Conversion of the kinetic indentation diagrams of ball indenter into stress-strain curves for metallic structural materials

Abstract

A brief review of known approaches to converting diagrams obtained by indentation into tension diagrams is presented. It is noted that most studies on the transformation of kinetic diagrams of indentation of a spherical indenter into tension diagrams are carried out within the limits of uniform deformation using both computational and experimental approaches including the finite element method (FEM) and neural networks. However, we consider that such a transformation from one diagram to another can be fulfilled successfully when using the proper relationship between indentation and tension deformations. This makes it possible to obtain both more reliable estimation of the mechanical properties from indentation tests and more accurate transformation of these results into the stress-strain curves. A relative indentation diameter is one of the main parameters used in the most frequently used formulas for determining plastic deformation. However, at the same values of the relative indentation diameters and a constant ratio of the average contact pressure (Meyer hardness) to the true tensile stress, the strain values upon indentation and tensile can differ significantly due to different ability of materials to strain hardening. We determined a relationship between the true elastoplastic deformation in tensile tests and the relative depth of unrecovered indent obtained in indentation tests with allowance for strain hardening. A methodology for converting the kinetic indentation diagram into a tension diagram in the region of uniform deformation has been developed with the possibility of determining the yield strength, tensile strength, and ultimate uniform elongation of tested materials. The developed method was verified by testing steels, aluminum, magnesium and titanium alloys which differ greatly in the modulus of normal elasticity, strength characteristics, ductility and strain hardening.