SIFT-Aided Rectified 2D-DIC for Displacement and Strain Measurements in Asphalt Concrete Testing

Two-dimensional digital image correlation (2D-DIC) is a widely used optical technique to measure displacement and strain during asphalt concrete (AC) testing.An accurate 2-D DIC measurement can only be achieved when the camera's principal axis is perpendicular to the planar specimen surface.However, this requirement may not be met during testing due to device constraints.This paper proposes a simple and reliable method to correct errors induced by non-perpendicularity.The method is based on image feature matching and rectification.No additional equipment is needed.A theoretical error analysis was conducted to quantify the effect of a non-perpendicular camera alignment on measurement accuracy.The proposed method was validated numerically using synthetic images and experimentally in an AC fracture test.It achieved relatively high accuracy, even under considerable camera rotation angle and large deformation.As a pre-processing technique, the proposed method showed promising performance in assisting the recently developed CrackPropNet for automated crack propagation measurement under a non-perpendicular camera alignment.2D-DIC method is not applicable when the test specimen surface is non-planar, or the out-of-plane displacement is non-negligible.On the other hand, the stereo-DIC method, which uses two synchronized cameras, was proposed to measure 3D displacement based on the binocular stereo-vision principle (Pan et al. 2009).The 2D-DIC remains one of the most popular optical technologies because of the following advantages: