Ultrasonic-Resonance-Based Imaging Method for Debonding Detection in Solid Rocket Motors

Solid rocket motors (SRMs) are widely used in rockets and missiles. Accurate evaluation of the debonding defect at the liner/propellant interface or the insulation/propellant interface (deep interface) is crucial for ensuring structural integrity and reliability. The deep interface, characterized by strong attenuation and weak reflection, remains one of the most challenging regions for ultrasonic inspection. This study proposes an improved ultrasonic resonance-based phased array imaging method for deep interface debonding detection in SRMs. The method introduces a damping-guided resonance frequency calculation and selection strategy that accounts for the viscoelastic losses of insulation and propellant materials to determine the optimal resonance frequency for defect detection. A closed-form multilayer delay law is further derived to achieve efficient ray path calculation across multiple interfaces without iterative ray-tracing. Building on these developments, a resonance-based focusing imaging technique is formulated to visualize debonding using a normalized damage indicator. Experimental results demonstrate that the proposed method effectively enables visualized detection of debonding at the insulation/propellant interface, with smaller errors compared to the full focusing method.