Calculator for fatigue strength of a drive shaft with keyway

drive
shaft loaded in torsion

Shaft diameter d

mm

Static shear strength of the shaft τ_{n}

MPa

Dynamic to static shear strength ratio τ_{e}/τ

Stress concentration factor K_{t} or K_{f}

key width b

mm

key height h

mm

keyway depth shaft t_{1}

mm

keyway depth hub t_{2}

mm

Critical diameter d_{k}=d-t_{1}

mm

Section modulus for torsion S=I_{p}/(d_{k}/2)=(π/16)d_{k}^{3}

10^{-6 }m^{3}

Maximum shaft torque statically loaded T=S·τ_{n}

Nm

Maximum shaft torque cyclically loaded T=S·τ_{e}/K_{t}

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 τ_{e}/τ=C_{f}·C_{e}/C_{m}
where C_{f} represent the influence factors
listed in eq(3.2), C_{e}
is the ratio of the endurance limit with the ultimate tensile
stress as listed in Table 3.1 and C_{m} is the ratio of
the shear stress and the tensile stress.