Difference between Yield stress and Proportional Limit

[Saladsamurai]

Is there a difference, when looking at the stress-strain diagram, between the "Proportional Limit stress" and the "Yield Stress" ?

Thanks!

 

[dlgoff]

I picked up my old "Introduction to mechanics of solids" text by Egor P. Popov and it states the following:

A study of stress-strain diagrams shows that the yield point is so near the proportional limit that for most purposes the two may be taken as one. However, it is much easier to locate the former. For materials which do not possesses a well-defined yield point, one is actually "invented" by the use of the so-call offset method.

Hope this helps a little.

 

[Saladsamurai]

So, looking at this stress-strain curve, would you say that the proportional limit and the upper yield are in distinguishable?

 

[dlgoff]

I would say yes but the porportional limit is somewhat vaguely defined.

 

[Saladsamurai]

That's because I defined it. I have no way of telling exactly where the non-linear curve begins... so I just "eyeballed'" it.