Papers by Author: Shi E Yang

Abstract: The mechanical process of single-crystal aluminium thin films under uniaxial tensile strain was simulated with molecular dynamics method at different temperature. The stress–strain curve and potential energy–strain curve of thin aluminium film under uniaxial tensile deformation were obtained by molecular dynamics simulations. With the changes of sample temperatures in uniaxial extension, the variation characteristics of stress–strain curves are alike at the elastic stage and different at the plastic one below and above 370 K, respectively. From the stress–strain curves, we gained the first local maximum stress-temperature curve and the strain at the first local maximum stress-temperature curve, and found that the strange temperature dependence of first local maximum stress: when the temperature is above 370 K, the stress goes down quickly with temperature, and when below 370 K, it descends slowly. With increasing temperature, the difference between two strain values corresponding to two maximal potential energies changes slowly below and above 370K but it goes up quickly about 370K. By these dependences, we have identified the critical temperature （370K） for the transition of plastic flow mechanism.

Abstract: The molecular dynamics simulations are performed with single-crystal copper thin films under uniaxial tensile and cyclic loading to investigate temperature effects on the mechanical responses. With the changes of sample temperatures in uniaxial extension, the variation characteristics of maximum stress, the Young’s modulus, the maximal potential energy, the atomic structure of the emerging dislocation, and activation volume and activation free energy at the maximum stress point make us identify and explain the critical temperature for the transition of deformation mechanism in a temperature range from 293 to 460 K. Under cyclic loading, with raising temperature, the number of cycles to failure of copper films increases under different manners in different temperature range, which can be explained by our constructing model based on the evolutionary features of dislocation. Thus, the mechanisms of the strange temperature dependence of tensile and cyclic deformation have been explained. When the temperature is above 370 K, the rate controlling mechanism is dislocation climbing during uniaxial loading, and the number of cycles to failure goes up quickly with temperature; when below 370 K, the mechanism of uniaxial tensility is mainly characterized by the overcoming of Peierls–Nabarro barrier and a few localized pinnings, the number of cycles rises slowly; and when about 370 K, the mechanism in single-axial tension is pipe diffusion, the number of cycles increases at middle speed.