Estimating constitutive equation of structural steel using indentation

• Nanoindentation of 576 combination materials was simulated using ABAQUS.
• Assumptions for material model of structural steel were used.
• A method for estimating the plastic parameters of structural steel was established.
• The method was verified by nanoindentaion and tensile tests of SS400 and SM490 steels.
• Constitutive equation of structural steel can be estimated using the proposed method.

Unlike other metal materials, structural steels show plastic plateau in their constitutive equations. The plastic plateau continues from yield strain to the starting-point of strain hardening. In this study, the constitutive equations of structural steels, including the plastic plateau, were extracted from the indenting load to depth curves of indentation experiments. While conventional equations were used to determine the elastic modulus of steel, new equations were developed to determine the yield strength and the strain hardening exponent of steel from the indentation results by considering the plastic plateau. Two dimensionless relationships between the constitutive properties of steel and the characteristics of indenting load to depth curves were derived. A finite element (FE) model to simulate indentation was developed and FE analyses for 576 combinations of steel constitutive properties were conducted. The dimensionless relationships were then established in polynomial equations by regression analyses of the FE results. Indentation and uniaxial tensile loading tests were also performed to verify the FE model and the proposed equations to extract the constitutive properties using indentation.