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Methods to make photoelastic samples
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Most of the transparent material around us have photoelastic properties. However for most of them we would need to load them so strongly to observe a photoelastic signal that we cannot really use it as photoelastic material. Another reason not to use any random transparent material to make a photoelastic sample is that most of the time no special attention have been paid while forming the material so that it is full of residual stresses and not really usable. As an example here is a pair of glasses:
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Most of the transparent material around us have photoelastic properties. However for most of them we would need to load them so strongly to observe a photoelastic signal that we cannot really use it as photoelastic materials. Another reason not to use any random transparent material to make a photoelastic sample is that most of the time no special attention have been paid while forming the material so that it is full of residual stresses and not really usable. As an example here is a pair of glasses:
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![IMG_0407](uploads/254a0670b5a0f6c15db9476fca0cfb7a/IMG_0407.JPG)
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That is why making a photoelastic sample is not simple. First of all, it is necessary to choose the material you will use as a function of:
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For all this reason, making a photoelastic sample is not a simple task. First of all, it is necessary to choose the material you will use as a function of:
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* the load you want to applied,
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* the shape of the sample you want to get,
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* How many sample you need,
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* how many samples you need,
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* what you expect to measure and
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* the money you have.
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This different criteria have to be carefully considered before choosing how you will make your photoelastic sample among the different methods presented below. The section below will guide you to make samples from just just using a piece of gel to casting polyurethane or cutting photoelastic pads. So first, you have to choose your material so that its photoelastic ability is enough to observe something significant in the range of stresses you want to apply. Second you have to make your sample without trapping any residual stress in it. Let's see it more carefully
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This different criteria have to be carefully considered before choosing how you will make your photoelastic sample among the different methods presented below. This section will guide you to make samples from simply using a piece of gel to casting polyurethane or cutting photoelastic pads. So first, you have to choose your material so that its photoelastic ability is enough to observe something significant in the range of stresses you want to apply. Second you have to make your sample without trapping any residual stress in it. Let's see it more carefully
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Cutting samples out of a sheet
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The first historical method consists in cutting the sample out of a sheet of photoelastic material. You pick the right material and cut it using different methods listed in [this tutorial](https://git-xen.lmgc.univ-montp2.fr/PhotoElasticity/Main/wikis/cutting-sample)
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The first historical method consists in cutting the sample out of a sheet of photoelastic material. This can be simply a plate of plexiglass or a rubber pad that you cut with a milling machine or a cookie cutter. You pick the right material and cut it using different methods listed in [this tutorial](https://git-xen.lmgc.univ-montp2.fr/PhotoElasticity/Main/wikis/cutting-sample). This is convenient to get 2D samples but cutting methods induce most of the time residual stresses so machining the pads can be tricky. Also, it can be quite expensive depending on the material you use
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Molding urethane samples
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A second method consist in directly molding your sample in the shape you want. In this case you need first to make a mold of the sample shape you want. Then you pick a urethane with the Young Modulus corresponding with the load you want to apply and finally you can cast the liquid urethane and get your sample. The complete method and tips are given in [this tutorial](https://git-xen.lmgc.univ-montp2.fr/PhotoElasticity/Main/wikis/molding-urethane)
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A second method consist in directly molding your sample in the shape you want. In this case you need first to make a mold of the sample shape you want. Then, you pick urethane with the Young Modulus corresponding with the load you want to apply and finally you can cast the liquid urethane and get your sample. The complete method and tips are given in [this tutorial](https://git-xen.lmgc.univ-montp2.fr/PhotoElasticity/Main/wikis/molding-urethane). This is the most versatil way since you can make the shape you want as long as you can make a mold, and you can easily tune the stiffness of the sample. Also it is a very cheap way to make photoelastic samples since urethane is not expensive.
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Molding gel samples
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