Challenges and solutions for ultrasonic phased-array inspection of polymer-matrix composites at production rates

More than ten years of Research and Development focused on phased-array inspection of aerospace Polymer Matrix Composites (PMCs) is presented. This work includes basic research designed to understand the propagation of ultrasound through composite materials, as well as optimization of phased-array probes and inspection strategies for composite parts. Successful implementations of these strategies for fully automated on-line inspections are presented including a discussion of how challenges were overcome and the promise of new acquisition and analysis tools. Composite materials present unique challenges for ultrasonic inspection including complex shapes and a wide range of potential flaws and defects. For automated inspections, part-to-part variability and the need to inspect at production rates pose additional challenges. The methodologies presented are based upon laboratory experiments performed in conjunction with modeling and simulations, which are used to optimize inspection strategies. A significant challenge that should not be under estimated is creating industrial-quality test specimens with realistic defects of known size and location that can be independently verified. In projects with industry and the Air Force Research Laboratory (AFRL), work has focused specifically on using surface-adaptive techniques to inspect parts with complex shapes including small convex and concave radii that are typically found on stringers, blades and wing structures. Experimental and simulation results have been evaluated for flat and curved linear arrays as well as matrix arrays, which are used with and without surface-adaptive techniques for purposes of comparison. Fully automated on-line inspections that have been operating for several years as well as recent large-scale implementations demonstrate the ability to inspect a wide range of different composite parts at production rates. Rapidly increasing computer processing power together with ultra-high data-transfer rates will continue to enable computationally intensive signal and image processing in near real time. These advancements hold promise for greater use of automated inspection and the ability to incorporate sophisticated data acquisition and analysis tools into portable systems that can then be used in the field, for example, in depots and onboard ships.