The Meyer hardness: A measure for plasticity?

The physical insight into the Meyer hardness is given on the basis of the experimental results for indentation load P versus indentation depth h relations and of a simple model for elastoplastic contact deformation. The quadratic relationships of P = k₁h₂ for loading and P = k₂(h − h_r)₂ for unloading with the residual depth of impression h_r are essential in the elastoplastic indentation processes and mechanisms. The indentation-induced residual strain energy stored in unloaded impression is properly taken into account. The Meyer hardness is an elastic and plastic parameter that depends not only on the plasticity but also on the elasticity of material indented and significantly depends on the geometry of indenter used. The Meyer hardness is given in terms of the energy consumed to create a residual indentation impression, leading to the concepts of “work of indentation” and “ductility index.”