Calculating Youngs Modulus

MatthewMansfield · Nov 13, 2020

Hello all

I wondering anyone could help me with the following:-

When plotting a stress strain curve for a material I believe it is normal practice to express Strain in %.

My question would be that when calculating Youngs modulus is it typical to use Strain in units of %?

I if was to plot my stress strain curve then my equations would be:-

Stress = Force / Area
Strain = (Change in Length / Original Length)*100 (Strain is now in units of %)

If I wanted to calculate Youngs Modulus then my equation would be either:-

Youngs Modulus = (Force/Area) / [(Change in Length / Original Length)*100]

Or

Youngs Modulus = (Force/Area) / (Change in Length / Original Length)

Can anyone help?

Thanks

EdStainless · Nov 13, 2020

The modulus is the slope of the line. Stress is in F/A, and strain is dimensionless. So the units of modulus are F/A. We multiply strain by 100 and express as a % just to make visualisation and communication easier.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

MatthewMansfield · Nov 14, 2020

EdStainless

Thank you, just needed to get this correct in my head.

I figured out that if i had used the equation:-

Youngs Modulus = (Force/Area) / [(Change in Length / Original Length)*100]

Then my units for Youngs modulus would be N/mm^2 * % which is very wrong indeed.

Thanks.

r13 · Nov 14, 2020

MM,

Look at any stress-strain diagram for units on each axis. Ed means when we talk, it is more convenient to say "2 percent strain", than "zero point zero two strain". Drop the 100 in your calculation, but keep it in your conversation.

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