The role of changing grain shape in abrasive wear and frictional resistance

In a range of applications — such as powder processing and geotechnical engineering — irregularly shaped grains interact with structural surfaces, resulting in abrasion. Traditional tribological analysis would imply that, when harder grains (e.g. sands) abrade against softer surfaces (e.g. metal), abrasive wear of the surface dominates the interaction mechanisms. However, this new research shows that this is not necessarily the case and wear of the harder grains themselves may dominate changes in shear behaviour. Studying this interaction is made more complicated by the irregular geometry of natural grains and the fact that their shapes evolve continuously during abrasion. Previous studies have substituted real grains with regularly shaped artificial abrasives (e.g. cones) to simplify the analysis. In contrast, this research creates high-resolution three-dimensional digital models of real grains, enabling direct measurement of shape characteristics as they change over time. From these digital reconstructions, a new ‘three-dimensional attack angle’ parameter has been defined, extending concepts previously restricted to simplified two-dimensional cases. This parameter can be updated in real-time as grains abrade, capturing the evolution of geometry in ‘real time’. Importantly, the three-dimensional attack angle correlates strongly with observed changes in frictional shear behaviour between irregular sand grains and stainless steel surfaces. This is the first study to establish a direct link between a measurable shape parameter of irregular grains and their evolving frictional characteristics. The framework developed here provides a basis for deeper understanding of grain-surface interactions and can be applied broadly across tribology and granular mechanics. • Grain geometry influences the frictional behaviour at a grain-surface boundary. • Grains subjected to cyclic shearing experience significant abrasive wear. • The changing contact geometry of grains can be captured using a ‘3D attack angle’. • A correlation exists between the 3D attack angle and frictional behaviour.