Study on correlation and scaling protocol between indentation stress-strain and uniaxial stress-strain

Most important mechanical structures produce complex local material changes during the moulding and servicing process. Obtaining the specific local mechanical properties of materials and conducting field tests are problems in structural integrity evaluation. The instrumented indentation technique (IIT) is a solution to these problems. However, the core challenge with the IIT is the quantitative correlation between indentation response and uniaxial stress-strain (USS) response. In this study, we investigate the scaling relationship between indentation stress-strain (ISS) and uniaxial stress-strain (USS). A new protocol for obtaining the mechanical properties of alloy steels using ISS curves is proposed, which can directly obtain the plastic stage of the USS curves from the ISS curves. We used a finite element inversion method based on existing theories. Models with different mechanical properties (USS curves) were established using the ABAQUS software to obtain the corresponding ISS curves. We then explored the relationship between the two; the strain-scaling factor and stress-scaling function were specifically identified. Our work proposes an ISS protocol for power-law-hardening materials. Two alloy steels (SA508 and 42CrMo) were experimentally verifieds. The predicted results are approximately consistent with the practical curves and the error was within +/- 10%. Because of the universality and reliability of the protocols, it is expected to provide a theoretical reference and technical approach for the development of IITs and structural integrity evaluation of important mechanical structures.