Bending Fatigue Life Calculation For Modified Herringbone Gears

Compact structure,light axial force,high contact ratio,large bearing capacity and high transmission efficiency are common characteristics for herringbone gears.Herringbone gears are widely used in high speed and heavy load transmission systems such as automobiles,ships and aerospace equipment.Studies show that gear bending fatigue is an important failure form for heavy load herringbone gear.The crack initiation and crack propagation are two stages of gear bending fatigue.Gear modification can effectively improve tooth edge contact,which significantly affects bending fatigue life of herringbone gears.Thus,bending fatigue crack initiation-crack propagation life for modified herringbone gears is calculated based on multiaxial fatigue criterion and fracture mechanics theory.The main contents are presented:(1)Finite element(FE)contact analysis for modified herringbone gears is carried out.Based on principle of generating method and gear modification method,threedimensional geometric models of standard and modified herringbone gears are established.FE contact analysis of standard and modified herringbone gears is carried out.Effects load and modification on tooth root bending stress are investigated.The results show that tooth root bending stress is symmetrically distributed without considering alignment error.The magnitude and distribution of tooth root bending stress will be nonuniform with different load and modification.(2)Bending fatigue crack initiation life for modified herringbone gears is calculated.The critical plane direction of nodes at tooth root are determined based on results of gear FE contact analysis.Bending fatigue crack initiation life calculation model of herringbone gear is established based on Dang van multiaxial fatigue criterion.Effect of modification on fatigue crack initiation life is studied.The results show that bending fatigue crack initiation life of herringbone gears can be increased with proper gear modification.(3)Crack propagation life calculation model and experimental verification are proposed.Standard compact tensile specimens homogenized with the gear are designed and manufactured.Crack growth rate tests of gear material are carried out.The correlation between crack growth rate and stress intensity factor at crack tip is analyzed.Crack growth parameters of gear material are determined.Based on Paris criterion,the FE analysis model of crack propagation is established.Crack propagation path and life of standard compact tensile specimens are calculated.(4)Bending fatigue crack propagation life of modified herringbone gears is calculated.FE analysis model of herringbone gears with initial crack is established based on the results of tooth root bending stress.Effects of load and modification on stress intensity factor at initial crack tip and bending fatigue crack propagation life of tooth root are studied based on crack propagation life calculation model.The results show that bending fatigue crack propagation life of herringbone gears can be increased with proper gear modification.