Anomaly in Torsional stresses?
Anomaly in Torsional stresses?
(OP)
Torsional stress calculation for rectangular structural stock is at the heighest at the middle of the outer fiber of the long side of stock cross section. Yet, when calculating torsional stress of a rectangular weld pattern, this stress is taken at the further radial position from the center which is at the corner of the pattern. So if you butt welded two such stock along a 'V' groove having the same depth as the stock thickness,which value of that welded pattern would you give credence.






RE: Anomaly in Torsional stresses?
With a rectangular-pattern fillet weld, the assumption is that you have two rigid bodies connected by the weld; therefore, where the greatest differential motion is must be the highest stress. But this is not the same as the strctural tube design.
RE: Anomaly in Torsional stresses?
According to my books for torsion on a box section the higher stresses occur at the inside corners of the box.
My book gives the formula's for the average shear stress on a box section under torsion at the midpoint of section as:-
s= T/(2*t(a-t)*(b-t))
where s=shear stress
T= torque
t= wall thickness of tube
a= width of tube
b= length of tube
I also concur with J.Stephen in his comment
regards desertfox
RE: Anomaly in Torsional stresses?
By the way be careful about the term that you used AVERAGE shear stress is not the same as TORSIONAL shear stress which you have shown the formula to be .
Yes I also agree with JStephen implication in his replyand that is how welds are used in systems when you evaluate stresses.
RE: Anomaly in Torsional stresses?
The formula's I gave refer to hollow box section not solid
rectangular section.
I read J.Stephens post and it mentioned rectangular tube.
The shear stress formula are for torsional shear stress on hollow box section.
regards
Desertfox
RE: Anomaly in Torsional stresses?
RE: Anomaly in Torsional stresses?
i'd also challenge the OP's post that ...
"Torsional stress calculation for rectangular structural stock is at the heighest at the middle of the outer fiber of the long side of stock cross section." maybe i'm being pedantic, but i thought that the torsional stress on the surface (= the outer fiber) was zero and that the peak stress was at the centroid of the section (assuming a regular solid section).
RE: Anomaly in Torsional stresses?
RE: Anomaly in Torsional stresses?
For the same reason as you note (under bending the surface shear stress is zero) since there is nothing outside the section to resist the section, the surface has zero stress, and the shear stress quickly builds up as you penetrate into the solid ... i was visualising the "sand pile" analogy for plastic torsional shear stresses.
RE: Anomaly in Torsional stresses?