Application of sensor technologies for local and distributed structural health monitoring

Abstract

The work presented in this paper deals with the application of different sensor technologies for fatigue crack damage monitoring of metallic helicopter fuselages. A test programme has been conducted, consisting of seven fatigue crack propagation tests on aluminium panels (skin with riveted stringers) representative of the rear fuselage of a helicopter. Electrical crack gauges and comparative vacuum monitoring sensors have been used locally to monitor propagating cracks. A network of optical fibre Bragg gratings is presented as a valid possibility for distributed monitoring (based on strain field dependence on damage), alternative to consolidated electrical resistance-based strain gauges. A Smart Layer based on piezoelectric transducers that emit and receive Lamb wave signals has also been analysed in this paper for distributed monitoring. Two damages have been considered: a skin crack artificially initiated on a panel bay and a skin crack propagating from a rivet hole after stringer failure. Damage sensitivity has been evaluated and compared among the considered technologies, thus providing useful recommendations for each considered system, together with advantages and drawbacks concerning their suitability for on-board installation and monitoring. The damage index sensitivity to operative condition, load in particular, is verified and compared with damage effect for distributed networks. A finite element model able to describe any selected feature sensitivity to the monitored damage is also presented as a useful tool for the optimization of the structural health monitoring system design process

Investigation of the effects of structure-sensor interaction on piezoceramic transducers for structural health monitoring applications

“…One of these was co-cured with CFRP by Lin and Chang (2002), (p919) the adhesive bond being formed by the matrix resin. Surface attachment of this package type with epoxy adhesive has been successfully demonstrated by Qing et al (2006b), Shark et al (2008), Chung et al (2009), andSbarufatti et al (2013).…”

“…It does however confine the occurrence of damage to one component of the system which simplifies the problem identification and it does provide a strategy on which more protective permanent fixation methods can be formed. That is using the bondline to protect the transducer, because for long term in situ monitoring applications it is desirable that transducers be permanently attached ( (Bhalla et al, 2002), p492), ((Schubert and Herrmann, 2012), p3635), ((Sbarufatti et al, 2013), p2).…”

“…This occurs when the aircraft experiences irregularities such as malfunctions, exposure to abnormal flight operations, or other discrepancies. It is expected that maintenance operations will detect defects early to "guarantee acceptable safety levels until the next scheduled maintenance" ( (Sbarufatti et al, 2013), p2).…”

“…This assessment by Roach of the stage of development is confirmed by publications of results of demonstrator panel and flight demonstrator projects for specific SHM systems. Publication of successful tests have occurred for Comparative Vacuum Monitoring (CVM) (Sbarufatti et al, 2013), Fibre Bragg gratings (FBG), (Read and Foote, 2001), (Lee et al, 2003), (Read et al, 2008) and PZT transducer based sensor systems (Read et al, 2008), (Purekar et al, 2009). …”

“…Sensors are categorised into local and distributed sensing ( (Sbarufatti et al, 2013), p3) and active and passive sensor types. PZT transducers fall into the active distributed category.…”