Three-dimensional fatigue crack initiation and propagation behavior of stress-corroded steel wires for bridge cables

The fatigue test was carried out to investigate the fracture morphology and fatigue life of stress-corroded steel wires. The influence of stress corrosion degree on the initial value of crack propagation and fracture toughness of steel wires was explored. The theoretical method of crack initiation and propagation life of corroded steel wires based on CM-EIFS (Corrosion Modified Equivalent Initial Flaw Size) model was proposed. Finally, the variation law of crack tip stress was studied through the numerical method considering the corrosion surface, and the general expression of shape factor of crack tip and the reduction factor of fracture toughness of corroded steel wires were given. The results showed that the fatigue life of steel wires had a good nonlinear decrease trend with the stress corrosion degree increase. The crack initiation is often located in the surface corrosion pit, and the initiation zone was related to the intermetallic compound containing Fe and Mn. It was necessary to consider the reduction of fracture toughness for steel wires with high degree of stress corrosion. When the stress corrosion degree reached 24 %, the fracture toughness of steel wire was only 50.86 MPa·m^0.5, which was 52 % lower than that of the non-corrosion ones. The higher the stress corrosion degree and stress concentration factor, the lower the proportion of crack initiation life. When the stress concentration reached a certain degree, the total fatigue life was mainly composed of crack propagation life. The depth-width ratio of corrosion pit and the residual thickness of corroded steel wires were the key factors affecting the stress intensity factor at the crack tip. The three-dimensional crack propagation results obtained by XFEM (Extended Finite Element Method) based on the corrosion surface were highly consistent with the test results.