Research on Small Punch Test Method for Evaluating the Yield Strength of Gradient Nanostructured Material

To assess the yield strength of gradient-nanostructured (GNS) material by small punch test, an analytical method is proposed in this paper. The constructed theoretical model of GNS material is integrated into the classical circular plate bending theory, and an analytical formula specific to GNS material with different microstructures is derived. In order to mitigate the influence of stress state, the analytical formula is modified. The yield strength obtained by the revised analytical formula is close to the standard tensile test results, with errors falling within permissible range. Additionally, the relationship between elastic modulus and surface microstructure of GNS material is established. Thus, the yield strength of GNS material could be evaluated by the surface grain size without measuring of the surface elastic modulus.