SBIR-STTR Award

Aircraft transparencies represent one of the most significant life cycle cost to the U.S. Air force. The major cause for the optical impairment is the degradation in plastics known as crazing which occurs due to surface stresses and is accelerated by the environmental factors. The objective of the project is to develop the necessary technique to measure and quantify the crazing and show feasibility of a portable instrument to carry out the evaluation in field. Such A capability affords USAF to validate accelerated crazing tests, enable purchase of the canopies based on life cycle cost, overall reduce cost and increase combat readiness. The prudent approach is well researched surface acoustic wave techniques which have been successful in locating minute cracks in metals and ceramics. The most important factor in choice of acoustic technique is their ability to measure the residual stresses which determine the remaining life of optical performance. We anticipate an elegant measurement scheme that can characterize the existing crazes and indicate the probable time of future occurrence.

The feasibility of the Ultrasonic Surface Wave technique for transparent enclosures was successfully demonstrated in the Phase I effort. These results can be considered as the needed breakthrough and strongly motivate the next phase of extensive research and development, leading to the commercial availability of products and techniques for nondestructive evaluation needed by the USAF, the DOD and civilian industries at large. Though the Phase I efforts were concentrated for the specific problems of stress measurements and detection of crazes in the top sheet, the Phase II research would have much broader scope. It would be applicable to many other aspects of transparency durability; for example, Coating Degradation, Delaminations and Stress Concentration (round cracks). The surface wave transducers devised in Phase I would be improved, reduced in size and would be modified to generate Lamb waves. In addition surface acoustic microscopy made possible by phase I results would be pursued by developing novel dry contact acoustic lenses (transducers). The application of this research to structural composites should be of great benefits to the USAF. The secon major component of research would be to develop portable instruments for field of use. These instruments would use state-of-the-art digitizing and computer components to create a new class of low cost ultrasonic instruments. A complete portable Nondestructive Evaluation System would be constructed and made available to the USAF for field demonstration and testing. The commercial potential is high since there is a lack of viable nondestructive stress measurement technique.