Projection speckle digital correlation for surface out-of-plane deformation measurement

Abstract

The paper presents a new study on the method of Projection Speckle Digital Correlation (PSDC) for surface out-of-plane displacement and tilt measurement. Considering that perspective and parallel devices differ substantially in the nature of pattern projection and imaging, four different camera-projector setups are modeled by optical triangulation. The different W-u relationships that the models give indicate the impact of the device properties on raw measurement. In assessing overall error sources and error structure in the PSDC measurement, sources and magnitudes of the error in relation to Digital Speckle Correlation (DSC) are evaluated since DSC is a core technique embedded in the P SDC for image in-plane motion extraction. Another category of the errors inherent to the PSDC is analyzed, which is due to the misuse of the field equations. For a particular PSDC setup, such systematic error is correctable by a calibration test using a planar sample with known rigid-body motion. A case application serves as a demonstration of the potential of the low cost system, in which DSC and PSDC are combined to resolve 3D deformation in a 1 mm2 area in a notched tensile sample.