Resolving the strength-to-stiffness ratio dependency for instrumented macroindentation based local mechanical properties

In case the distribution of mechanical material properties is inhomogeneous, for example in welded joints, an indentation based measure can be adopted to obtain local estimates. However, the property precision and accuracy is often lacking and a next step to reveal the one-to-one relation between instrumented macroindentation and material stress strain curve was set, proposing semi-analytical model improvements and deploying Monte Carlo based numerical model simulations for verification. Utilizing experimental data for DH36 and S355 steel, high-precision Young’s modulus estimates were obtained within 95 [%] reliability of the uniaxial tensile test reference values and less than a 10 [%] error. For high reliability, the number of indentation tests must be sufficiently large. Contact radius information is at least required to obtain the yield strength and several formulations provide estimates within ∼ 20 [%] error for a large range of material properties. A significantly more accurate value can be obtained if the Young’s modulus is not involved, providing an error within 10 [%]. Introducing a proportional plastic strain offset criterion rather than the well-established constant one to obtain an indentation based yield strength estimate, the strength-to-stiffness ratio dependency was eliminated. Accuracy is improved to a ∼ 20 [%] error range with 95 [%] reliability. Using the material proof strength rather than the yield strength even reduces the 95 [%] reliability error estimate to ∼ 15 [%]. Experimental instrumented macroindentation based yield strength estimates are within 10 [%] error compared to the uniaxial tensile test values. • Proposed novel spherical macroindentation based local mechanical properties model. • Improved indentation based strength-to-stiffness independent yield strength estimate. • Explored precision and accuracy of three contact radius models. • Verified model using Monte Carlo FE simulations. • Validated model using tensile tests and macroindentation tests.