‘Elastic’ and ‘Plastic’ Hardness of Hard Materials

Abstract

IN the majority of the micro-hardness tests¹, the indenter has to be removed to measure the indentation, and this is also the case in designs where the indenter is mounted in the front lens of the microscope objective (Zeiss–Hanemann; Cooke, Troughton and Simms). Therefore, all these instruments measure only the hardness after the load has been removed, that is, plastic hardness. With elongated indenters and partly with square-base pyramid indenters, it can be assumed that the recovery in the direction of the diagonal or longest diagonal is zero; while this seems to be correct for large deformations, it has not yet been proved correct for very small deformations² on hard materials.