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I am having trouble understanding the difference between elastic limit and yield stress. I searched the internet for a few hours and found some conflicting answers. I have found 3 (maybe) different answers:

From the elastic limit to the yield point, the material is transitioning from elastic to plastic. This area is called the elastoplastic region. I got this conclusion from here.

The yield point is the same as the elastic limit. The yield point is only found in the elastic point which is impractical to find precisely. I got this conclusion from here.

The elastic limit is where the elastic region ends and the yield stress is just where a permanent deformation of 0.2% is formed. I got this conclusion from here and here. This runs counter to what I am told by my lecturer which is that the yield stress is where the elastic and plastic region is separated.

So far, I have 3 answers answering the same question. Which one is the actual answer? Thank you

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There is not AN answer. Between 0 and 0.2% strain is a mixture of elastic and plastic. The 0.2 % is primarily applied to steels. "Yield" has both a physical and legal or practical definition. Most specifications for steel have a legal definition of 0.2% although some ( API) use 0.5% total strain as the definition.

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The elastic limit is the range/region of the material that behaves elastically in the stress vs strain curve. The yield stress is a characteristic point of the material, beyond which, the material is said to be out of its elastic range.

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Elastic limit and yield point can be the same. For steels, there are 3 possibilities:

  • clearly defined yield point $R_e$ without subsequent stress reduction
  • clearly defined yield point with subsequent stress reduction, where upper and lower yield points, $R_{eH}$ and $R_{eL}$, are recognised
  • yield point unclear, where 0.2 % or 1.0 % "proof strength", $R_{p0.2}$ or $R_{p1.0}$, become useful (usually high-alloy steels)

You can see the differences here. Some useful information might also be here.

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