Role of microstructural geometry in the deformation and failure of polycrystalline materials

A deeper understanding of the deformation and failure mechanisms in polycrystals is of utmost importance for their reliable use as engineering materials. These mechanisms are strongly influenced by the geometry of the granular arrangement. In this work, two-dimensional intergranular quasi-static crack propagation in brittle polycrystals and grain boundary sliding in creeping polycrystals have been numerically investigated with the aid of a Generalized Finite Element Method. The role of the parameters defining the cohesion of the grain boundaries in intergranular crack propagation has been investigated. It is shown that under certain circumstances crack paths are not affected by variations of cohesive law parameters. Moreover, beyond a certain brittleness threshold, the load-displacement curves can be mutually scaled and obtained from each other using simple linear elastic fracture mechanics relations. The insensitivity of crack paths to variations of cohesive law parameters and the mutual scaling of load-displacement curves can be exploited to avoid computationally expensive simulations. The uniqueness of the crack path with respect to cohesive law parameters has also enabled the study of the scaling properties of crack profiles in brittle polycrystals. The results of this study shed light on the roughening mechanism in 2D brittle solids. Finally, it has been shown that microstructural randomness has a strong influence on the response of creeping polycrystals with free grain boundary sliding. This study provides an understanding of the role of microstructural geometry in polycrystalline materials undergoing intergranular fracture and grain boundary sliding.