**3. Artificially accelerated corrosion fatigue experiment under coupled loading and environment**

#### **3.1 Experiment content and its implementation**

Accelerated corrosion experiment was conducted on lassos using an acidic salt spray environment. The cable consisted of high-strength galvanized parallel steel wire. The strength level of the lasso is 1860 MPa, the yield strength is 1660 MPa, and the diameter φ is 5.2 mm. The loading force for both alternating stress and static stress is 1100 MPa, which is close to the stress corrosion threshold. At the end of the experiment, the steel wire was wiped with 10% dilute sulfuric acid to remove the surface corrosion, the mass loss of the steel wire subjected to corrosion was measured, and the mechanical properties of the corroded steel wire were tested to discuss the mechanical property response of the steel wire to the corrosive environment and to provide an experimental data basis for evaluating the corrosion damage and evolution of the steel wire. The main experimental equipment is shown in **Table 1**.

The salt solution was 5% NaCl solution, adding concentrated sulfuric acid in the solution to adjust the pH to 1. The experiment temperature reference document [11]


#### **Table 1.**

*Main experimental equipment.*

will be set at 50°C 2°C, the air pressure is controlled between 70–170 kPa. Spray volume reference document [11] CASS experimental standards, taken as 250 ml/m<sup>2</sup> /h. The specific implementation steps of experiment are as follows: All the treated steel wire were weighed with a balance, the diameters were measured, and the raw data were recorded. The experiment was arranged in three loading methods: stress-free, static stress, and alternating stress. The stress-free loading method cut the steel wire into 1.2 m sections, marked them, and put them directly into the corrosion chamber for continuous corrosion without interruption. When subjected to static stress loading, the steel wire is cut into 5.4 m sections, marked and through the corrosion box and the counter-weight table reserved hole, and anchored with a tensioning jack, the rest of the process is same as stress-free loading. Alternating stress loading, the same steel wire is cut into 5.4 m sections, the loading cycle for 4 h, that is, 2 h loading, 2 h unloading, the rest of the work is same as stress-free loading, every 24 h to open the corrosion box, take pictures, and record data, reconfigure and add solution. After the experiment, first, clean the corrosion products on the specimen with dilute sulfuric acid, then wash the steel wire with a large amount of water, blow dry with a blowing air and then weigh again, the diameter should be randomly measured three times for each specimen section, and take its average value and record. The last is the corrosion of steel wire mechanical tensile experiment.

In this experiment, at least five steel wires were used in each batch, two of which were alternately stressed, two were statically stressed, and the others were unstressed wires. The peak stress applied is 1100 MPa. The specific arrangement is shown in **Figure 2** [12].

Before conducting the formal tensile experiment, three intact steel wire samples with a length of 1 m were taken and tensile experiments were performed on them with a universal testing machine. Their elastic modulus *E*, tensile strength *R*m, yield strength *Rp0.2,* and post-break elongation *A* were measured to determine the original mechanical properties parameters of the steel wire. It provides a reference for the test results of mechanical properties of steel wire after corrosion. The data obtained from the tensile experiment are given in **Table 2**.

In order to ensure the safety of the bridges, considering the safety factor of the steel wire used in cable-stayed bridges, the stresses applied during their operation should be less than their yield strength and tensile strength. Therefore, it is reasonable to apply a maximum tensile stress of 1100 MPa to the galvanized steel wire to ensure that they do not yield and fracture during the experimental process.

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

#### **Figure 2.**

*Experimental specimen arrangement.*


**Table 2.**

*Steel wire static performance experiment data.*
