Sepúlveda Nelson, Melo Francisco, Vivanco Francisco
Laboratorio de Física no Lineal, Departamento de Física, Universidad de Santiago de Chile, Av. Ecuador 3493, Casilla 307 correo 2, Santiago, Chile.
Phys Rev E Stat Nonlin Soft Matter Phys. 2014 Nov;90(5-1):052202. doi: 10.1103/PhysRevE.90.052202. Epub 2014 Nov 7.
We present a study on the effects of particle shape (disks, hexagons, and pentagons) on the macroscopic coefficient of friction of a two-dimensional, monodisperse, single-shaped, granular system, subjected to shear. We found that the mechanism of stress relaxation in disks is based on the sliding of adjacent planes parallel to the applied deformation direction. In hexagons, stress is relaxed through the creation of rigid pivots, which require hexagonal domains to nucleate and are responsible for the large fluctuations in the dilatancy and shear force. In pentagons the stress relaxation mechanism is through the rotation of individual pentagons, which is a consequence of their permanent misalignment, and are responsible for the small but relatively rapid fluctuations in the shear force. We observed that the friction coefficient is larger for polygonal particles than for the rounded ones. A maximum in the friction coefficient is observed in hexagon granulates with an initial width around 6.5 grains caused by the increased frequency in nucleation of rigid pivots. In mixtures of disks and hexagons we observed three different friction coefficient behaviors, which depended on the relative concentration of hexagons; in low concentrations of hexagons, <20%, the friction coefficient corresponds to that obtained in solely disks, at intermediate concentrations, <80%, the coefficient varies linearly with concentration, and at larger concentrations the friction coefficient corresponds to the values obtained for solely hexagons. On the contrary, mixtures of pentagons and hexagons showed two regimes; a low constant friction regime at concentrations lower than 60%, and an increased in friction observed with higher concentrations of hexagons.
我们展示了一项关于颗粒形状（圆盘、六边形和五边形）对二维、单分散、单一形状、受剪切作用的颗粒系统宏观摩擦系数影响的研究。我们发现，圆盘中的应力松弛机制基于与施加变形方向平行的相邻平面的滑动。在六边形中，应力通过刚性枢轴的形成而松弛，这需要六边形区域成核，并导致剪胀和剪切力的大幅波动。在五边形中，应力松弛机制是通过单个五边形的旋转，这是它们永久错位的结果，并导致剪切力的小但相对快速的波动。我们观察到多边形颗粒的摩擦系数比圆形颗粒的大。在初始宽度约为6.5个颗粒的六边形颗粒中观察到摩擦系数的最大值，这是由于刚性枢轴成核频率增加所致。在圆盘和六边形的混合物中，我们观察到三种不同的摩擦系数行为，这取决于六边形的相对浓度；在低浓度的六边形中，<20%，摩擦系数与仅由圆盘获得的摩擦系数相对应，在中等浓度下，<80%，系数随浓度线性变化，而在较高浓度下，摩擦系数与仅由六边形获得的值相对应。相反，五边形和六边形的混合物表现出两种状态；在浓度低于60%时为低且恒定的摩擦状态，而在六边形浓度较高时观察到摩擦增加。
