Ductile failure is a multi-scale phenomenon. In metals, atomic deformation mechanisms interact with micromechanical length-scales defined by the size and distribution of microscopic defects to trigger damage through void nucleation and growth. Coarser length-scales appear with inter-void interactions that coalesce to form mesoscopic damage zones. Finally, the interaction of damage zones with component scale causes macroscopic failure. Coupling between these scales is complicated by the anisotropic nature of plasticity, which is governed by dislocation slip and twinning.
Nanotwinned materials are comprise engineered microstructures that host a copious number of nanoscale twins. These nanoscale twins often play a dual role as agents of material yield strengthening (by acting as barriers to dislocation motion) and softening (via twin boundary migration). Our ongoing focus is on understanding the interaction between these plasticity mechanisms and voids in such layered engineered materials. In this talk, we present the deformation stability and failure of nanotwinned materials whose grain-scale anisotropy is brought about by size effects associated with fine-scale growth twins. Using a length-scale dependent crystal plasticity finite element framework, we investigate the role of twin boundary mediated microstructural evolution in the damage due to nano-void evolution. The interaction between the rates of twin boundary migration and void growth is discussed from the vantage point of macroscopic deformation stability. While the investigation pertains to nanotwinned materials, the observations and analysis may be relevant to analogous situations in multi-layered materials with moving interfaces.
