Methodology to extract constitutive equation at a strain rate level from indentation curves

In this study, a methodology to determine constitutive equation at a strain rate level from indentation curves was proposed. The constitutive equation for structural steel consists of elastic modulus (E), yield strength (σy), work hardening (n), and a plastic property (α) that represents the plastic plateau stage of structural steel. Four dimensionless equations that show the basic relationship between constitutive parameters, strain rate, and the characteristics of the loading-unloading curve were established. A finite element model to simulate the indentation process was developed for the necessity of constructing four accurate dimensionless equations in the forms of third order polynomial equations. The proposed methodology was then used to determine constitutive equations at a strain rate level from indentation curves for SS400 and SM490 structural steel. The resultant constitutive equations were validated through loading tensile tests for SS400 and SM490 structural steel. Moreover, the proposed methodology was used to determine the strain rate sensitivity of SM490 steel via nanoindentation experiments.