报告题目：Originsprinciple of shear dilation and failure geo-granular materials
报告人：王东，美国杜克大学物理系博士
报告时间：2017年10月31日9周二下午2：30
报告地点：笃学楼107室
报告人简介：王东，美国杜克大学物理系博士，毕业于中国科技大学应用物理学。主要从事凝聚态物理领域内软物质细观／宏观等不同尺度下相关力学特性研究。对不同摩擦力以及不同颗粒形状的颗粒材料在发生剪切变形过程中，研究宏观尺度上的剪涨与破坏现象与细观尺度上颗粒之间的接触，颗粒间的相对位移以及颗粒的受力情况之间的耦合关系。并结合颗粒光弹测试技术提出了由三个颗粒为基本单元的“TRIMER”模型。相关研究成果已在EPL、Phy. Rev. E等多个学术期刊上发表。并多次在物理学顶级会议March Meeting、Division of Fluid Dynamics和Gordon Research Conferences上报告和展示。同时，在2017年3月应March Meeting邀请作了特邀报告。
摘要：
Shear Jamming occurs for frictional granular materials with packing fractions in φS <φ<φJ, below the lowest isotropically jammed frictionless state at φJ. This phenomenon occurs when the material is subject to shear strain, γ, starting from a force-free state. Shear jammed states have anisotropic networks of particles carrying strong forces, e.g. force chains. We identify a new paradigm to understand how such states/networks arise in response to volume-preserving shear strain. We argue that key small scale geometric structures enable this process. We identify these structures, trimers and branches, in physical experiments consisting of two dimensional frictional discs, and verify their role in shear jamming. Trimers are triplets of grains where two outer grains contact a center grain. Branches occur where three or more quasi-linear force chain segments intersect. Certain trimers respond to shear by compressing and by bending; the latter is a nonlinear process that can push particles in the dilation direction faster than the affine dilation. Trimer bending and branches both contribute to increasing the average contact number per particle, Z, above the isostatic value, Ziso > 3 needed for jamming 2D frictional grains, and thus provide micro-mechanisms for shear jamming.
