Effect of crack closure on gear crack propagation

Computational and experimental studies were performed in order to investigate the propagation of cracking in a spur gear tooth. The stress intensity factors were numerically calculated by the definition of weight functions and by finite element analysis. The influence of the hardness and the residual stress was evaluated and a computational procedure, based on crack tip opening displacement, was defined in order to assess the crack closure effect. Different propagation laws were adopted and life predictions were made. Experimental results were obtained by using special equipment with which it is possible to carry out fatigue tests on gear teeth. These results were compared with the life predictions. The comparison clearly indicates the importance of residual stresses, hardness and, particularly when the loads applied are lower, the crack closure effect.