Molecular Dynamics simulations have been performed for uniform triaxial expansion of single-crystal copper at high strain-rate (5x10⁹/s) with different initial temperatures. We have used the LAMMPS (Large-scale Atomic/Molecular Massively Parallel Simulator) code for this study. It is found that the macroscopic Nucleation and Growth (NAG) model is valid at the atomistic scale. There is a monotonic decrease in the void nucleation and growth thresholds with increase in temperature. When we approach the melting point of copper, we observe a double-dip in the pressure-time profile. The analysis of this double-dip shows that the first minimum corresponds to the loss of long-range order but there is no void nucleation at this juncture. The second minimum corresponds to the void nucleation and incipient growth of voids.