Affordable NDE of Aerospace Composites with Laser Ultrasonics

Abstract

Over the past twenty years, composite material usage in primary aircraft structures has increased dramatically. Providing high strength, stiffness, and weight savings, these structures are often large and complex in shape, and usually flight critical. Fighter aircraft manufacturing requires 100% inspection of all flight critical parts prior to installation. Periodic in-service inspections of some components may be necessary for the life of the vehicle. Automated ultrasonic systems, using piezoelectric transducers and mechanical scanners, have been used by the aerospace industry for inspecting flat or mildly contoured composite parts in the production environment. These conventional systems are typically slow, require significant setup time for highly contoured parts, and are generally inappropriate for in-service inspections where access is limited to a single side. In view of the increasing usage of composite parts in fighter aircraft, conventional ultrasonic inspection systems will not be able to meet the demanding NDI needs in the production and in-service testing of next-generation fighter aircraft. The laser ultrasonic testing (Laser UT) method, which has been shown to have many advantages over conventional UT systems, can meet these challenging needs [1]. The advantages of Laser UT are: (1) the method is non-contact, requiring no couplants, (2) it can rapidly scan large areas, (3) it is able to inspect at angles far off normal, (4) it does not require expensive part fixtures, and (5) prior knowledge of the surface contour is not required. Laser UT can significantly reduce the time and cost of inspecting complex contoured composite parts by reducing or eliminating part fixtures and long setup times. Furthermore, by using optical scanning techniques, Laser UT is capable of testing complex contoured composite structures at speeds that can not be matched by conventional mechanical scanning systems.