Torsional Stiffness
Torsional Stiffness
(OP)
(newbi - please be gentle!)
I trying to calcule the torsional stiffness of rotor, the construction is a simple rolled bar with 6 arms welded down the rotor body.
Is there an equation for the Polar moment for this type of rotor construction?
Help
TonyCro
I trying to calcule the torsional stiffness of rotor, the construction is a simple rolled bar with 6 arms welded down the rotor body.
Is there an equation for the Polar moment for this type of rotor construction?
Help
TonyCro





RE: Torsional Stiffness
RE: Torsional Stiffness
k = T/(delta R)
There are books which give you equations for the stiffness, ranging from simple bars through to complex crankshafts. Names (authors) I can think of are Kerr Voss and Bicera. I do have access to these at work, but I'm on holiday today - sorry.
Cheers,
-- drej --
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RE: Torsional Stiffness
RE: Torsional Stiffness
RE: Torsional Stiffness
Thanks
TonyCro
RE: Torsional Stiffness
if the information is at all critical, and construction is feasible, then make a physical model and measure the stiffness. Even better, make several and measure the stiffness. I think you will find variance among physical models and even more variance between Acad SolidWorks and the physical models, particularly when welded construction is involved.
RE: Torsional Stiffness
To a first approximation I'd just smear the ribs out over the rest of the shell and use the equation for a tube, but, IF the stress flow argument holds that will overestimate the torsional rigidity of the shaft.
Cheers
Greg Locock
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RE: Torsional Stiffness
Be forewarned about using AutoCAD to calculate your polar moment of inertia. If your cross section is a closed section (tubular or box type), the value that AutoCAD calculates is correct. If your section is open (I, C, plate, L), the value calculated by AutoCAD can be much higher than the actual. This discrepancy is due to the fact that AutoCAD neglects open cross section warping. In addition, Roark's Formulas For Stress & Strain is a usual source for hand methods to calculate moments of inertia.