Torsion Test Simulation: Understanding Von Mises Criteria and Its Approximations

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The discussion centers on the simulation of torsion tests in materials, following successful tension and compression tests. The user, Vishal, applies the Von Mises criteria to relate equivalent tensile stress and strain to shear stress and strain. However, he encounters a discrepancy of 6-8% between the results from torsion tests and those from uniaxial tension and compression tests. Vishal questions whether this variation is due to approximations in the Von Mises criteria. He references a source indicating that torsion equivalent stresses derived from the Von Mises relationship are approximately 6.5% lower than those calculated using the Bishop-Hill formulation, which is suggested to be more accurate. He seeks confirmation on whether it is valid to conclude that torsion equivalent stresses are generally lower than those from uniaxial tension tests.
svishal03
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Hi all,

I am simulating torsion tests (after being successful with tension and compression tests). For tension and compression, I got a good comparsion with experimental and behaviour in tension is same as in compression (of course leaving the necking part).

For torsion tests, I have taken equivalent tensile stress = shear stress*sqrt(3) and equivalent tensile strain as = shear strain / sqrt (3).

This is based on Von Mises criteria.

But I have a problem, doing this I find that there is a variation of about 6-8 % from the uniaxial tension test and compression test . IS there some approxiamtion in Von Mises criteria of equivalent tensile stress and strain?

I tried to google and more and this what I found:


http://books.google.co.in/books?id=...orsion test equivalent tensile strain&f=false



From this ; am I correct below (you can read the abstractabove as well):

“Torsion equivalent stresses obtained using Von Misesrelationship (as I have done) are 6.5% lower than those obtained using BishopHill formulation which is more accurate”

So, can we say that torsion equivalent stresses will bearound 6.5% less than that obtained using uniaxial tension ?

Warm regards,

Vishal
 
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