Numerical modelling of intergranular fracture in polycrystalline materials and grain size effects

Abstract

In this paper, the phenomenon of intergranular fracture in polycrystalline materials is investigatedusing a nonlinear fracture mechanics approach. The nonlocal cohesive zone model (CZM) for finite thicknessinterfaces recently proposed by the present authors is used to describe the phenomenon of grain boundaryseparation. From the modelling point of view, considering the dependency of the grain boundary thickness onthe grain size observed in polycrystals, a distribution of interface thicknesses is obtained. Since the shape andthe parameters of the nonlocal CZM depend on the interface thickness, a distribution of interface fractureenergies is obtained as a consequence of the randomness of the material microstructure. Using these data,fracture mechanics simulations are performed and the homogenized stress-strain curves of 2D representativevolume elements (RVEs) are computed. Failure is the result of a diffuse microcrack pattern leading to a mainmacroscopic crack after coalescence, in good agreement with the experimental observation. Finally, testingmicrostructures characterized by different average grain sizes, the computed peak stresses are found to bedependent on the grain size, in agreement with the trend expected according to the Hall-Petch law.