Experimental Study on Hidden Corrosion/Delamination Detection with Ultrasonic Guided Waves
Hidden corrosion detection is critical in the aerospace industry. Occurring on the inside surfaces or at the interfaces of an aircraft’s skin, the corrosion must be detected from the outside surface. Surface waves are, therefore, not suitable for detecting such defects/failures. Ultrasonic bulk wave methods can be used to detect the corrosion caused thinning in the wall or a delamination of a structure [1,2]. However, since the method is based on point-by-point testing, it becomes a tedious time consuming procedure for large area inspection. Guided wave methods are being developed to tackle this problem [3–6]. An experimental study of hidden corrosion/delamination detection in single/multiple layer aluminum plates is conducted with specially selected ultrasonic guided wave modes. Both corrosion simulation specimens by machine cutting, and real corrosion specimens by electrochemical processing, Two-layer specimens have been prepared with such corroded sheets to form an artificial interface corrosion/delamination. Various wave modes are subsequently generated on these specimens to examine the implications of thinning on mode cutoff, group velocity changes, mode frequency shifts, and transmission and reflection amplitudes. Finally, a practical problem of skin to honeycomb core delamination detection with guided waves is also addressed.