Multiple contact compression tests on sand particles

Particle crushing has been recognised as being of key importance for many engineering applications. In soil mechanics, this phenomenon has become crucial for defining a complete framework capable of describing the mechanical behaviour of sands. In this study, the effect of multiple discrete contacts on the breakage of grain particles was investigated by crushing coarse grains of a quartz sand and a crushed limestone sand between a number of support particles, thereby varying the number of contacts, i.e., the coordination number. The stress at failure was calculated when the particles broke, which occurred through a number of distinct modes, namely, chipping, splitting or fragmenting, which were observed with the use of a high-speed microscopic camera. The Weibull criterion was applied to calculate the probability of surviving grain crushing, and the fracture modes were observed for each configuration of supporting particles. The data showed that in addition to the number of contacts, the nature of those contacts, controlled by particle morphology and mineralogy, also plays a significant role in determining the strength of a particle. The sphericity affected the strength of the softer limestone sand, while the local roundness at the contacts was important for the harder quartz sand. Catastrophic explosive failure was more often observed in particles with harder contacts, while softer contacts tended to mould relative to their neighbouring particles inducing a more frequent ductile mode of crushing.