# Failure Mechanism and Structural Analysis of Chain Slings with Non-Standard Connections
## 4 Structural Analysis
### Analysis Results  
The analysis results of Case 1 are presented in Figure 18. When the tensile elongation reaches 50.042 mm, the maximum stress is 1150.5 MPa, and fracture occurs. The corresponding maximum tensile load (or fracture load) is 62,300 N. Although this shows a relatively large error of approximately 17.73% compared to the actual fracture load of the product (73,351 N), the deviation is only 0.77% when compared with the fracture load value of 62,784 N specified in the material certificate, indicating a very close correlation. However, as noted in Section 4.1, the material properties of the chain used in the actual test could not be precisely identified. Therefore, rather than comparing absolute values with the actual product, this study focuses on comparing the relative behavior across the different cases. The analysis results of Case 2 are shown in Figure 19. When the tensile elongation reaches 25.453 mm, the maximum stress is 1125 MPa, and fracture occurs. The maximum tensile load at this point is 46,800 N. Compared to the standard product in Case 1, the aged chain failed at approximately 75.12% of the tensile load capacity of the new product. This can be attributed to the reduction in effective cross-sectional area caused by a decrease in chain diameter and an increase in pitch, which significantly intensified the tensile stress and thereby led to earlier yielding and fracture behavior. In other words, the reduction in the chain's diameter caused stress concentration under loading, which--as described by the Johnson-Cook model--results in rapid accumulation of plastic strain, leading to premature fracture. As expected, the initial fracture occurred in the A-(r)section of Chain A, where the diameter reduction and pitch increase were the most severe. The analysis results of Case 3 are presented in Figure 20. In this case, a standard connection method was applied, in which an intermediate link (coupling link) and a master link were used together in the chain slip configuration. This is the most commonly used connection method in industrial settings and is designed to ensure that the load is evenly distributed throughout the entire chain slip. It is characterized by high reliability in actual lifting and securing operations, while minimizing the occurrence of abnormal stresses such as chain twisting or bending. According to the analysis, when the tensile elongation reached 50.037 mm, the maximum stress in the chain rose to approximately 1156.1 MPa, at which point fracture occurred in the entire chain slip system. The maximum tensile load applied at the moment of failure was approximately 124,500 N, which aligns with the theoretical expectation that a two-leg configuration can support nearly twice the load of a single-leg configuration. In fact, in  
Figure 18: Analysis results of case 1: (**a**) Total deformation (displacement); (**b**) Equivalent stress. Case 1, where a single chain of the same specification was used, the fracture load was approximately 62,800 N, and the failure in Case 3 occurred at about 1.98 times that load. The structural advantages of the connection method using intermediate and master links can be summarized as follows:  
First, the chain's connecting parts form a symmetrical structure, and the load is evenly distributed in the vertical direction relative to the tensile axis, preventing stress concentration from occurring locally on the chain. Second, the indirect connection through the master link reduces friction and torsional stress between the chains, thereby restricting free deformation of the chains and increasing the overall stiffness of the system. Third, this type of connection is recommended by international standards such as ISO 16872 and EN 818-4 [36; 37], and is also suggested in industrial safety guidelines as a connection method that minimizes deformation and fatigue accumulation due to repeated use. Figure 19: Analysis results of case 2: (**a**) Total deformation (displacement); (**b**) Equivalent stress.