TourTour Drive shaft loaded in torsion
 Shaft diameter dk 10-3 m
 Static shear strength τ MPa
 Dynamic to static shear strength ratio τe
 Stress concentration factor Kt or Kf
 Section modulus for torsion S=Ip/(dk/2)=(π/16)dk3 10-6 m3
 Maximum shaft torque statically loaded T=Sτn Nm
 Maximum shaft torque cyclically loaded T=Sτe/Kt Nm
Shaft diameter dk: Local diameter at the critical area (grooved section).

Dynamic shear strength τe: The ratio τe/τ=CfCe/Cm where Cf represent the influence factors listed in eq(3.1),  Ce is the ratio of the endurance limit with the ultimate tensile stress as listed in Table 3.1 and Cm is the ratio of elastic limit and the ultimate tensile strength.

Stress concentration factors: For high strength steel grades and brittle materials the notch sensitivity in not far from unity so Kt=Kf. For ductile materials the lower value of the fatigue stress concentration factor Kf can be applied. It is always save to use the geometrical stress concentration factor Kt which based on (numerical) calculation. Examples of how to limit the stress concentration factor see fig 3.7 and 3.8.