Roughness and humidity effects on contact, friction, and contact plasticity revealed by micromechanical testing and analysis

Understanding the effects of surface roughness, surface lubrication, and environmental conditions on inter-particle contact mechanics is important for a broad range of applications of granular materials. In this paper, a new micromechanical testing apparatus was developed and used to characterize smooth and rough soda lime glass particles in carefully controlled dry, humid, and lubricated environments during normal compression and shearing. From surface profilometry measurements and digital image correlation, we observed a humidity independent correlation between hysteresis, contact plasticity, and surface roughness in normal compression tests. From analysis of shear test data, we observed an increase in friction with increasing surface roughness, contact hold times, and water lubrication. Our work highlights roughness and environmental effects on contact and friction of silicate materials.