Tensile Failure of Single-Crystal and Nanocrystalline Lennard-Jones Solids Under Uniaxial Strain

We investigate using molecular dynamics, the tensile failure of single-crystal and nanocrystalline Lennard-Jones solids under uniaxial strain. Stresses are relaxed by plasticity and tensile failure, which are induced via stacking faults, twin planes, void nucleation and growth, and their interactions. Stacking faults and twin planes as well as multiple nanovoids are nucleated at grain boundaries in a nanocrystalline solid. Void formation is characterized by under-coordinated atoms with coordination number ≤ 7, and the critical void size is comparable to a vacancy. For a single crystal, the number of stacking faults and twin planes decreases during failure mostly due to the absorption by nanovoids. In contrast, it increases with strain monotonically for a nanocrystalline solid, where abundant grain boundaries help the nucleation and deter the propagation and absorption of the stacking faults and twin planes, inducing effective dislocation pile-ups at grain boundaries even in the presence of nanovoids.