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

Molecular Dynamics (MD) simulations of uniaxial tension at nanolevel have b een 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 workmate rials due to void formation, their coalescence into nanocracks, and subsequ ent fracture or separation were observed similar to their behavior at macro scale. The engineering stress-strain diagrams obtained by the MD simulation s of the tensile specimens of various materials show a rapid increase in st ress up to a maximum followed by a gradual drop to zero when the specimen f ails 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 ducti lity of the material decreases. In this investigation, the strain to fractu re is observed to be lower with the BCC materials than FCC materials. In th e case of BCC crystals, no distinct linear trend in the engineering stress- strain characteristics is observed. Instead, rapid fluctuations in the forc e values were observed. If the drop in the force curves can be attributed t o 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 re ported in the literature. While good correlation is found between the D- an d alpha -parameters of the Morse potential with the ultimate strength and t he strain to failure for the FCC metals, no such correlation is found for t he BCC metals. From this, it appears that Morse potentials may not represen t the deformation behavior of BCC metals as accurately as FCC metals and al ternate potentials may need to be considered. (C) 2001 Elsevier Science Ltd . All rights reserved.