Polar Moment of Inertia - Weld Treated As line
Polar Moment of Inertia - Weld Treated As line
(OP)
I'm doing a torsion weld calc on a pipe and cant figure out why the polar moment of Inertia formula (Jw) for a weld treated as a line is different than the standard polar moment of inertia formula for a circle.
In my text book, the polar moment of Inertia (J) of a circle (with axis on CG)is J=Iy+Ix.
For a 4" pipe I calculate (J) as 25.133in^4 using the textbook formula.
Using formula taken from the attached sheet Jw = 50.26in^4
Why are these two values different? Jw = 2xJ
Thanks in advance for the help.
In my text book, the polar moment of Inertia (J) of a circle (with axis on CG)is J=Iy+Ix.
For a 4" pipe I calculate (J) as 25.133in^4 using the textbook formula.
Using formula taken from the attached sheet Jw = 50.26in^4
Why are these two values different? Jw = 2xJ
Thanks in advance for the help.





RE: Polar Moment of Inertia - Weld Treated As line
Odd this question should come up, I had a weld torsion problem this morning myself and dug out the old Shigley and Miske to refresh.
Regards,
Mike
RE: Polar Moment of Inertia - Weld Treated As line
RE: Polar Moment of Inertia - Weld Treated As line
Ix = Iy = πR3 = πD3/8
Ix + Iy = πD3/4
RE: Polar Moment of Inertia - Weld Treated As line