A 3D deformation measurement method to resist the effects of defects based on grating phase analysis

This study proposes an innovative local displacement unwrapping algorithm combined with the sampling moiré technique to overcome the limitations of conventional global phase unwrapping in the presence of grating defects and noise. The method enables non-contact, full-field 3D strain measurement by capturing grating patterns with a stereo camera system and deriving wrapped displacement fields. Local correction of displacement derivatives allows accurate reconstruction of strain while suppressing error propagation from defective regions, which can also be reliably identified during measurement. Compared with traditional phase unwrapping approaches, the proposed strategy significantly enhances robustness and precision for 3D deformation measurement. A stereo camera system was used to acquire orthogonal grating images for 3D strain reconstruction. The method was validated through cylindrical surface reconstruction, controlled translation tests with 3D-DIC comparison, and numerical simulations with prescribed strain fields and artificial grating defects. The results demonstrate high reconstruction accuracy, good agreement with reference measurements, and strong robustness against local grating degradation. The method was further applied to welded aero-engine components, successfully capturing full-field welding-induced residual strain distributions. This work provides a robust, non-contact, and full-field optical approach for residual strain measurement in complex engineering structures.