Based on the space meshing theory

the spiral bevel gear tooth surface equation and meshing reference point are established.The influence law of crack position and crack depth on the torsional mesh stiffness of gear is investigated by using the FEM.On this basis

Westinghouse formula is modified to calculate torsional mesh stiffness of gear with penetrating crack.Calculated results show that the effect of crack on the torsional mesh stiffness is strongly marked when the gears mesh in a single pair of teeth.