Chapter 5 Lock-in Thermography for the Wide Area Detection of Paint Degradation and Incipient Corrosion R. Jones, R. Jones Centre of Expertise in Structural Mechanics, Department of Mechanical and Aeronautical Engineering, Monash University, Clayton, Victoria, AustraliaSearch for more papers by this authorM. Lo, M. Lo Centre of Expertise in Structural Mechanics, Department of Mechanical and Aeronautical Engineering, Monash University, Clayton, Victoria, AustraliaSearch for more papers by this authorM. Dorman, M. Dorman Aircraft Structural Integrity – Directorate General Technical Airworthiness (ASI-DGTA), RAAF Williams, Laverton, Victoria, AustraliaSearch for more papers by this authorA. Bowler, A. Bowler Maritime Systems Project Office (MPSPO), RAAF Base Edinburgh, Edinburgh, South Australia, AustraliaSearch for more papers by this authorD. Roles, D. Roles Maritime Systems Project Office (MPSPO), RAAF Base Edinburgh, Edinburgh, South Australia, AustraliaSearch for more papers by this authorS.A. Wade, S.A. Wade Swinburne University of Technology, Hawthorn, Victoria, AustraliaSearch for more papers by this author R. Jones, R. Jones Centre of Expertise in Structural Mechanics, Department of Mechanical and Aeronautical Engineering, Monash University, Clayton, Victoria, AustraliaSearch for more papers by this authorM. Lo, M. Lo Centre of Expertise in Structural Mechanics, Department of Mechanical and Aeronautical Engineering, Monash University, Clayton, Victoria, AustraliaSearch for more papers by this authorM. Dorman, M. Dorman Aircraft Structural Integrity – Directorate General Technical Airworthiness (ASI-DGTA), RAAF Williams, Laverton, Victoria, AustraliaSearch for more papers by this authorA. Bowler, A. Bowler Maritime Systems Project Office (MPSPO), RAAF Base Edinburgh, Edinburgh, South Australia, AustraliaSearch for more papers by this authorD. Roles, D. Roles Maritime Systems Project Office (MPSPO), RAAF Base Edinburgh, Edinburgh, South Australia, AustraliaSearch for more papers by this authorS.A. Wade, S.A. Wade Swinburne University of Technology, Hawthorn, Victoria, AustraliaSearch for more papers by this author Book Editor(s):Raman Singh, Raman SinghSearch for more papers by this authorBaldev Raj, Baldev RajSearch for more papers by this authorU. Kamachi Mudali, U. Kamachi MudaliSearch for more papers by this authorPrabhakar Singh, Prabhakar SinghSearch for more papers by this author First published: 08 March 2019 https://doi.org/10.1002/9781118987735.ch5 AboutPDFPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShareShare a linkShare onFacebookTwitterLinked InRedditWechat Summary This chapter focuses on the use of lock-in infrared (IR) thermography, and in particular the combined use of phase images that are associated with the first and second harmonics, to detect incipient corrosion and paint degradation associated with 7075-T6 wing skins on RAAF AP-3C (Orion) aircraft. Lock-in thermography is a particular form of IR thermography that works by applying a sinusoidal heat input at a frequency to the structure and measuring the components of the temperature field at both the input frequency (the first harmonic) and, in some instances, the second harmonic. The lock-in thermography tests reported in the chapter were performed using a Cedip Jade 3 mid-wavelength IR camera on a section of an RAAF AP-3C Orion wing that was located at DSTO. The lock-in IR thermography test apparatus consisted of a bank of heat lamps and an IR camera connected via lock-in hardware manufactured by Cedip. Non-Destructive Evaluation of Corrosion and Corrosion-assisted Cracking RelatedInformation

This paper describes the results of a study into a new class of multi-site damage problems, viz: the interaction between multi-layer intergranular cracks and cracks that grow from small naturally occurring material discontinuities at a hole. The nature of the intergranular cracks, which are perhaps better thought of as delaminations rather than cracks, are chosen so as to approximate those found at fastener holes in RAAF AP3C (Orion) aircraft which arise due to ingress of the environment down the holes in the wing structure. The particular form of the multi-site damage studied involves two intergranular cracks (delaminations) that (in the vicinity of the hole) divide the plate thickness into thirds) interacting with cracks that emanate from the bore of the hole in a 7075-T6 aluminium plate.We first determine the effect of the intergranular cracks (delaminations) on the stress field at the hole. We then evaluate the effect of these intergranular cracks on the stress intensity factors associated with cracks that emanate from small naturally occurring material discontinuities at the hole and then on the reduction in the time for a crack at a hole, with multi-layer intergranular cracking, to grow to a size where it will be readily detectable.

This paper examines the growth of cracks at a fastener hole containing intergranular cracking with a focus on dome nut hole' coupons that are representative of a critical location in the Royal Australian Air Force AP-3C Orion wing. It is shown that crack growth under operational flight loads can be captured using the NASGRO formulation and that the scatter in these various tests can also be captured by allowing for small variations in the value of the cyclic stress intensity fatigue threshold. In this context, it is shown that crack growth can be captured using both a cycle-by-cycle analysis and also a United States Air Force characteristic K' approach. We also see that, for the operational load spectra considered, the crack growth history is approximately exponential so that the United States Air Force risk assessment computer program (PRobability Of Fracture) can be used to assess the risk of failure by fracture. The results of this study also suggest that, provided that intergranular cracking does not turn and break through to a free surface, it should have little effect on crack growth at a fastener hole.