Contact/scratch-induced surface deformation and damage of copper–graphite particulate composites

The elastoplastic surface deformation and damage under frictional sliding contact of copper–graphite particulate composites with Cu-content ranging from 0 to 40 vol% are examined in indentation and scratch tests using a load controlled test system. The contact areas in indentation and scratch tests are estimated with the Field–Swain approximation. The characteristic material parameters of the elastic modulus E′, yield stress Y, interfacial shear strength s,   and the scratch resistance pm′ are discussed in relation to the Cu-content of the composites. The microscopic mechanisms and processes for the surface deformation and damage induced by frictional sliding contact are also examined. With the increase in the normal contact load, the scratch-induced surface deformation and damage are transiently followed with the sequential four stages: (I) the elastoplastic grooving, (II) plastic plowing, (III) microcracking, and (IV) the inter- and intra-fractures and chipping of graphite particles. The Cu-content in the composite plays the key role in controlling the characteristic contact pressures for these transitional deformation/damage processes.