TourTour drive shaft loaded in torsion
 Shaft diameter d mm
ISO 724 Static shear strength of the shaft τn MPa
 Dynamic to static shear strength ratio τe
 Stress concentration factor Kt or Kf
 key width b mm
 key height h mm
 keyway depth shaft t1 mm
 keyway depth hub t2 mm
 Critical diameter dk=d-t1 mm
 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
Key dimensions: Parallel keys are most commonly used. The key and key seat cross section are ISO standardized. The key length should be less than about 1.5 times the shaft diameter to ensure a good load distribution over the entire key length when the shaft becomes twisted when loaded in torsion.

Fatigue strength: The ratio τe/τ=CfCe/Cm where Cf represent the influence factors listed in eq(3.2),  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 the shear stress and the tensile stress.

Bearing pressure >>

Stress concentration factors:

Stress concentration factor Kf for: Bending Torsion
Annealed 1.6 1.3
Quenched / drawn 2 1.6
Annealed 1.3 1.3
Quenched / drawn 1.6 1.6