DIC is well suited to measure deformations from applied loads, but residual stress is not so easy. Since you generally do not have a reference measurement prior to the introduction of residual stresses, there is no way to simply measure residual stress with DIC. You would have to take a reference measurement, then relax the residual stresses by removing some material in the specimen. Then you have to solve an elastic inverse problem to calculate the residual stresses from the deformation after partial relaxation.

At that point, you are potentially better off trying a more standard relaxation method like hole drilling or slitting. Those are only occasionally applied to glass because of the difficulty in making the hole or slit in brittle glass.

You can see tensions in the glass in polarized light (colors are created in regions with tensions). This simplest method is used to distinguish a glass with stress from a stress-free glass.

https://www.youtube.com/watch?v=vD2VY7mDKGc

Dear Prof. Verlotski,

This is interesting to visualize presence of stresses by the method you have suggested however i am looking for a quantitative measure which can be reported. Thank you for your response.

Kind Regards,

using digital image correlation to measure residual stress.

Dear Ajitanshu Vedrtnam!

I agree with Mohsin Aswad, digital image correlation may be not a bad idea, you just need a good photo camera and some open source DIC software.

But you can use this method only if you are able to take the "zero" image of the specimen before the treatment and the image after the treatment, and during the treatment there are not any changes in the specimen surface, that are not related to residual stresses, and no motion of the camera relative to the specimen (anless you use 3D DIC). Also the surface must have a stochastic speckle pattern for this method to work (I suggest adding some pigment particles to the glass).

By the way, what if just measure the glass specimens before and after the treatment and evaluate their elongation/shortening?

Could you provide more details on same ?

As the outer layer of glass comes in compression and the inner layer in tension for balance, I can't understand how could I quantify the stress profile by this method.

measuring elongation and shortening due to treatment is very difficult at different layers along the thickness of glass by strain gauges or any other way especially at the intermediate thicknesses of glass.

I hope this video will clarify to you how the method works. This is three point bending of organic glass specimen. Color map is quantitative horizontal strain distribution. Red zone - tension, blue zone - compression.

DIC is well suited to measure deformations from applied loads, but residual stress is not so easy. Since you generally do not have a reference measurement prior to the introduction of residual stresses, there is no way to simply measure residual stress with DIC. You would have to take a reference measurement, then relax the residual stresses by removing some material in the specimen. Then you have to solve an elastic inverse problem to calculate the residual stresses from the deformation after partial relaxation.

At that point, you are potentially better off trying a more standard relaxation method like hole drilling or slitting. Those are only occasionally applied to glass because of the difficulty in making the hole or slit in brittle glass.

If you have a Focused Ion Beam (FIB) available, then you can use the FIB-DIC ring-core method. Here is an example of Residual Stress evaluation in Bulk Metallic Glass.

Article Experimental and modelling characterisation of residual stre...

Hope this helps.

Dear Enrico Salvati ,

Thanks for your response but I think its a costly affair. Introducing cuts on glass surface SEM with DIC would be very difficult. I am unsure how at the higher thickness of glass exact residual stress profile can be obtained by this method.

Dear Michael B. Prime I have already made unsuccessful attempt of hole drilling for residual stress measurement of glass having 7 mm thickness and on LG it is even difficult.

Best Regards,

If it is about thin samples or about a surface, then it is convenient to use a tenzometriya. Values of deforamtion on strain gages are measured, and then a sample are cut and data are measured again.

Ajitanshu Vedrtnam,

first of all, the technique I suggested relies on the use of FIB for the very localised material removal process, exactly the same as the ring-core technique but at the micron-scale. FIB allows you to perform machining even if the material is very brittle. SEM imaging and DIC are then used to quantify deformation taking place during FIB material removal. Therefore, the technique is not very difficult to implement and it works on glasses, provided the sample is coated by a conductive layer.

High thicknesses of materials can be resolved by through-thickness sectioning and subsequent multiple local measurements across the sample thickness.

If your lab is equipped with SEM/FIB capability, this is not an expensive technique.

Hope this helps

Enrico

Thanks for the information Enrico Salvati , it was helpful. However, due to the unavailability of the required facilities, the question is still open.

You might consider to use GASP. However, this method only works on the tin side of float glass, and needs a fairly plane shape of the glass body. There are several companies worldwide which offer GASP instruments.

There are some polarimeters provide measurement of residual stress. (https://www.astm.org/Standards/C148.htm)

Hope, that these articles will be helpful

http://article.sapub.org/10.5923.j.jlce.20150301.02.html

Article On the Test Method for Determining Residual Stress on the Su...