Polarization and stress analysis

[clockdoc]

Hi all,
While I am on a polarization 'kick' I thought I'd share some images that show how polarized light can be used in industry to detect stress in materials. The first image is the plastic cover from my polarizer filter case shot under polarized light. That is, I had a polarizer filter in back of and in front of the subject. What is clear plastic to the unaided eye shows varying levels of stress in the plastic when shot under such conditions.
<a href="http://www.flickr.com/photos/8359753@N07/801451497/" title="Photo Sharing"><img src="http://farm2.static.flickr.com/1319/801451497_eb02ab9f6d_m.jpg" width="240" height="190" alt="DSC01323_filter cover" /></a>

The next shot is a clear plastic sticky tape dispenser. Again, the variations in color show where stress is present in the structure.
<a href="http://www.flickr.com/photos/8359753@N07/801451451/" title="Photo Sharing"><img src="http://farm2.static.flickr.com/1070/801451451_bb5434ff52_m.jpg" width="240" height="180" alt="DSC01321_tape_2" /></a>

The same dispenser shot from the other side. Engineers can build models of structures out of clear plastic and while subjecting them to different points/levels of stress, observe how they respond to stress by using polarized light.
<a href="http://www.flickr.com/photos/8359753@N07/801451333/" title="Photo Sharing"><img src="http://farm2.static.flickr.com/1204/801451333_559d9350d5_m.jpg" width="240" height="201" alt="DSC01320_tape dispenser_1" /></a>

[matthewchj]

Whoa, that's really interesting. I didn't know that. Thanks for sharing.

[wulf]

Yet another reason to want a polarising filter!

Thanks - very interesting.

Wulf

[ryan s]

Is this is a means used in the plastic industry on a regular basis? I've never heard of it being used like that. It makes some quite interesting pictures, for sure :)

[clockdoc]

Hi Ryan,
This technique was used 30-40 years ago when engineers would build models out of plastic so they could visibly see where stress points were effected under varying pressure loads. Today, I am sure this process is done with modeling on a computer and with much more accuracy.

[RandomConnections]

It still makes for neat photography.

I've got two large (8X6 inch) pieces of polarizing plastic. I may have to experiment with my polarizing filter with these and see if I can come up with something interesting.

[clockdoc]

Great! Use one in back of the subject. I placed a piece of typing paper over the back of the polarizing filter to make the light more uniform as the illumination comes from the rear through the filter . Place the subject in front of that filter and then shoot the subject item through your polarizing filter on your camera. Rotate the lens to get the best effect. I look forward to seeing your results.

[praesentire]

I think they use this type of photography technique to detect micro fractures on airplanes during maintenance.

Very cool.

[RandomConnections]

Clcokdoc - I'm guessing your subjects must be clear or at least translucent for this to work.

I'll try to dig out my filters and some suitable subjects this evening.

[clockdoc]

Yes, that is correct. I have not tested the process with translucent plastic but it would be interesting to see if the diffusion on the translucent plastic cancels the color patterns. Another test is to shoot the plastic under normal conditions and then induce stress from a clamp or other device and see how the color patterns change. My quick shots were of the items in their "unstressed" condition (other than that caused from manufacturing.) I look forward to seeing what you come up with.