Holographic and shearographic NDT applications in aerospace manufacturing

Laser nondestructive testing (NDT) techniques based on interferometric imaging, primarily holography and shearography, have seen growing acceptance since the 1980s. With an increase in the use of composite materials and sandwich structures, the need for high speed, large area testing for fracture critical, subsurface discontinuities, such as disbonds, delamination, sheared cores or nonvisible damage in aircraft, missiles and marine composites, led to broad acceptance of laser based NDT techniques. Laser NDT techniques employing holography and shearography imaging interferometers complement ultrasonic testing, thermography and other NDT techniques as highly developed, mature and cost effective technology. As with all NDT methods, strengths and weakness must be completely understood, applications qualified through probability of detection verification with written procedures and rigorous training for operators and engineers alike. Once qualified for a particular application, holography and shearography systems can operate with extraordinary efficiency, reaching throughputs of 2.3 to 111 m(2) (25 to 1200 ft(2)) per hour, 2.5 to 120 times the test rate for ultrasonic C-scans. As these technologies become more widely known, commercial applications in aerospace, electronics, marine composites, high performance tires and medical devices have greatly increased. In 2001, laser techniques reached a fundamental milestone with the inclusion of holography and shearography in SNT-TC-1A for Level III certification (American Society for Nondestructive Testing, 2001). This paper will present an overview of laser NDT technique applications in aerospace, electronics and marine composites, where they serve as highly effective, fully integrated industrial process controls, improving manufacturing quality while reducing costs.