Microstructural Modeling of the Mechanical Behavior of Face-Centered Cubic Nanocrystalline-Twinned Systems

Nanocrystalline-twinned materials exhibit significantly higher strength and ductility than nanocrystalline face-centered cubic (f.c.c.) materials without twins. In this investigation, a dislocation-density-based multiple-slip crystalline constitutive and a nonlinear finite element formulation have been used to understand how twin volume fractions, grain and twin orientations and texture, dislocation-density accumulation, and large inelastic strains affect the competing effects of strengthening and toughening mechanisms in nanotwinned materials. The predictions have indicated that grain and twin orientations with respect to different loading axes significantly affect how dislocation densities evolve, and that this has a dominant effect on both ductility and strength. The predictions were validated with experiments pertaining to nanotwinned f.c.c. copper aggregates. The validated predictions can potentially be used as design guidelines for optimizing the mechanical behavior of nanotwinned crystalline materials, such that behavior can be mitigated and controlled at the nanocrystalline scale.