Shear Stress in a tensile test

[Hoomanya]

Hi,
I was under the impression that in a simple tensile test there is no shear present but have now been told by my mentor that even in a simple tensile test shear is present. To understand this I was told to think of Mohr's circles and rotate the coordinate system by 45 degrees. I am struggling to understand this and have looked for references but fail to find any. I would appreciate any guidance ASAP.
Thanks,
Hooman

 

[KootK]

Try this:

1) draw a square representing your infinitesimal stress element.
2) add arrows to the sides of the square representing shear stresses for the pure shear case. Make sure that the arrows are drawn such that the element is in equilibrium. You should have two corners with just arrow heads and two with arrow tails.
3) cut your square along a diagonal connecting the arrow tails and isolate one of the resulting half square triangles as a free body diagram.
4) sketch the resulting force required on the diagonal to keep the new free body diagram in equilibrium. It should be a pure tension force oriented normal to the diagonal.

The above procedure shows that, where there is pure shear, there is tension. If you accept that the reverse is also true, then you should be convinced that, where there is pure tension, there is shear..

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Ron]

Read a bit about Poisson's ratio in elastic materials. There will be some shear stress developed in either "pure tension" or "pure compression".

 

[desertfox]

try this

http://www.google.co.uk/url?sa=t&rc...cd=1&cad=rja&uact=8&ved=0CCEQFjAA&url=http://

http://www.engr.mun.ca/~neil/5312/n...HmgvgN&usg=AFQjCNGWKdCuTUuMZuG5q0gAOb45Cm0sag

 

[rb1957]

metals typically fracture in shear along a plane at 45deg to the loading direction. From Mhor's circle, the applied tension load is the max principal stress (axial, along the part) and at 45deg is max shear.

For me, the part was loaded in tension. Part of the "similtude" between the test piece and the work piece is how well does the work piece mimic the test piece ?

another day in paradise, or is paradise one day closer ?

 

[Hoomanya]

Thank you all! much appreciated.

 

[JeanLucPicard]

This is a common confusement, it's because we usually discard or forget about Poissons ratio, but it's allways there

Live long and prosper!