Thank you Reg,
The objective is to just detect the presence of a crack and a relative indication of depth (i.e. indicate that a crack is deeper than another).
- NO precise depth measurement
- NO shape of the crack
- NOT its location
It has to just detect that when the probe passes above it there is a crack under it. Any suggestions?
Thanks
A use case would be a huge help. I'm a retired research level reflection seismologist. So very heavy multichannel DSP and remote sensing background. I'm also very familiar with every imaginable manufacturing process. Lifelong fascination with how things are made.
Ultrasonic and x-ray are the standard methods for testing welds. I can't say for certain as I've not done a mathematical analysis, but I don't think that eddy current sensing will detect a horizontal crack in a sheet coming out of a rolling machine to make up an example. Ultrasonic certainly would, but I don't think x-ray would. I cannot think of anything, but ultrasonic that would work.
There are obvious difficulties with ultrasonic sensing of say a hot roll line output, but one can use a high power laser to create impulses and a laser interferometer to sense the reflection response which allows you to avoid the contact problem. John Scales at the Colorado School of Mines was able to rotate a rock core on a turntable, create impulses with a high power CO2 laser and measure all 36 coefficients of the elastic tensor with an interferometer. That was over 20 years ago. To detect cracks which are at an angle to the surface one would require more than one sensor, but that could be implemented by scanning and mirrors.
A good use case is important as inspecting a single part is very different from inspecting product from a processing line. To continue with my hot roll example, the NRE cost would be in the low 7 digit range, but I see no fundamental barrier to continuous inspection of rolling line output for cracks in real time with very high reliability. Not quite nuclear grade inspection, but close. Unit cost would be quite low.
On the other hand a cold roll line would be much easier and cheaper to design the system for as you could use contact sensors.
If you don't want to discuss details publicly, send me a PM.
Reg
Edit: I had a look in my library. Get a copy of:
Electrical and Magnetic Methods of Nondestructive Testing
Jack Blitz
Adam Hilger 1991
it has analytic solutions for inspecting tubing for defects.