Dual-Use Strain Sensors for Simultaneous Quasi-static Strain Measurement and Acoustic Source Location

ABSTRACT The use of metal strain gauges and ultrasonic transducers has long been studied in the field of nondestructive evaluation (NDE) as a part of structural health monitoring (SHM). Strain gauges use electrical resistance to monitor strains during the loading of a component. Ultrasonic transducers are piezo devices that use a crystal-like sensing element with very low excitation energy that can monitor small strains such as acoustic emissions (AEs). These devices have been used to locate the sources of AEs from artificial sources, such as Hsu-Nielsen pencil lead break (PLB) tests or natural sources, such as crack propagation. The ultrathin silicon membrane (USM) sensor is a piezoresistive sensor incorporating the best aspects of a conventional strain gauge and ultrasonic transducer. The sensor can measure both the strain of a component and any AE that is emitted from the component. To the author’s knowledge, this is the only sensor capable of simultaneous measurement of these two data types. This study compares the sensor to commercial ultrasonic transducers in an unloaded PLB test to determine the ability to measure Lamb waves for source location estimation. In addition, the USM sensor is compared to commercial strain gauges and ultrasonic transducers during a PLB test under a quasi-static tensile load, where the USM sensor yields measurements similar to those of both commercial sensors. This duality of the USM sensor demonstrates the sensor’s inherent usefulness to the NDE and SHM fields. The sensor offers capabilities comparable to commercially available sensors in a smaller package, with less power consumption and lower cost.