I am having a hard time trying to understand the effect of geometry on a specimen's yield and tensile strength or if there even is one.

If there is an effect or not, why is it so?

Thanks in advanced!


Usually no. However, yes in a manner of speaking.


Primarily both properties are material specific. Therefore, no there shouldn't be an effect of the geometry on either the yield or the tensile stress.

yes : (*)

A typical example where geometry appears to have an effect on yield and tensile stress is the effect of thickness of sheet of steels. Usually thinner steels exhibit higher yield points (see cold roll sheet catalog page.8) and ultimate tensile strengths (see Steel construction) However, in truth that is more of an effect of process.

Sheets of steel, that come out of rolling processes (especially cold rolling processes), have their grains refined. In most cases what happens is that the grains of the material become more elongated.

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This turns the material behaviour to slightly orthotropic and exhibits higher tensile strengths in the direction of the rolling. The result is that thinner materials exhibit better yield and uts values with thinner materials.

See also this question

  • $\begingroup$ Wow. Thank you so much!! :DD $\endgroup$ – hhu6403 Sep 12 '20 at 4:17
  • $\begingroup$ :) It seems like that answered your question. Since you seem to be a new member, if I did answer your question, you can press the tick button underneath my answer. $\endgroup$ – NMech Sep 12 '20 at 5:40
  • $\begingroup$ As an aside, note that in an Instron tensile test machine, this effect is readily apparent, as follows: You will notice on the stress/strain curve that beyond the ultimate strength peak of the test sample, the strength of the material decreases until the failure point is reached. This happens because the geometry of the sample is changing as the test proceeds: it is necking down (decreasing in cross-sectional area) which increases the stress experienced in the necked-down region, where all the plastic deformation is then concentrated. This is an artifact of the test method. $\endgroup$ – niels nielsen Sep 12 '20 at 19:41
  • $\begingroup$ @nielsnielsen, I hadn't mentioned that because like you said its an artifact. To me the reasoning behind true and engineering stress (and prevalence of the latter) has probably been one of the most interesting and efficient compromises in mechanical design. $\endgroup$ – NMech Sep 12 '20 at 20:26
  • $\begingroup$ yes yes, agree. -NN $\endgroup$ – niels nielsen Sep 13 '20 at 1:28

And the question you did not ask ;what about shape/crossection . That is, round and rectangular are both very common specimens .And rectangular with a curved crossection- full wall thickness pipe body. They also make very little if any difference. Note specifications often permit round tensile bars or full thickness tests with the same required mechanical properties.


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