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Design+Question+Solutions

# Design+Question+Solutions - Design Questions Solutions(1...

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Design Questions: Solutions (1) The approach here is—as it will be for any design problem you encounter —to first extract the design criteria (what properties do you need your selected material to exhibit? is there a threshold value or a window you need to design for with regards to a certain property (yield stress, stiffness, e.g.)) and then to determine what material best meets those criteria. In this problem statement we are told that we need a ski boot to be flexible (less stiff) at one temperature and much stiffer at another. If we estimate a temperature range, we would need a material that could be more flexible while I am in the ski lodge or, in other words, at around room temperature (22-25 degrees C). We need it to be stiffer outdoors in what we know is winter weather (snow is on the ground and isn’t melting much or we couldn’t ski well) so around 0 degrees C or less. What property do we know of that permits a marked change in stiffness with temperature? Glass transition temperature! So we need a material with a glass transition temperature between about 22 degrees C and 0 degrees C. Since we are engineering with practicality in mind, we might prefer to pick a material with a glass transition temperature not at 22 C or at 0 C exactly but somewhere in between. We know that amorphous materials can have a glass transition temperature. The amorphous materials that we have discussed in class are glasses or polymer-based materials. So now we need to involve another design criteria to make our final choice. It is a ski boot so, once off the slopes, we’ll need to walk around in it. We know that glasses tend to be denser/heavier than polymers. Unless we want some serious strength training, the lighter boot is probably better. Furthermore, we know that glasses tend to be more brittle than polymers and, at least for me, skiing can involve less than dignified crashes and stops. We need, therefore, good impact strength or a less brittle material. Conclusion: We would like a polymer-based material with a lower density, relatively high strength, and glass transition temperature between 0 and 22 degrees C.

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Design+Question+Solutions - Design Questions Solutions(1...

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