Granular material response with respect to loading direction and material instability
The paper examines the emerging roles of instabilities towards characterizing various modes of failure in geomaterials. We show that conventional analysis of failure through a failure criterion is no longer sufficient and it is also important to study the causes leading to failure. Micromechanical in character, these causes relate to local instabilities such as inter-granular slippage, overriding, buckling, grain crushing, among others. We briefly investigate the phenomenon of instability using an elasto-plastic model. Hill’s stability criterion, based on the second-order work, is employed to capture the existence of material instability inside classical plastic limit surface. The postulate of flow rule is another subject matter discussed here. Through discrete element analysis, we show that this postulate fails under general three-dimensional conditions and the plastic response is a function of loading direction.
Keywords: failure, material instability, flow rule, discrete elements