@@ -90,7 +90,11 @@ Before casting urethane, you need first to choose the best for what you want to
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@@ -90,7 +90,11 @@ Before casting urethane, you need first to choose the best for what you want to
The castable urethane we use here is a [Clear Flex](https://www.smooth-on.com/product-line/clear-flex/): 'a water white clear urethane liquid rubber compound designed for applications that require absolute clarity'. It is available in three different shore stiffness: 30, 50, 95. The one we use here is the [Clear Flex 50](https://www.smooth-on.com/products/clear-flex-50/). It is the most commonly used for centimetric samples that experience up to a few Newtons of load. Also, note that playing (non linearly) on the quantity of cross-linker (part A) you add in the urethane, you can tune the material stiffness. But be careful because changing ratios also changes the curing time, and can introduce more mechanical nonlinearity!
The castable urethane we use here is a [Clear Flex](https://www.smooth-on.com/product-line/clear-flex/): 'a water white clear urethane liquid rubber compound designed for applications that require absolute clarity'. It is available in three different shore stiffness: 30, 50, 95. The one we use here is the [Clear Flex 50](https://www.smooth-on.com/products/clear-flex-50/). It is the most commonly used for centimetric samples that experience up to a few Newtons of load. Also, note that playing (non linearly) on the quantity of cross-linker (part A) you add in the urethane, you can tune the material stiffness. But be careful because changing ratios also changes the curing time, and can introduce more mechanical nonlinearity!
If you want to color the sample for imaging purpose, you should use [So Strong](https://www.smooth-on.com/products/so-strong/) dye. In the following, we color our sample in green because it is usually the color which optimizes contrast in a polariscope. Coloring your sample can also simulate the effect of using an optical filter or illuminating with monochromatic light - in this case it is helpful to keep in mind that the stress-optic coefficient is a function of wavelength: coloration, in addition to stiffness and material thickness, controls the resolution and dynamic range of your photoelastic measurements. Longer wavelength (redder) light produces fewer fringes for the same strain than shorter wavelength (bluer) light.
If you want to color the sample for imaging purpose, you should use [So Strong](https://www.smooth-on.com/products/so-strong/) dye. In the following walkthrough of the casting method, we lightly tint our sample green because that coloration usually optimizes contrast in a polariscope.
More aggressive addition of dye can simulate the effect of using an optical filter or illuminating with monochromatic light.
In this case it is helpful to keep in mind that the stress-optic coefficient is a function of wavelength: coloration, in addition to stiffness and material thickness, controls the resolution and dynamic range of your photoelastic measurements. Longer wavelength (redder) light produces fewer fringes for the same strain than shorter wavelength (bluer) light.
