Low temperature dependence of mechanical process of ultrathin aluminium films: molecular dynamics simulations

The mechanical process of aluminium thin films under uniaxial tensile strain was simulated with molecular dynamics method in a low temperature range from 40 to 250 K. The stress-strain curve and potential energy-strain curve of aluminium thin film under uniaxial tensile deformation were obtained. The variation characteristics of stress-strain curves with temperature are alike at the elastic stage. However, at the plastic stage the stress-strain curves are grouped into three categories (40 K ≤ T < 100 K, 100 K ≤ T < 200 K, 200 K ≤ T ≤ 250 K). From the stress-strain curves, we found the strange temperature dependence of the local maximum stress, maximal potential energy and their corresponding strain: when the temperature is below 100 K, they go down quickly with temperature, and when above 100 K and below 200 K, they descend slowly and do very slowly above 200 K. Therefore, we have identified two critical temperatures for the transition of plastic flow mechanism.