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.
Highlights
The plastic deformation in metals results from shear stress which causes the formation and movement of dislocations at the slips systems in the crystals
The grain orientations are helpful in understanding the slip systems and the anisotropy in the grains with respect to rolling process
The Knoop hardness number is measured for all 6 orientations for both the DC04 steel sheet and the zinc coating on the steel sheet
Summary
The plastic deformation (yielding) in metals results from shear stress which causes the formation and movement of dislocations at the slips systems in the crystals. Hill's quadratic yield criterion has been most commonly used to describe the anisotropic yielding in most metals [2]. The von Mises and Tresca yield criterions [3,4] for isotropic materials have been generalized and given a non-quadratic model defined in the principal stress space by Hosford in Ref. Since in sheet metal forming processes, the out-of-plane stresses are neglected, the yield loci can be plotted in the planestress plane. Anisotropic yield criteria specific to sheet metals have been developed in the principal stress space in Refs. The Vegter yield criterion [7,8] has been used to develop and characterize the yield loci for sheet metals in the plane-stress plane
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