Strength And Life Analysis And Structural Improvement Of Flexible Coupling With Compound Spiral Tube

Flexible coupling is widely applied. Whether in aviation or other fields, flexible couplings play a very important role in industry. The flexible coupling with multi-layer structure compound spiral tube which was studied in this paper has characteristics of small size, high transmission power and long lifespan. In this paper, the torsional stiffness and strength of the single spiral tube is firstly analyzed with theory and method of the finite element according to the structural characteristics, then emphasis is put on studying the stiffness, strength, as well as lifespan issues under different loadings of the flexible coupling with compound spiral tube making use of nonlinear finite element method. The results are obtained as following:1. Nonlinear finite element model of contact is set up, non-linear characteristic of the torsional stiffness of the coupling is detailedly analyzed and studied. The results show that the torsional stiffness of the coupling is closely related to the loading and linearity in the initial stage, the stiffness performs staggered linear increase as the load increasing, and that is associated with the coupling's structure. The stiffness is also influenced by changes of speed, because the centrifugal force is associated with the contact stress of the coupling.2. Under dynamic loading, when the ratio of frequency is smaller than 1, the equivalent stiffness of the coupling decreases as the ratio of frequency increasing; when the ratio of frequency is bigger than 1, the equivalent stiffness increases as the ratio increasing. In a certain shafting, in order to have a damping effect of the coupling, it means Km<1, according to the minimum frequency of the torque increases as the stiffness increasing; and the rate of increase gradually slow down. The maximum total torque transferred by coupling does not change under step load. In order to have a damping effect of the coupling under pulse load, the maximum pulse time of the torque decreases as the stiffness increasing, and the rate of decrease gradually slow down.3. The maximum stress of the coupling increases as the torque increasing for influence of nonlinear contact, and the rate of increase gradually slow down. In a certain speed range, the maximum stress of the coupling decreases as the speed increasing. When the torque is relatively small, the radial deflection of the coupling doesn't have much influence on the maximum stress; when the torque is big enough, the radial compensation function of the coupling is weakened.4. By the method of determining life based on stress, several equivalent methods of asymmetrical stress cycling are used to calculate and analyze the fatigue life of the coupling on the basis of different fatigue damage theory. Then the results is compared, which provides the basis for the applications and improvement of the coupling.5. The structures of the coupling are correspondingly improved, a new flexible coupling with compound spiral tube is obtained. Its maximum stress decreases by 27% than before under the same torque, and structural weight also decreases by 14.82%.The research has an important active significance to the development of the flexible coupling.