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Reasons Why Autoclaves Do Not Work as Shearography Test Chambers
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  Reasons Why Autoclaves Do Not Work as
Shearography Test Chambers

Lockheed F-22 System

1. Shearography NDT of fan cases using pressure reduction (vacuum stress) requires the test part and the shear camera do not touch the wall of the pressure vessel, since this wall will move during the vacuum cycle and de-correlate the image. LTI shearography test chambers are designed to isolate the camera and test part support fixture from any relative motion.

2. The pressure reduction rate is for shearography testing is critical. Shearography test chambers operate at rates of 0 to -2 psi in 10 seconds followed by a return to atmospheric pressure by 3-5 seconds. Slower rates increase the image noise, slow throughput and the chance that slow leaks in the panel will allow defects to go undetected.

3. Autoclaves are expensive and it is a waste of money to tie up shearography testing in an autoclave that should be producing product. Shearography test chambers are designed for their function and are relatively inexpensive.

4. All the shearography tooling, test part fixtures (heavy) and through wall electrical connections must be removed during autoclave production and re-installed. Even if it would work as a shearography chamber, and it does not, the autoclave would have to be at ambient temperature, generating lost time waiting for cool down and reconfiguration. Constant moving of the shear camera increases the risk it is dropped or knocked over.

5. The bottom of the chamber is curved and the fixtures would need spacers and shims to stabilize.

6. Access into the chamber to mark multiple defects on the fan case requires multiple entries into the autoclave and moving around inside with the shearography equipment set up.

7. Over the years several companies attempted shearography in an autoclave. The instant pressure was reduced, the images decorrelated and the set up was worthless. They purchased test chambers from LTI.

8. Autoclaves and shearography test chambers are designed for entirely different functions. You can not cure composites in a shearography test chamber and you can not do shearography NDE in an autoclave.

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