Surface Acoustic Wave Technique for Craze Detection and Stress Measurement ofAircraft Transparencies

摘要

A nondestructive testing technique that employs surface acoustic waves wasdeveloped for detecting and characterizing flaws and degradation in transparent enclosures of fighter aircraft. The focus of research has been acoustic measurement of craze and stresses (i.e. residual stress) in the acrylic top layer of laminated transparencies. The craze severely degrades the optical performance of the transparent enclosure and is one of the major causes of the limited service life. The stress accelerates the incipience of craze in addition to causing eventual fracture. The acoustic detection technique uses silicone rubber wedges to launch and receive surface acoustic waves. Both Rayleigh surface wave and critical angle longitudinal (L-cr) wave transducers were developed and produced favorable test results. L-cr waves are recommended for stress measurement and Rayleigh surface waves are recommended for craze detection.