
#1
Mar512, 09:06 PM

P: 132

I need to compute the yield point for an experimental true stress vs true strain plot of a material as attached in the screenshot.
See attached; I have true stress vs true strain plot. I took some initial points on the curve and fitted a straight line which gives me the elastic part of the curve. I constructed a line parallel to this straight line (parallel line has same slope as straight line, I got the constant of y = mx + c of the parallel line by putting x =0.002 when y = 0). But from the graph it is evident that yield point is around 1500 MPa but the offset method gives me a yield point around 1235 MPa. Please can anyone suggets/help what is going wrong? 



#2
Mar712, 10:25 AM

Sci Advisor
PF Gold
P: 2,234

What material are you testing? 



#3
Mar712, 11:07 PM

P: 132

The units on x axis are not percentages.
I say that it is evident that yielding occurs at 1500MPa. because at yielding material just flows. We can also say that one gets yield point by joining origina with breaking point (this getting a line) and then drawing a line parallel to this line such that the line drawn parallel is tangent to the stress strain curve.This point where the parallel line is tangent is the yield point (http://composite.about.com/library/g...ldefy6168.htm). From the graph it looks that 'flowing' occurs at around 1500MPa definitely not 1235 



#4
Mar712, 11:34 PM

P: 132

0.2 percent offset for computing the yield point
The material is a metal




#5
Mar812, 11:34 PM

Sci Advisor
PF Gold
P: 2,234





#6
Mar1612, 01:34 AM

P: 132

Thanks a lot for the help...I will come back after getting some more information from the experimentologist.
I shall be grateful if you can provide some insight here: http://www.physicsforums.com/showthread.php?t=587471 Vishal 



#7
Mar1712, 05:51 AM

P: 1

You really should make the pic show more about the elastic area. No need to have the strain go up to 0,5 if you're studying the area of up to 0,005 or something.



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