What is inside plastic?

Photoelasticity is wonderfull phenomenon. It describes changes in the optical properties of a material under mechanical deformation. It is a property of all dielectric media and is often used to experimentally determine the stress distribution in a material, where it gives a picture of stress distributions around discontinuities in materials. Photoelastic experiments (also informally referred to as photoelasticity) are an important tool for determining critical stress points in a material, and are used for determining stress concentration in irregular geometries. [https://en.wikipedia.org/wiki/Photoelasticity]. Experimenting with photoelasticity photography gives some nice photos at least. It is usefull tool for visualisation of the internal stresses within (transparent) material.

My experiment setup:

Photoelasticity photography setup

Main tool for photographing photoelasticity is polarized light. If you read this, you probably have a polarized light source in front of you (1). Every LCD screen has polarizer and it is handy light source. Next, I attached macro lens (4) to the camera and added circular polarizing filter (3) on it. I turned filter to remove background light from the LCD monitor and placed a specimen (2) directly on the monitor.The object was just usual separaing wall from the “mars” box:

Specimen under normal light


This is what I photographed:

Tranparent piece of plastic under polarized light


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