PSI - Issue 22

S.C. Wu et al. / Procedia Structural Integrity 22 (2019) 211–218

216

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Author name / Structural Integrity Procedia 00 (2019) 000 – 000

Fig. 3. The difference methods for fitting P-S-N curves of specimens and axle: (a) compared with TGM, (b) compared with BSIM

As shown in the figure, the P-S-N curves of specimens and axle calculated by the ISIA present a downward opening bell shape and are same as that obtained by TGM. Based on the BSIM and the ISIA, the parameters of fatigue life distribution under various stress levels for EA4T axle steel are determined as list in the above table. Combing with the different methods to fit the P-S-N curve, the fitting results of the ISIA are compared with that of the TGM or the BSIM in Fig. 3 . As shown in the figure, the P-S-N curves of specimens and axle calculated by the ISIA present a downward opening bell shape and are same as that obtained by TGM. Combing with Table 1, when survival probability is 97.5%, the comparison of slope and intercept for P-S-N curve based on the ISIA and TGM are shown as Table 2.

Table 2. Comparison of the S-N curve parameters calculated by the methods Parameters Methods intercept

Small-scaled specimens 、 P 97.5%

Full-scale-axle 、 P 97.5%

slope

intercept

slope

TGM ISIA

2.868 2.871

-0.0539 -0.0553 2.532%

2.962 2.965

-0.0852 -0.0866

Relative error 1.617% As shown in Table 2, the relative error for intercept is less than 3% and the intercept does not exceed 1%. Therefore, the correctness and reliability of the ISIA for processing the ( X-x-x-x ) data are fully proved. According to Eq. (6), Fig. 2 and Fig. 3 , the fatigue life of full-scale axle for the BSIM is 1.82×10 16 km and for the TGM is 9.26×10 15 km, but the life for the ISIA is 4.7×10 14 km, which is about 5% of TGM and 2% of the BSIM. Obviously, the prediction results of the ISIA are more reliable. 3.2. ( x-x-x-x ) type test program To verify the validity of the ISIA for this kind of test data, the calculation results are shown in Table 3. Comparing the ISIA with TCM or the BSIM, the P-S-N curves for small-sized specimens and full-scales axle are obtained as shown in Fig. 4 . During fitting the P-S-N curve, the TCM treats the STD as the constant value and the P - S-N curves are parallel to each other as shown in Fig. 4 (a). Obviously, the treatment of TCM is unreasonable. 0.104% 0.101%

Table 3. Fatigue life data of EA4T steel

ISIA

BSIM

S j (MPa)

Number

m j

N ji

μ ISIA 5.45 5.72 6.01 6.32

σ ISIA

μ BSIM 5.45 5.72 6.01 6.32

σ BSIM 0.32 0.38 0.44 0.50

1 2 3 4

450 425 400 375

5

5.503, 5.402 5.698, 5.802 6.0845, 5.936

0.039 0.0.61 0.084 0.106

10 10

7

6.307, 6.272, 6.329