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

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.

该研究项目旨在开发基于微力学的颗粒材料的本构方程，例如土壤和工程粉末，这些方程可以涵盖从弹性响应到失败的广泛行为。为此，将描述颗粒材料中形成的颗粒柱屈曲的简单模型纳入了Chang和Misra（1990）等提出的均匀应变模型中。发现只有一个控制屈曲的参数才能导致致密和松散的颗粒材料对失败制度的合理响应。现在，我们正在探索以物理方式从颗粒材料的其他微型特性确定屈曲参数的方法。晶粒形状的效果可能是成功的关键问题。它也是项目开发图像处理工具的重要目标，用于从Spring-8的Micro X射线CT实验中获取有用的微机械信息。 Spring-8是一种同步辐射设施，在该设施中，可以使用非常精确的微型X射线CT系统。我们开发的图像处理技术可以自动识别组件内的每个不规则形状的谷物。使用此技术，获得了一些有关不规则形状晶粒的3-D填料结构的有用信息。此外，我们还开发了一种方法，可以在加载过程中按时间顺序鉴定三轴标本内的晶粒，这导致各种信息对颗粒材料的微力学有用。此外，该微力学研究用于研究月球土壤的机械行为。