# Failure Mechanism and Structural Analysis of Chain Slings with Non-Standard Connections
## 3 Failure Cause Analysis
### Experimental Evaluation of Chain Fracture  
As summarized in Table 3, the supplier's test certificate for the chain specifies a Safe Working Load (S.W.L) of 1600 kgf, a Proof Load of 3200 kgf, and a Breaking Load of 6400 kgf. Based on these values, the maximum Safety Factor is indicated as 4. To verify whether the chain meets the specifications stated in the manufacturer's certificate and to assess the extent of strength degradation in the failed chain sling, a Breaking Load Test was conducted  
The breaking load tests were conducted on both the failed chain slings and new chain slings of the same specification, with two test repetitions performed for each case. The new chain slings were tested in two configurations: a single-leg lifting setup and a double-leg setup in which the chains were directly wrapped around and connected to the eye bolts. The test results are summarized in Table 4, and Figures 8-10 present the respective test reports for Chain A, Chain B, and the new chain. The results for Chain A showed that in the first test, the breaking load was measured at 7370 kgf, approximately 1.15 times higher than the reference breaking load of 6400 kgf. However, in the second test, the breaking load was only 3970 kgf, which is about 62% of the standard value, indicating a significant reduction in durability. For Chain B, the first test yielded a breaking load of 7585 kgf (1.18 times the standard), while the second test result was 6242 kgf, or approximately 97% of the standard breaking load. Although Chain B demonstrated higher breaking strength than Chain A, the fact that one result fell below the reference value suggests that deformation or aging may have already progressed. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & & **Slinging Method** & **Breaking Load** \\ \hline \multirow{2}{*}{Chain A} & 1 & 1-Leg & 7307.09 kgf (71,683 N) \\  & 2 & 1-Leg & 3970.08 kgf (38,946 N) \\ \hline \multirow{2}{*}{Chain B} & 1 & 1-Leg & 7585.83 kgf (74,471 N) \\  & 2 & 1-Leg & 6242.52 kgf (61,239 N) \\ \hline \multirow{2}{*}{New Chain Sling} & 1 & 1-Leg & 7477.17 kgf (73,351 N) \\  & 2 & 2-Leg 1 & 12,529.13 kgf (122,911 N) \\ \hline \hline \end{tabular}  
* The chain is directly connected to the eyebolt (without an intermediate link).  
\end{table} 
Table 4: Breaking load testing results. \begin{table}
\begin{tabular}{c c c} \hline \hline
**S.W.L** & **Proof Load** & **Breaking Load** \\ \hline
1600 kgf & 3200 kgf & 6400 kgf \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Material test certificate provided by the chain supplier. In the single-leg test of the new chain, the breaking load was measured at 7477 kgf, which corresponds to 1.17 times the reference value. Theoretically, the double-leg configuration should yield a breaking load of approximately 14,954 kgf--twice that of the single-leg test. However, the actual measured value was 12,529 kgf, only 1.67 times higher. This reduction in strength is interpreted as a result of the chain being wrapped around eye bolts and hooks, which introduces not only tensile loads but also bending and torsional stresses. These additional stresses contribute to the degradation of the chain's overall durability performance. Meanwhile, at the accident site, a dual-leg sling configuration was applied to both Chain A and Chain B, resulting in a total of four legs supporting the load. Theoretically, given that the rated breaking load per single leg is 6400 kgf, the four-leg configuration should have been capable of withstanding a total breaking load of 25,600 kgf (6400 \(\times\) 4). However, in practice, chain failure occurred under a load of only 5260 kgf. This discrepancy  
Figure 8: Breaking load test reports: (**a**) Test result of chain A-1; (**b**) Test result of chain A-2. Figure 9: Breaking load test reports: (**a**) Test result of chain B-1; (**b**) Test result of chain B-2. is believed to be due not only to the degradation of the chains' durability caused by aging, but also to the uneven distribution of the load among the four chains.