# Failure Mechanism and Structural Analysis of Chain Slings with Non-Standard Connections
## 4 Structural Analysis
### Analysis Results
Figure 20: Analysis results of case 3: (**a**) Total deformation (displacement); (**b**) Equivalent stress. The analysis results of Case 4 are shown in Figure 21. In this case, a non-standard connection method was applied in which the chain sling was directly wrapped around an M30 eyebolt, and the mechanical behavior of the chain under tensile loading was quantitatively evaluated. Initially, Chain 1 is in contact with the eye bolt and supports the applied load. As the load gradually increases, excessive force causes deformation in Chain 1, and relative sliding between the chains leads Chains 2 and 3 to come into contact with the eye bolt as well. When the load exceeds approximately 780,000 N, all three chains (Chains 1 to 3) begin to share the load, and bending deformation also occurs in Chains 2 and 3. However, since Chain(1)has been supporting the load from the beginning, it accumulates significant stress and deformation over time, ultimately leading to its failure before the others. According to the analysis, when the tensile elongation reached approximately 41.505 mm, the maximum stress in the chain rose to about 1178.9 MPa, immediately followed by fracture. The maximum tensile load applied at that moment was measured to be 106,500 N.  
This value is approximately 85.54% of the maximum tensile load observed in Case 3 (124,500 N), where the standard connection method was used. This result indicates that even with chains of the same specification, the mechanical strength can vary significantly depending on the connection method. In the non-standard method, the chain is directly wrapped around the eyebolt, causing the chain links to experience not only tensile force but also additional bending and compressive loads. Especially when the chain is wrapped over the curved surface of the eyebolt, the curvature of the chain is constrained, and at the contact region, radial compressive stress and localized bending stress are induced. This leads to much higher stress concentration than in a case of pure tensile loading and acts as a major factor promoting structural damage and fatigue crack initiation. Such a nonlinear stress distribution, as also explained by the Johnson-Cook cumulative damage model, creates conditions where plastic strain rapidly accumulates in specific regions of the chain, making crack initiation more likely. In the present analysis, abnormal stress concentration occurred near the chain's contact area, and accordingly, the fracture also took place in that vicinity. This implies that the non-standard connection method alters the intended load transfer path of the chain, thereby reducing the overall structural stability. The analysis results of Case 5 are presented in Figure 22. This case also applied a non-standard connection method, in which the chain was directly wrapped around an eyebolt. Figure 21: Analysis results of case 4: (**a**) Total deformation (displacement); (**b**) Equivalent stress; (**c**) Contact location between the chains and the eye bolt (After the applied load exceeds 780,000 N). However, unlike Case 4, both legs of the chain were configured to support the load symmetrically after being wrapped around the eyebolt. This setup was intended to simulate a scenario commonly observed in the field, where chains are wrapped in a symmetrical fashion, and to analyze the influence of contact direction on the structural response. In Case 5, Chains 1 and 1 are in direct contact with the eye bolt. Unlike Case 4, however, there is no change in the contact location as the load increases. This means that Chains 1 and 1 carry the entire load until failure occurs. Chains 1 and 1 are subjected to direct tensile loading, while also experiencing bending deformation due to contact with the eye bolt. In contrast, Chain 1 is not part of the direct load path, but tensile and bending deformation are induced indirectly as a result of the tensile forces acting through Chains 1 and 1.