Molecular dynamics (MD) simulation of uniaxial tension of some single-crystal cubic metals at nanolevel

Abstract

Molecular Dynamics (MD) simulations of uniaxial tension at nanolevel have been carried out at a constant rate of loading (500 m s −1) on some single-crystal cubic metals, both FCC (Al, Cu, and Ni) and BCC (Fe, Cr, and W) to investigate the nature of deformation and fracture. Failure of the workmaterials due to void formation, their coalescence into nanocracks, and subsequent fracture or separation were observed similar to their behavior at macroscale. The engineering stress–strain diagrams obtained by the MD simulations of the tensile specimens of various materials show a rapid increase in stress up to a maximum followed by a gradual drop to zero when the specimen fails by ductile fracture. The radius of the neck is found to increase with an increase in the deformation of the specimen and to decrease as the ductility of the material decreases. In this investigation, the strain to fracture is observed to be lower with the BCC materials than FCC materials. In the case of BCC crystals, no distinct linear trend in the engineering stress–strain characteristics is observed. Instead, rapid fluctuations in the force values were observed. If the drop in the force curves can be attributed to the rearrangement of atoms to a new or modified crystalline structure, it appears that BCC materials undergo a significant change in their structure and subsequent realignment relative to the FCC materials, as previously reported in the literature. While good correlation is found between the D- and α-parameters of the Morse potential with the ultimate strength and the strain to failure for the FCC metals, no such correlation is found for the BCC metals. From this, it appears that Morse potentials may not represent the deformation behavior of BCC metals as accurately as FCC metals and alternate potentials may need to be considered.