## 1 Introduction  
Due to the coupling effect of corrosive medium and fatigue load during bridge service, corrosion defects tend to appear on the surface of high-strength steel wire used in bridge cables. Studies have shown that defect morphology on steel wire surface under chloride erosion is mainly dominated by uniform corrosion and pit corrosion. The micro-cracks are formed by the continuous evolution of the corrosion pits, and the continuous crack propagation eventually leads to the fracture failure of the wire. In recent years, there have been a number of safety accidents caused by cable fracture, resulting in huge casualties and property losses. Therefore, it is necessary to study the laws of fatigue crack initiation and propagation of cable wire and evaluate the service life of the wire and the whole bridge. At present, some achievements have been made by domestic and foreign scholars in the research of mechanical behavior and fatigue property of corroded steel wire. [PERSON] [1] studied the tensile properties of corroded steel wire and found that the elongation of steel wire was greatly affected by corrosion. [PERSON] [2] pointed out that the influence of corrosion on the elastic modulus and ultimate strength of steel wire was not significant, but the ductility of steel wire would decline due to corrosion pits. [PERSON] [3] analyzed the fracture toughness of the cable wire. [PERSON] [4] made an in-depth study on the initiation process and threshold value of steel wire surface cracks. [PERSON] [5] studied the crack propagation behavior and section morphology characteristics of the surface cracks of the circular section specimen of 45# Steel under cyclic tensile loading. The results show that there is an obvious relationship between the crack propagation morphology and the initial prefabricated crack depth under uniaxial cyclic tensile load, and the influence of the initial crack depth on the crack morphology gradually weakens with the cracks gradually extending. [PERSON] [6] studied the initiation and propagation of the scythe-shaped surface cracks of the circular section specimen under cyclic tensile and bending loads. [PERSON] [7] carried out experimental studies on the propagation of semi-elliptic surface cracks. [PERSON] et al. [8; 9] compared the mechanical properties of the indented wire and the corroded steel wire and concluded that the notch shape was the main factor to reduce the fatigue strength of steel wire. [PERSON] [10] conducted a fatigue property test on the corroded high-strength steel wire used in arch bridge derricks, and pointed out that the fatigue property of the steel wire was first sensitive and then insensitive to the degree of corrosion. [PERSON] [11] carried out static tensile, fatigue and torsion tests on the steel wire respectively, and obtained the S-N curve of the steel wire. [PERSON] [12; 13] studied the influence of the geometric shape and crack size of the leading edge of fatigue crack propagation on the crack propagation in stay-cables. [PERSON] [14] investigated the damage evolution process and corrosion fatigue performance and predicted the service life of steel wire with machine-cut notch via experiments and numerical simulation. At present, the fatigue crack propagation tests of high-strength steel are mainly aimed at the base material or intact wire specimen, that is, high-strength steel is processed into the standard specimen specified in the specification for testing. It is rare to carry out crack propagation test on high-strength wire with initial defects. Because the diameter of steel wire is relatively small, and the cracks along the depth direction are not easy to measure, it is difficult to study the fracture morphology and crack propagation rate of steel wire.