Lattice softening and failure in severely deformed molecular crystals

Atomic force microscope observations have revealed the presence of permanen t lattice and molecular distortions in molecular crystals that had undergon e plastic deformation by shock or impact. These distortions have led to the suggestion of a deformed lattice potential. Here, the deformed lattice pot ential is extended to the case of severe plastic deformation in which the l attice softens and may eventually fail. This generalized lattice potential has been incorporated into descriptions of plastic flow and the associated energy dissipation due to dislocation motion by quantum tunneling. The resu ltant predictions are compared with experiments in which molecular crystals were subjected to severe plastic deformation during impact. (C) 2001 Ameri can Institute of Physics.