Research On Fretting Fatigue Life Of Point Contact Under Low Normal Load

Contact between parts exists wildly in mechanical structure. There is fretting fatigue failure in contact zone, when parts are bearing alternating load. Fretting fatigue is one of the reasons that cause the failure of core parts in aviation industry and nuclear industry. The structure design at present is dominated by strength analysis, and ignores the fretting fatigue caused by contact between parts. Various possibilities should be considered in the design of core parts in nuclear power equipments and aircraft. Fretting fatigue has been taken into consideration in the design of equipment at present. Therefore, research on fretting fatigue under various contact forms is very necessary.Taking structure loaded by fretting bridge as research object, the forming law of indentation of point contact under low normal load and the effect of indentation on fretting fatigue life are studied by finite element calculation and indentation experiment based on Hertz contact theory. The main work and results in this thesis are as follows:1. The indentation experiments of point contact under low normal load are carried out.According to the structure loaded by fretting bridge, forming law of indentation is explored by finite element analysis of point contact under low normal load. The relationships between the normal load PN, the radius of specimen R1, the radius of fretting bridge foot R2 and the depth of indentation d, the curvature radius of indentation root ρ are obtained. The change laws of indentation size under alternating load are obtained. The relationships between the geometry size of indentation and the stress concentration factor are obtained.2. Taking Von Mises equivalent stress as characterization parameter, the stress-time history of nodes in contact zone is analyzed under low normal load. The competition relationship of fatigue damage between middle point and edge point in contact zone is discussed under fretting condition. The results show that fretting fatigue life is determined by contact stress cycle and axial tension stress cycle. Furthermore, the method to predict fretting fatigue life is proposed, and has been proved to be safe by comparing with the experiment results.