How do you analyze a shaft under combined bending and torsion?

For combined loading, calculate equivalent bending moment Me = √(M² + T²) for equivalent stress, or Te = √(M² + T²) for equivalent torque using maximum shear stress theory. Using von Mises: σe = √(σb² + 3τ²). Design diameter from d = ∛(16Me/πσall) or d = ∛(16Te/πτall). This is critical for automotive drive shafts and machine elements.