Fatigue life prediction of engaging spur gears using power density

Abstract

The high cycle fatigue performance of an input spur gear pair found in the gearbox of a 4LZ-2 combined harvester with a maximum walking power of 15 kW is investigated. A three-dimensional finite element model of the two engaging spur gears is developed to estimate the fatigue life of the pinion gear subject to bending induced crack initiation and propagation. The critical point of the pinion gear is obtained along with the associated bending stress-time history. The novel concept of power density is applied to the finite element result to correlate fatigue crack initiation and subsequent crack growth with the number of loading cycles undergone. After the location of crack initiation is identified, fatigue crack propagation is modelled using linear elastic fracture mechanics. The estimated fatigue life of the pinion gear is 886 h. A fatigue test rig is employed to physically demonstrate the feasibility of the power density concept for predicting gear fatigue life. It is shown that the power density concept is preferred over the Miner rule for higher accuracy in fatigue life prediction.