Fatigue Crack Growth Analysis in Spur Gears for railway gearbox

초록

Gears are commonly used machine component for power transmission and gear box in railway vehicle. In gearboxes, gear damage detection is often very critical and can lead to increased safety in railway vehicle. Vibration monitoring is a very effective technique for gear box health monitoring and fault detection. Health monitoring of gear box is an important aspect to avoid failure of the railway vehicle in advance. Two kinds of teeth damage can occur on gears under repeated loading due to fatigue. One is the pitting of gear teeth flanks and the other is the tooth breakage in the tooth root. To prevent failure of gear box, it is important to detect vibration signals before the tooth breakage. Therefore, it is neccessary to understand the mechanism of cracks growth and the critical crack length should be determined. The objective of this paper is to present a computational model for determination of crack growth rate and critical crack length of a gear tooth root. The proposed model is used on a specimen spur gear made from high strength alloy steel with additonal surface treatment. The procedure in the proposed bending fatigue model is to first compute stress concentration in the critical section of the gear tooth root. For simple cases the the relationship between the stress intensity factor(KI, KII) and the crack length can be determined using the methodology given in the literature. Howerver, it is necessary to use alterative methods for more complicated geometry and loading case. In this work, the finite element package FRANC2D has been used for simulation of the fatigue crack growth. Four load cases are considered with the same tooth geometry to calculate the stress intensity factor. Finally, the crack growth rate and the critical crack length of the gear tooth root are estimated