Directional-dependence in shock-induced melting of fcc metals

Shock-induced melting in single crystals was investigated as a function of shock direction utilizing a new equilibrium molecular dynamics method for following the dynamical evolution of condensed matter subjected to shock waves\footnote{R. Ravelo, B.L. Holian, T.C. Germann and P.S. Lomdahl, Phys Rev B, 70, 014103 (2004).}. The solid-liquid Hugoniots of Al, Cu and Lennard-Jones single crystals were enerated as a function of shock direction .The interatomic potentials describing Cu and Al are described by the embedded atom method (EAM). It is foound that in all these systems, the shear stresses at the shock-front dominate the melting process. As a function of orientation, melting occurs at lower pressures (temperatures) for (110) shocks and at higher pressures (temperatures) for (100) shocks. The magnitude of the shear stress at the melting pressure correlates with the orientations: (100):(111):(110) (smaller to largest value as a function of orientation).