# Failure Mechanism and Structural Analysis of Chain Slings with Non-Standard Connections
## 4 Structural Analysis  
### Analysis Model and Boundary Conditions  
In this study, a structural analysis was conducted to compare and evaluate the stress distribution and failure behavior under two different loading scenarios: (1) axial tensile loading in a single-leg sling configuration, and (2) combined loading due to bending when the chain sling is directly connected to an eye bolt. The analysis focused on both a standardized chain and an aged, field-failed chain (Chain A). According to the KS B 2818  
Figure 11: Deformed and fractured eyebolt. standard (see Table 1), a nominal chain with a diameter of 7.1 mm was modeled as the reference, while the damaged chain (Chain A) used in the actual accident (see Table 2) was also modeled. A total of five cases were configured for simulation. Cases 1 and 2 represent single-leg sling configurations. Case 1 consists entirely of standardized chain elements, whereas Case 2 incorporates both standardized chains and the field-measured geometry of Chain A. This was done to investigate how differences in chain length or reduced diameter affect failure characteristics depending on the assembly conditions. For both cases, only five chain links were modeled to improve computational efficiency. Cases 3 through 5 represent double-leg sling configurations, all based on standardized chain elements. Among these, Case 3 models a standard connection using a master link, while Cases 4 and 5 simulate non-standard configurations in which the chain sling is looped directly around an M30 eye bolt. To analyze the influence of the chain's contact orientation with the eye bolt on stress distribution and failure patterns, Case 4 assumes that both legs of the chain share the load simultaneously, while Case 5 assumes that only one leg bears the load. For simplification, the analysis domain in Cases 4 and 5 was limited to the contact region between the chain and the eye bolt, consisting of nine chain links. For all cases, the boundary conditions were defined by fixing one end of the chain slip while applying a gradually increasing tensile load to the opposite end. The maximum tensile loads applied were 70,000 N for Cases 1 and 2, and 150,000 N for Cases 3 through 5. The analysis evaluated the variations in stress and deformation as the load increased, as well as the maximum elongation length immediately prior to failure. Detailed analysis parameters are summarized in Table 7 and illustrated in Figures 12-14. In this analysis, a coefficient of friction of 0.3 was applied to define the contact conditions. This value represents a moderate level of resistance to sliding and was selected to ensure numerical stability and convergence during the simulation. Although the coefficient of friction between steel surfaces in dry conditions is typically around 0.4, the value was conservatively limited to 0.3 in order to avoid excessive computation time and divergence issues commonly encountered in nonlinear contact analysis. Unlike bonded contact, where the state of contact pairs remains fixed throughout the analysis, frictional contact exhibits true nonlinear behavior due to its sensitivity to displacement-dependent stiffness changes. This allows for a more realistic simulation of physical phenomena such as sliding, sticking, and separation between contact surfaces. In addition, all chains were modeled as flexible bodies rather than rigid bodies. This modeling approach enables a more accurate representation of structural responses, allowing for local deformation, global displacement, contact reaction forces, and material nonlinearity under external loads and contact interactions. The use of flexible body modeling is particularly suitable for simulating the actual behavior of chains under increasing load conditions, including continuous deformation, inter-chain sliding, stress concentration at contact points, and eventual fracture. Therefore, incorporating flexible body definitions along with nonlinear material models and contact conditions is essential for evaluating potential failure in chain systems.