Determining Yield Strength of Metals by Microindentation with a Spherical Tip

Abstract

A method of nondestructive testing of the yield strength of steels is considered that is based on processing the diagram of dynamic spherical-tip indentation into the material being tested. The distinctive feature of the method is that it uses a part of the impact indentation diagram that covers two stages of deformation: purely elastic and elastoplastic. The range of strains in which the plastic flow of material starts developing under impact microindentation is theoretically justified. The possibility is shown for recording processes occurring at the initial stage of microplastic deformation with the equipment already available. Experiments have been carried out on deforming low- and medium-carbon steels, as well as pipe steels. As a result of comparing the average contact pressure under dynamic indentation with the static yield strength determined in sample stretching, a linear relationship has been revealed between the two. It is shown that the developed method allows one to determine the yield strength of steels with sufficient accuracy, viz., the measurement error does not exceed 60 MPa, or 13%, in the considered range from 230 to 1400 MPa.