# Research on TBM Cutterhead Crack Damage and Fatigue Reliability
###### Abstract  
The cutterhead of a tunnel-boring machine (TBM) is the main weighted part in the process of tunneling and bears loadings in different directions. A fatigue failure of a cutterhead would severely affect the construction progress and safety. Therefore, it is of great importance to study the fatigue reliability of its cracks. In this study, the area of the cutterhead with a higher stress was found using static strength analysis and we analyzed the dynamic stress characteristics. In addition, the stress intensity factor of a cutterhead crack was calculated using the submodeling technique, and the crack propagation mechanism and damage characteristics of a cutterhead crack were also analyzed. Then, combined with crack fatigue theory, we proposed a fatigue reliability evaluation method based on the Joint Committee on Structure Safety method (known as the JC method), and the effects of different factors on the reliability were discussed for different geological conditions. The results show that the crack propagation was of the open and tear types in the deepest part of the crack tip, but there are three kinds of propagation modes at both ends. As the initial crack depth increased, the fatigue reliability of the cutterhead decreased significantly. The reliability was positively correlated with the crack shape ratio. However, there were no significant relationships between the reliability and the depth of the critical crack.  
TBM cutterhead; crack propagation mechanism; fatigue reliability model; JC method 2021111. 1211. 11. 1211. 11. 1211. 11.  
a prediction method for the TBM cutterhead dynamic tunneling performance based on the CSM (Colorado School of Mines) model. By considering the translational velocity and angular velocity characteristics, [PERSON] et al. [21] proposed a method for the dynamic performance evaluation of a TBM cutterhead. In addition, many scholars used machine learning models to predict TBM performances [22; 23; 24; 25]. To calculate the cutterhead crack propagation life, [PERSON] et al. [26] used the finite element method to calculate the dynamic stress of the cutterhead and calculated the crack initiation life of the cutterhead using rainflow-counting combined with the S-N curve. [PERSON] et al. [27] studied the stress intensity factor of a TBM cutterhead crack and proposed a method to calculate the crack propagation life combined with the eight-level load spectrums of a cutterhead. Despite many studies on TBMs, there has been little research regarding the cutterhead crack damage mechanism and fatigue reliability.  
Considering the current state of the art described above, first, we calculated the stress intensity factor of the cutterhead crack by applying submodeling technology and investigated the crack damage characteristics. Second, we constructed a TBM cutterhead crack fatigue reliability evaluation model based on the basic crack fatigue theory, selecting the crack fatigue life as the basic variable. The reliability of a cutterhead under load in several geological conditions were solved using the Joint Committee on Structure Safety method (known as the JC method). Finally, we discussed the influence of different random variables on the reliability of a cutterhead. The overall flowchart is shown in Figure 1.