Study on couple stress and shear band development in granular media based on numerical simulation analyses
Study on couple stress and shear band development in granular media based on numerical simulation analyses
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DOI：
10.1016/s0020-7225(99)00132-9
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发表时间：
2000-10-01
影响因子：
6.6
通讯作者：
Iwashita, K
中科院分区：
文献类型：
--
作者：
Oda, M;Iwashita, K
模拟结果与室内试验结果吻合较好，说明离散单元法模拟试验为模拟颗粒介质的微观和宏观行为提供了有力的工具。尤其是在传统的旋转阻力中引入了旋转阻力时，更是如此。基于模拟和实验室试验，我们得出以下结论：应变硬化过程中发生的最重要的显微组织变化之一是形成平行于主应力方向生长的柱状组织。破坏后，柱状结构在应变软化过程中通过在接触点滚动而不是滑动的方式重建，从而产生较高的颗粒旋转梯度，在相对较窄的剪切区由负变为正。剪切带中出现较大的空洞，由此产生的局部空洞比可以超过标准方法确定的相应的最大空洞比。这一事实有力地表明，导致这种特殊微结构的独特应力条件可能在剪切带中发育。实际上，剪切带中存在偶应力，其方式与粒子旋转梯度由负到正的变化相一致。尽管存在偶应力，但应力张量几乎对称，说明偶应力的大小很小。小偶应力的存在对剪切带微观结构的发展仍然起着重要的作用。(C)2000爱思唯尔科学有限公司。保留所有权利。
From the reasonable accordance between the simulation and laboratory tests, it is concluded that the simulation test using the distinct element method can provide a powerful tool to simulate the micro- as well as macro-behavior of granular media. This is true, in particular, when the rotational resistance is introduced into the conventional one. Based on both the simulation and laboratory tests, we reached the following conclusions: One of the most important changes in microstructure, which takes place during a strain hardening process, is the formation of column-like structure growing parallel to the major principal stress direction. After failure, the column-like structure is reconstructed during a strain softening process by means of rolling, not sliding, at contact points so that a high gradient of particle rotation is generated, changing from negative to positive in a relatively narrow shear zone. Large voids appear in the shear band, and the resulting local void ratio can exceed the corresponding maximum one determined by a standard method. This fact strongly suggests that unique stress condition, which leads to such special microstructure, may develop in the shear band. III fact, couple stresses exist in a shear band in a manner consistent with the change of the particle rotation gradient from negative to positive. In spite of the presence of the couple stress, the stress tensor is nearly symmetric, indicating that the couple stress is very small in magnitude. The presence of the small, couple stress still plays an important role in the development of microstructure in shear bands. (C) 2000 Elsevier Science Ltd. All rights reserved.