Calcolatrice Sollecitazione Linguetta — Formula

Parallel Key Stress Analysis

A key transmits torque between a shaft and a hub (gear, pulley, coupling).

Formulas

The tangential force at the shaft surface: F = 2T / d

Shear stress = F / (w x L) (shear across the key width)

Bearing stress = F / ((h/2) x L) (crushing on half the key height)

where T is torque, d is shaft diameter, w is key width, h is key height, and L is key engagement length. Bearing stress is usually the governing criterion.

Esempio Risolto

A 12x8 mm key, 40 mm long, on a 40 mm shaft transmitting 200 N-m.

  1. F = 2 x 200,000 / 40 = 10,000 N
  2. Shear stress = 10,000 / (12 x 40) = 20.8 MPa
  3. Bearing stress = 10,000 / (4 x 40) = 62.5 MPa
  4. Bearing stress governs. For mild steel key (allowable bearing ~90 MPa), the key is adequate.