Fatigue Crack Gauge

MDC has developed an extremely simple “fuse-style” sensor for monitoring fatigue crack growth. A fuse-style sensors could just be a single conductive trace with a binary response; either a crack has grown long enough to break electrical continuity or not. Multiple traces can be patterned to produce a pseudo-digital response. MDC has developed a continuum crack gauge fabricated using commercial carbon nanotube (CNT) sheets embedded into a conformal sensor comprising of film adhesive and electrode layers. Any crack growth below the sensor disrupts the CNT electrical network, therefore increasing the network resistance. Using orthogonal parallel pairs of electrodes, one would be able to not only measure extent of a crack, but also deduce the orientation based on relative changes seen by each pair. Thus far, experimental data has matched analytical predictions, and presently a statistical model assisted probability of detection (MAPOD) curve is being generated according to MIL-HDBK-1823A. This CNT sensor will be coupled with RFID technology to provide a passive (RF power harvesting) wireless fatigue crack monitoring capability.