I know that to calculate the yield strength I need to find the elastic region of the curve and it's slope and then use the 0.2% offset method. But what if my stress-strain curve is not exactly linear in the elastic region?
I would find the linear portion of the curve just above the first "kink" in the curve (y-value~20) and use the 0.2% offset rule. That should give you a conservative value for the yield strength.
This type of curve occurs on steel samples made of materials that were subjected to strong plastic deformation before testing, exceeding the elastic limit, but not reaching the strength limit. If you need a canonical curve, perform heat treatment with recrystallization - restore the original state of the material.
Hello.
Thanks for your answer. Dmitriy Zhukov
This graph is the stress-strain curve obtained from a tensile test for an aluminum alloy specimen produced by friction-stir welding.
Hello,
If you are worried about the slightly curved section, then in vain, it is never perfectly flat on real samples. This is especially noticeable on materials with an incomprehensible number of dislocations and zones of internal stress - to which yours can be attributed. I support the answer given by Mark Thomas Summers.
Have a great day!
Hello Dmitriy Zhukov
Thank you for your detailed explanation.
Have a nice day.
Dear Reza Amirifar, it is curiously what value of yield strength of your aluminum alloy was obtained in the upshot?
Hello dear Serge V. Shil’ko
The yield stress value obtained for this specimen was 68.2 MPa.
To my opinion, there is not very high but plausible value for aluminum alloy after friction-stir welding.
Serge V. Shil’ko
The highest yield stress obtained from FSWed specimen was about 100 MPa. ( different weld parameters from the uploaded curve )
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