###### Abstract
[14] used the XFEM to study the tensile, fracture, and fatigue properties of the Ti6 Al4V alloy, simulated the crack propagation process, and analyzed the fatigue life of the samples with a central crack and a double-face crack. [PERSON] et al. [15] benchmarked the XFEM and the boundary element method (BEM), giving close results, with the latter using less computational power. CZM is a phenomenological model that avoids the stress singularity of a crack tip in linear elastic fracture mechanics (LEFM) and predicts the failure behavior of materials by calculating the stress and fracture energy during the cracking process. [PERSON] et al. [16] simulated the multi-crack behavior of ultra-high-performance fiber-reinforced concrete (UHPFRC) by using CZM. The cracks of mortar of structural members were simulated by using a discrete cohesive crack model, which was realized by using a six-node three-dimensional cohesive interface element in ABAQUS. The VCCT has the advantages of no special treatment for the crack tip element and a low requirement for mesh size, and it can clearly separate the crack of mixed mode. [PERSON] and [PERSON] [17] proposed an algorithm based on VCCT to predict the three-dimensional fatigue delamination behavior of laminated composites, which was called Sequential Static Fatigue (SSF). A concrete example was used to simulate the fatigue expansion process of lamination defects in laminated composites. Compared with the direct cycle (DC) algorithm based on ABAQUS, it has higher calculation accuracy and efficiency. There are several modern finite element simulation tools for fatigue crack propagation problems, including ANSYS, ABAQUS, FRANC3D, etc. Relevant models and technical methods have been added to these simulation software; therefore, researchers can efficiently perform FCGR analysis [18; 19; 20; 21; 22]. Three primary methods have been widely applied to analyze material fatigue life: the fracture mechanics method developed by [PERSON] and [PERSON] [23], the strain-life method introduced by [PERSON] [24], and the stress-life method proposed by [PERSON] [25]. In this study, the fracture mechanics approach is utilized to predict fatigue life, allowing for the detailed characterization of the crack tip using stress intensity factor \(K\). Under typical conditions, the stress intensity factor range \(\Delta K\) is dependent on the crack configuration in addition to applied stress range \(\Delta\sigma\) and crack size \(a\):  
\[\Delta K=Y\times\Delta\sigma\times\sqrt{\pi a} \tag{1}\]  
where \(Y\) is the crack configuration factor, which takes into account variables such as crack shape, location, and specimen geometry. The jacket material for ITER is JK2 LB, and FCGR analysis [26] has been conducted on this jacket under the principal stress that is caused by the electromagnetic force generated in one cycle plasma operation of ITER using a single-jacket model. FCGR tests [27] indicate that the JK2 LB material exhibits significantly lower crack growth rates compared to the Cefival 316 LN jacket material. Additionally, the fracture toughness of the JK2 LB material is approximately 35% lower than that of the Cefival 316 LN jacket material. FCGR data for the Nitronic\({}^{\otimes}\) 50, JK2 LB, and 316 LN stainless steels have been compiled into one study [28] for a comparison, and N50 in particular contains several significant outliers that warrant further investigation. Firstly, this paper introduces the key parameters of the device as well as the research and development progress of the jacket. Then, the combination of FEM and the maximum likelihood estimation method (MLEM) [29] is used to evaluate the maximum tolerance threshold for initial defects in the fusion CS magnet jacket. To achieve a more precise characterization of the dependence of the stress intensity factor range \(\Delta K\) on jacket defect depth \(a\), a full model incorporating 12 coils is utilized under the actual cyclic loads.