Detecting Cracks and Corrosion in Aircraft Longerons

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Aircraft are the backbone of several industries and, as such, are subjected to intense and near-continuous use, making preventive maintenance critical. Maintenance protocols are exhaustive but time-consuming, especially when fuselage and wing longerons are involved. Longerons usually carry larger aircraft loads and help to transfer skin loads to the internal structure. Longerons nearly always attach to frames, ribs, or the skin of the aircraft. Fatigue and stress cracks eventually appear around the fasteners used to secure longerons to structures. Such cracks risk going undetected because they are small (typically 1.25 mm or 0.05 in.), they are near and under fastener heads, and often under surface coatings. The faying surface between longerons and skin is also prone to corrosion and must be inspected.
Transcript
  • 1. Detecting Cracks and Corrosion in Aircraft Longerons Application Note
  • 2. Introduction Aircraft are the backbone of several industries and, as such, are subjected to intense and near-continuous use, making preventive maintenance critical. Maintenance protocols are exhaustive but time-consuming, especially when fuselage and wing longerons are involved. 2 © Eddyfi 2014
  • 3. The Challenge Characterizing fatigue and stress cracks in the vicinity of longeron fasteners and mapping corrosion in a multilayered aluminum structure. • Longerons usually carry larger aircraft loads • Longerons help transfer skin loads to the internal structure • Longerons nearly always attach to frames, ribs, or the skin of the aircraft • Fatigue and stress cracks eventually appear around the fasteners used to secure longerons to structures 3 © Eddyfi 2014
  • 4. The Challenge Such cracks risk going undetected because they are: • Small(typically 1.25 mm or 0.05 in.) • Near and under fastener heads • Often under surface coatings The faying surface between longerons and skin is also prone to corrosion and must be inspected. 4 © Eddyfi 2014
  • 5. The Challenge These situations present some interesting technical problems: • Potential cracks in the vicinity of fasteners are: • Short • Spread in all directions • Often subsurface • Difficult to locate • Hidden corrosion between the layers of multilayered aluminum structures: • Is hard to locate • Has a detection threshold typically 10% in material loss 5 © Eddyfi 2014
  • 6. The Challenge To be truly practical, the solution must be able to detect these completely different types of defects with only one probe and one test instrument. 6 © Eddyfi 2014
  • 7. The Solution Using a single multiplexed, custom-designed ECA probe to locate surface cracks and subsurface corrosion. Three-part solution: • Hybrid ECA surface probe • Ectane®2 test instrument • Magnifi®acquisition and analysis software 7 © Eddyfi 2014
  • 8. The Solution —ECA Probe Eddyfi developed a hybrid eddy current array (ECA) surface probe that can detect both types of defects within their respective tolerances. The probe incorporates: • Two arrays of coils using proprietary coil topology. • The first array is a high-resolution array using small, high-frequency coils to detect the surface cracks around fasteners. • The second array is designed to detect subsurface corrosion. 8 © Eddyfi 2014
  • 9. The Solution —ECA Probe The probe is also designed to be: • Semi-flexible: Makes the probe capable of conforming to skin curves. • Rugged: Compared to other available solutions, the casing is much more adapted to the rough handling to which probes are often submitted. Thanks to this powerful all-in- one design, the probe is able to: • Detect corrosion build-ups ±5 % of the layer thickness (e.g., down to 0.5 mm of a 10 mm layer) — approximately twice as powerful as the initial requirement. • Detect 1.25 mm (0.05 in.) longitudinal, transverse, and oblique stress cracks along the load path. 9 © Eddyfi 2014
  • 10. The Solution —Ectane 2 Eddyfi’s workhorse testing instrument. • Can be configured for almost any type of inspection technique, including ECT and eddy current array (ECA). 10 © Eddyfi 2014
  • 11. The Solution —Magnifi Eddyfi’s cutting-edge acquisition and analysis software for graphical display (C-scan), record keeping, and reporting. 11 © Eddyfi 2014 Actual corrosion scan data Actual cracking scan data
  • 12. The Benefits Eddyfi’s unified solution offers the following benefits: • Improved planning —By easily identifying cracks and corrosion between skin and longeron, it is easier to plan long-term maintenance. • Faster execution —Switching from the crack inspection setup to the corrosion inspection setup is very quick. Because it does not require a new hardware setup and that the array probe offers wider coverage, inspections have gone from hours to mere minutes. • Better use of qualified personnel —Because they spend less time switching between inspection setups, qualified personnel can perform more inspections. • Data archives —Having access to archived inspection data allows performing advanced trending analysis to, for example, monitor crack/corrosion growth and extrapolate their behavior. 12 © Eddyfi 2014
  • 13. www.eddyfi.com Follow us on:
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