PSI - Issue 13

Wei Song et al. / Procedia Structural Integrity 13 (2018) 2227–2232 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

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3.3 Low and high cycle fatigue life of CLWJ The low cycle fatigue life of CLWJ from the weld toe and root failure is shown in Fig. 6. These test data was fitted by linear relationship. Since geometric variations (penetration length) in CLWJ change the quasi-static and cycle loading capacity, the fatigue life are also influenced by specimens geometry. Fig. 7(a) gives the comparison of low cycle fatigue life between weld toe and weld root failure including the material mismatch effect. It shows that the fatigue life of weld toe failure is higher than weld root failure based on the nominal strain range-N curves. With the increases of nominal strain loading, the fatigue life reflects increasing difference due to material heterogeneity. Thus, the material mechanical mismatch are more obvious with lower cycle fatigue failure of CLWJ.

Fig. 6. Fatigue life of CLWJ failure from weld toe and weld root. (a) weld toe failure; (b) weld root failure

Fig. 7. Comparison of low (a) and high (b) cycle fatigue life against nominal strain/stress range between weld toe and weld root failure.

Fig. 7(b) compared the high cycle fatigue life of weld toe and root failure in CLWJ. Meanwhile, fatigue test results were compared with the corresponding geometrical FAT class in IIW S-N curves. The design curve for high cycle (N f >10 4 ) weld toe fatigue failure in CLWJ is equivalent to FAT 63 with a slope of m=3. For the weld root failure in LCWJ, the corresponding fatigue class is FAT36 with the same slope of weld toe failure. In the high cycle fatigue regime, the fatigue life of weld root failure is lower than the weld toe failure obviously. However, the FAT 160 with a slope of 5 in IIW recommendation can be employed to assess the low cycle fatigue of LCWJ. It is observed that the test data are above the mean IIW S-N curves either high cycle fatigue regime or low cycle fatigue regime in Fig. 8(a). It should be noted that the fatigue weld toe failure FAT class in low cycle fatigue is effective to assess the weld root failure of CLWJ. The estimated equations of effective notch strain for weld root failure can be obtained from the reference of K. Saiprasertkit (2012). The weld root fatigue data extracted from the fatigue tests