In many instances of mechanical interaction between two materials, the physical
contact affects only the outermost surface layer, with little discernible influence on the bulk of the material. The resultant high pressures in these localised regimes can induce surface structural changes such as deformation, phase transformation and amorphization. The understanding of these physical phenomena is critical in the study of common 'contact loading' processes such as scratching, grinding, milling, polishing, indentation testing, wear, friction and erosion.