FORMATION OF NANODISLOCATION DIPOLES IN SHOCK-COMPRESSED CRYSTALS

Molecular-dynamics modeling has been used to study the evolution of a dislocation nanostructure from the shock compression of a vacancy cluster in a body-centered-cubic lattice. Detailed calculations have revealed the atomic displacements by which the clustered vacancies collapse. The energetics of the process were also monitored in detail. Stable [100] and [111] Burgers-vector dislocations have been identified in dipole configurations. These dislocations relate to a periodic nanodislocation dipole structure proposed in a model by Armstrong, Miller, and Sandusky (AMS) to occur by the reaction of dislocations just behind the shock front. The postshock stability of the AMS dipole nanostructure was also evaluated on a molecular-dynamics basis and the stress-strain behaviors of the crystal for the pre- and postshock compression conditions were compared.