3. Thermal stress (10pts) The assembly shown consists of an aluminum shell(E. =10x10' psi,a,-13x10/F)fully bonded to a steel core (E, 30x10 psi, a, 6.5x10 /F) and is unstressed in the beginning. a) Derive the axial stresses in shell and rod as functions of temperature change for arbitrary two materials. (by considering compatibility, material law, and equilibrium) b)For the materials given, if the stress in 8 in 0.75 in. Aluminum is not to exceed 6ksi,what is the largest allowable temperature change? Aluminum shell Steel 1.25 in. core