## 3 Test Results and Analysis
In logarithmic form, the following formula can be obtained:  
\[\lg N=\lg C-m\lg S_{a} \tag{2}\]  
Based on the curve fitting toolbox in MATLAB, the logarithmic S-N curves and linear correlation coefficients of specimens in group A-G can be obtained as follows:  
Group A : \[\lg N=14.18-3.741\lg S\;\mathrm{R}=0.9967\] (3) Group B : \[\lg N=14.08-3.732\lg S\;\mathrm{R}=0.9965\] (4) Group C : \[\lg N=15.00-4.115\lg S\;\mathrm{R}=0.9871\] (5) Group D : \[\lg N=14.78-4.005\lg S\;\mathrm{R}=0.9994\] (6) Group E : \[\lg N=15.52-4.347\lg S\;\mathrm{R}=0.9826\] (7) Group F : \[\lg N=14.31-3.830\lg S\;\mathrm{R}=0.9988\] (8) Group G : \[\lg N=15.95-4.511\lg S\;\mathrm{R}=0.9828\] (9)  
It can be seen that the linear correlation coefficients of the fitting formulas of the specimens in groups A-G are all close to 1. The closer the correlation coefficient is to 1, the higher the linear correlation property is. The results show that that the fatigue stress range and life of high-strength steel wire maintain a good linear relationship under the double logarithmic coordinate, and the different slope of the curve reflects the different corrosion fatigue characteristics of steel wire under different environmental conditions. Figure 14 shows the logarithmic S-N curves of the steel wire with machine-cut notch subjected to the fatigue loads and sodium chloride solution, which are the power exponential curves obtained by MATLAB fitting toolbox. The five curves correspond to corrosion free, by sodium chloride at pH value of 7 and concentration of 3.5 wt%, by sodium chloride at pH value of 7 and concentration of 0.5 wt%, by sodium chloride at pH value of 3 and concentration of 3.5 wt%, and by sodium chloride at pH value of 3 and concentration of 0.5 wt%, respectively. It can be seen that, with the increase in stress range, the life of steel wire is significantly reduced. The life of steel wire corroded by the corrosive medium is much shorter than that in air, which indicates that the interaction between corrosive medium and fatigue load accelerates the material failure. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Stress Range** & & & & & **Cyclic Number** & & \\
**/MPa** & **Group A** & **Group B** & **Group C** & **Group D** & **Group E** & **Group F** & **Group G** \\ \hline
720 & 3531 & 3351 & 3040 & 2709 & 2592 & 2571 & 2362 \\
600 & 7229 & 5769 & 5077 & 4388 & 4278 & 5186 & 4267 \\
480 & 12,864 & 10,881 & 7634 & 10,702 & 5869 & 10,341 & 5638 \\
360 & 41,244 & 34,835 & 30,342 & 34,583 & 26,074 & 32,875 & 26,464 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: The life of steel wire in groups A-G. It can be seen from Figure 14 that, under the same stress range, the steel wire without consideration of corrosion has the longest fatigue life, followed by steel wire with a pH of 7, and steel wire with a pH of 3 has the shortest life. The life of steel wire is shortened with increasing acidity of corrosion solution. When the stress range is large, the difference between the three is relatively small. In Figure 14, 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 pH of 3 and concentration of 0.5 wt% is reduced by 36%. It can also be seen from Figure 14 that, under the same stress range, the steel wire without corrosion has the longest fatigue life, followed by steel wire subjected to the corrosion concentration of 3.5 wt%, and steel wire subjected to the corrosion concentration of 0.5 wt% has the shortest life. The life of steel wire does not decrease with the increase of the 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.