Study on Random Fracture and Crack Growth of Gear Tooth Waist

Abstract

The gear tooth fracture usually occurs at the root, but sometimes also occurs at the waist, or even at the top. The random fracture is defined as the rupture at the waist or top of the tooth. The random fracture at the waist is studied in this paper. In order to simulate a manufacturing defect on the tooth surface, a mic-notch (a minute notch) was cut at the waist of the twelve teeth in the two test gears. A gear-running test was carried out under ladder loading till a gear tooth fractured. The fracture appearance illuminates that the failure is fatigue fracture. The initial crack of the notch grew in the five teeth, and no crack propagation was not found in the other seven teeth. The stress intensity factor and the crack propagation length are comparatively studied by three methods such as linear elastic fracture mechanics theory (LEFMT), FRANC3D simulation and the test. In the early stage of crack propagation, the theory values of LEFMT are close to the simulation, but the difference gets larger and larger with the increase in crack length till the gear tooth is broken. However, the difference of crack propagation length between simulation and the test is less, and the error is in the range of 2.4–13.3%. Therefore, the simulation could truly predict the crack growth length.