Direct observation of partial interface slip in micrometre-scale single asperity contacts

Abstract

Observation of partial interface slip prior to sliding is reported in micrometre-scale single asperity contacts formed of diamond tips and various substrate materials. Using a dual-axis nanoindenter, an increasing oscillating lateral load is applied to contacts indented under constant normal load. Lateral load-displacement curves are extracted, with partial slip signalled by a steady decrease in contact stiffness as the magnitude of oscillation increases, dropping to zero during sliding. Both elastic and plastic contacts are examined, and contact radii from 215 to 485 nm. An interfacial strength τ0 is measured, which appears independent of radius, tip geometry, and elastic/plastic state of the substrate. This behaviour is observed in both amorphous silica and single crystal quartz contacts and a significant friction anisotropy in sapphire is demonstrated.