Method of obtaining the constitutive relation in DP steel based on nanoindentation and finite element modeling

The present study was aimed at a method of obtaining the constitutive relation in DP Steel. A set of dimensionless functions are constructed to solve the key parameters from nanoindentation experimental P-h curves, and the reverse analysis algorithms is established. The datas were used in finite element modeling to simulate process of nanoindentation and update the key parameters, the representative stress and corresponding representative strain. By combining the reverse analysis with finite element modeling, a complete method of solving constitutive relation from nanoindentation can be established. The results illustrated that the representative strain was not a constant value of 0.033 as commonly used but varied from 0.0277 to 0.0355. The loading response of nanoindentation was P = Ch1.82 through calculation but not P = Ch2 previously. The constitutive relation of ferrite and martensite has been derived. The average yield stress and strain hardening indexes of martensite and ferrite in DP600 are 805.06 MPa, 0.177, and 185.57 MPa, 0.267 respectively. For WQ950, the yield stress and strain hardening index are 954.26 MPa and 0.190. The results of uniaxial tensile are 416.81 MPa and 0.2.