As aircraft age, metal fatigue can lead to the appearance and growth of cracks in high-stress areas, such as at fasteners near the wing-body interface. These cracks are severe safety concerns, since they can lead to fuel leaks and wing damage. The U.S. Air Force, therefore, is seeking an innovative nondestructive evaluation technology to detect cracks as small as 0.03 inch occurring near buried surfaces in multilayer wing structures. To meet this Air Force need, RAN Science & Technology, LLC, proposes to develop a new Acoustic Subsurface Crack Imager (ASCI), a one-hand-portable measurement device that will accurately and rapidly locate and describe subsurface cracks. The ASCI applies an ultrasonic stimulus directly to the fastener, from which it is coupled into the structure. The induced vibration can be determined by measuring motion of the surface. Any subsurface cracks distort the surface vibration signature. The ASCI interprets such distortions as green, yellow, or red LED signals to the operator, describing no cracks, small cracks, or significant cracks. In Phase I RAN will prove the ASCI principle through computer modeling and prototype testing, and perform optimization tradeoff studies that will guide engineering sample development for Phase II.
Benefit: A reasonably-priced system for detecting buried corrosion in multilayer structures would be a significant addition to the NDE market. While several methods are available for detecting surface defects and subsurface defects in single-layer materials, there is no current nondestructive method of detecting subsurface defects in multilayer structures composed of dissimilar materials. The PASCAL has this capability, making it useful in such diverse fields as aircraft inspection, certification of building welds, and earthquake retrofit services. Use of PASCAL in aircraft maintenance and test would reduce the likelihood of corrosion-related crashes while simultaneously reducing aircraft inspection time.
Keywords: Corrosion Detection, Multilayer, Ultrasonic, Phased Array, Subsurface Defects, Aging Aircraft, Nondestructive Evaluation, Nondestructive Test
