Investigation of Moving Load Distribution with the Effect of LDR and LSR on Three-dimensional Fatigue Fracture Behavior of Spur Gear Drive

The tooth fracture failure modes in the spur gear tooth root are mainly influenced by the magnitude and positions of bending fatigue load along the gear face width. Numerous studies in the literature used 3D finite element (FE) models to analyze crack propagation, but they did not take into account the effect of the load distribution ratio (LDR) throughout the gear face width, either in a moving load model or a uniform load model. In this study, an effort is made to investigate the impact of LDR and Load Sharing Ratio (LSR) in the modeling of moving loads for various loading positions and measure the actual crack propagation behavior of a spur gear with a root fracture using the 3D FE technique. Further, the influences of FE spur gear models on the variation of Actual Load Distribution with the effect of LSR, Stress Intensity Factors (SIFs), and crack propagation paths are also studied. A 3D FE crack propagation modeling procedure is validated with the experimental results of the SAEJ1619 fatigue test procedure. The experimental investigation using standard SAEJ1619 fatigue test procedure shows that the symmetric crack propagation failure at the crack front of the spur gear tooth was observed for a given uniform bending fatigue load. The results show that the mode I SIFs (K_I) and mode II SIFs (K_II) are dominant at the crack opening displacement for the positions of moving load between the Highest Point of Single Tooth Contact (HPSTC) and Highest Point of Tooth Contact (HPTC) lines. But, the K_II is highly influenced by K_I for further crack growth when the load is moved to the HPSTC line than the HPTC line. This study provides the guidelines to predict the actual crack propagation path failure behavior for various positions of moving load for various gear drive systems with root crack.