68. A
welded thin-wall steel tube is subjected to a torque 
as shown in the figure. The thickness
of tube is 
and the length is 
. The tube has a round section
with a diameter of 
. The shear modulus is 
.
If the allowable anlge of twist is 
, estimate probability of failure
using the FOSM. Note that 
and 
are independent.
Answer:
