Eddy Current Testing, a NDT methodology, is often used for coatings and surfaces. Here is a brief summary presented at SPIE about the application. http://www.lmp.u-bordeaux1.fr/IMG/pdf/EM_Lecture_Spies_Part2.pdf

Focusing a search on NDT (nondestructive testing) methodologies will yield some useful results.

I am agree with Don Hargis about the application of eddy current testing for the determination of residual stresses in coatings.

I want to add X-RAY DIFFRACTION METHOD which is most widely used NDT technique for residual stress measurement. Please go to the file

http://www1.chm.colostate.edu/Files/Residualstress.pdf

Great ideas from Kumar and Hargsi .When dealing with coatings you will need a method that can help you resolve stresses over depths that are in the range of less than mm .You can research as well on ULTRASONICS ,NUETRON DIFFRACTION and possibly Electrochemical Etching were you control the depth of penetration induced by chemical .The relieving of the locked up stresses induces deformatiuons which can be monitrored by strain gauge .You can then regard the experiment as mimicking the stress profile by using an equivalnet loading system .You will need a bit of Fracture Mechanics to understand the crack tip stresses .

I agree to the use of Eddy Current and X-Ray Diffraction to investigate residual stress in coatings, because they are surface sensitive. Neutron Diffraction in contrast is a method more adapted to bulk investigations.

Thanks Bernd for the clarification

If thick coatings (200-400 microns) are in question, then we have published few works recently on measuring residual stress using neutron diffraction technique, e.g.

http://www.sciencedirect.com/science/article/pii/S1751616111001901

http://www.sciencedirect.com/science/article/pii/S0257897212003039

In one of the article above, we have for the first time compared hole drilling method with neutron diffraction in thick coatings.

One has to be very careful in using these methodologies, as residual stress is sensitive to crystallographic plane peaks.

I would not recommend using X-ray diffraction technique for residual stress measurement for thick coatings (not good enough if interested in through thickness stress profile).

Visit MIE Deapartment at U of Toronto, you may find some interesting info.

Visit MIE Department at U of Toronto, you may find some interesting info

Where u want residual stress distribution, either in coated layer or in the interface?

I am very skeptical about determination of residual stresses in coatings by Eddy Current method. I have used this method. The device that I used does not distinguish compressive and tensile stresses.

I also agree with the above sirs, about using eddy current testing

For the same problems as stated above, i am asking to clear your question , that is where you need the stresses

I am interesed in all information about the methods for determination of residual stresses in the thick and thin coatings. Methods of X-ray and neutron diffraction, incremental hole-drilling method are well known for determination of RS in the solid homogeneous materials, and they could be applied for investigation of stressed state in the coatings with or without some assumption.

But for example conventional ultrasonic method is not very good for determination of stresses in coatings because of averaging of stresses thru the thickness of a coating and a substrate.

Curvature measurement of surface after layer by layer removal is developed and used mostly for determination of stresses in the coatings. Curvature can be measured by mechanical contact or optical non-contact methods.

It assumes that removing layer of the coatings which causes of stress relieving and surface deforming. Using of changes of surface's curvature as a parameter gives possibility to calculate initial stresses.

There is dependance of electrical resistivity of material on residual stresses and this could be base of a method for determination of RS.

I am looking for methods which are designed or adapted for coatings.