Research On The Strength And Life Of The Engine Intermediate Case Under Multiaxial Loads

Intermediate case is an important part of the turbofan engine components. It not only has complex structure, but also bears complicated loads in different directions and phases. It is a typical component bearing multiaxial load. The research on the strength and fatigue of the casting titanium alloy intermediate case under multiaxial load is presented in this paper. The character of the intermediate case structure and load is analyzed in detail. Then the states of stress and strain of 38 aerodynamic load states, 141 maneuvering load states and combined load states are calculated with Finite Element Method. It indicates that the stress level of the casing isn't very high in every load state; in most states the stress is in the elastic range. The stress concentrating point stays still in the aerodynamic load state, but it changes with the maneuvering load state. Some part of the casing reaches plastic range in the combined load state and the casing may be cracked under 1.5 times of the combined load. The aerodynamic cycle life and standard cycle life are predicted with uniaxial fatigue theory. The result indicates that the intermediate case meets the request of the low cycle fatigue in the aerodynamic load state and the combined load state. The multiaxial fatigue theory based on the critical plane theory is stated in detail and it is fit for random load combined with weight function method. Based on the uniaxial rain-flow counting method, a multiaxial counting method is presented and corresponding program is made. At last, the aerodynamic cycle life and standard cycle life are predicted with multiaxial fatigue theory. The result similarly indicates that the low cycle fatigue request of the intermediate case is satisfied in the aerodynamic load state and the combine load state. Compared with the result of uniaxial fatigue theory, the life of muliaxial fatigue theory is lower.