Research On Design Method Of Curvic Couplings And Fretting Fatigue Life Prediction Model

Curvic couplings are widely used in all kinds of high speed and heavy load driving devices of large mechanical equipment due to its advantages of load bearing capability, accurate positioning, automatic centering as well as easy assembling. However, the present method for Curvic couplings design is imperfect, such as it does not take into account the effect of fretting fatigue damage. Fretting fatigue could significantly reduce the fatigue life of the jointing components, but the experimental and theoretical research for now is not good enough to consider so many influence factors on fretting fatigue. Therefore, systematical research on design method of Curvic couplings and fretting fatigue life prediction model are required which will be a great contribution to the theoretical study and engineering applications.The main contents of this thesis are summarized as following.An improved design method of Curvic couplings is developed. The design method of Curvic couplings with double circular-arc root fillet is established and the stress concentration on the fillet area is dramatically reduced. The grinding wheel cross-sectional is designed in detail to avoid the tooth bottom or root fillet manufacturing defects. Curvic couplings design method based on parametric modeling is built and corresponding program is developed to establish the geometry Curvic couplings model for analysis. Numerical calculation(ANSYS) indicated the maximum equivalent(von-Mises) stress of Curvic coupling decreased by 8.9% by only replace the single circular-arc root fillet with double circular-arc root fillet.A unique fretting fatigue test frame for Curvic couplings fretting fatigue test is designed and manufactured. The total number of 30 tests of three types of Curvic couplings fretting specimen with tooth pressure angle of 20°, 30°, 40°,respectively, are conducted. The results show that fretting fatigue life is decreased with increased axial load, and raised with increased normal load. The Curvic couplings fretting specimen with tooth pressure angle of 40° has a longer fretting fatigue life than the specimen with tooth pressure angle of 30°. The specimen with tooth pressure angle of 20° is failed on the fillet area as a result of the normal fatigue instead of fretting fatigue. Fretting fatigue can significantly reduce fatigue strength and fatigue life of the components.A new fretting fatigue life prediction model is proposed based on the multi-axial nonlinear theory of continuum damage mechanics. The damage accumulation process is considered in the life prediction model. The advantage of this approach is that this model is obtained from normal low cycle fatigue test data of material and the bridge-type fretting fatigue test data to predict the fretting fatigue crack initiation life. The new method is applied to predict fretting fatigue life of simplified dovetail joint and Curvic couplings. Comparing with the experimental results, all of the estimated fretting fatigue life by developed model fall within the scatter bands of ±2N(±50%), and the predicted crack initiation location correlated well with experimental results, which verifies the effectiveness of the proposed method.Structural optimization model of Curvic couplings is established, and an optimization design method is induced based on BP neural network and genetic algorithm. Two schemes of optimization design are carried out, respectively, assigning the minimum equivalent(von-Mises) stress and maximum fretting fatigue life as optimum objective function. Comparing with the original single circular-arc root fillet structure, the maximum equivalent stress of the optimum Curvic coupling with double circular-arc root fillet is significantly decreased and the Curvic root stress distribution is more homogenous. The strength of the structure can be enhanced by increasing the tooth pressure angle and the tooth width and finally the fretting fatigue life can be extended.