关键词: 大直径盾构, 刀盘, 焊缝抗疲劳设计, 等效结构应力, 主S-N曲线

Abstract:  The fatigue resistance of field welds on the cutterhead of super-large-diameter shields is critical for shield tunneling. In this study, a finite element model of a super-thick steel butt joint, including the weld details, is established, with the weld stress concentrated into the toe stress and core parameter representing the equivalent structural stress. The multi-axis fatigue life of a joint with different groove angles and residual heights is then calculated to determine the influence of the groove angle and residual height on the fatigue life of super-thick plate welds. Finally, a sub-model, including a local fine mesh of welds, is established using sub-model technology based on the optimal dimension parameters of the welds. The fatigue lives of the welds installed by the cutterhead are comprehensively evaluated using an equivalent structural stress method. The results are summarized as follows. (1) The fatigue resistance initially increases and then decreases with increasing weld groove angle, and a groove angle of approximately 55° is the optimum for designing symmetrical X-shaped joints. (2) When the joint adopts an asymmetric X-groove, the fatigue life of the toe at the small end of the weld is lower than that at the big end of the same groove angle, and the fatigue resistance of the asymmetric X-groove joint can be improved by selecting 40° and 55° at the big and small ends, respectively. (3) The influence of the weld residual height on the fatigue performance of the joint is not as significant as that of the groove angle. The residual height of the symmetrical and asymmetric X-groove welds at the big end is 2－3 mm, and the residual height of the asymmetric X-groove at the small end is 1 mm, which meets the anti-fatigue design requirements of the shield cutterhead.

Key words: large-diameter shield, cutterhead, anti-fatigue design of field welds, equivalent structural stress, principal S-N curve