TENSILE TESTS

A microstructural model of intergranular fracture in textured material s is presented. In this model, the material is represented by a two-di mensional microstructure with non-regular polygonal grains which repre sents material's texture and grain shape measured in experiments or ca lculated from Monte Carlo simulations. The grain boundary character, g rain boundary energy, and fracture stress are assigned to each grain b oundary according the grain boundary character distribution. Intergran ular fracture susceptibility is analyzed by defining the probability o f finding a continuous path along the grain boundaries which are intri nsically susceptible to fracture. In this analysis the orientations of the grain boundary with respect to the applied or residual tensile st ress axis is considered. The probability of intergranular fracture for each grain boundary depends on the intergranular fracture resistance, the interface orientation relative to the stress axis, and a value of the tensile stress acting on the grain boundary. The crack arrest dis tance and the fracture toughness are calculated in terms of the freque ncy of low-energy grain boundaries, fracture stress of low-energy grai n boundary, angle distribution of grain boundary interfaces, and aniso tropy of grain shape. The results indicate that the fracture toughness increases and the crack arrest distance decreases dramatically with i ncreasing the frequency of the low-energy grain boundaries. Lowering t he grain boundary energy can improve the fracture toughness and decrea se the crack arrest distance. The angle distribution of grain boundary interfaces and the grain shape factor are also very effective in cont rolling the fracture toughness. High fracture toughness of polycrystal line materials is related to the presence of a high frequency of low-e nergy boundaries which are resistant to fracture. The best fracture to ughness for brittle materials can be achieved by controlling the frequ encies of the low-energy grain boundaries, the grain boundary characte r, and the boundary inclination.