# How to find yield strength and Young Modulus from S-S curve

I have a S-S curve and am not sure how to find yield strength from it as when I did 0.2% strain (0.002 * strain at fracture) I get a small number that plots close to (0,0)?

For young modulus, I am not sure where to take the values as it’s not a completely straight line?

Are there any other methods here please?

• What you will need to do depends on the application and the underlying theoretical assumptions. E.g., for the young's modulus you can compute tangent moduli at each point and take the average, or compute the secant modulus between two points. – Biswajit Banerjee Apr 13 at 21:13
• I guess no one uses "drop of the beam" anymore. – blacksmith37 Apr 14 at 0:00

## 1 Answer

if the material is mild steel then the easiest way to find the yield stress is to plot the stress strain and find the first knee in the curve. if the material does not have a clear yield point, what you do, is you start from 0.2% strain and draw a straight line parallel to the Elastic part of the line (see below). The proof stress 0.2% (equivalent to yield stress) is the point where the straight line and the curve meet. Regarding the Young's modulus, the best practice is to take two points from the proportional (elastic) range. See image below. • Hi, thank you NMech. Do I take 0.2% of the fracture strain please? – Emmanuelle Apr 13 at 21:03
• No. You just take 0.2% (absolute value). – NMech Apr 13 at 21:06
• Hi I think I see what to do, thank you! Youre too good – Emmanuelle Apr 13 at 21:09
• NMech, so can I call it just 0.2% of the x axis length then please? – Emmanuelle Apr 13 at 21:15
• It would be easier if you took a photo with the example and show what you tried to do, and updated the question. I am not sure what you mean by "so can I call it just 0.2% of the x axis length" – NMech Apr 13 at 21:17