On Accurate Approach for Molecular Dynamics Study of Ideal Strength at Elevated Temperature

Influence of temperature on ideal shear strength (ISS), τc, of two fcc metals (Al and Cu) was studied by means of molecular dynamics simulations. To get reliable results we investigated influence of parameters of the applied Parrinello-Rahman stress control method and implemented damping of simulation cell fluctuations to avoid occurrence of structural instability assisted by too high fluctuations. The damping successfully reduces strain and stress fluctuations during simulations if the damping factor is specified properly. We also investigated simulation cell size effect to evaluate minimal number of atoms providing reliable results in order to reduce computational efforts and estimate the possibility of applying ab initio calculations. Recently developed embedded atom method (EAM) interatomic potentials for both metals were also examined to find most appropriate for our study. EAM potential developed by Zope et al. and Mishin et al. were revealed to be most suitable for Al and Cu, respectively. It is essential to choose appropriate simulation parameters and interatomic potentials for the valid evaluation of ISS at elevated temperatures. We find almost linear decrease in ideal strength with increasing temperature for [112](111) shear deformation, while critical strain decreases in a nonlinear manner. At room temperature, reduction of shear strength for Al(Cu) is less than 35%(25%) compared to that at 0 K.