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

本研究项目旨在开发一种基于细观力学的颗粒材料本构方程，如土壤和工程粉末，可以涵盖从弹性响应到破坏的广泛行为。为此，在Chang和Misra（1990）等人提出的均匀应变模型中引入了一个描述颗粒材料中形成的颗粒柱屈曲的简单模型。研究发现，只有一个参数来控制一个屈曲导致合理的响应致密和松散的颗粒材料的破坏制度。我们正在探索如何从颗粒材料的其他微观性质中以物理的方式确定屈曲参数。晶粒形状的影响可能是一个成功的关键问题。它也是在该项目中的一个重要目标，开发一个图像处理工具，从SPring-8的微观X射线CT实验中获得有用的微观力学信息。SPring-8是一个同步辐射装置，其中有非常精确的微型X射线CT系统。我们开发的图像处理技术能够自动识别组件内的每个不规则形状的颗粒。利用这种技术，获得了一些有用的信息的三维堆积结构的不规则形状的颗粒。此外，我们还开发了一种方法，以确定在加载过程中的时间序列，这导致了各种有用的信息，粒状材料的细观力学的三轴试样内的颗粒。此外，还将细观力学研究应用于月壤的力学行为研究。

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.