engleski

Influence of Moving Tooth Load on Gear Crack Path Shape and Fatigue Life

A computational model for determination of the service life of gears in regard to bending fatigue in a gear tooth root is presented. Two cases are being explored, first in which gear tooth was loaded with normal pulsating force acting at the highest point of single tooth contact, and second in which the fact that in actual gear operation the magnitude as well as the position of the force changes as the gear rotates through the mesh is taken into account. The fatigue process leading to tooth breakage is divided into crack initiation and crack propagation period. The critical plane damage model has been used to determine the number of stress cycles required for the fatigue crack initiation. The critical plane methods predict not only fatigue crack initiation life, but also the initiated crack direction, which makes a good starting point for further fatigue crack propagation studies. Finite element method and linear elastic fracture mechanics theories are then used for the further simulation of the fatigue crack growth under a moving load. Moving load produces a non-proportional load history in a gear's tooth root. Consequently, the maximum tangential stress theory will predict a unique kink angle for each load increment, but herein crack’ s trajectory is computed at the end of the load cycle. An approach that accounts for fatigue crack closure effects is developed to propagate crack under non-proportional load. The total number of stress cycles for the final failure to occur is then a sum of stress cycles required for the fatigue crack initiation and number of loading cycles for crack propagation from the initial to the critical length. Although some influences (non-homogeneous material, traveling of dislocations, etc.) were not taken into account in the computational simulations, the presented model seems to be very suitable for determination of service life of gears because numerical procedures used here are much faster and cheaper if compared with the experimental testing.

crack initiation; crack propagation; crack closure

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