Failure in Granular Materials in Relation to Material Instability and Plastic Flow Issues

Abstract

This work has its beginnings in the seminal works of Hill (1958) concerning a largely theoretical question as to the condition of instability in materials. The question has now taken on a more important and practical relevance over the intervening years, this in part motivated by various forms of failure such as strain localization and diffuse instability in geomaterials. According to classical theories, failure is largely seen as a condition of plastic limit with the implication of strain localization and surface discontinuities. However, other forms of failure such as of the diffuse type in the absence of any localization can be observed well before plastic limit conditions are met. Within this backdrop, we first examine Hill’s stability criterion as a means to detect diffuse instability. Then, we discuss issues of controllability and sustainability in various load controlled conditions. Finally, we turn our attention to a related issue, i.e. unstable plastic flow in elastoplastic materials. Through discrete element simulations, we explore the nature of the plastic incremental response of a granular material and verify whether the plastic flow rule postulate holds under general three-dimensional conditions.