Electro-mechanical insights into the mixing of conductive and non-conductive sands at an interface

This paper investigates the electrical behaviour of an electrically conductive sand particle when mixed with non-conductive silica sand, commonly used in the railway industry. Laboratory tests and numerical simulations are conducted to assess the effect of mixing on the electrical conduction properties at the metal-to-metal interface under mechanical loading. Results from compression tests demonstrate that mixing with even 5 % mass of conductive particles can significantly reduce electrical resistance at the interface; however, the decrease in electrical resistance gradually slows down when the mixing ratio of conductive particles exceeds 10 %. Discrete element modelling of high pressure torsion tests – enhanced with a newly proposed electro-mechanical contact model – reveal that fine conductive particles are more effective than coarse particles in reducing interfacial electrical resistance at equal mixing ratios. A heatmap is proposed to estimate the percentage of conductive particles required to bring the resistance of the interface below the critical threshold of 10 Ω for track circuit, which links the resistivity of various conductive particles with their required mixing ratio.