Development of Micromechanics-basd Elasto-plastic Constitutive Model for Granular Materials and its validation using SPring-8 Micro X-ray CT experiments

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This research project aims to develop a micromechanics-based constitutive equation of granular materials such as soils and engineering powders that can cover a wide range of the behavior from elastic response to failure. For this purpose, a simple model to describe the buckling of granular column formed in granular material is incorporated into uniform strain model proposed by Chang and Misra (1990) and others. It is found that only one parameter to control a buckling leads to reasonable response of both dense and loose granular materials up to failure regime. We are now exploring the way to determine the buckling parameter from other micro properties of granular materials in a physical way. The effect of grain shape may be a key issue for success.It is also an important objective in the project to develop an image processing tool for getting useful micromechanical information from micro X-ray CT experiments at SPring-8. SPring-8 is a synchrotron radiation facility in which very precise micro X-ray CT system is available. The image processing technique we developed enables to automatically identify each irregularly-shaped grain inside an assembly. Some useful information on 3-D packing structure of irregularly-shaped grains is obtained using this technique. Moreover, we are also developing a method to identify the grains inside a triaxial specimen in time sequence during loading, which leads to various information useful for micromechanics of granular materials. Additionally, this micromechanics study is applied to investigate the mechanical behavior of lunar soil.