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A simple question for a science fair project.

Postby lpowell » Thu Dec 13, 2007 5:01 pm

I am doing a project suggested to me by the Science Buddies website (the wizard was very helpful, by the way). Information about the project is located here. Here's a summary: "The goal of this project is to test the weight-bearing capacity of polystyrene structural beams with various cross-sectional geometries. Which is strongest? Which has the best strength-to-weight ratio?"

The material of the beams is polystyrene. What, exactly, makes this material ideal for this specific project? Is it simply cheap, or are there other considerations? Would you recommend another material anyway, or is polystyrene the way to go? Thanks.

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Postby Craig_Bridge » Thu Dec 13, 2007 5:46 pm

Polystyrene is easy to cut with a knife or "hot wire knife". It is light weight. Most samples are uniform (they don't have grain like wood) so there aren't any orientation issues. When the material breaks, it doesn't shatter and cause a significant safety hazard. It isn't brittle so it will bend and crush prior to breaking so it is easy to observe the failure mechanisms if you increase loads slowly.

Keep it away from open flames and wear eye protection primarily for dust and you have about covered the major safety issues.

For a project that is investigating how beam geometry affects load bearing capabilities independent of material properties, this is a great material to use.

Many products come packed in molded polystyrene inside cardboard boxes so around Christmas you can probably scrounge around in the trash and find what you need without having to buy it.

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Postby pdoshi » Sat Dec 15, 2007 11:41 am

Here is a helpful website on further information on what is Polystrene about. It starts of saying that it is a hard plastic and how it is used in our daily lives.
This site also gives you futher diagrams and helpful structures of Polystrene. Hope this helps!

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Postby lpowell » Sun Dec 16, 2007 9:25 am

Thank you both very much for your help. That is all the information I needed.

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Postby bradleyshanrock-solberg » Mon Dec 17, 2007 3:49 pm

If you stick with engineering to the machine shop level you'll find plexiglas is also very popular for similar reasons.

1. It's easy to work with machine shop tools, and it's possible to work with even hand tools. It's kind of similar to wood that way.

2. Unlike wood, there is no "grain" to fuss about, it's properties are pretty uniform

3. You can glue it together with solvents that form a bond as strong as if it was formed as a single piece. Done well, the seal is watertight, even airtight. Plastic is nice that way. Most other glues you have to fuss with building a mechanical joint and putting an adhesive between the two pieces...and you still have the adhesive being a potential weak point.

4. It's reasonably cheap on the scale of high school or college projects.

Polystyrene is even better if you're just doing an experiment as opposed to building something you want to use. It's very cheap and very easy to work, yet reasonably light and strong.

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