The Acousto Ultrasonic Structural Health Monitoring Array Module (AUSAM+) for Damage Detection in Structures

Abstract

An area of considerable interest within the aerospace community is the use of structurally-integrated transducers for detecting and monitoring damage in aircraft structures. Such Structural Health Monitoring (SHM) systems offer the possibility to provide non-destructive inspections on-demand and consequently provide a basis for condition-based maintenance on airframes. This approach potentially offers maintenance cost savings and possible improvements in performance when compared to current time-based techniques for detecting and monitoring structural damage. A wide-area damage detection technique under extensive investigation by researchers, on small-scale coupons to full-scale test articles, is acousto-ultrasonics (AU) using structurally-integrated piezoelectric transducers. For any SHM technique to be successfully applied to an operational aircraft in the field the SHM hardware needs to be fit for purpose i.e. easy to use, compact, portable, light, electrically and mechanically robust and provide reliable and accurate measurements. Additionally, in order for researchers to extend, demonstrate and validate AU based SHM techniques under various aerospace structural scenarios, instrumentation is required that is functionally flexible, expandable and relatively inexpensive. In order to facilitate the development, validation and implementation of AU based SHM in the aerospace community the Australian Defence Science and Technology Group (DST Group) has developed a compact device for AU excitation and interrogation, called the Acousto Ultrasonic Structural health monitoring Array Module (AUSAM+). The module, which has the footprint of a typical current generation smart phone, provides autonomous control of four send and receive piezoelectric elements, which can operate in pitch-catch or pulse-echo modes and can undertake electro-mechanical impedance measurements for transducer and structural diagnostics. Other key features include an ability to (1) accommodate larger transducer arrays by operating synchronously with other units, via an optical link; (2) cater for fibre optic sensing of acoustic waves with four intensity-based optical inputs; (3) measure temperature and strain; (4) be triggered externally; and (5) allow the users to easily access the full hardware functionality via a Matlab or Python hardware object, thus providing enormous flexibility for the creation of custom interfaces. This paper provides an overview of the system and its capabilities and demonstrates the efficacy of the system via a simple laboratory AU study on a flat plate.