Characterization of yield criteria for zinc coated steel sheets using nano-indentation with knoop indenter

Abstract An indentation based method to characterize the yield locus for steel sheets is developed and implemented. Knoop hardness based indentation experiments have been performed on the surface as well as on the cross sections of an uncoated steel sheet to obtain the corresponding yield locus in the deviatoric and plane-stress situation. Stress ratios following the indenter's geometry are used to plot the yield locus from indentation data. The stress ratios have been corrected for the anisotropy of the material by an optimization algorithm. Points are then plotted in the plane-stress plane using the corrected stress ratios, the strain increment vectors and indentation hardness data. The parameters for the Hill's quadratic yield criteria are obtained from the indentation data based on a curve fitted yield locus. The results obtained using nano-indentation have been compared with those obtained from the standard characterization tests for steel sheet and shown to have good agreement. The method is also applied to the yield locus characterization of zinc coatings on steel sheet for multi-scale modelling of friction in deep drawing.