In-plane displacement measurement by gradient-based digital image correlation

A fast and high accuracy gradient-based digital image correlation method uses only fine search at the integer pixel level resolution and the subsequent algorithm of spatial-gradient-based sub-pixel registration. In this algorithm the basic assumption is the rigid body translation of the interrogated subset, however, this is in contradiction to the real circumstances where strains exist. Theoretical error analysis showed that the assumption of subset rigid body translation in gradient-based DIC and the linear approximation of the deformation mapping in N-R method yield identical subset center displacements. Then four real experiments were presented to explore the feasibility and sensitivity of this algorithm. The experiment of uniform uniaxial tension test of aluminum specimen was investigated as a state when strains exist. The displacements calculated by the proposed method were compared with the ones obtained from N-R method. The results showed that the experimental data are in good agreement with the theoretical solution, but the proposed algorithm was much faster than N-R method.