Determining the stress level of monotonic plastically pre-hardened metal sheets using the spherical instrumented indentation technique

摘要

In this paper, a methodology, for calculating the stress level of monotonic plastically pre-hardened materials, using the instrumented indentation technique (IIT) coupled to the inverse analysis technique (IAT) is presented. In this methodology, the Voce work-hardening law is always considered as the work hardening law of the studied material. This methodology has shown a very good efficiency in determining the stress levels and the plastic strains undergone by two pre-hardened pseudo-materials. That was encouraging for applying this methodology on real metal sheets. Three metal sheets were studied (DC01 and DP600 steels and aluminum alloy 2017). In the case of the as-received sheets, the identified laws show precise results for plastic strains between 3 % and 6 % which correspond approximately to the representative strain in the case of spherical indentation. Tensile samples were then pre-hardened by imposing a monotonic plastic strain. Three levels of plastic pre-strains were imposed. Concerning low pre-hardening levels, very satisfying results were obtained where this methodology showed a great efficiency in determining the stress level and the plastic pre-strain undergone by the pre-hardened sheet. For high pre-hardening levels, a small under-estimation of the stress level and the plastic pre-strain was obtained. In this latter case, work is being carried out to improve the results by enriching the experimental data provided for the inverse analysis computations.