I am trying to calculate the torsion in a rectangular bar.
I have found closed form calculations in Shigley, Roark, and a NZ structural code which all agree (within 10% or less).
However, the solid works simulation of the same geometry is higher:
b = 4"
t = 1"
L = 3"
T = 10,000 in*lbf
Tau (Shigley) = 8.63 ksi
Tau (Roark) = 8.63 ksi
Tau (NZS 4404) ~9 ksi
Tau (FEA) = 11.65 ksi
The FEA results are 35% higher.
Has anyone every experienced this
Results are attached below:
Apparently, the torsional shear stress is influenced by the stresses in bars with a short length.
I increased the length of the bar to 12" long and checked the torsion at a plane located at the mid length and the stresses
agree closely (with ~ 2%) with Roark and Shigley.
Initially, I made 2 mistakes.
1. I was checking stresses at the ends instead of the mid length.
2. I was checking the shear stresses in the wrong directions.
Here are my new results:
TauYZ is the shear in the Z-direction acting along the X-Z plane.
The Y axis is orthogonal to the X-Z plane, thus TauYZ notation.