RE: carbon fibre driveshafts

["Robert K. Davis" <bob@btv.ibm.com>]

>>carbon fibre (when properly applied and cured) is
>>immensely stong in twist and compression.

>does this mean that it is always strong with respect to twist and compression,
>_or_ that it is possible (but not necesarily essential) to apply it such that 
>these characteristics are obtained?

>Would not a shaft made up with threads perpendicular to the direction of 
>rotation allow a shaft so constructed to wind up?

Actually, it is the ability to make a carbon fiber drive shaft very strong with respect to torsional loads that would make it an ideal choice for this.

In order to do this, one would wind the fibers in a helical fashion down the shaft.  The torsional stiffness is at a maximum when the wind angle is 45 degrees.  This gives a peak torsional stiffness of about 48,000 N-m/rad for a 102 mm I.D. by 3.2 mm wall by 3050 mm long shaft.  So the shaft good take high torsional loads with out much windup.  An aluminum driveshaft would probably show and order of magnitude higher twist (for instance, 1 degree of twist for carbon fiber to 10 degrees for aluminum - or steel).  Yes, if you twisted the carbon fiber driveshaft that same 10 degrees as the metal, it would probably fail, but at a *much* higher torsional load than the metal.

--
Bob Davis