顆粒材料二維及三維剪切帶之識別

Abstract

顆粒材料於外界給予作用力下，其材料的破壞方式呈現局部性的剪切破壞，並產生應變局部化之情形，而此局部化之區域可稱之為剪切帶。一般而言，剪切帶上與其鄰近區域間往往呈現一個微觀性質的不連續現象，因此，吾人可依據此現象來判別剪切帶之位置、大小、方向等，進而了解剪切帶之形式與材料演化之行為。至今，眾多文獻對於剪切帶上之局部宏觀效應已有諸多之研究結果，然而，對於其中許多微觀特性之比較尚無較清楚的探討。 本研究主要利用離散元素法(Discrete Element Methods)來模擬顆粒材料於軸向試驗下，形成剪切帶之過程。模擬之工作可分為兩部分，第一部分為利用PFC2D軟體，來模擬二維軸向試驗之剪切帶形成；而第二部分為例為EDEM軟體，來模擬三維軸向試驗之剪切帶形成。 此外，本文參考諸多文獻之推導，引進六種微觀物理量來進行剪切帶識別之工作，此六種識別指標分別孔隙率、自旋角速度、接觸顆粒數、微迴旋張量之體膨脹、微迴旋張量之旋轉、以及剪切強度。藉此，來探討各指標之微觀性質於二維及三維剪切帶上之呈現，並作各辨識指標之比較、分類及統整的工作。

Failure of granular materials under external forces is presented by localized strain bands. This localized strain failure is called “ shear bands“. In general, microscopic properties are discontinuous between the shear bands and their neighborhood. Therefore, based on the phenomenon of shear bands, we can determine the location, size, and direction. The Morphologies of shear bands and their evolution are also of interest. Although the macroscopic phenomena had been addressed in many exist literature, microscopic features were largely omitted. In this dissertation, we use the discrete element method (DEM) to simulate the process of granular materials forming shear bands. This simulation is divided into two part. First, We use PFC2D software to simulate a two-dimensional axial test that produces shear bands；Secondly, we use EDEM software to simulate a three- dimensional axial test. There are six microscopic quantities are defined for theoretical modeling. They are the porosity, spin angular velocity, number of contact particles, the bulk part of the gyration tensor , the rotation part of the gyration tensor and the local shear intensity. We investigate the shear bands with these six parameters and discuss the m- icroscopic properties in the 2D and 3D shear bands. Companion, classification and summarization of the granular material proportion using these parameters are performed.