Coupling digital image correlation and finite element analysis to determine constitutive parameters in necking tensile specimens

A general framework is described for coupling digital image correlation (DIC) with finite element analysis to determine material parameters from measurements of nonuniform displacement fields in a specimen. The approach is to minimize the difference between measured and computed displacement fields and external forces applied to the specimen by repeatedly correcting the material parameters in a chosen constitutive model. The minimization can be accomplished analytically, and the resulting nonlinear system of equations solved using a Newton-Raphson procedure that integrates naturally with standard nonlinear finite element computations. As a representative application, the method is applied to measure the flow behavior of tensile specimens beyond uniform elongation. The results of a series of tensile tests on tapered HSLA 590FB steel specimens show that the effective stress-strain behavior can reliably be extracted to a strain of 60%, well beyond the limits of 20% commonly achieved using traditional engineering analyses on straight-gauge specimens.