Fatigue Crack Initiation Prediction Tool for Rotorcraft Spiral Bevel Gears

Current life prediction methods, such as AGMA, are empirical-based, deterministic in nature and cannot consider the effects of gear manufacturing processes, material microstructure and lubrication on fatigue strength. The estimated life is as good as the information entered by the user and it requires considerable design, manufacturing and field experience. In addition, current methods cannot take into account the influence of surface finish and residual stress profile (due to shot peening) on gear life. This leads to excessive overdesigns and conservative life predictions. In this program, Sentient will develop probabilistic fatigue crack initiation prediction tool using finite element method (FEM), mixed-elastohydrodynamic lubrication (EHL) model, microstructure model, and probabilistic physics-based fatigue damage method. FEM and mixed-EHL methods will be used to estimate contact pattern and true stresses in spiral bevel gear. The microstructure model along with fatigue damage model will be used to predict time to crack initiation. When complete, the life prediction tool can be used to predict the influence of variation in manufacturing processes (carburization, shot peening), and material macro and microstructural properties on gear fatigue life.