| As the characteristic of high efficiency, compact structure, reliable operation and stable transmission ratio etc, gear transmission is widely used in mechanical transmission field. Of all gear fatigue failure forms, fatigue broken of teeth takes up a largest proportion, followed by surface contact fatigue. Therefore fatigue damage is one of the main forms of gear failure. The research on gear fatigue life and tooth root crack simulation method has important theoretical significance and great engineering application value to improve the reliability and service life of gear.The project is supported by National Key Technology R&D Program of China. With mechanical fatigue analysis theory, fracture mechanics theory, finite element method and boundary element method, a comprehensive numerical simulation analysis of gear fatigue life has been carried out. The main research work in this paper can be summarized as follows:1) After carrying out rain-flow counting for random load histories of wind turbine input torque in every working condition, the relation of load cycles, mean value and amplitude of the torque is obtained. Meanwhile, the total load spectrum of torque is combined.2) In ANSYS, 3D contact finite element model of output gear pair of speed-increase gearbox is built to calculate the stress-strain of helical gear pair under static load. Considering S-N curves and strain-life curves of materials, fatigue life of the helical gear pair is calculated by nominal stress method and local stress strain method respectively in FE-SAFE. Furthermore, the influence of load magnitude, residual stress, tooth surface roughness and profile modification on fatigue life of helical gear pair is researched.3) Boundary element analysis of spur gear model with a semioval initial crack is carried out with 3D fracture analysis software FRANC3D to calculate stress intensity factors of tooth root crack front, and then the influence of load magnitude, crack size and crack shape to stress intensity factors on tooth root initial crack is researched.4) Using the boundary element based crack automatic propagation function of FRANC3D, growth trajectories of cracks in tooth root and tooth surface are simulated. The crack opening displacement and stress intensity factors are analyzed in the process of crack growth in tooth root, and then the tooth root crack growth life is predicted. |
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