Fastener Failure Detection Using a Surface Acoustic Wave Strain Sensor

Surface acoustic wave (SAW) strain sensors are presented for use in the detection of aircraft fastener failures. SAW sensors have the potential for the development of passive wireless systems. The SAW devices employed four orthogonal frequency coding spread spectrum reflectors in two banks on a high temperature piezoelectric substrate. Three SAW devices were attached to a cantilever panel with removable side stiffeners. Damage in the form of fastener failure was simulated by removal of bolts from the side stiffeners. During testing, three different force conditions were used to simulate static aircraft structural response under loads. The design of the sensor, the panel arrangement and the panel testing results are reported. The results show that the sensors successfully detected single fastener failure at distances up to 655 mm from the failure site under loaded conditions.