Residual stress distribution measurement 1

[Best99]

I would like to know what technique can measure residual stress distribution in coil spring after shot peening.

Currently, I had consulted with XRD’s lab and they can measure only stress on outer surface not distribution stress.

In addition, on nowadays technology, which machine or technique can measure residual stress distribution in term of mass production or quality assurance.


Please advise me.
Thanks.

 

[EdStainless]

Neutron diffraction.

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Plymouth Tube

 

[TVP]

Bodyslam,

X-ray diffraction is the standard technique used for evaluating residual stress distribution of shot peened springs. The outer layer is first measured, then a small amount of material is removed by electropolishing followed by a second XRD measurement, more electropolishing, a third XRD measurement, etc. This is such an established technique that it is difficult for me to comprehend an "XRD lab" not being familiar with it. If you need experienced labs to perform this, try Proto, TEC, or Lambda:

http://www.protoxrd.com/

http://www.tecstress.com/

http://www.lambda-research.com/

 

[NickE]

I've also used the method that TVP mentioned, never really tried the neutron diffraction method... how expensive is it? (Relatively)

In favor of the electropolishing method is that it does very little to disturb the mechanical structure of the spring. Mechanical machining produces its own residual stresses.

I routinely would process high fatigue parts to a surface residual stress level ~1/3 the yeild strength. (100ksi (275+ksi yield)) I've fatigue tested and seen correlation between cycle count/residual stress/magnitude of alternating applied stress. I have to agree with the current practices at this point.

nick

 

[TVP]

As NickE mentioned, electropolishing does not disturb the surrounding area nearly as much as mechanical machining processes like drilling. I'm sure that the stress magnitude is somewhat different from that measured using neutron diffraction, but I would guess that it is less than 25% different, and probably more like 10% at most. With regards to neutron diffraction, the method requires that a stream of neutrons be developed, which essentially requires a nuclear reactor or spallation source, meaning that this method is limited to government labs, high-level University physics labs, etc. Definitely not ready for primetime...

 

[EdStainless]

One of the keys to the X-ray/EP method is that after each EP the spring will change shape a little. You need to calculate the stresses involved in those changes.
The drilled hole method has huge uncertainties. It is good at high stresses, but not suitable for low levels.

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Plymouth Tube

 

[unclesyd]

You might want to look at this paper. In 2000 we had a graduate student who had done some work with this method and said that it had tremendous potential. I don't know how commercial it is.
I understand there is an ultrasonic machine to get Young's Modulus.

http://www.ndt.net/article/wcndt00/papers/idn785/idn785.htm