Error Analysis and Application of Digital Image Correlation Based on Bilinear Displacement Approximation

Error distribution investigation of measured results in digital image correlation method(DIC)is important to improve measurement accuracy.Measurement error distribution of deformation field in a sub-region by DIC was theoretically analyzed based on bilinear displacement mode.Results show that when actual deformation of a specimen can be described by bilinear displacement approximation,the maximum deformation measurement error usually appears at the boundary or the node of sub-region.Therefore,if specimen is subjected to constant strain deformation,such as in uniform tencile,an optimal sub-region can be selected by correlation coefficients,and measured strain at the center of optimal sub-region can be considerd as the true strain of specimen.Zero deformation experiment was used to verify the reliability of this measurement scheme.At last,digital images of a light guide plate in mobile phone subjected to uniaxial tensile load were analyzed,and its elastic constants was measured by above proposed method.