Calculating Young's Modulus, Yield Stress, etc. from Force-Elongation Graph

[DuncanBain]

Evening all,

I have a Force vs. Elongation graph of a specimen (Aluminium). From this I need to derive the values of Young's Modulus, Yield Stress, Yield Strain, Ultimate Tensile Strength and so forth.

I assumed this was fairly straight forward, but when I tried calculating the UTS, my answer was way way off of what it should roughly be.

The calculation I tried is as follows:

The maxima of the curve was 53.5kN and the A₀ of the specimen was 76.9mm².

UTS = F/A₀ = 53500 / 76.9x10^-6 = 695.7MPa

The answer should be around the 69GPa mark.

Any ideas where I'm going wrong? I get similar results when trying to calculate any other values from the graph.

Many thanks.

 

[Astronuc]

695.7MPa (~100 ksi) is about right for Al. That's pretty strong for Al.

69 GPa would be about right for the elastic (Young's) modulus.

 

[DuncanBain]

Thanks for the reply. Made a mistake in my post in saying Young's Modulus should be around 69GPa rather than say that the UTS should be around 400MPa? So I guess it's really not that far off.

I also calculated Youngs Modulus but got around 13GPa which seems very low.