Numerical modeling of the mechanics of nonlinear porous media under dynamic loading

A multiphase continuum model that couples nonlinear deformation to porous flow has been developed and adapted for numerical analyses of dynamic and quasistatic behavior in the explicit finit-difference code TENSOR. In a physical sense the model describes a solid skeletal material containing flaws configured either as pores or stress-induced tensil cracks. These flaws may be filled with a multiphase fluid (e.g., air and water) whose transient behavior is governed by a dynamic flow model that reduces to classical Darcy flow for a single-phase fluid in the limit of quasistatic behavior. Dynamic mixture theory is used to account for coupling effects between phases. Nonlinear material behavior representing the drained response of the porous solid has been combined with the multiphase flow model to account for the effects of pore pressure on compaction, shear failure, and tensile failure. Numerical calculations are presented using both the multiphase model and a single-phase model to simulate the spherical response from explosive experiments performed on grout spheres. Good agreement with the measured particle velocity is obtained with both models. However, the phenomenology associated with explosively generated cavities using the multiphase model differs markedly from that obtained with a single-phase model. Notably, a region of liquefaction surroundingmore » the cavity is created as a result of pore-pressure-induced tensile failure during shock wave passage. This precludes the development of a residual stress field adjacent to the cavity, as typically calculated with a single-phase model. A small residual stress field is formed beyond the liquefied region. The formation of the residual stress field using the multiphase model and its stability during subsequent readjustment caused by pore-fluid migration is greatly enhanced with a small initial amount of air-filled porosity. 46 references, 15 figures.« less