Material point method modeling of porous semi-brittle materials

Abstract

Accurate characterization and modeling of low-density snow under rapid loading is desirable for researchers in a broad range of fields, from avalanche prediction to ground-vehicle dynamic studies. This study uses a progressive damage model to study the reaction forces and subsequent mechanical behavior of snow under three different controlled load conditions–indentation with varying indenter sizes, unconfined compression and unconfined tension. Each test probes one aspect of the material behavior, and the results can be used to facilitate the development of effective material models. The simulations use realistic microstructure obtained from 3D X-Ray MicroTomography of natural snow, in conjunction with a meshfree Generalized Interpolation Material Point method. The maximum tensile strength failure criterion is used to form an elastic-brittle constitutive law to model the progressive damage occuring in the ice matrix. A "no-tension" model, in which failed particles can sustain a compressive but not a tensile stress, is used to model the particles post-failure, which allows for compaction of the ice particles. The pressure-displacement results show an initial peak stress, followed by a sustained residual stress. Most of the damage occurs at the beginning of the load. The results from varying indenter sizes reflect the size effect expected for random heterogeneous materials, and the simulation with the largest indenter size show behavior approaching that of unconfined planar compression, that is, the compressive strength of the material.