Nguyen Duc-Hanh, Azéma Émilien, Sornay Philippe, Radjaï Farhang
LMGC, Univ. Montpellier, CNRS, Montpellier, France.
CEA, DEN, DEC, SFER, LCU, F-13108, Saint-Paul-les-Durance, France.
Eur Phys J E Soft Matter. 2018 Apr 11;41(4):50. doi: 10.1140/epje/i2018-11656-1.
We investigate sheared granular materials composed of crushable particles by means of contact dynamics simulations and the bonded-cell model for particle breakage. Each particle is paved by irregular cells interacting via cohesive forces. In each simulation, the ratio of the internal cohesion of particles to the confining pressure, the relative cohesion, is kept constant and the packing is subjected to biaxial shearing. The particles can break into two or more fragments when the internal cohesive forces are overcome by the action of compressive force chains between particles. The particle size distribution evolves during shear as the particles continue to break. We find that the breakage process is highly inhomogeneous both in the fragment sizes and their locations inside the packing. In particular, a number of large particles never break whereas a large number of particles are fully shattered. As a result, the packing keeps the memory of its initial particle size distribution, whereas a power-law distribution is observed for particles of intermediate size due to consecutive fragmentation events whereby the memory of the initial state is lost. Due to growing polydispersity, dense shear bands are formed inside the packings and the usual dilatant behavior is reduced or cancelled. Hence, the stress-strain curve no longer passes through a peak stress, and a progressive monotonic evolution towards a pseudo-steady state is observed instead. We find that the crushing rate is controlled by the confining pressure. We also show that the shear strength of the packing is well expressed in terms of contact anisotropies and force anisotropies. The force anisotropy increases while the contact orientation anisotropy declines for increasing internal cohesion of the particles. These two effects compensate each other so that the shear strength is nearly independent of the internal cohesion of particles.
我们通过接触动力学模拟和用于颗粒破碎的粘结单元模型，研究了由可破碎颗粒组成的剪切颗粒材料。每个颗粒由通过内聚力相互作用的不规则单元铺砌而成。在每次模拟中，颗粒的内聚力与围压之比（相对内聚力）保持恒定，并且填料受到双轴剪切作用。当颗粒之间的压缩力链作用克服内聚力时，颗粒会破碎成两个或更多碎片。随着颗粒持续破碎，剪切过程中粒度分布会发生演变。我们发现，破碎过程在碎片尺寸及其在填料内部的位置方面都是高度不均匀的。特别是，许多大颗粒从不破碎，而大量颗粒则完全破碎。结果，填料保留了其初始粒度分布的记忆，而由于连续的破碎事件，中间尺寸颗粒的分布呈现幂律分布，从而失去了初始状态的记忆。由于多分散性增加，填料内部形成了密集的剪切带，通常的剪胀行为减弱或消失。因此，应力 - 应变曲线不再经过峰值应力，而是观察到向伪稳态的渐进单调演变。我们发现破碎率受围压控制。我们还表明，填料的剪切强度可以通过接触各向异性和力各向异性很好地表示。随着颗粒内聚力的增加，力各向异性增加，而接触取向各向异性下降。这两种效应相互补偿，使得剪切强度几乎与颗粒的内聚力无关。
