A strain-pattern-based spherical indentation method for simultaneous uniaxial tensile residual stress and flow property determination

Abstract

In this study, a strain-pattern-based method was proposed to simultaneously determine the uniaxial tensile residual stress and flow property from a single-cycle spherical indentation test. The variation of the plastic zone radius (at the specimen surface) with uniaxial tensile residual stress was analytically investigated by the expanding cavity model. The analysis proved that the circular plastic boundary will be elliptical under the action of uniaxial residual stress (with a shrunken plastic zone radius along the loading direction and an extended plastic zone radius vertical to the loading direction), and this difference can be used to calibrate the magnitude of the residual stress. The analytical result was verified and modified through finite element calculations, after which a set of regression functions for Holloman hardening metals was established for load compensation, proportional limit correction, and hardening exponent calculation. The effectiveness of the method was verified through finite element calculations of spherical indentation tests on 16 Holloman hardening and 6 metals used in engineering applications at different residual stress levels. The verification proved that maximum errors for strength and residual stress calculations are about 10% and 15%, respectively, and the potential of the new proposed method was validated.