torsional rigidity of sway bar or torque tube

[formula94lt1]

The equation I found for this is assuming the use of mild steel and is as follows.

R= (5x10^6 x D^4)/(.4244LA^2 +.2264B^3)
D=diameter
A=effective lever arm length
B=lever arm length (same as above no? unless arm is at an angle)
L=length of bar or tube or whatever

R=roll bar rate

Now I am curious if anyone else is familiar with this equation and if it is in Ib/ft per degree or what?

 

[NormPeterson]

You must be reading what somebody else copied/posted from Fred Puhn's book (the A/B/L notation you show differs from Puhn's original variable naming, I don't think your exponent for the "constant" in the numerator is correct, and you apparently didn't get Puhn's little diagram).

Two structural beam formulas for displacement have been merged into one for simplicity. Several smaller terms have been assumed negligible. For a front sta-bar, A usually does not = B due to the space requirement for steering the wheels.

Do a dimensional analysis of the equation and see what you end up with for units once you do some cancelling. The 5E6 in the numerator is in units of psi if you're working in inches/lbs/seconds.


Norm

 

[NormPeterson]

IIRC, the 5E6 is 500,000 or 5E5 in the book. 0.5E6 (?)


N

 

[formula94lt1]

Thank you very much, I was searching the net and came across it, so I started fiddling with it. Thanks for the clarification.