密实散粒体剪切破坏能量演化的离散元模拟

Energy evolution of dense granules subjected to shear failure by discrete element method

砂土等散粒体在剪切过程中的能量存储及耗散是其宏观力学响应的深层原因,但因量测难度较大而研究较少。将考虑抗转动的接触模型引入离散元软件PFC2D,基于热力学第一定律建立各种能量量测方法,并在平面应变双轴压缩试验中采用该方法统计密实散粒体在剪切过程中的能量演化规律。采取了4种耗散类型,即滑动-滚动(S-R)、滑动-非滚动(S-NR)、非滑动-滚动(NS-R)和非滑动-非滚动(NS-NR)。结果表明:密实散粒体加载时能量耗散以滑动摩擦为主;且小应变加载阶段,外力功主要转化为弹性应变能,但同时也存在均布于试样的耗散能;随着应变的增加,外力功的转化形式逐渐过渡为以耗散能为主,且集中分布在带状区域内;各个加载阶段的摩擦耗散均存在各向异性。

Energy storing and dissipation are the underlying mechanisms of the macromechanical responses of granular materials subjected to shear failure,while they are difficult to measure in laboratory.We implemented a user-defined contact model considering rolling resistance to the commercial software PFC2D,and made a calculable method to count the energy components based on the first law of thermodynamics.Then the energy storing and dissipation through the whole sample are investigated in a series of numerical biaxial compression tests by discrete element method（DEM）.Four kinds of friction are adopted,i.e.sliding and rolling（S-R）,sliding and non-rolling（S-NR）,non-sliding and rolling（NS-R） and non-sliding and non-rolling（NS-NR）.The results show that the energy is mainly dissipated in the type of sliding rather than rolling.And at a small biaxial strain,the input energy is mainly stored as elastic energy with a small portion dissipated and the dissipated energy is globally distributed through the whole sample.While a large biaxial strain is achieved,the dissipated energy gradually turns dominant and the majority of energy dissipated in a narrow zone,showing the significant localization.In addition,the main direction in which the energy is dissipated shows strong anisotropy at all loading stages.