Tribology in Particulate Systems

In manufacturing processes involving particulate solids (e.g. pharmaceutical tablets and capsules, nuclear fuel rod, near net shape forming) friction and adhesion could cause mechanical and cohesive arching/jamming, adversely affecting productivity to the extent that it constitutes major technology bottleneck currently. There is therefore a great technological interest to mitigate them. Understanding and modelling friction and the role of flow-aids in controlling it for the transport of granular flows is hence of paramount importance. There is a need to understand small scale interfacial processes and their role in affecting macroscopic/bulk flow processes. Our current research on friction includes an EPSRC sponsored project called Friction: The Tribology Enigma, in which we focus on assessing the mechanism of magnesium stearate as a flow-aid and modelling frictional interaction in granular system as a function of surface roughness and adhesion using Discrete Element Method (DEM).

The work is also relevant to micro- and nano-particles in various other technologies, including powder-based materials processing (e.g. additive manufacture/3D printing), nanostructured lubricants and abrasives. On the micron-scale, for example, interactions between discrete micron-scale particles or surface asperity-asperity interactions there are many unknowns relating to how materials deform, react with their environment, fracture and adhere. Multiscale experimental and theoretical simulations are bringing advances in understanding of the processes that control friction at such interfaces. The information is important for the development and operation of machines with micron-sized components (e.g. MEMs and other actuation devices), and also in determining the bulk properties of granular flows and particle reinforced lubricants.