sensors Letter Defect Detection in Aerospace Sandwich Composite Panels Using Conductive Thermography and Contact Sensors David I. Gillespie 1,2, * , Andrew W. Hamilton 3 , Robert C. Atkinson 1 , Xavier Bellekens 1 , Craig Michie 1 , Ivan Andonovic 1 and Christos Tachtatzis 1 1 Department of Electronic and Electrical Engineering, University of Strathclyde, Royal College Building, 204 George Street, Glasgow G1 1XW, Scotland, UK; [email protected] (R.C.A.); [email protected] (X.B.); [email protected] (C.M.); [email protected] (I.A.); [email protected] (C.T.) 2 Collins Aerospace, Prestwick, 1 Dow Avenue, Prestwick International Aerospace Park, Ayrshire KA9 2SA, UK 3 National Manufacturing Institute Scotland, University of Strathclyde, 85 Inchinnan Drive, Renfrewshire PA4 9LJ, UK; [email protected] * Correspondence: [email protected] Received: 23 October 2020; Accepted: 19 November 2020; Published: 23 November 2020 Abstract: Sandwich panels consisting of two Carbon Fibre Reinforced Polymer (CFRP) outer skins and an aluminium honeycomb core are a common structure of surfaces on commercial aircraft due to the beneficial strength–weight ratio. Mechanical defects such as a crushed honeycomb core, dis-bonds and delaminations in the outer skins and in the core occur routinely under normal use and are repaired during aerospace Maintenance, Repair and Overhaul (MRO) processes. Current practices rely heavily on manual inspection where it is possible minor defects are not identified prior to primary repair and are only addressed after initial repairs intensify the defects due to thermal expansion during high temperature curing. This paper reports on the development and characterisation of a technique based on conductive thermography implemented using an array of single point temperature sensors mounted on one surface of the panel and the concomitant induced thermal profile generated by a thermal stimulus on the opposing surface to identify such defects. Defects are classified by analysing the differential conduction of thermal energy profiles across the surface of the panel. Results indicate that crushed core and impact damage are detectable using a stepped temperature profile of 80 ◦ C The method is amenable to integration within the existing drying cycle stage and reduces the costs of executing the overall process in terms of time-to-repair and manual effort. Keywords: aerospace composite; dis-bond; honeycomb; impact damage; maintenance repair overhaul; non destructive inspection; quality assurance; re-manufacture; sandwich structure; thermography 1. Introduction Aerospace Maintenance, Repair and Overhaul (MRO) services are critical to ensuring safe and certified commercial aircraft operation. The demand for these services in the UK alone accounts for an estimated £15 billion turnover annually and with the rapid increase in the number of commercial flights year-on-year, the value is set to increase [1]. For MRO service providers, lean innovation is central to ensuring that the capability in meeting the increased demand is satisfied through transitioning from traditional inspection Sensors 2020, 20, 6689; doi:10.3390/s20226689 www.mdpi.com/journal/sensors
Defect Detection in Aerospace Sandwich Composite Panels Using Conductive Thermography and Contact Sensors
Jun 24, 2023
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