A key longstanding objective of the Structural Health Monitoring (SHM) research community is to enable the embedment of SHM systems in high value assets like aircraft to provide on-demand damage detection and evaluation. As against traditional non-destructive inspection hardware, embedded SHM systems must be compact, lightweight, low-power and sufficiently robust to survive exposure to severe in-flight operating conditions. Typical Commercial-Off-The-Shelf (COTS) systems can be bulky, costly and are often inflexible in their configuration and/or scalability, which militates against in-service deployment. Advances in electronics have resulted in ever smaller, cheaper and more reliable components that facilitate the development of compact and robust embedded SHM systems, including for Acousto-Ultrasonics (AU), a guided plate-wave inspection modality that has attracted strong interest due mainly to its capacity to furnish wide-area diagnostic coverage with a relatively low sensor density. This article provides a detailed description of the development, testing and demonstration of a new AU interrogation system called the Acousto Ultrasonic Structural health monitoring Array Module+ (AUSAM+). This system provides independent actuation and sensing on four Piezoelectric Wafer Active Sensor (PWAS) elements with further sensing on four Positive Intrinsic Negative (PIN) photodiodes for intensity-based interrogation of Fiber Bragg Gratings (FBG). The paper details the development of a novel piezoelectric excitation amplifier, which, in conjunction with flexible acquisition-system architecture, seamlessly provides electromechanical impedance spectroscopy for PWAS diagnostics over the full instrument bandwidth of 50 KHz–5 MHz. The AUSAM+ functionality is accessed via a simple hardware object providing a myriad of custom software interfaces that can be adapted to suit the specific requirements of each individual application.
Composite patches bonded to defective aircraft structures are a recognized cost‐effective repair or reinforcement technique for many types of structural problems, such as metallic cracking, repairing corrosion damage, and reducing fatigue strain at structural hot spots. However, certification concerns limit the application of composite bonded repairs in critical components. For certification and management of repairs to critical structure, the smart patch approach may be a useful approach from the airworthiness perspective in facilitating certification. The smart patch consists of a number of in situ sensors used to monitor the structural condition (health or well‐being) of the patch system and the status of the remaining damage in the parent structure. In summary the smart patch is an in situ structural health monitoring (SHM) technology applied to a composite bonded repaired structure. The demonstration of the smart patch on an operational aircraft offers an excellent vehicle to demonstrate autonomous SHM technology in an operational environment. This article describes the development, evaluation, and implementation of the self‐powered wireless smart patch system, including issues such as system design, functionality and certification testing, and installation. This system had no primary power source (i.e., battery) and was powered instead by energy harvested from the local strain environment. It was wirelessly interrogated using a magnetic transceiver and employed piezoelectric elements for both powering and health monitoring functions. The article gives a brief overview of the various available power‐harvesting techniques considered and discusses several key issues that arose when designing and developing the self‐powered smart patch system, namely, (i) demand—power requirements, (ii) supply—energy generation from vibration or strain‐based sources, and (iii) conversion—issues and efficiencies associated with energy conversion from mechanical to electrical energies. Flight data from the system and lessons learned during the program are also presented.
A new acoustic sensing capability, consisting of a flexible high-density linear piezoelectric sensor array coupled to a high-bandwidth interrogation device, is developed and applied to in situ wavenumber–frequency modal decomposition of acoustic emissions in plates. An experimental assessment of the capability is undertaken using acoustic emissions generated by a ball-drop impact on aluminium and composite panels. A new method for acoustic source localisation based on this new sensor array is described, and it is shown to be more accurate than a conventional multilateration technique using single-point piezoelectric receivers. The potential of this new capability for acoustic emission detection, location and possible quantification is discussed.
With any structural health monitoring (SHM) system, verification of the health of the sensing elements is essential in ensuring confidence in the measurements furnished by the system. In particular, SHM systems utilised for structural hot spot monitoring applications will conceivably require transducers to operate reliably after sustained exposure to severe mechanical loading. Consequently, a good understanding of the long term mechanical durability performance of structurally integrated piezoelectric transducers is vital when designing and implementing robust SHM systems. An experimental facility has been developed at the Australian Defence Science and Technology Organisation (DSTO) capable of performing an autonomous long-term mechanical durability test on piezoceramic transducers. The Autonomous Mechanical Durability Experimentation and Analysis System (AMeDEAS) incorporates a general purpose data acquisition program controlling up to three 8-channel relay multiplexers and two instruments. AMeDEAS is highly flexible, allowing user-specified channel configurations and automatic interrogation of selected instruments. The system also interfaces with the uni-axial mechanical testing machine to provide control of the load sequence allowing transducer elements to be interrogated under stable load-free conditions after being subject to a predefined loading regime. AMeDEAS was used to investigate the fatigue characteristics of a low-profile layered piezoceramic transducer package developed by DSTO. A total of 16 transducers were tested under tension-dominated cyclic loading with peak-to-peak strain amplitude increasing from 400 με to a maximum of 3000 με, with periodic acoustic transduction efficiency and electromechanical impedance measurements taken throughout the test. This paper details the AMeDEAS and includes preliminary results which confirm the efficacy of the new facility.
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