Investigating fatigue failure of core motion mechanism for a small oil-free wobble-plate compressor

Abstract

Abstract The study is driven by a recent experimental test for a small-size high-speed oil-free wobble-plate compressor, in which abrupt local fatigue failure of the wobble plate is encountered. To explore the causes, a fatigue prediction method is proposed, which involves the dynamic force calculation, stress prediction, and fatigue analysis. The dynamic forces is obtained by solving the coupled dynamic, thermodynamic and kinematic models. The dynamic stress with thermal effect is predicted, where the temperature field is calculated by solving the thermal conduction equation with the experimentally measured solid-surface temperature acting as boundary conditions, and the obtained temperature distribution is incorporated into the FEM (finite element method) prediction for thermal-dynamic stress. It is found that intensive friction heating causes the wobble plate significant local temperature rise and it is largely responsible for the structural failure. The Goodman mean stress correction method and wobble plate material S–N (Stress amplitude versus cycle Number) curves are incorporated to predict the fatigue life of wobble plate. The predicted fatigue life is comparable to the experimentally measured, which has verified the developed method. The wobble plates of 7075-T6 aluminum alloy and H62 brass alloy are compared, and the former produces a smaller dynamic stress for its smaller elasticity modulus and larger specific heat but a shorter fatigue life due to its S–N curve smaller stress amplitude.