Contribution of the Imaging System Components in the Overall Error of the Two-Dimensional Digital Image Correlation Technique

Digital image correlation (DIC) is one of the most widely used non-invasive methods for measuring full-field surface strains in a wide variety of applications. The DIC method has been used by numerous researchers for measuring strains during the plastic range of deformation where the strains are relatively large. The estimation of the amount of background strain error in the measurements is of prime importance for determining the applicability of this method for measuring small strains (such as the elastic strains in metals, ceramics, bone samples, etc.). In this study, the strain errors in 2D-DIC measurements associated with different types of imaging systems were investigated. In-plane rigid-body-translation, experiments were used to estimate the overall amount of error in DIC displacement and strain measurements. Different types of cameras having different types of sensors and different spatial resolutions were used in the study. Also, for the same type of camera, different types of lenses were used. Results show that the DIC measurement accuracy depends on the magnitude of image displacement and that different error estimation parameters can be used for quantifying the accuracy of the measurements. Also, the effect of the lens on measurement accuracy is more pronounced than that of the camera. Furthermore, imaging conditions such as image sharpness and camera gain also affect the accuracy. Further still, the measurement accuracy was found to be influenced by the direction of translation. The results indicate that measurement error can be reduced by orienting the camera such that the major displacement direction is parallel to the width direction of the image. The experimental approach used in this study can be used for quantitatively assessing the quality of the different types of cameras and lenses and to determine their suitability for use in experimental techniques that depend on image analysis such as DIC and particle image velocimetry (PIV).