Why do photoelastic stress patterns produce colors?

[Ryoukomaru]

I am writing a paper on "Photoelastic Stress Test by Polarization" and let me tell you that it is not at university level. It is my Extended Essay for IB -if you know what IB is.

I am looking for a simple explanation on why these colorful stress patterns form. So far I found out that when object is under stress it creates some local differences at the index of refraction of object so at different parts of the object, light travels at different speeds and bends more or less. But I don't understand why we get colors.

 

[Gonzolo]

I'm not too familiar with photoelasticity, but this should help you.

Index of refraction depends on wavelength, and so does the change in index of refraction when the material is stressed. Since each wavelength experiences a different index, they are refracted at different angles.

 

[Ryoukomaru]

Since so many ppl seem not to know much about this topic, maybe i ll post my paper when I get my IB diploma. :P

thx for reply gonzolo

 

[PerennialII]

Remember once doing a labwork related to photoelasticity, was related to determination of near crack tip stress fields. The fringe patterns were really 'cool', even though our quantitative analysis failed miserable (crack tip stress fields were somewhat difficult to quantify with any accuracy). Perhaps these might give some added info if you haven't come across them yet :

http://www.fas.harvard.edu/~scdiroff/lds/LightOptics/Photoelasticity/Photoelasticity.html
http://web.mit.edu/mando/www/6.163/Researches/initial.pdf
http://www.engr.iupui.edu/me/courses/me272lab/exp6.pdf

 

[Astronuc]

Just saw this post -

http://www.shodor.org/~jingersoll/weave4/tutorial/node18.html - on photoelastic stress.

http://scholar.hw.ac.uk/site/physics/topic8.asp?outline=

There is a lot more to it, but this is what's readily avialable in a pinch. Somewhere I have more info, but its buried in the archives.