# Failure Mechanism and Structural Analysis of Chain Slings with Non-Standard Connections
## 1 Introduction
[13] conducted fatigue analyses that considered both out-of-plane bending (OPB) and in-plane bending (IPB), allowing for a quantitative assessment of fatigue damage. [PERSON] et al. [14] developed a reliability-based fatigue damage prediction model based on S-N curves that includes degradation effects from mean load and corrosion, enabling quantitative assessment of the fatigue failure probability of mooring chains. [PERSON] et al. [15] experimentally evaluated the low-cycle fatigue behavior of mooring chains made from R4 high-strength steel under varying strain amplitudes and strain ratios, and elucidated the fatigue damage accumulation mechanisms using strain energy-based damage indicators. [PERSON] et al. [16] experimentally evaluated the effects of natural corrosion on fatigue crack growth and remaining fatigue life of mooring chain steel, revealing that corrosion does not significantly impact fatigue life. [PERSON] et al. [17] applied crack growth modeling to assess the remaining fatigue life of corroded mooring chains and quantitatively analyzed the impact of corrosion on fatigue life. [PERSON] et al. [18] analyzed S-N data for new and corroded mooring chains under various mean load conditions to evaluate the effects of mean load and corrosion level on the fatigue life of mooring chains. [PERSON] et al. [19] conducted chemical and fractographic analyses on failed chains, identifying coarse carbides as a primary failure cause, and used finite element analysis (FEA) to predict stress concentration sites and fatigue life. [PERSON] et al. [20] evaluated the effects of fatigue, corrosion, and loading conditions on chain performance through fatigue testing of mooring chains. Several other studies have examined the stress distribution and mechanical properties of chains depending on their configuration and fastening conditions. [PERSON] et al. [21] used neutron diffraction and hole drilling methods to measure residual stresses in mooring chains, validating stress redistribution under corrosion and cyclic loading through FEA. [PERSON] et al. [22] used nonlinear FEA to analyze the structural strength of steel chains in contact with knuckle-type plates, suggesting the need for optimal designs that account for stress mitigation, material properties, and angular conditions. [PERSON] et al. [23] investigated how installation conditions influence stress distribution, showing that improper installation can lead to localized stress concentrations and eventual failure. [PERSON] et al. [24] applied finite element analysis (FEA) to simulate crack initiation and growth in mooring chains for offshore structures and evaluated the potential of combining ultrasonic guided waves (UGW) and acoustic emission (AE) techniques for damage detection and localization. [PERSON] et al. [25] analyzed the microstructure and mechanical properties of chain steels subjected to tempering at various temperatures. Failure case studies have also been conducted to identify root causes and support design improvements. [PERSON] et al. [26] investigated permanent mooring system failures, revealing the structural weaknesses of components and unexpected failure mechanisms, and highlighting the limitations of existing design criteria and the need to improve integrity management. [PERSON] et al. [27] evaluated the feasibility of detecting, locating, and monitoring corrosion-fatigue damage in studless R4 mooring chains operated offshore for about 20 years using non-contact underwater acoustic emission (AE) technology. Furthermore, research has actively addressed safety policies related to slinginging operations and improvements in chain design. [PERSON] et al. [28] compared domestic and international regulations to enhance the safety of lifting chain slings used in industry and proposed improvements based on accident case studies. [PERSON] et al. [29] emphasized the need for certification systems for rigging and slinging operations to reduce falling object accidents on construction sites. [PERSON] et al.