I think of X-ray techniques, applications of magnetic fields or something in this direction.
Dear Christian,
It is very possible to measure internal stresses in the material using X-ray diffraction analysis, using a reference material. Internal stresses lead to peak broadening and skewing and therefore can be used to even identify the direction and nature of stress (compressive and tensile) on a very local level.
I hope this helps.
Regards
http://www.tandfonline.com/doi/abs/10.1080/01418618608245293
If your sample is transparent (like glass) you may use photo-elasticity (Spannungsoptik) techniques by applying crossed polarizers. The magnitude of the stress you can achieve by reference measurement.
You may also use photoelastic surface coatings for deformation inspection of your sample. I must admit that in this case the internal stresses are detected indirectly.
Please 'google' for 'photoelastic coating'. You will get a quick introduction into photoelasticity applications.
Hi Yi,
which are these 'other techniques you can consider' ?
We are all eager about these techniques: Just a keyword or two....
May eddy-currents work (at least for magnetic materials or those having sufficient permeability)?
For detecting internal cracks this technique works for conducting materials; but for stress/strain I do not think so.
My specimen are sedimentary rocks (sandstones, mudrocks, carbonates etc.). At first my question was a general one because I wanted to know if there are techniques which can measure internal stress. I read about oscillating magnetic fields which measure the stress in steel. But the rocks I have do not have magnetic minerals.
You can use acoustic emission technique.
There are many research work on using AE in rock and brittle materials
Dear Mr. El-Galy,
yes, you are right. There are a lot of publications on AE, especially in rocks. To my knowledge you can measure the stress or strain when the first (micro)cracks initiate. But my question refers to a kind of spatial distribution of stress inside a specimen.
Best regards
Neutron scattering is also possible (if you have a nuclear reactor at hands).
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