I am doing a class project and part of the project is measuring the bending of my skateboard deck (TB V2 ). In order to do that I need the young modulus/ modulus of elasticity. Any help would be greatly appreciated! The project starts tomorrow, so its a bit of a time crunch. Also I apologies if I labeled this incorrectly I wasn’t sure what to put it under.
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Just measure the deflection under stress and compare that to the relaxed state
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What part would you like help with? I think the distance over which the deck is being bent could be tricky, going from the inside of the trucks is probably fine.
The other thing is because of how there is little bending force when your feet are far apart and a lot when you are standing in the middle so your best bet might be to go to a gym and use a bench and a bar to add a set amount of weight and have all the weight right on a single point in the centre. It’s also easier to take measurements when you aren’t standing on it obviously.
From there you can probably plug it into a formula.
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I would say put it on a hard surface, measure the distance from the bottom of the deck to the ground, then get on it with your feet as close together and as close to the middle as possible, measure again.
You know the applied weight, you know the distance from the pivot points so you should be able to math the rest.
The problem is the modulus is different depending on where on the deck you apply the force. Possibly you could find the modulus for 3/8" Baltic Birch, but that doesn’t account for any bending if it’s not a flat deck; nor any epoxies applied.
Despite doing physics, I’m not very good with the different types of stress and strain and the moduli for each, but if you’re trying to do deck flex, wouldn’t you want the Flexural modulus? Flexural modulus - Wikipedia
That would be quite easy, I’d think. Measure the distance between the trucks and the height of the deck off the ground with different weights in the center, right? You could also take it off the trucks and put it across two objects so it is clearer the exact length being stressed.
As it says in the wiki I linked, for wood and other anisotropic materials, that is different than the Young’s modulus. With the way decks are constructed, I’d expect it to be even more true for a skateboard than for regular wood.
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What is the objective of your class project? Is it to run both a theoretical calculation and an empirical test … and compare results?
E: Young’s Modulus (or Modulus of Elasticity) A decent starting point for a fiberglass composite deck… E ~ 10e6 psi or 70 GPa . You can probably find some composite calculators online to get a more refined or accurate value based on your deck’s specific layup.
I: Moment of Inertia. A decent starting point is the recrangular cross section formula bh^3/12. Appropriate for a perfectly flat deck, but any concave will increase it substantially.
Simply supported beam equation with point load in center… you’ve calculated your expected deflection.
As for the empirical measurement, I see good ideas above^^^. It will be easier to make accurate deflection measurements if you can use static weights.
You pretty much got the objective exactly. I know I can calculate the youngs modulus from deflection (I would us an LVDT for that). The thing is it would make the experiment more complicated, if I use a known value it would greatly simplify my uncertainty calculations. Thank you for all the help so far.
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