Suhr Bettina, Six Klaus
Virtual Vehicle Research Center, Inffeldgasse 21/A, 8010 Graz, Austria.
Comput Part Mech. 2017;4(1):23-34. doi: 10.1007/s40571-016-0119-2. Epub 2016 Jun 13.
In the discrete element simulation of granular materials, the modelling of contacts is crucial for the prediction of the macroscopic material behaviour. From the tribological point of view, friction at contacts needs to be modelled carefully, as it depends on several factors, e.g. contact normal load or temperature to name only two. In discrete element method (DEM) simulations the usage of Coulomb's law of friction is state of the art in modelling particle-particle contacts. Usually in Coulomb's law, for all contacts only one constant coefficient of friction is used, which needs to reflect all tribological effects. Thus, whenever one of the influence factors of friction varies over a wide range, it can be expected that the usage of only one constant coefficient of friction in Coulomb's law is an oversimplification of reality. For certain materials, e.g. steel, it is known that a dependency of the coefficient of friction on the contact normal load exists. A more tribological tangential contact law is implemented in DEM, where the interparticle friction coefficient depends on the averaged normal stress in the contact. Simulations of direct shear tests are conducted, using steel spheres of different size distributions. The strong influence of interparticle friction on the bulk friction is shown via a variation of the constant interparticle friction coefficient. Simulations with constant and stress-dependent interparticle friction are compared. For the stress-dependent interparticle friction, a normal stress dependency of the bulk friction is seen. In the literature, measurements of different granular materials and small normal loads also show a stress dependency of the bulk friction coefficient. With increasing applied normal stress, the bulk friction coefficient reduces both in the experiments and in the simulations.
在颗粒材料的离散元模拟中，接触建模对于预测宏观材料行为至关重要。从摩擦学角度来看，接触处的摩擦需要仔细建模，因为它取决于几个因素，例如仅举两个例子，接触法向载荷或温度。在离散元法（DEM）模拟中，使用库仑摩擦定律是颗粒 - 颗粒接触建模的常用方法。通常在库仑定律中，对于所有接触仅使用一个恒定的摩擦系数，该系数需要反映所有摩擦学效应。因此，每当摩擦的影响因素之一在很宽的范围内变化时，可以预期在库仑定律中仅使用一个恒定摩擦系数是对现实的过度简化。对于某些材料，例如钢，已知摩擦系数与接触法向载荷有关。在离散元法中实现了一种更符合摩擦学的切向接触定律，其中颗粒间摩擦系数取决于接触中的平均法向应力。使用不同尺寸分布的钢球进行了直剪试验模拟。通过改变恒定的颗粒间摩擦系数，展示了颗粒间摩擦对整体摩擦的强烈影响。比较了具有恒定颗粒间摩擦和应力相关颗粒间摩擦的模拟。对于应力相关的颗粒间摩擦，可以看到整体摩擦的法向应力依赖性。在文献中，对不同颗粒材料和小法向载荷的测量也显示了整体摩擦系数的应力依赖性。随着施加的法向应力增加，整体摩擦系数在实验和模拟中均降低。
