Friction of Shear-Fracture Zones

Abstract

A shear fracture of brittle solids under compression undergoes a substantial evolution from the initial microcracking to a fully formed powder-filled shear zone. Experiments covering the entire process are relatively easy to conduct, but they are very difficult to investigate in detail. Numerically, the large strain limit has remained a challenge. An efficient simulation model and a custom-made experimental device are employed to test to what extent a shear fracture alone is sufficient to drive material to spontaneous selflubrication. A "weak shear zone" is an important concept in geology, and a large number of explanations, specific for tectonic conditions, have been proposed. We demonstrate here that weak shear zones are far more general, and that their emergence only demands that a microscopic, i.e., fragment-scale, stress relaxation mechanism develops during the fracture process.

Gravity Governs Shear Localization in Confined Dense Granular Flows

“…In granular flows created by slowly shearing the boundaries, the strain often localizes in narrow regions of the order of a few particle diameters near the moving boundary [12,13]. Nevertheless, wide shear zones can also be created when a shear fracture [23] propagates in the bulk away from the boundaries, and the sides of the fault move past each other in deep layers-the process that is of particular importance in geology; see Fig. 1 for an example of a circular fault line in the bulk.…”