Embedded Sensors for Monitoring Fatigue Damage in Harsh Environments

This Phase II will demonstrate practical, low cost, and adaptable field inspections for small cracks (less than 0.03 in.) at fastener holes that cannot be reliably inspected with other available or emerging NDT methods. Pressing U.S. Air Force needs include structural features with no access for conventional inspections and other unsolved buried layer cracking problems. In Phase I, a JENTEK MWM®-Rosette with “pillars” (a thin, eddy current fatigue crack gage exhibiting enhanced durability) was successfully demonstrated as a smart washer (mounted under a fastener nut in a fatigue test representing a USAF second layer crack detection need). The biggest remaining obstacle to implementation is a lack of defined requirements for embedded damage gages. The Phase II objectives are to (1) develop a USAF acceptable embedded sensor performance verification/validation methodology, (2) demonstrate POD curve generation with performance exceeding requirements, (3) demonstrate durability exceeding requirements and pass environmental/fuel exposure qualifications, and (4) enhance packaging/cabling/installation tooling, and complete subcomponent testing. The MWM-Rosette solution is simple, practical, and matured to a level that makes this SBIR highly likely to succeed. In a tight budget climate, such lower cost and practical solutions must be transitioned to reduce maintenance costs and ensure platform availability. BENEFIT: If this Phase II is successful, the Air Force will finally have a low cost, mass producible, and practical solution to the need for small crack detection in buried layers – by mounting MWM-Rosettes under fasteners (heads, nuts, washers, Hi-Lok collars, FTI/ForceTec retainers, or between skin/structural layers) at one or many inaccessible locations. The benefits are (i) avoiding extended time in depot for inspections, e.g. to gain access to a fuel tank and to remove fasteners, (ii) preventing costly part replacements by detecting cracks small enough, in the field, to enable over-sizing of holes and life extension, and (iii) enabling more frequent, low cost, field inspections if damage tolerance requirements shift to lower crack detection sizes. This is mostly a U.S. military and FMS need for fighter aircraft and rotorcraft. Commercialization of this technology is highly likely, once a clear performance validation procedure (including POD studies) is accepted by the ASIP community, and once specific applications are unequivocally solved.