Testing materials' hardness science, technology & application

In everyday life solid material objects come in contact with each other, exerting and transferring forces. What happens to the materials at the contact depends on the relative hardness of the two and the magnitude of the stresses induced relative to their yield or fracture strengths. To be able to predict what can happen, the hardness of materials is tested and measured. The science of mechanics of materials aims to relate hardness to the more fundamental properties, such a modulus of elasticity, fracture strength, onset of plastic deformation, plastic flow and strain hardening. Depending on the ratio of applied stress to material strength, the resulting deformation can be elastic (Hertzian), or a permanent deformation which can be brittle (Griffith's fracture) or ductile (von Mises yielding). A review of the most common methods of hardness testing is presented, followed by a study of the interface between glass and polymer matrix using nano-scratch technique.