The contact mechanics of sand and rock grains

砂和岩石颗粒的接触力学在土木或石油工程问题中可能是至关重要的，这些问题需要离散而不是连续的方法，例如泥石流，油井行为，但颗粒土力学的最新技术在于颗粒的实验（X射线CT）和数值（离散元-DEM）研究，其中通常假设简单，光滑的形状和简单的接触定律。从长远来看，随着计算机能力的提高，所有的岩土建模都可能是离散的。监督员目前对压载物的拨款旨在为DEM重新创建现实的粒子，但为粒子间接触制定本构律将需要另一个纯粹的基础项目。地质来源的颗粒具有表面粗糙度（0.1-10米）和复杂的形状。唯一可用的接触模型是针对工程表面、法向载荷和许多20世纪70年代的接触模型。在粗糙表面的现有模型中，假设粗糙体弹性变形，或塑性变形，或两者兼而有之，没有共识，但对于土壤/岩石颗粒都没有很好的效果。人们需要后退一步，才能为土壤/岩石颗粒之间的接触产生适当的本构律。这需要设计颗粒间试验来研究接触行为的特定方面，表征接触表面，并根据弹性和塑性理论制定本构关系，但要根据这些结果。Baudet基于先进的分形理论开发了一种新的方法来量化晶粒表面粗糙度及其随载荷的演变。她打算让著名的印度科学研究所的摩擦学家/土壤力学博士Murthy参与进来，UCL全球参与办公室鼓励与之合作。她和Murthy通过皇家协会和DUO印度奖学金计划建立了牢固的联系。UCL土壤实验室拥有独特的颗粒间测试设备，由Coop建造（图1），能够控制和解决法向和切向载荷的载荷（1-1，000 N，分辨率为0.01N）和位移（0- 5 mm，分辨率为0.02m），以及用于粗糙度测量的先进光学轮廓仪。

The contact mechanics of sand and rock grains can be critical in civil or petroleum engineering problems that require a discrete not continuum approach e.g. debris flow, oil well behaviour, but the state-of-the-art in particulate soil mechanics lies in experimental (x-ray CT) and numerical (discrete element-DEM) studies of grains where simple, smooth shapes and simplistic contact laws are often assumed. It is probable that in the very long term, as computer power increases, all geotechnical modelling will be discrete. The supervisors' current grant on ballast aims at recreating realistic particles for DEM, but developing constitutive laws for the inter-particle contact would require another, purely fundamental, project. Grains of geological origin have surface asperities (0.1-10 m) and complex shapes. The only contact models available were derived for engineered surfaces, for normal loading and many in the 1970s. In available models for rough surfaces, it is either assumed that asperities deform elastically, or plastically, or both, without consensus, but neither works well for soil/rock grains. One needs to take a step back to be able to generate the appropriate constitutive laws for contact between soil/rock grains. This requires designing particle-to-particle tests to investigate specific aspects of contact behaviour, characterising the contact surfaces and developing constitutive laws from elastic and plastic theory but informed by these results. Baudet has developed a novel method to quantify grain surface roughness and its evolution with loading based on advanced fractal theory. She intends to involve Dr Murthy, tribologist/soil mechanics from the prestigious Indian Institute Science with which collaboration is encouraged by UCL Global Engagement office. She and Murthy have established strong links through Royal Society and DUO-India Fellowship schemes. UCL soil laboratory possesses a unique apparatus for inter-particle testing, built by Coop (fig.1), able to control and resolve loads (1-1,000N with 0.01N resolution) and displacements (0-5mm with 0.02m resolution) for normal and tangential loading, and an advanced optical profilometer for roughness measurements.