Research On Corrosion Characteristics And Mechanical Behaviors Of Steel Wire For Long-span Bridge Cable Under Tensile Stress Condition

The cable system is an important guarantee for the spanning capacity and safe service of modern long-span high-strength-stayed bridges.However,the high-strength wire endures corrosion issues during long-term service,which seriously affects the safety of long-span bridges.At present,the solution to this problem is usually to replace new cables.Although this method satisfies the safety requirements of long-span bridges,it sacrifices economy and environmental protection.In recent years,the production process and anti-corrosion technology of ultra-high-strength steel wire have made great progress.The newly developed zinc-aluminum alloy coated high-strength steel wire has reached a tensile strength of 2000 MPa.The thesis investigates common problems such as corrosion characteristics and degradation of mechanical behaviors based on the artificial accelerated corrosion test of ultra-high-strength and high-corrosion-resistant steel wire,which can be treated as the basis for the design,maintenance and life extension of long-span bridge cable system.The main research contents are as follows:Firstly,the reconstruction method of 3D point cloud data of corroded high strength steel wire.In order to simulate the corrosive environment and stress condition of the high-strength wire in the real environment,the artificial accelerated alternating cycle salt spray corrosion test was carried out.The ultra-depth-field microscope is employed to collect homogenous 2D color image data and 3D point cloud data.Point cloud data is reconstructed with the aid of 2D color image and high-precision and complete corrosion data of high-strength wire surface was obtained.The problem of obtaining high-precision corrosion depth data sets for the entire surface of corroded high-strength steel wires was solved.Secondly,the evolution of corrosion chracteristics affected by tensile stress condition.The time-varying model of uniform corrosion depth statistical parameters is established.The evolution of geometric characteristics and 3D morphology of the corrosion pits under applied tensile stress is revealed based on the statistical analysis.The influence of tensile stress condition on the preferred growth orientation of corrosion pits is revealed.Thirdly,the mechanical behaviors of corroded high-strength steel wire.Mechanical tests are carried out to determine the macroscopic mechanical parameters of corroded high-strength steel wires.Correlation between corrosion characteristic and mechanical behavior parameters is established.The influence of the tensile stress condition on the corrosion characteristic and mechanical behavior is revealed.Based on the TEM observation results,the influence of static tensile stress on the evolution of pearlite lamellar structure is revealed.Based on SEM/TEM observation,the propagation behavior of the Type I fatigue crack in the microstructure of the base material,the effect of microstructure on the corrosion pits,and the deflection of fatigue crack growth path induced by corrosion pits are observed.Fourthly,the research on fatigue behaviors of corroded high-strength steel wire based on finite element model.The resolution enhancement method of corroded highstrength steel wire point cloud data is proposed to establish a fine finite element model of high-strength steel wire with more details of corrosion pits.In addition,the influence of corrosion pit parameters on the stress field is explored based on FE method.Based on the FE simulation results,the fatigue life of the corroded high-strength steel wire was predicted based on the critical distance method.