Quantitative discrimination of debonding defects and non-debonding defects in coated propellant grain based on shearography

During the production of coated propellant grains, micro-bubble defects inevitably form within the liner layer. Although these non-debonding defects do not compromise structural integrity, current shearography-based non-destructive testing cannot reliably distinguish them from critical interfacial debonding defects, leading to frequent misjudgments in product qualification. This study proposes a quantitative discrimination criterion based on a normalized out-of-plane displacement parameter, derived from thin-plate and moderately thick plate theories. To enable reliable calculation of this parameter, a vibration-resistant electronic shearography system and a modified UNet architecture are employed for accurate displacement extraction and defect size measurement, respectively. Experimental validation on standard specimens and actual propellant samples demonstrates that the normalized parameter remains insensitive to loading pressure while exhibiting a clear order-of-magnitude separation between debonding and non-debonding defects, achieving zero misclassification. This work provides a theoretical foundation and practical approach for quantitative defect discrimination in coated propellant grains, thereby reducing quality misjudgment risks.