[new2subaru]

Some info

5.5 SAFETY
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Safety is greatly enhanced with composite
shafts. Composites absorb energy upon impact. They can be
designed to, and will normally, break apart during an accident
rather than entering the passenger compartment catapulting the
vehicle, or whipping a broken end through a tank or valuable cargo.


2 shows a broken composite driveshaft. Note
the broken pieces rather than the bent and twisted club that is
usually left with metal. Impact with hard objects like frame
rails will cause a composite shaft to disintegrate and quickly
dissipate energy. A failure in a bond joint would simply result
in a loss of power. The shaft would probably stay in place
with the loose end spinning inside of it.


Above 128 mph the driveshaft gets into a bending
and vibration frequency that would eventually tear it apart.”
They continue that,to eliminate this problem most high
speed European cars usually have a two piece shaft connected through a center bearing.” Carbon fiber driveshafts can alleviate this problem


http://www.acpt.com/resources/documents/sae_1966.pdf