Experimental Study of Measurement Errors in 3D-DIC Due to Out-of-Plane Specimen Rotation

Abstract

In practice, out-of-plane motions usually are not avoidable during experiments. Since 2D–DIC measurements are vulnerable to parasitic deformations due to out of plane specimen motions, three-dimensional digital image correlation (3D-DIC) oftentimes is employed. The 3D-DIC method is known to be capable of accurate deformation measurements for specimens subjected to general three-dimensional motions, including out of plane rotations and displacements. As a result, there has been limited study of the deformation measurements obtained when using 3D-DIC to measure the displacement and strain fields for a specimen subjected only to out-of-plane rotation. This paper presents experimental results regarding the effect of out-of-plane rotation on strain measurement using 3D-DIC. Specifically, full-field deformation results are obtained during rigid body, out-of-plane rotation in the range −40° ≤ θ ≤40° using a two-camera stereovision system. Results indicate that (a) the measured normal strain in the foreshortened direction increases in a non-linear manner with rotation angle, (b) the normal strain along the direction of the rotation axis is essentially zero for all rotation angles and (c) the in-plane shear strain is small but increases linearly with rotation angle. Results also indicate that the magnitude of the errors in the strain are a strong function of how the calibration process is performed, with measurement errors exceeding ±1400 μe for what would normally be considered “small angle” calibration processes.