Force-Elongation Graph

1. Nov 29, 2009

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.

2. Nov 29, 2009

Staff: Mentor

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.

3. Nov 30, 2009

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.