Molecular Dynamics Study of Uniaxial Deformation in Perfect and Defective Aluminum

Abstract

In materials, strength is usually controlled by the occurrence of grain boundaries, dislocations, voids, and other microstructural defects. molecular dynamics (MD) simulations with the embedded atom method potential have been employed to investigate the uniaxial tension and compression of single crystal aluminum with and without defects. In this paper, defect refers to a void or grain boundary. For perfect crystal aluminum, the ideal strengths and stress-strain curves obtained from the MD simulations agree well with those obtained by first principles calculations. The strength and ductility of Al decrease with the occurrence of void and grain boundaries. The effect of void size on the uniaxial stress-strain relations is investigated. Also, dislocation nucleation and emission from the void free surface are observed. In order to study the effect of a grain boundary, we generate a symmetric tilt grain boundary Σ5(310) and strain is imposed perpendicular to the boundary interface. We can clearly see that fracture starts in the grain boundary. The observed defect pattern is expected to provide some helpful insights into the damage mechanism of ductile materials at the microscale. The effects of temperature, strain rate, and crystalline direction on the ideal strength are also discussed.