Torsion of Circular Bars. In designing a torsional mechanism using an aluminum alloy (shear modulus G = 72 GPa), you have the choice between a solid circular shaft or a hollow shaft with inner diameter d = 6 cm. The shaft will be subjected to a torque of Tmax 100 103 N.m and must be able to support a maximal shear stress of Tmax: = 120 MPa. = (a) What outer diameters would be required for solid and hollow shafts, respectively? (b) By what factor could the weight of the shaft be reduced by choosing either the solid or hollow shaft if the length of the shaft is L = 1 m?