# Failure Mechanism and Structural Analysis of Chain Slings with Non-Standard Connections
## 6 Conclusions  
This study investigated the root causes of chain failure accidents and established technical measures for prevention by reviewing relevant regulations and technical standards, conducting visual and dimensional inspections, performing actual fracture tests, and carrying out structural analyses. In particular, the mechanical behavior differences between standard fastening methods (using intermediate and master links) and non-standard fastening methods (directly wrapping around eyebolds) were quantitatively analyzed. Five structural analysis cases were established, and for each case, the maximum tensile load and stress distribution were compared. 1. Dimensional measurements of the chain slings revealed that in some cases, the wire diameter had decreased by more than 10%, or the pitch had increased by more than 5%, compared to standard values. In particular, the diameter of Chain A-3 had decreased by approximately 15% to 6.03 mm compared to the standard 7.1 mm, exceeding the discard criteria. This indicates that plastic deformation and elongation occurred during repeated use, highlighting the necessity of dimensional inspections and immediate disposal of non-compliant products before use. 2. The fracture test results showed that the aged Chain A failed at 3970 kgf during the second test--only about 62% of the standard fracture load of 6400 kgf. Chain B also failed at 6242 kgf, falling below the standard. These results demonstrate that external and dimensional degradation directly leads to reduced strength, emphasizing the importance of strictly enforcing discard criteria. 3. Clear differences emerged based on the fastening method. When the new chain was used in a single-leg configuration, the fracture load was 7477 kgf. In contrast, when configured as a two-leg sling using a non-standard method, the fracture load was 12,529 kgf--only 83.8% of the theoretical value of 14,954 kgf. This reduction is attributed to the combined bending and torsional loads applied to the chain wrapped around the eyebolt. Notably, in the four-leg sling configuration (theoretically 25,600 kgf), failure occurred at just 5260 kgf, indicating a severe reduction in strength. 4. Structural analysis showed that Case 3 (standard fastening) allowed the load to be evenly distributed throughout the chain, with a maximum stress of approximately 1156 MPa and a maximum tensile load of about 124,500 N. This aligns with the chain's design strength, and fracture occurred in a region with appropriate stress distribution rather than at the joints. In contrast, in Cases 4 and 5 (non-standard fastening), the chain was directly wrapped around the eyebolt, resulting in combined bending and compressive loads. The maximum stresses reached approximately 1179 MPa and 1213 MPa, while the maximum tensile loads were reduced to 106,500 N and 105,000 N, respectively--more than a 15% decrease. The failure points were located near the eyebolt contact area, clearly indicating nonlinear stress concentration and structural weakness. 5. This performance degradation was caused by the complex loading conditions--local bending, compressive stress, and contact friction--arising from wrapping the chain around the curved surface of the eyebolt. These conditions are consistent with the local plastic deformation and stress concentration predicted by the Johnson-Cook damage accumulation model. In particular, the non-standard fastening method distorts the chain's intended load path, significantly reducing structural strength and increasing the likelihood of unexpected failures. 6. This study structurally validated the fastening methods prescribed by international standards such as DIN EN 818-4 and ISO 3056 (using shackles or master links), and quantitatively analyzed the impact of non-standard fastening methods on chain strength and service life, making it a meaningful practical case. 7. The findings provide the following practical implications: * Standard fastening methods (using auxiliary connectors) must always be followed.