Quasistatic and dynamic regimes of granular material deformation under impulse loading

A two-dimensional computer code, using a multi-material Eulerian finite element formulation, was used to investigate the dynamic micromechanical behavior of granular material. The main results are: The strain-rate insensitive material model provides the correct increase in the dissipated energy with an increase of shock pressure; An increase in the initial porosity or the pressure results in the transition from the quasistatic to the dynamic regime of particle deformation, which can be characterized by the intensive localized plastic flow on the particles' interfaces. A new space scale is introduced into the system-the width of localized plastic flow; The macro and micro-scale responses of the granular material do not depend on the particle size for a rate independent material model; The energy of the shock wave compression at high pressures cannot be completely dissipated during the pore collapse at the shock front; The transition pressure from the quasistatic to the dynamic deformation regime does not depend on the density of the solid material for a given porosity with the other material properties fixed; A well developed dynamic regime correlates with a critical value of the microkinetic energy, which is comparable to the geometrically necessary energy for complete pore collapse. The results of computer calculations are in qualitative agreement with the experiments. (C) 1997 Elsevier Science Ltd.