On the correlation of scratch testing using separated elastoplastic and rigid plastic descriptions of the representative stress

The correlation of hardness values at scratch testing is studied within the framework of a differentiated description of representative stress values. The analysis is based on hardness values determined from a comprehensive finite element study of scratching of classical elastoplastic materials using a conical indenter. Large deformations are accounted for and the strain-hardening behaviour is varied in order to achieve generality of results. It is shown that good accuracy predictions for different material classes can be achieved by using a combination of stresses at different levels of plastic strains to define representative quantities at scratching. It is also shown that this correlation must account for the difference in mechanical behaviour at elastoplastic and rigid plastic scratching. From a practical point of view the results are valuable both when describing the mechanical behaviour at scratching and at material characterization. From the generality of the analysis, both elastoplastic and rigid plastic behaviour are accounted for, predictions based on the present study can be made for scratching of highly elastic materials such as polymers and ceramics but also for scratching of metals when plasticity dominates.