Yielding stress

  • Thread starter Dell
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as depicted in the diagram below
stress-strain.JPG
the stress strain for an alloy with an average nucleus size of 100 micron
find
1)the modulus of elasticity for the alloy
2) the yielding stress


for 1) i assume that the red line is meant to be at 0.0005 therefore
E=dσ/dε=100e6/0.0005

E=200Gpa

for 2) i dont know what i can do, all that i do know is that the slant of the line from ε=0.002 to the point of σy is equal to 200Gpa (from the E i found before), but how can i use this to find the stress, i do not know the strain for σy, since i was given the nuclesu size i think i must somehow use that, but how??
 

chemisttree

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Ignore the 100 micron nucleus info. The sample yields where there is a deviation from a linear stress/strain relationship, right?
 
591
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but how can i use that information, when you say a deviation from stress strain relationship, do you mean a deviation from the young modulus? i dont think that thats true, is there not a small portion where the line is not linear but before yielding?
even on the graph there is a portion between the linear section and the point marked as 2 with the green line
 
591
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i think i need to use the imaginary linear line that starts at 0.2% and rises to yielding stress at a slant equal to E
 

Mapes

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Agreed.
 
591
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now i assume that the apropriate strain for the yielding stress is 0.003, is that correct?

σ/0.001=E=200Gpa

σ=200MPa

is this correct? according to the graph it cannot be
 

Mapes

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It's simpler than that. The convention is to use the stress where the 0.2% offset line meets the actual stress-strain curve.
 
591
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but i dont know the function of the actual curve, do you mean the linear section,
where
σ=200Gpa*ε
(ε=0.002)

σ=400MPa

dont think thats what you mean,

how can i find the curve after the linear section?
 

Mapes

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You read it off by eye.
 
591
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is there no way to calculate it?
 

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