A novel method for predicting local plastic mechanical properties of metal structures by integrating microstructure and instrumented indentation technique

Abstract

Most important mechanical structures produce complex variations in local material mechanical properties during molding and in-service processes. Accurate testing of material mechanical properties is fundamental to structural integrity assessment. Instrumented indentation technique (IIT) plays a critical role in on-site testing of local structural mechanical properties. However, establishing a precise correlation between the indentation response and uniaxial stress-strain remains challenging in IIT. In this study, we utilized finite element inversion method to explore the quantitative relationship between the indentation response and plastic mechanical properties. Considering that the plastic deformation stages of these metals may exhibit either linear hardening or power-law hardening behavior, a single constitutive model cannot meet the accuracy requirements of IIT. Hence, methods for acquiring mechanical properties suitable for power-law hardening and linear hardening were established respectively based on the analysis of the microstructures of materials exhibiting different hardening behaviors. An integrated IIT approach, considering both microstructure and corresponding material constitutive models, was proposed.Moreover, the influence of elemental composition on microstructure and hardening behavior was investigated. The accuracy of the method was validated with various materials, including austenitic stainless steel, structural steel, and low-alloy steel. Given the universality and reliability of this approach, it is expected to provide theoretical and technical references for the advancement of IIT and structural integrity assessment in important mechanical structures.