another opportunity to better understand the NDT indications they might encounter. The infrared image (Figure 8 bottom) shows three of the four holes as well as inconsistencies in the carbon laminate of panel 1. Ultrasonics on the other hand, saw very little difference in the two panels. This illustrates the importance of
properly designed and fabricated reference standards. First, as with any inspection, the materials and structure of the reference standard must match the structure to be inspected. Secondly, the artificial flaws must be carefully selected relative to both the type of flaw of interest and the inspection technique to be used. From these examples it is clear that many flaws give entirely different responses to different interrogating techniques. Finally, in addition to all these technical
Figure 7. Carbon panel with inclusions
an aluminum plate (Figure 7 top). The carbon laminate contained a variety of inclusions which were readily detectable by infrared (Figure 7 bottom), but many of them were undetectable by ultrasound. While demonstrating the appropriate NDT techniques on all possible types of composite material, structure and flaw combinations may be beyond the scope of a class, the importance of the technician understanding the basics of how an interrogating energy interacts with a flawed component is clear. That knowledge in turn allows the technician to determine which
Figure 8. Carbon panels with holes.
technique, method and reference standard will or will not work in particular situation. Another example is the two specimens
made by students shown in Figure 8. This shows two panels with carbon laminates bonded to an aluminum block. One panel has a layer of fiberglass between the carbon and aluminum and both panels have holes drilled to the aluminum bond line. They thought the specimens had exactly
the same materials, the same flaws and were cured exactly the same way, but this was clearly not the case when examined with infrared and ultrasound, providing yet
reasons for providing refresher and composites training, there is also the fact that most of the aviation industry requires technicians be trained, qualified and certified, in accordance with NAS-410, National Aerospace Standard for Certification and Qualification of Nondestructive Test Personnel. This specification requires that technicians be trained and examined on materials and components that are typical of what they will encounter on the job. Therefore it is not sufficient to be trained and examined by a provider who deals only with bridges, power plants or other infrastructure. Training and examination must be performed by someone who has the knowledge, experience, and resources to provide the necessary aerospace point of view. AM
Figure 9. Students working on aircraft at AANC
36 Aviation Maintenance |
avmain-mag.com | October / November 2011
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