Grain fracture and comminution are important dissipative processes that influence the grain-scale features, mechanical properties, and inelastic behavior of granular ensembles in various engineering and geological settings. Although fracture and comminution have been extensively studied for single grains using experiments and simulations, in situ experimental data on ensembles remains limited. In this study, we used x-ray diffraction (XRD) and x-ray computed tomography (XRCT) to study fracture and comminution in situ during uniaxial and triaxial compaction of granular solids composed of sapphire, quartz, and copper grains. We used up to one thousand grains with sizes ranging from 100-250 microns to study the relationship between grain stresses, grain angularity, inter-grain forces, inter-grain contacts, fracture plane orientations, ductile material flow and pore-filling, and crystal plane orientations. We used finer-grained quartz powders to further explore the relationship between comminution and grain properties. These studies elucidate the factors affecting the presence and orientation of grain fractures and their influence on mechanical properties and energy dissipation. The results provide new in situ data that can be used for model development and validation. We will discuss ongoing efforts to develop and validate LLNL’s code geodynL with the results of these experiments.
Part of this work was performed under the auspices of the U.S. Department of Energy (DOE) by LLNL under contract DE-AC52-07NA27344. R.C.H. and E.B.H. acknowledge support from Lawrence Livermore National Laboratory’s (LLNL) Laboratory Directed Research and Development (LDRD) program under award 17-LW-009. All authors acknowledge support from LLNL’s LDRD program under award 16-ERD-010. The authors acknowledge the Advanced Photon Source (APS) for synchrotron beamtime under proposal GUP-45260. Use of APS was supported by the U.S. DOE under Contract No. DE-AC02-06CH11357.