Estimation of Single-grain Properties of Steel through Inverse- engineering of Microindentation Experiments: Uniqueness of the Solution

Abstract

Cleavage fracture of steel is governed by micromechanical mechanisms, but it is modelled with simple continuum- level models. These models are starting to reach the limits of their applicability, so there is interest to look deeper into micromechanical modelling of fracture processes. In order to model fracture on the microstructural level, a plasticity model of the grains themselves is needed. In prior studies, a method of finding the single-crystal properties by an inverse engineering approach has been described. By this method, a single crystal is indented, and the material input to a FE model of the experiment is iteratively changed until agreement is achieved. These prior studies have shown that methods like this provide ambiguous results. In this paper, the uniqueness of the solution is assessed by evaluating the difference between experiments and simulations for a variety of material input parameters. The results show that with a power law hardening relationship, martensite produces two unique minima (at n=0 and 0.1). This may represent the Lüder's plateau and the subsequent hardening, respectively. The ferrite material featured a minimum that was flat, but the flatness was over a very short range of hardening exponents.