## 7 Conclusions  
In this paper, the corrosion fatigue performance of bridge wire with initial defects was studied. To simplify the initiation process of pitting pits caused by electrochemical inhomogeneity, machine-cut notches are used to be equal to the corrosion pits. The influence of the action mode of corrosion and fatigue, the concentration of corrosive solution and pH value, the shape and dimension of machine-cut notch on the fatigue life of steel wire with the initial defect was explored, and the S-N curves of steel wire subjected to the corrosive solution and fatigue load were obtained. The main conclusions are as follows:  
(1) The test device designed in this paper can effectively realize the synchronous pulsation fatigue loading, and simultaneously apply different fatigue stress ranges to multiple steel wires, which greatly reduces the test time;  
(2) With the increase of the fatigue stress range, the life of steel wire decreases significantly. Under the coupling action of CF, the life of steel wire with an initial defect is significantly lower than that only subjected to fatigue loads.  
(3) Under the coupling action of CF, the life of steel wire decreases with the increase of acidity. When the stress range is equal to 360 MPa, the life of wire subjected to NaCl with a pH of 7 and a concentration of 0.5 wt% is 16% shorter than that of wire without corrosion, while that subjected to NaCl with a pH of 3 and a concentration of 0.5 wt% is reduced by 36%. However, the life of steel wire  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Stress Range** & \multicolumn{3}{c}{**Cyclic Numbers**} \\
**/MPa** & **Semi-Ellipsoidal Notch** & **Trapezoid Notch** & **V-Notch** \\ \hline
720 & 3531 & 1688 & 1628 \\
600 & 5769 & 4656 & 4388 \\
480 & 10,881 & 8416 & 6483 \\
360 & 34,835 & 22,472 & 15,589 \\ \hline \hline \end{tabular}
\end{table}
Table 7: The life of steel wire with machine-cut notches of different shapes.  
Figure 20: Logarithmic S-N curve of steel wire with different notches of different shapes.  
does not decrease with the increase of concentration of NaCl solution. The reason for this may be that the excessive concentration of chloride ions affects the dissolution and diffusion of oxygen in the solution so that the corrosion effect of the solution on the steel wire is reduced.  
(4) The life of steel wire decreases gradually with the increase of depth and the decrease of width of semi-ellipsoidal notch. Under each level stress range, when the depth of semi-ellipsoidal notch increases from 0.6 mm to 0.8 mm, the decline of wire life is the highest, and the life falls by more than 25%; when the depth of semi-ellipsoidal notch increases from 0.6 mm to 1.2 mm, the life falls by more than half. The growth rate of wire life is highest, and by more than 20% when the width of the defect increases from 3 mm to 4 mm. The stress concentration will lead to a sharp reduction in wire life. Under the same stress range, the steel wire with V-notch has the shortest life, followed by the steel wire with a trapezoidal notch, and steel wire with the semi-ellipsoidal defect has the highest life. When the stress ranges are equal to 720 MPa and 360 MPa, the life of steel wire with the semi-ellipsoidal notch is more than twice of that with V-notch.  
Conceptualization, Y.W.; Methodology, Y.W.; Software, W.Z.; Validation, Y.Z.; Formal Analysis, W.Z.; Writing-Original Draft Preparation, Y.W.; Writing-Review & Editing, Y.Z.; Funding Acquisition, Y.W. All authors have read and agreed to the published version of the manuscript.  
The works described in this paper are substantially supported by the grant from National Natural Science Foundation of China (Grant No. 51678135); Natural Science Foundation of Jiangsu Province (No. BK20171350); Six Talent Peak Projects in Jiangsu Province (JNHB-007); China Scholarship Council (No.201906090261), which are gratefully acknowledged.  
The authors declare no conflicts of interest.