The specimen shown is made from a $25-$mm$-$diameter cylindrical aluminum rod with two $40-$mm$-$outer$-$diameter sleeves bonded to the rod as shown. Knowing that $)=(69$GPa and is subjected to a $4\mathrm{.}0kN$ tensile load. Determine;

a$)$ the total deformation of the specimen,

b$)$ the deformation of its central portion $BC.$