Application of Single-Sided NMR and Acousto-Ultrasonic Methods for NDE of Composite Structures

New advanced non-destructive evaluation (NDE) methods such as single-sided nuclear magnetic resonance (NMR) and Acousto-ultrasonic methods are being developed for their advantages and high resolution for defect detection in composite structures. Glass fiber-reinforced plastics (GFRP) composites are being used for many industrial applications. Rubber lining in layers is done to the composite inner surface to meet the industrial requirements. The interface of GFRP composite and rubber lining is very critical. Any de-bond (separation of adhesively bonded liner from composite surface) at the interface and delamination between rubber layers may lead to failure of composite structure due to corrosive gases and liquids. NDE of such structures is challenging due to their high attenuation of ultrasound and poor radiography defect signatures. The present study reports application of proton single-sided NMR method to evaluate the de-bonds of rubber liner with composite and delamination between rubber layers. Results are compared with Acousto-ultrasonic method, which uses low-frequency mechanical waves for inspection. Results indicate application of both these techniques for evaluation of bonded interfaces. Advantages of both the techniques over conventional techniques have been discussed.