13th International Conference on Fracture June 16–21, 2013, Beijing, China -3- Temperature spectrum：T=(40±2℃) Humidity spectrum：RH=(90~95)% Roast lamp irradiation spectrum (Lighting) Period soakage spectrum Dipping inliquor Drying in liquor Figure 2. Accelerated environment spectrum The surface of specimen was airproofed by the aviation silica gel. One hour in the environment box was equal to 0.135 years in the natural environment [5], the 4 years、12 years and 20 years were simulated separately in the natural parking environment. After the accelerated environment test, the specimen of no- corrosion surface was chose to test. The fatigue test was carried out by the MTS810 500KN fatigue test machine at room temperature with sine wave, the frequency was 20Hz, the stress ratio R was 0.06, every group would be picked up 4 valid data and the stress level had 3 groups. 2.3. The result of test Provided that the result of test obeyed the lognormal distribution [7], the median-fatigue life could be calculated by the formula (1). ∑ = = n t i i t N t n N 1 ( ) lg 1 50(t) 10 （1） Where, t nis the number of accelerated specimen, 50 (t) N is the median-fatigue life, (t) iN is the fatigue life for the i specimen. Table 1. Specimens’ median-fatigue life Stress/MPa 50 (t) N /10,000 cycle 250 26.68 310 12.93 4 372 6.48 240 26.54 310 12.22 12 372 5.97 265 20.73 310 11.83 Accelerated environment test 20 372 4.60 250 14.28 290 7.83 The specimen of retired aircraft 320 6.53
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