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 2D-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 nonperpendicularity. The method is based on image feature matching with scale-invariant feature transform (SIFT) and rectification. No additional equipment is needed. A theoretical error analysis was conducted to quantify the effect of a nonperpendicular 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 angles and large deformation. As a preprocessing technique, the proposed method showed promising performance in assisting the recently developed CrackPropNet for automated crack propagation measurement under a nonperpendicular camera alignment.