Laserxenon
Mechanical
- Jun 2, 2003
- 45
I am wanting to understand the difference between J & Ju. I understand that Ju is the unit polar moment of inertia and it must be multiplied by an area (throat for example) to calculate the stress at that point. I am good with the throat area derivation.
The way I am thinking about it, if you want to know the torsional shear stress at a specific point (say the extreme fiber for max shear) you would use J= 0.707*h*Ju.
If you want to calculate the average torsional stress, you would use J= Total Weld Throat Area * Ju. For example, two parallel, vertical welds each of length d, would be J= 1.414*h*d*Ju
Why in practice would you look at average torsional shear vs. max torsional shear (if I am understanding this correctly)? Wouldn't you always just check for max shear at the extreme fiber and not care what the average is? I believe that I have seen it done both ways.
I think that the total area is used for calculating the direct shear (F/Total Weld Throat Area), but still don't understand the difference between why you would use J=0.707*h*Ju (seemingly to evaluate max torsional shear at an extreme fiber) vs. J=Total Weld Throat Area * Ju (ie two parallel, vertical welds each of length d, would be J= 1.414*h*d*Ju )
Thanks.
The way I am thinking about it, if you want to know the torsional shear stress at a specific point (say the extreme fiber for max shear) you would use J= 0.707*h*Ju.
If you want to calculate the average torsional stress, you would use J= Total Weld Throat Area * Ju. For example, two parallel, vertical welds each of length d, would be J= 1.414*h*d*Ju
Why in practice would you look at average torsional shear vs. max torsional shear (if I am understanding this correctly)? Wouldn't you always just check for max shear at the extreme fiber and not care what the average is? I believe that I have seen it done both ways.
I think that the total area is used for calculating the direct shear (F/Total Weld Throat Area), but still don't understand the difference between why you would use J=0.707*h*Ju (seemingly to evaluate max torsional shear at an extreme fiber) vs. J=Total Weld Throat Area * Ju (ie two parallel, vertical welds each of length d, would be J= 1.414*h*d*Ju )
Thanks.
