Depth characterization of local thickness-reduction defects using dual-channel speckle interferometry and local curvature ratio

A nondestructive testing method based on dual-channel speckle interferometry and local curvature ratio is proposed for quantitative depth characterization of local thickness-reduction defects. The method combines digital speckle pattern interferometry (DSPI) and digital shearography (DS) to obtain complementary deformation information. The DSPI channel measures the out-of-plane displacement field, from which the local curvature is calculated. The DS channel extracts deformation features associated with the defect boundary. After the defect boundary is reconstructed, local sampling is performed along the boundary normal, and the local thickness-reduction defects is estimated from the curvature ratio between the two sides of the boundary. Numerical simulations and experimental validations are conducted for circular and elliptical local thickness-reduction defects. The experimental results show that the estimated depth of the circular defect is 3.07 mm, with an absolute error of 0.07 mm, whereas the estimated depth of the elliptical defect is 2.97 mm, with an absolute error of 0.03 mm. All the results indicate that the proposed method is an effective tool to measure local thickness-reduction defects precisely.