*Corrosion Fatigue Behavior and Damage Mechanism of the Bridge Cable Structures DOI: http://dx.doi.org/10.5772/intechopen.109105*

With the increase in corrosion time, the local adjacent corrosion pits interlocked, forming larger corrosion pits, and the corrosion pit depth also gradually increased. Under the alternating stress condition and static stress condition, the stress in the pitting area is concentrated and cracks are gradually formed and expanded. The selected corroded wire is cleaned to ensure no residue and then dried in the drying oven. For observation, the dried steel wire was placed on the sample plate to sketch the position, then the sample plate was placed in the sample chamber, the sample chamber was sealed, and the steel wire was observed under the electron microscope. As an example, **Figures 5** and **6** [15, 16] show the microcracking phenomenon on the steel wire surface under alternating stress and static stress conditions.

According to **Figures 5** and **6**, it can be seen that the depth and size of the corrosion pits are gradually developed with the corrosion process. Under the coupling effect of stress and corrosive environment, the nucleation of the corrosion pits of the corroded steel wire is first cracked and forms nanoscale cracks, while the alternating stress makes the nanoscale cracks continuously elongate and retract, resulting in the accelerated formation of microcracks in the steel wire.

As shown in **Figure 7** [17], the local corrosion map of 300 times under each working condition was imported, and the hue was measured at the parts where the steel wire corrosion was obvious, and the histogram of the hue distribution was derived and the distribution amount was counted to calculate the frequency of corrosion pits. After the numerical processing, combined with the distribution histogram to obtain the corrosion characteristics of the specimen surface parameters can be seen that the corrosion

**Figure 5.**

*Alternating stress microcrack extension [15, 16] (a) 300 times (b) 6000 times.*

#### **Figure 6.** *Static stress microcrack extension [15, 16] (a) 1380 times (b) 6000 times.*

**Figure 7.** *Corrosion histogram [17] (a) stress-free, (b) static stress, and (c) alternating stress.*

characteristics of the steel wire basically conform to the normal distribution. In the salt spray environment under stress-free conditions, there is no obvious corrosion pit in the specimen and the corrosion rate is about 32.58%. The corrosion rate under alternating stress conditions is about 55.49%. Under the static stress condition, the corrosion rate of steel wire is between the previous two conditions, about 40.12%. Wire corrosion is more uniform under stress-free conditions, and the standard deviation of its histogram is larger, with a color tone level of about 104, while the color tone level of the peak gray standard deviation of the static stress condition is about 92, which is between the alternating stress condition and the stress-free condition. For the alternating stress condition, the steel wire surface tone value concentration and corrosion pits with the elongation and retraction of the steel wire to accelerate the development of the peak where the tone level is about 74. Therefore, under the alternating stress condition, the corrosion frequency and corrosion rate of the steel wire are greater than the rest of the conditions, and the damage to the specimen is the largest.

#### **4.2 The mechanical property analysis of corroded steel wire**

The corroded steel wire was stretched in one direction on the universal testing machine, and its mechanical property data were recorded, and the broken steel wire of each steel wire was packed and numbered after completion. Select the middle length of the steel wires as a 1-meter section of the experimental section for tensile experiments, the ratio of the maximum load measured before the experimental section is


*Corrosion Fatigue Behavior and Damage Mechanism of the Bridge Cable Structures DOI: http://dx.doi.org/10.5772/intechopen.109105*

#### **Table 4.**

*Mechanical property data of steel wire.*

pulled off and its nominal area is the tensile strength, that is, the nominal tensile strength. The mechanical property data are shown in **Table 4**.

According to the analysis of the changes in the mechanical properties data of the steel wire in **Table 4**, it can be seen as follows:


In summary, the mechanical property of the specimens under different loading states was affected to different degrees by the prolongation of corrosion time, and the modulus of elasticity, yield strength, tensile strength, and elongation after fracture all showed a downward trend. Among them, tensile strength and elongation after a break are the most sensitive to corrosion, while the modulus of elasticity is less sensitive to corrosion, tensile strength decreases slowly in the early stage of corrosion, and in the middle and late stages, it decreases in a leap and becomes more sensitive to corrosion, the different loading methods have a greater impact on the yield strength.
