Neutron Diffraction Techniques in Granular Mechanics

Abstract

Granular materials demonstrate unique mechanical properties stemming from their discrete nature. At large length scales granular assemblies are often viewed from the perspective of continuum theory where they show complex behaviour such as elastic and plastic anisotropy related to the load and deformation history. This complex behaviour is inextricably linked to the micromechanics of load sharing and force transmission at the particle level. At these scales, bulk stress is not shared homogeneously between particles, but rather by a network of `force chains' that form a skeleton supporting the vast majority of the applied load. The formation and failure of these structures govern much of the bulk behaviour of these materials. Neutron diffraction techniques are now providing a window into the mechanics of granular materials at both bulk and particle scales. Through a combination of tomographic neutron imaging and diffraction based strain measurement it is now possible to directly examine the stress within individual particles in granular assemblies. Results of these experiments in two and three dimensions are presented and the outlook for this approach to studying the mechanics of granular materials is discussed.