re: carbon fibre driveshafts

[David Eaton <david.eaton@computerland.co.nz>]

thank you bob; phil, i stand corrected.  thinking of formula 1
suspension components, clearly there is *no* flex in these applications,
but you have explained it very well bob, thanks.

so audi make c/f driveshafts with a deliberate degree of flex...

actually thinking about it, maybe this helps to explain their habit of
making amazing starts in the races...

dave
'95 rs2
'90 ur-q

>
>Date: Tue, 27 Jan 1998 14:57:17 -0500
>From: "Robert K. Davis" <bob@btv.ibm.com>
>Subject: RE: carbon fibre driveshafts 
>
>Actually, I was a little hasty in my assumption that the carbon fiber
driveshaft would fail with 10 degrees of twist.  The driveshaft I used
in the example had 3.2mm wall thickness, 102mm I.D. by 3050mm long. For
a 102mm I.D. by 3050mm long shaft of the same material with 0.2mm wall
thickness, the  critical buckling torque is about 30,000 Nm.  Now, the
critical buckling torque is dependent on the wall thickness raised to
the 2.25 power.  So, for a 3.2mm wall thickness, the critical buckling
torque would be on the order of 15,000,000Nm.  Given that the torsional
stiffness is 45,000Nm/rad, this relates to 341rad, which does seem
excessive.  If the claim is 2*pi rad of windup, then the critical
buckling torque need only be 283,000Nm.  Clearly it seems that such a
driveshaft is within the realm of possibility.
>