Application of Digital Image Correlation to Material Parameter Identification

This paper expounds the parameter identification of material models using simulation-based optimization and experimental results obtained using Digital Image Correlation (DIC). DIC is an optical method which provides full-field displacement measurements for mechanical tests of materials and structures. It can be used to obtain strain field histories from an experimental coupon which can be combined with the corresponding fields obtained from a Finite Element Analysis to identify constitutive properties. The methodology, which involves the solution of an inverse problem, has been implemented in the optimization code LS-OPT®. A core feature is multi-point curves: response curves which are evaluated at multiple locations and extracted from simulations and experimental data. An interface to a commercial optical measurement package was created and an example of a tensile test was used to demonstrate the methodology based on the measurement of point-wise strains vs. tensile force. The Hockett-Sherby flow curve function, using two parameters, was used to model the material. The example validated the code but revealed potential problem areas requiring further investigation. A prominent issue is the method used for matching the experimental and computational curves. To identify sources of ill-posedness of the regression problem, several diagnostic tools are suggested. Some of these tools, notably sensitivity analysis will be demonstrated at the conference.