A mesoscale model for interface-mediated plasticity: Investigation of ductile and brittle fracture

The presence of grain boundaries significantly impacts the mechanical properties of crystalline materials, particularly when dealing with micro- or nano-scale samples. The nature of dislocation-grain boundary interactions governs the macroscopic plastic behavior. We employ a mesoscale interface boundary condition, incorporating with a two-dimensional continuum dislocation dynamics framework, to investigate these dislocation-grain boundary interactions, examining both single- and multiple-slip numerical cases. The simulations show that, apart from affecting strength and ductility, the accumulation of dislocations near a grain boundary generates stress concentrators and initiates intergranular brittle fracture. Consequently, dislocation-grain boundary interactions manifest a competition between ductile and brittle failure modes upon loading. We further analyze the upturn in strain hardening rate across a range of interfacial reaction kinetics, which can be attributed to the competition between the rates of dislocation accumulation and interfacial reactions at the grain boundary.