Superficial Plastic Response Determination of Hard Isotropic Materials Using Ball Indentations and a FEM Optimization Technique

This article introduces a novel method for determining the superficial relation between stresses and elastoplastic strains for hard and commonly brittle isotropic materials. An experimental-computational procedure is developed based on a finite element method simulation of successive ball indentations with increasing loads onto machine elements, which are in their final geometry and heat treatment. The imprint profiles, measured by means of profilometry, are used as input data to a finite element method-supported optimization algorithm. The goal of the optimization procedure is to determine the constitutive stress strain curve, expressed as a multilinear hardening law. The proposed method yields superficial plastic properties accurately, extending forward already existing models that determine bulk-flow material data using ball indentations. The developed procedure is demonstrated with the aid of 100Cr6 through hardened bearing steel, annealed at different temperatures.