Statically indeterminate

A torque $T=40$kip$*in.$ is applied at end $A$ of the composite shaft shown. Knowing that the

modulus of rigidity is $11\mathrm{.}2{10}^6$ for steel and $4{10}^6$ for aluminum, determine $($a$)$ the

maximum shearing stress in the steel core, $($b$)$ the maximum stress in the aluminum shell, $($c$)$ the

angle of twist at $A.$