Fatigue S-N curve of corroded steel wires based on fracture mechanics
High-strength cold-drawn steel wire is widely used in cable load-bearing structures due to its excellent performance,but the corrosion and fracture of steel wire pose a threat to the structure safety in service. Pitting corrosion on the wire surface can lead to fatigue cracks due to stress concentration effects. Therefore,the residual life of corroded steel wire depends mainly on the crack propagation stage,and crack growth is significantly influenced by the corrosion degree (initial damage). Accurate characterization of the corrosion degree and precise assessment of the remaining life of corroded steel wire remain a challenge in maintenance. In this study,the maximum depth of corrosion pit was used to represent the corrosion degree,and the stress intensity factor range was used as the driving force indicator for crack propagation of the tensile steel wire. A theoretical model for crack propagation was established using the Paris equation based on fracture mechanics,from which the fatigue S-N curve of tensile corroded steel wire was derived. Extensive comparisons between the results of numerous corrosion wire fatigue tests and the theoretical predictions can validate the rationality and effectiveness of the proposed theoretical model and the S-N curve. Finite element simulations of crack propagation in steel wire with multiple corrosion pits demonstrate that an equivalent single crack can be used for simplified analysis of the fatigue life of steel wire with corrosion pits. Finally,parameter analysis indicated that pit depth and corrosion environment were key influencing factors on the fatigue strength of corroded steel wire,while stress ratio and fatigue loading frequency had minor effects. The proposed S-N curve can remain applicable for evaluating the remaining life of corroded steel wire under normal service conditions and yields reasonable predictive results. The theoretical approach based on fracture mechanics and the fatigue S-N curve presented here can serve as a reference for assessing the fatigue strength and residual life of corroded steel wires.
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