Single-walled carbon nanotube-modified epoxy thin films for continuous crack monitoring of metallic structures

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Journal titleStructural Health Monitoring
Pages589601; # of pages: 13
SubjectAccurate measurement; Catastrophic failures; Continuous monitoring; Crack evolution; Crack length; Crack monitoring; Crack sensors; Crack sizes; Crack surfaces; Current change; Electrical discharge machining; Epoxy nanocomposites; Fatigue cycles; Gauge factors; Growth monitoring; Host structure; Linear correlation; Maximum load; Measured currents; Metallic hosts; Metallic structures; Nanocomposite thin films; Single-walled carbon; Small load; Stable modes; Strain sensing; Visual inspection; Aluminum; Carbon nanotubes; Crack detection; Epoxy resins; Fatigue testing; Mechanical properties; Nanocomposite films; Nanocomposites; Sensors; Single-walled carbon nanotubes (SWCN); Structural health monitoring; Cracks
AbstractCracks are one of the primary forms of damage that can lead to the catastrophic failure of metallic structures. This study focuses on the application of epoxy nanocomposite thin film sensors for continuous monitoring of crack evolution in metallic structures. The core approach was to monitor the current (or resistance) change in these nanocomposite films, as cracks develop and propagate in the metallic host structure. Based on optical, electrical, and mechanical properties of epoxy resins modified with different contents of single-walled carbon nanotubes, two different nanocomposites (with 0.3 and 1.0 wt%) were chosen for the development of a crack sensor. The performance of the nanocomposite sensors was evaluated under tension-tension fatigue tests, on aluminum coupons with centrally located through thickness electrical discharge machining notches. Crack growth in the aluminum was found to transfer to the nanocomposite films in a stable mode. Once the crack was established, a linear correlation was found between the measured current and crack length with a slope of -10 -11 and -10 -8 A/mm for 0.3 and 1.0 wt% nanocomposites, respectively. Contact between the asperities formed on the crack surfaces in the nanocomposite film while the crack was closed at small loads (<30% of maximum load) was found to be an important limiting factor causing a large variation in measured currents during each fatigue cycle. Hence, a normalized variable based upon current change during each cycle was defined, providing a more accurate measurement of the crack size, with a crack gauge factor of ~0.04 mm -1. In summary, the nanocomposite thin film sensor developed in this study offers both continuous crack growth monitoring and the possibility of strain sensing. The sensor is also suitable for visual inspection of the host structure due to the transparency of the developed nanocomposite film. © The Author(s) 2012.
Publication date
AffiliationNational Research Council Canada (NRC-CNRC); Aerospace (AERO-AERO); NRC Steacie Institute for Molecular Sciences (SIMS-ISSM)
Peer reviewedYes
NPARC number21269393
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Record identifier54bcefca-a988-4609-8cbf-ad61697452cd
Record created2013-12-12
Record modified2016-05-09
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