Title: Frictional weakening of a granular sheared layer due to viscous rolling revealed by Discrete Element Modeling Show Chinese title

Title: 粘性滚动导致颗粒剪切层的摩擦弱化，通过离散元建模揭示

Abstract: Considering a 3D sheared granular layer modeled with discrete elements, it is well known the rolling resistance significantly influences the mechanical behavior. Even if the rolling resistance role has been deeply investigated as it is commonly used to represent the the roughness of the grains and the interparticle locking, the role of rolling viscous damping coefficient has been largely overlooked so far. This parameter is rarely used or only to dissipate the energy and to converge numerically. This paper revisits the physical role of those coefficients with a parametric study of the rolling friction and the rolling damping for a sheared layer at different shear speeds and different confinement pressures. It has been observed that the damping coefficient induces a frictional weakening. Hence, competition between the rolling resistance and the rolling damping occurs. Angular resistance aims to avoid grains rolling, decreasing the difference between the angular velocities of grains. Whereas, angular damping acts in the opposite, avoiding a change in the difference between the angular velocities of grains. In consequence, grains keep rolling and the sample strength decreases. This effect must be considered to not overestimate the frictional response of a granular layer. Show Chinese abstract

Abstract: 考虑到一个用离散元方法建模的三维剪切颗粒层，众所周知滚动阻力显著影响机械行为。 即使滚动阻力的作用已经被深入研究，因为它常用于表示颗粒的粗糙度和颗粒间锁定，但滚动粘性阻尼系数的作用到目前为止被很大程度上忽视了。 这个参数很少被使用，或者仅用于耗散能量和数值收敛。 本文通过在不同剪切速度和不同约束压力下的剪切层中对滚动摩擦和滚动阻尼的参数研究，重新审视这些系数的物理作用。 观察到阻尼系数会导致摩擦减弱。 因此，滚动阻力和滚动阻尼之间会发生竞争。 角度阻力旨在防止颗粒滚动，从而减少颗粒角速度之间的差异。 而角度阻尼则起相反作用，防止颗粒角速度之间差异的变化。 因此，颗粒保持滚动，样品强度降低。 为了不过高估计颗粒层的摩擦响应，必须考虑这种效应。