Slide
7
To
understand what torsional stiffness is, we can think of the shaft
as a torsional spring with torque equal to a spring constant, k,
times rotation phi. From previous relations, we already know that
T=G J phi over L. Comparing these two relations, we find that the
torsional stiffness, k, is k=G J over L. The stiffness increases
with increasing shear modulus, increases with the fourth power of
the shaft diameter since J is proportional to r to the fourth power,
and decreases as the shaft gets longer.
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