13th International Conference on Fracture June 16–21, 2013, Beijing, China -6- reliability ratio is 0.95 [11]. 0 0 max (1 ) 0.94 0.47(1 ) 0.53(1 ) m DFR m R X R X R σ σ σ σ − = − + + − （9） Where, DFR σ is the Detail Fatigue Rating; 0 310 mσ = MPa; R is the stress ratio; S is the pitch coefficient, 2 S = ; 5 lg N X S − = ; N is the safe life 95/95 N for the confidence level 0.95 and the reliability ratio 0.95. If three parameters are known, then the other can be calculated among the other parameters. First, the character life β for test data of every group should be calculated according to the Weibull distribution: 1/ 1 1 n i i N n α α β = ⎡ ⎤ = ⎢ ⎥ ⎣ ⎦ ∑ （10） Where, 4 α= . Then, the life should be calculated for the confidence level 0.95 and the reliability ratio 0.95: 95/95 R C N S S S τ β = （11） Where, the specimen coefficient 1 S τ = , the reliability coefficient 2.1 RS = for the aluminium alloys, the confidence level coefficient CS =1.175 for the confidence coefficient 0.95 and n=4. 4. Analysis and validation 4.1. The confirmation of model parameters The standard S-N curve was fitted based on the test data from table 1 after accelerated environment test as Table 2 shown. Table 2. S-N curve under different accelerated time accelerated time /a S-N curve confidence level /% 4 3 0.2796 8.2725 10 × = SN 0.998 12 3 0.296 9.7538 10 × = SN 0.992 20 3 0.2243 4.1727 10 × = SN 0.986 The change rule of the shape parameters C andαwas gained along with time according toTable 2, as the formula (12) shown. 2 2 ( ) 0.238 0.01317 0.000695 (T) 4883 1067.96 T 55.175 T T T C T α⎧ = + × − × ⎨ = + × − × ⎩ （12） The change rule of the shape parameters of S-N curve was established in the formula (12) for different parking calendar year. Therefore, the declining degree of S-N curve could be calculated at different parking time according to formula (12), and then the life of fatigue critical component could be reasonablly analysed and forecasted.
RkJQdWJsaXNoZXIy MjM0NDE=