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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?

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  • $\begingroup$ 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. $\endgroup$
    – Biswajit Banerjee
    Apr 13 '21 at 21:13
  • $\begingroup$ I guess no one uses "drop of the beam" anymore. $\endgroup$
    – blacksmith37
    Apr 14 '21 at 0:00
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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.

enter image description here

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.

enter image description here

Regarding the Young's modulus, the best practice is to take two points from the proportional (elastic) range. See image below.

enter image description here

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  • $\begingroup$ Hi, thank you NMech. Do I take 0.2% of the fracture strain please? $\endgroup$
    – Emmanuelle
    Apr 13 '21 at 21:03
  • $\begingroup$ No. You just take 0.2% (absolute value). $\endgroup$
    – NMech
    Apr 13 '21 at 21:06
  • $\begingroup$ Hi I think I see what to do, thank you! Youre too good $\endgroup$
    – Emmanuelle
    Apr 13 '21 at 21:09
  • $\begingroup$ NMech, so can I call it just 0.2% of the x axis length then please? $\endgroup$
    – Emmanuelle
    Apr 13 '21 at 21:15
  • $\begingroup$ 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" $\endgroup$
    – NMech
    Apr 13 '21 at 21:17

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