# Homework Help: Using stress strain curve

1. Oct 14, 2014

### Name:riley

Hello I'm having trouble wrapping my head around finding things from stress strain curves

I need to find:
Elastic modulus (Young’s modulus)
•Yield strength
•Tensile strength
•Uniform and total elongation (ductility)

elastic modulus I think is 1240/0.02 = 62000

but I'm unsure of how to find the others.

Thank you to anyone who helps out.

2. Oct 14, 2014

### billy_joule

No, that is not the Youngs modulus.

Can you define any of the terms in your own words? i.e. do you know what you are looking for?

3. Oct 14, 2014

### Name:riley

I am OK with yield and tensile strength it turns out.

I know what the elongation is and understand the formula Lf - Lo/Lo I just don't understand where to get the lengths from in the curve, I believe the strain is the elongation of the material but don't know where to get the original an final lengths from. Either from uniform at the 0.2% point or the total elongation.

The elastic modulus is the measure of the elasticity of the material, I know that is measured form 0 to 0.02 ( the 2% rule) of the strain as this is the beginning of the plastic region. As E= stress/strain I thought but it seems that's not the case.

I hope these explanations are satisfactory, I understand why you asked for them I guess I should have showed more of an effort to find the answers.

Last edited: Oct 14, 2014
4. Oct 14, 2014

### SteamKing

Staff Emeritus
You need to review the definition of 'engineering strain':

http://www.engineeringtoolbox.com/stress-strain-d_950.html

Scroll down until your reach the section titled 'Strain'.

This rule only applies to materials for which there is no region where Hooke's law applies, i.e., the stress is not a linear function of the strain anywhere on the stress-strain curve. Steel, for example, has a well-defined region where the stress-strain curve is linear; aluminum does not, and therefore the 2% rule is used to estimate Young's modulus for aluminum and aluminum alloys.