Identification of plastic stress-strain parameters by global digital image correlation, the virtual fields method and the total strain theory

A procedure for identifying plastic constitutive parameters from measured displacement fields based on virtual fields is proposed in this paper. The displacement fields of the specimen surface are obtained through measurements using global digital image correlation. Then, material property identification is implemented by utilizing piecewise virtual fields. In order to identify the material properties from the displacement fields obtained at an instant, the total strain theory is used as the constitutive equation. The relations between the material properties, measured displacement fields, measured tractions, and virtual displacements are obtained from the principle of virtual work, and they are solved numerically to obtain material properties. The effectiveness of the proposed method is demonstrated by applying it to displacement fields obtained by an elasto-plastic finite element method and experimentally obtained displacement fields of a pure aluminum specimen. The results of the numerical validation show that the elasto-plastic material properties can be identified from a single set of displacement fields under proportional loading. Meanwhile, the results of the experimental validation show that the elasto-plastic material properties can be evaluated but the discrepancy between the inversely identified stress-strain curve and the directly measured one is observed.