Continuum Crack Gauge for Hot-Spot SHM

ABSTRACT:MIL-STD-1530C dictates how to maintain USAF aircraft through the Aircraft Structural Integrity Program (ASIP), which uses damage tolerant analysis (DTA) to set inspection intervals. While effective and safe, DTA can also be quite conservative, leading to excessive down-time for depot transit, tear-down, manual inspection, re-assembly, and return to fleet. In the interest of increasing fleet readiness, introducing condition-based maintenance (CBM) to strategic aircraft location could greatly promote asset availability. To deploy CBM, structural health monitoring (SHM) sensors are permanently integrated within aircraft to frequently/continuously indicate integrity of components, rather than relying on predictive models based on assumed loading profiles to dictate inspection intervals. While more complex SHM methodologies have been demonstrated with various levels of maturity, great benefit could be realized by extremely simple fuse-style sensors, which have the advantage of being easier to interpret data and potentially more straightforward to qualify according to MIL-HDBK-1823A. In its simplest embodiment, a fuse-style sensor is binary; a crack has grown or not grown. Generally, the more rungs introduced to the sensor, the more detail that can be provided about the crack. The proposed technology employs carbon nanotube (CNT) sensors, providing a continuum of crack gauge elements for determining crack length and orientation.BENEFIT:Once successfully demonstrated through a Phase II effort, there exists a broad commercial market for this SHM method. One of the key success factors for this technology is its versatility; the ability not only to be integrated into new applications, but to be retrofitted into an existing asset designs. The continuum crack gauge could be applied to composite or metallic structure, be used to find new damage, track existing damage growth, or be applied as part of a bonded repair to check effectiveness in crack arrest. Initial relevant markets would include DoD fixed-wing aircraft, but the technology could easily proliferate into any DoD asset, ranging from rotorcraft to ships and ground vehicles, to aid in condition based maintenance. Once demonstrated in defense applications, comparable commercial opportunities exist, particularly for aircraft and potentially buildings and civil infrastructure once the production cost has been driven low enough. MDC will work through strategic partners to license the technology for production and deployment.