Non-equilibrium MD modeling and simulation to extract mechanical properties of copper nanoparticles under ultra-high strain rate loading

Abstract

Molecular dynamics (MD) simulations have been carried out to evaluate the mechanical properties of Cu nanoparticles under tensile and compressive loading at ultra-high strain rate regime. Simulations have been carried out in a way analogous to real experiments; but at strain rates of magnitude several orders greater than those used in the experiments for bulk Cu. The engineering stress-strain curves obtained from tensile loading have shown an initial linear elastic region, followed by a plastic region that involves deformation by local necking. However, under the ultra-high strain rates considered in the present simulation, no uniform plastic deformation region is observed. A significant rise in temperature of the nanoparticles has been observed during the tensile and compressive deformation, as a natural consequence of any deformation process. The yield strength and Young’s modulus of Cu nanoparticles have been calculated from the engineering stress-strain curves generated by a set of MD simulations and correlated with strain rate, equilibration temperature, particle size, etc. The tensile deformation at various ultra-high strain rates shows the ductile-to-brittle transition behavior of the Cu nanoparticles after exceeding a certain critical strain velocity which decreases with the increase in particle size. The extrapolated results have indicated that the Cu nanoparticles are several times stronger than bulk Cu and their mechanical properties are highly dependent on the particle size. The present study would provide a useful guideline for the design of nanoparticles under the condition of mechanical loading in advanced applications.