Diagnosis of Mechanical Properties with Instrumented Indentation Technique Using Multiple Pyramid Indenters

Abstract

Abstract This paper presents a semi-nondestructive method for diagnosing mechanical properties through an instrumented indentation technique using multiple pyramid indenters with different dihedral angles. In the developed method, an approximated true stress–true strain curve can be obtained from the plots of the representative stress–representative strain relation estimated for each of the four different pyramid indenters. A functional relation between the representative stress and the indentation load–depth curve was derived from dimension analysis using the π theorem. Then, specific values of constants in the functional equation were determined for each of the pyramid indenters using experimentally validated finite element analysis of the instrumented indentation test. Meanwhile, the representative strain levels were quantified according to the dihedral angle of the pyramid indenters. The developed method was applied to estimate the true stress–true strain curve of non- and prestrained steels. As a result, a small difference could be seen only in non-strained steel with Lüders strain, but the estimated results are nearly in agreement with those obtained by tensile tests. The approximated curves were also used to estimate yield stress and prestrain. The results showed that estimation accuracy of yield stress was better than that based on an empirical correlation with Vickers hardness, and the estimated values of prestrain were in good agreement with those actually introduced by tensile tests. It is expected that the developed multi-indenter method will become useful for semi-nondestructively diagnosing mechanical properties for steel.