Pitch-Catch Ultrasonic Technique for Evaluating Adhesive Bonding in Sandwich Composite Radome Structures

Abstract

Sandwich composites with lightweight cores and high-stiffness facesheets are widely used in aerospace and automotive industries. Ensuring the integrity of the adhesive bond between the facesheet and core is critical for structural performance and safety. This review examines the pitch-catch ultrasonic method as a non-destructive evaluation (NDE) technique for assessing adhesive bonding in such structures. The paper summarizes working principles, experimental setups, advantages, limitations, and recent developments in pitch-catch technology, including guided wave and Lamb wave applications. Comparative analysis with other NDE methods and future research directions are also discussed.

Introduction

The design of radomes—aerospace structures protecting antennas—requires balancing electrical and structural demands. Structurally, radomes must withstand aerodynamic drag and bird impacts due to their external, forward-mounted position on aircraft. They commonly use sandwich composite structures with a lightweight core (often honeycomb) bonded to strong facesheets. The strength and durability of these sandwich structures heavily depend on the quality of the adhesive bond between the core and facesheets.

Non-destructive ultrasonic testing (UT), particularly the pitch-catch method, is widely employed to inspect the bond integrity in these composites. The pitch-catch technique uses paired ultrasonic transducers to send and receive waves, detecting defects like disbonds by analyzing changes in wave amplitude, phase, and time-of-flight. It can distinguish actual bonding defects from probe lift-off (loss of contact), reducing false positives.

There are three main pitch-catch modes—RF, impulse, and swept—each differing in signal processing and frequency use. The swept method, for example, varies frequency to differentiate lift-off from real disbonds more clearly.

Testing on a 1m x 1m sandwich radome panel with glass fiber reinforced polymer skins and aramid honeycomb core demonstrated that the pitch-catch method effectively detected both naturally occurring and artificially introduced disbonds. It proved to be a fast and reliable inspection method, though it faces challenges like complex signal interpretation, material variability, and coupling issues.

Conclusion

Composites sustain invisible damages in case of impact incidents, which if not evaluated or inspected may cause catastrophic conditions for the aircraft safety. Out of all the damages facesheet to core/honeycomb dis-bond is difficult to inspect. It is difficult to inspect sandwich structures for defects due to the shear presence of honeycomb. The empty spaces create multiple reflection thus from a regular A-scan it requires a highly trained operator to carry out such inspections. The same is relatively easy using a pitch catch method. Despite the challenges and the limitations the pitch-catch ultrasonic technique represents a powerful tool for evaluating adhesive bonding in sandwich composite Radome structures. Its ability to detect internal flaws non-destructively, combined with technological advancements, makes it an indispensable component of modern structural health monitoring and quality control systems. Moreover it provides a accurate methods to inspect large areas in limited time, which otherwise are difficult with conventional pulse-echo methods. Continued research and integration with digital technologies promise to further elevate its effectiveness and adoption in critical applications.

References

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Copyright

Copyright © 2025 Mandeep Singh, A. C. Niranjanappa, B. Durga Prasad. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.