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UNDER CONSTRUCTION
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Cutting samples out of photoelastic material
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[Precision Urethane](http://www.precisionurethane.com/) large diversity of shapes
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[Vishay](http://www.vishaypg.com/micro-measurements/)
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Historically the first method to get photoelastic sample was to cut them out of a photoelastic sheet using any blade. This works fine for 2D samples but necessitate skills to cut the sheet without inducing residual stresses. Also it is quite expensive especially if you consider using [Vishay](http://www.vishaypg.com/micro-measurements/) material. In the following section we go more into detail about the material choice and the different ways to cut it.
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Material sheets
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You can buy [sheets](http://www.precisionurethane.com/urethane-sheets.html) or [pads](http://www.precisionurethane.com/polyurethane-pads.html) depending on the thickness you want.
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pick thickness dimension and hardness we strongly encourage you not to buy to hard material (>70A) because the material can be knocked or folded during the shipping and residual stress can be induce. unless you specify it to the company.
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[Pads from Vishay company](http://www.vishaypg.com/micro-measurements/photo-stress-plus/category/coating/?subCategory=materials)
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Most of the time, photoelastic sheets or pads are made of transparent urethane rubber. But for strong loading you can also consider using plexiglass or polycarbonate. This latters can be bought from any local supplier. Just make sure that they have not been bent or knocked so that there are no residual stresses. If it is the case, you can still get ride of them by annealing them in an oven at ~90 degrees during ~2 hours (parameter to adapt as a function of the material you use and the amount of residual stresses you have). The same process can be used if residual stresses are induced by the cutting process.
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Rubber-like sheets or pads are more dedicated for lower stresses. They are the most used. You can buy them from [Vishay](http://www.vishaypg.com/micro-measurements/photo-stress-plus/) which is the most well known company for photoelastic pads. But companies like [Precision Urethane](http://www.precisionurethane.com/) also have a large diveristy of [sheets](http://www.precisionurethane.com/urethane-sheets.html) and [pads](http://www.precisionurethane.com/polyurethane-pads.html) of different thickness hardness and color. They are not initially dedicated to photoelasticity but works perfectly well. For the most common use, pads of thickness 1/4'' and of hardness 60A are usually good. Also, if you buy harder material (>70A), because the material can be knocked or folded during the shipping, residual stress can be induced. So be carefully to specify to the company that plates must not be folded and must be properly packed.
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Cookie cutter method
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For circular particles, we can make a custom cookie cutter tool which acts as a spinning disk cutter to create circular particles of a specified diameter and with little waste. We usual fix the material sheet with double sided tape on a flat plate to make sure the particle stay at the same place during cutting.
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Circular samples made of rubber-like material, can be cut out using custom cookie cutter tool. This latter acts as a spinning disk cutter and create cylinder of specified diameters with little waste. Examples of such a cutter are described in [1] and reported in the figure below.
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![Capture_du_2019-01-07_14-51-09](uploads/55e779ee380203d143d01255ba56706c/Capture_du_2019-01-07_14-51-09.png)
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It can be rotated using a driller or a milling machine. The rotation and downward speeds have to be properly chosen as a function of the material not to induce residual stresses when cutting. We usually fix the sheet or pad with double sided tape on a flat plate to make sure the circular samples stay at the same place during the cutting process.
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Milling machine method
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... | ... | @@ -31,6 +31,7 @@ We has to lubricate the cutter with dish soap rather than the usual machine oil, |
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More details for Cookie cutter method and Milling machine method can refer [Duke Physics Machine shop](https://phy.duke.edu/instrument-shop), where these methods were originally developed, and they provide photoelatic particles cutting services.
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Water jet cutting method
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