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The effect of hydrostatic pressure on the shear deformation behavior of 10 Cu symmetric tilt interfaces has been investigated in the athermal deformation regime (10 K) using molecular dynamics simulations. Cu bicrystals were deformed under shear with a superimposed hydrostatic stress, until initial yield. For most interfaces, the shear strength increased with increasing compressive hydrostatic pressure. However, for the Σ 9 { 221 } and Σ 5 { 210 } interfaces, this trend was reversed. Neither the sign nor the magnitude of the pressure-induced elevation in shear strength was found to correlate with interface structure or particular deformation mechanism(s). The findings suggest that in general, metrics of interfacial excess volume and dilatation cannot reliably predict the pressure-sensitivity of shear strength; however, for interfaces containing the E structural unit, the annihilation of free volume appears to correlate well with the observed pressure-sensitivity.

Over the past decade, numerous efforts have sought to understand the influence of twin boundaries on the behavior of polycrystalline materials. Early results suggested that twin boundaries within nanocrystalline face-centered cubic metals have a considerable effect on material behavior by altering the activated deformation mechanisms. In this work, we employ molecular dynamics simulations to elucidate the role of twin boundaries on the deformation of 〈 1 0 0 〉 columnar nanocrystalline copper at room temperature under uniaxial strain. We leverage non-local kinematic metrics, formulated from continuum mechanics theory, to compute atomically-resolved rotational and strain fields during plastic deformation. These results are then utilized to compute the distribution of various nanoscale mechanisms during straining, and quantitatively resolve their contribution to the total strain accommodation within the microstructure, highlighting the fundamental role of twin boundaries. Our results show that nanoscale twins influence nanocrystalline copper by altering the cooperation of fundamental deformation mechanisms and their contributed role in strain accommodation, and we present new methods for extracting useful information from atomistic simulations. The simulation results suggest a tension–compression asymmetry in the distribution of deformation mechanisms and strain accommodation by either dislocations or twin boundary mechanisms. In highly twinned microstructures, twin boundary migration can become a significant deformation mode, in comparison to lattice dislocation plasticity in non-twinned columnar microstructures, especially during compression.

This paper presents the application of a recently developed concurrent atomistic continuum (CAC) methodology in coarse-grained (CG) atomistic simulations of dislocation nucleation and migration in face-centered cubic (fcc) Al, Ni and Cu crystals, using an EAM force field and an adaptive mesh refinement strategy. The CAC method is based on recently developed atomistic field theory (AFT) that frames the problem in terms of a continuum field representation of lattice and sublattice atomic arrangements. Four sets of CG models with different finite element mesh refinement are constructed to test the accuracy and efficiency of the CG method relative to full molecular dynamics (MD). Simulation results show that the CG method is able to reproduce key phenomena of dislocation dynamics in initially defect free fcc crystals, including strain bursts caused by dislocation nucleation and migration, the structure of leading and trailing partial dislocations separated by equilibrium stacking faults in Al, formation of intrinsic stacking fault ribbons in Ni and Cu, and 3D migration of curved dislocations, all comparable with results of MD simulations. CG simulations have also revealed that the yield strength of Al depends on the thickness of the specimens as well as the operative deformation mechanisms. The effects of mesh size and adaptive mesh refinement on CG simulation results are analyzed and discussed.