... | ... | @@ -19,7 +19,10 @@ This different criteria have to be carefully considered before choosing how you |
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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. 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 material whose deformability is compatible with th load you want to apply and you 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. However, most of the time cutting methods induce residual stresses so machining the pads can be tricky. Also, it can be quite expensive depending on the material you use. All the details are available [here](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, a cookie cutter or waterjet. You pick the material whose deformability is compatible with the load you want to apply and you 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. However, most of the time cutting methods induce residual stresses so machining the pads can be tricky. Also, it can be quite expensive depending on the material you use. All the details are available [here](https://git-xen.lmgc.univ-montp2.fr/PhotoElasticity/Main/wikis/cutting-sample).
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The sample on the left (cross) is cut using a milling machine, while one on the left (cylinder) is cut with a rotating cookie cutter.
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Molding urethane samples
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... | ... | @@ -27,13 +30,24 @@ 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 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 versatile way to make sample 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 varying the cross-linker quantity. Also it is a very cheap way to make very clean photoelastic samples since raw urethane is not expensive at all.
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![100_4746](uploads/4ac6d6f7f55264d8e784cc0ab8c94f0b/100_4746.JPG)
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Squeezed piece of urethane between crossed polarisers.
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Molding gel samples
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Not only plastic polymers are good photoelastic materials convenient to mold. Some gels can also be used to make photoelastic samples:
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* Gelatine for example have been used in different labs by [lim *et al.*](https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.119.184501), [Kilcast *et al.*](http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2621.1984.tb12494.x/full) and [Workamp and Dijksman](https://arxiv.org/abs/1709.10311). This material is very clear, easy to make and to mold and nicely photoelastic but not very stable on the long run even if it can be cross-linked for a better stability as explained [here](https://git-xen.lmgc.univ-montp2.fr/PhotoElasticity/Main/wikis/molding-gel#making-cross-linked-gelatin-discs).
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![100_4737](uploads/02aecc17f3d266b6cef29cf415ee74f5/100_4737.JPG)
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Squeezed piece of gelatine between crossed polarisers.
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* Agar-agar gel can be used as a photoelastic material too, just like [Tamlinson and Taylor](https://www.spiedigitallibrary.org/journals/Optical-Engineering/volume-54/issue-8/081208/Photoelastic-materials-and-methods-for-tissue-biomechanics-applications/10.1117/1.OE.54.8.081208.short) did. Just like gelatine, it is easy to make and to mold and quite nicely photoelastic. However it is not perfectly transparent and the material is quite brittle when loaded dynamically and plastic-like when loaded very slowly.
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![100_4735](uploads/76da575d21ad6d75f25052769f041474/100_4735.JPG)
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Squeezed agar gel of urethane between crossed polarisers.
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* Many other biologic or synthesized gels like konjac...
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The different methods associated with these different materials are explained in [this tutorial](https://git-xen.lmgc.univ-montp2.fr/PhotoElasticity/Main/wikis/molding-gel).
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