Understanding and quantification of elastic and plastic deformation during a scratch test

Abstract

An understanding of abrasion resistance and the associated surface deformation mechanisms is of primary importance in the materials engineering and design of many important industrial components undergoing wear and abrasion. Instrumented scratch testing has been shown to be a useful tool for characterization of the abrasion resistance of materials. Although most studies on scratch resistance have been limited to the theoretical case of purely plastic materials, experiments on metals and polymers have shown that the contact mechanics and indentation behavior are strongly influenced by the elastic behavior. In this work, the normal and tangential scratch forces, the penetration depth relative to the initial surface and the three-dimensional topographic relief of the scratched surface are measured. These parameters have allowed us to accurately calculate the actual contact area between the indenter and the material, taking into account both elastic deformation and pile-up phenomena. This contact surface was used to estimate the real mean contact pressure during scratch testing. This pressure was compared to the static hardness of the studied materials, as well as to the classical definitions of the scratch hardness. The ratio between the plastic and elastic deformation during a scratch test with a Berkovich indenter was then related to the ratio of the Elastic modulus to the hardness for the tested bulk materials. This scratch experiments were performed on a wide range of materials from polymers to metals and demonstrate the importance of taking both elastic deformation and pile-up into account in order to accurately understand and characterize the scratch resistance of materials.