基于DIC的颗粒间接触力计算及力链分析

The quasi-static response of granular materials to a concentrated loading

首次利用数字图像相关方法(Digital Image Correlation method,DIC),依据牛顿力学理论和颗粒线性动量平衡,分析了集中力作用下的二维钢珠颗粒体系,定量地获得了颗粒间接触力。采用CCD相机进行观测并采集了集中力作用下钢珠颗粒体系的变形图像;利用数字图像相关方法对采集的序列图像进行处理,获得了全场位移及应变,并根据胡克定律求得全场应力。对每个颗粒面积区域内各点应力值求和并取平均,获得各个颗粒的平均应力。对采集的数字图像进行图像分析,得到各个颗粒及接触点的排列结构。以颗粒平均应力和颗粒的排列结构作为初始条件,根据牛顿力学理论和颗粒线性动量平衡,最终获取了颗粒间接触力的大小和方向,实现了真实颗粒体系接触力的定量计算。另外从受力方面对集中力作用下颗粒体系内部力链的发展与演变进行了分析。研究结果表明:力链起源于加载位置,随着外荷载的部分耗散,颗粒间接触力逐渐发生变化,力链向四周扩展而形成力链网络。通过对不同压入深度颗粒间接触力变化和分布的分析,定量地描述了加载过程中颗粒间的滚动或滑动引起的力链断裂和重构的现象。

Based on Newtonian mechanics theory and the balance of particle linear momentum, contact forces of real granular materials are obtained. The two-dimensional granular materials under the concentrated loading are performed and during deformation process, the deformation images are recorded on a CCD camera constantly. These time-dependent images would provide the deformation history of the granular materials. The digital image correlation method(DIC) is used to analyze these images captured by CCD camera, the displacement and strain field can be obtained. According to Hooke's law, the stress field and the average stress of each particle also can be acquired. Then the average stresses and particle arrangement structure can be used as initial information, the particle contact force is obtained combined with Newtonian mechanics theory and balance of particle linear momentum. The development and evolution of force chain in particle system is also analyzed. Results obtained show that the force chain originates in the loading position, along with the external load dissipation, the contact forces between the particles gradually change, force chains extend to the surrounding, forming force chain network. Changes and distribution of contact force in different depth quantitatively describe the phenomenon that force chain breaking and reconstruction caused by rolling or sliding of the inter particle.