Calculating Young's Modulus from a range of values

[MegaDeth]

Homework Statement

I don't need to give any information, I just need to know the best way to calculate E from a range of values for load and displacement given the length and diameter. I've calculate it for a few values and the value appears to decrease so I'm not sure where to take the value for E from.

 

[SteamKing]

It kinda depends on what material you are testing.

 

[MegaDeth]

I'm doing it for both steel and aluminium, though I've just realized I have to calculate it for the maxiumum load so everything is fine now.

 

[SteamKing]

Mild steel will have a region where there is a linear stress-strain relationship, while there is no such region for aluminum.

 

[MegaDeth]

Sorry, I misread my sheet, it just says to calculate Young's Modulus. So how would I calculate it for my aluminium data?

 

[SteamKing]

Have you studied how Young's modulus is determined for non-ferrous metals?

 

[MegaDeth]

I just need to know how to calculate it without having a linear portion on the graph.

 

[Chestermiller]

Force divided by area times length divided by displacement.

 

[AlephZero]

Mild steel will have a region where there is a linear stress-strain relationship, while there is no such region for aluminum.

Aluminum does have a linear stress-strain relationship for small strains, but unlike mild steel it doesn't have an obvious "yield point" where the linear relationship ends.

For some structural applications the maximum allowable stress for aluminum is in the nonlinear region. If the material is loaded up to that stress level, its behavior is not elastic and it does not return to its original length when unloaded. But for other applications aluminum is assumed to be a linear elastic material, with a lower stress limit.

Some measured stress strain data for Al and other materials here: http://fp.optics.arizona.edu/optomech/references/OPTI_222/OPTI_222_W4.pdf