Expert: Ray Wilkinson - 1/5/2011

Question
Hello Ray,

I have two tensile bars with the same cross sectional area.  

One of the tensile bar cross sections happens to be round and the other is rectangular.

Would there be an even distribution in tensile stress for both bars?  Would the corners of the rectangular bar adversely affect the yield and tensile values as compared to the round bar?  Do the corners act like stress risers resulting in a lower UTS and Yield?

Thanks,
Allen

Answer
Hi Allen

The usual assumption is that tensile stresses are evenly distributed across cross sections (provided the difference in cross section isn't extreme), unlike compressive stresses. This should mean that different bars of equal area are equally stressed. This is achieved by a small variation of elastic or plastic deformation to even out the stress across the section. However, I'm not a structural engineer, so don't bet the farm on this one!