The stress concentration effect of different corrosion pits is different, the shapes of corrosion pits can be seen as semi-ellipsoidal, the short half axes、long half axes and depth of corrosion are 、 and , through finite element analyze, we can see that the stress concentration factors increase with the increase of , but the stress concentration factors decrease with the increase of .

Grey relational method is a data process method used to sort out the correlation extent of influence factors in a system with uncertain information. In this paper, it is applied to evaluate the effect of environmental factors on Atmospheric corrosion of Aluminum alloys and find out the main factors. Analysis results indicate that the influence order of the meteorological factors in atmospheric corrosion exposing for one year, three years, six years and ten years is always the same: Fog﹥RH﹥Humidity over 80%﹥Rain﹥T﹥Precipitation﹥Dew. But for pollutant factors, the sorted result is changeable at different exposure time. The effect of , is obvious all the time, and plays an important role in the initial stage of corrosion, yet is turned to be the dominant factor with increase of the exposure time.

The corrosion of LY12CZ aluminum alloy in aircraft under service environment is regarded as a stochastic process and the time series theory is used to analyze and to predict the corrosion depth of LY12CZ under airport environment by means of ARIMA(3,1,1)model.The application result show that the ARIMAmodel can predict the value and propagation trend of corrosion depth realistically and effectively,demonstrating the expedient and easy application of time series theory and method.

Considering the degradation effect of corrosion damage on fatigue behavior of aero aluminum alloy, the present thesis made a research on corrosion fatigue crack growth rate. Taking into account the effect of load frequency on fatigue crack growth, a concept of corrosion fatigue frequency factor is proposed. Based on the fact that low frequency will lead to high corrosion fatigue crack growth rate, and frequency higher enough will make little difference between corrosion fatigue and pure mechanical fatigue behavior, an exponential expression of corrosion fatigue frequency factor is proposed. The crack growth rate prediction from proposed formula is proved to be in good agreement with experimental results for steadily extended corrosion fatigue crack.

Using of a safe life approach is necessitated by the small critical crack sizes and rapid crack growth rates resulting from the severe vibratory environment of rotorcraft. However Based on the success of damage tolerance initiative for airframe structure, a crack growth based on damage tolerance approach is being examined for implementation into the design and management of dynamic components. In this paper the crack growth behavior in low cycle fatigue (LCF) and high cycle fatigue (HCF) are compared and the accuracy of several damage tolerance analysis methods in determining the crack growth life from an initial detectable crack size 1.25 mm to 12 mm for a rotorcraft main rotor yoke are investigated. The real rotorcraft materials measured by experiment and the fatigue load mean frequency spectrum based on statistical usage spectrum are adopted. The crack growth equations used in the programs are discussed to provide a basis for understanding the results. The results show that the load less than the safe fatigue limit has an important effect on crack growth life and it is reasonable for the material that the cut-off stress ratio for the threshold stress intensity factor range is set 0.7.