This Small Business Innovation Research Phase I project is aimed at combining hermetically packaged differential variable reluctance transducers capable of peak strain detection (DVRT-PD's) with shape memory alloy (SMA) actuators to produce improved passive peak strain detectors which can withstand harsh environmental conditions (moisture, salt, and vibration) and can be reset for repeated uses. Critical civil and military structures require "smart" sensors in order to report their strain histories; this can help to insure safe operation after exposure to potentially damaging loads (such as earthquakes, hurricanes, military action, etc.). Sensors in smart structures generally require system power in order to operate, but if power outages occur, in a loss of key data may result. Therefore, sensors which can record peak information without power (passively) are needed. Previous passive peak strain detectors have relied on measuring the magnetic properties of transformation induced plasticity (TRIP) steels. However, these devices have several drawbacks, including bulky size, low resolution, high nonlinearity, and a one time use limitation due to material yielding. The research will address these problems by using modified, microminiature, DVRT PD's. A Phase 0 study was performed using bonded resistance strain gauges as a standard; DVRT-PD's were found to be repeatable, fast, and accurate. Health monitoring has the potential to greatly enhance the safety and life of military, aerospace, and civil structures. Sensate structures equipped with passive networks of peak strain, acceleration, pressure, and torque measurement devices, could be interrogated for their response to test loads or potentially damaging events, and either replaced, or their embedded sensors reset for future interrogation. Applications include health monitoring of composite structures, aircraft, bridges, dams, and buildings. Military and commercial market potential for these systems is significant.
