Issue 38

C. Xianmin et alii, Frattura ed Integrità Strutturale, 38 (2016) 319-330; DOI: 10.3221/IGF-ESIS.38.42 325 The consistent index b is closely related to statistical parameters α and β of fatigue life distribution and can be solved by Monte Carlo sampling test according to Eq. (2) . When α is assumed as 4, the quantitative relation between index b and scale parameter β can be obtained through large number of sample tests, the results are shown in Tab. 6. Note that the general trend is that b decreases with β and b stay constant in some interval of β instead of changing continuously with β . β (8×10 3 ,10 4 ] (10 4 ,5×10 4 ] (5×10 4 ,10 5 ] (10 5 ,10 6 ] b 1.011 1.010 1.009 1.008 β (10 6 ,6×10 6 ] (6×10 6 ,5×10 7 ] (5×10 7 ,5×10 8 ] (5×10 8 ,10 10 ] b 1.007 1.006 1.005 1.004 Table 6 : Quantitative relation between the consistent index b and scale parameter β(α=4). E XPERIMENTAL VERIFICATION OF THE STATISTICAL FATIGUE DAMAGE MODEL UNDER SPECTRUM LOADING Fatigue tests under spectrum loading he specimens are the same as those used in the fatigue tests under constant amplitude loading [15]. The load spectra and fatigue life results are listed in Tab. 7. spectrum Load order 1 2 3 4 5 Cycles to failure 5-level Sa(MPa) 17.09 27.77 42.73 36.32 21.36 500826 ， 686156 ， 2445490 ， 1201897 ， 2 253944 cycles 1000 500 200 600 900 3-level Sa(MPa) 27.77 42.73 36.32 \ \ 371112 ， 522772 ， 670298 ， 507405 ， 426 219 ， 364397 cycles 500 302 600 \ \ Table 7 : Fatigue test results of straight lugs under spectrum loading. Using the data in Tab. 7, the statistical parameters of fatigue life under spectrum loading can be obtained by BJPM, including ˆ  ,E ， σ , N 95/95 and the interval of 95% fatigue life ( β 1 , β 2 ), ( E 1 , E 2 ) and ( σ 1 , σ 2 ) . Here σ is the standard deviation of the test results, demonstrating the scatter characteristics of fatigue lives. Experimental verification of the fatigue damage model Statistical parameters for each stress level of the multilevel spectrum are obtained via the S-N curves described in section 3, including characteristic life β , the average life E , N 95/95 and the self-consistent index a , listed in Tab. 8. Sa(MPa) 17.09 27.77 42.73 36.32 21.36 statistical parameters β 158271738 1605853 198884 437239 6180778 E 143457895 1455549 180269 396314 5602272 N 95/95 65467281 664242 82266 180859 2556608 self-consistent index a 1.006 1.007 1.008 1.008 1.008 Table 8 : Statistical parameters of fatigue life distributions under constant amplitude loading. Two thousand values of N f can be acquired using Eq. (6) from 2000 groups of random sampling based on the fatigue life T