An approach to dry friction and wear for small volumes

Fracture and contact mechanics can synergistically contribute to the fundamental understanding essential to scaling of small volumes. Consider two levels of scale in terms of contact area: (i) light wear of tribological contacts at the nanometre level; (ii) delamination of hard protective coatings or ductile metal films at the micrometre level. We first briefly address two phenomena-one showing that oxide film fracture is responsible for yield excursions during nanoindentation and the other showing that analysis of acoustic events can sort out some of the discontinuous events of yield and fracture on the nanometre scale. These concern mostly the fracture process concomitant with a localized plasticity event. However, they do not address the fundamental aspects of what controls the size of the yield event or what controls the size of a localized fracture event, for example delamination. We propose that one way of understanding these two levels of scale and their interconnectivity is through a volume-surface area concept. At present, we show two levels of understanding for contacts to single-crystal surfaces and how these provide insight and potentially quantification of light wear contact.