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Abstract. An appropriate fatigue crack growth model is the key to accurately evaluate fatigue life of component. Researching on the McEvily model, considering the influence of elastic-plastic behaviour and crack closure, a modified elastic-plastic small crack propagation characterization model is proposed. The effects of parameters on growth rate of fatigue crack was studied using scanning electron microscopy (SEM) in-situ observation by experimental results on 6151-T6 aluminium alloy. Results indicate that the modified model is able to characterize small crack propagation behaviour, expanding the region to be precisely predicted, which is remarkably important for fatigue life prediction and damage tolerant analysis of aluminium structure.

Based on the theory of finite rotation beam, together with the finite element method, the rotor dynamic model is established, and the relationship of strain and displacement in the strain energy of blade is solved by introducing the generalized Danielson-Hodges strain and Green-Lagrange strain. The three-dimensional nonlinear analysis is decoupled into two-dimensional linear profile analysis and one-dimensional nonlinear blade analysis. Hartenberg-Denarit augmented transformation matrix is introduced in kinetic modeling. According to the Hamilton principle, the nonlinear implicit dynamic equations of the rotor are established. Blade flap under the influence of gust wind is calculated; the safety criterion of the ground starting of the helicopter is put forward.