Ductile damage measurement and necking analysis of metal sheets based on digital image correlation and direct current potential drop methods

In this study, a damage measurement procedure is proposed, which combines both digital image correlation and direct current potential drop techniques to evaluate quantitatively the ductile damage in metal sheets during uniaxial tensile loading. Digital image correlation and direct current potential drop techniques are applied to measure the full-field deformation and overall electrical resistance of the region of interest of the specimen during tensile loading. The basic principles, methodology and derivation process are presented in detail. A professional data processing system based on MATLAB is developed to characterize the deformation–resistance–damage relationship during uniaxial tensile loading. The ductile damage can be evaluated conveniently by the proposed approach, and the experimental results so obtained are consistent with those derived by using micro-hardness technique. The necking stage during uniaxial tension is discussed in detail, and it has been shown that the onsets of diffused necking and localized necking can be determined according to the relationship between the major principle true strain and loading steps. Further, the onset of the localized necking can be used to estimate accurately whether the material is going to rupture.