| Corrosion fatigue of materials is the brittle fracture of materials under the interaction of corrosion medium and fatigue stress.Currently,corrosion failure is one of the main reasons that lead to the failure of cables prior to the design life.Under the action of traffic load,the coupling effect of corrosion and fatigue would lead to more serious wire breakage.Therefore,the study of corrosion fatigue behavior of cable steel wire is of great significance to engineering practice.Taking the parallel wire cables for analysis,the interaction between corrosion and fatigue loads of corroded steel wires is analyzed experimentally,and a method for evaluating the service life of suspension bridge suspension cables considering corrosion fatigue effect is presented.The main work accomplished are as follows:Three theoretical methods for fatigue analysis are introduced,and the basic models for fatigue life analysis of steel wires are given.On the basis of theoretical methods,three failure modes of steel wires under corrosive environment are introduced,namely pitting corrosion,stress corrosion and corrosion fatigue.Through the AASS salt spray corrosion test of galvanized steel wire and Zn-Al alloy coated steel wire,the salt spray resistance of the two coatings is analyzed,and the mathematical model of uniform corrosion depth of Zn-Al alloy coated steel wire is given.Static tension tests were conducted on corroded Zn-Al alloy coated steel wires to evaluate the effect of corrosion on mechanical parameters with elastic-plastic constitutive relation of bilinear four parameters to describe the relationship between corrosion and steel wire constitutive relation.The results show that the artificial accelerated corrosion only affects the ductility of steel wire.Fatigue tests were conducted on corroded Zn-Al alloy coated steel wires to evaluate the fatigue life under different mass loss rates,and the effect of corrosion on plane strain fracture toughness was analyzed.The results show that the corrosion degree is negatively correlated with the plane strain fracture toughness.The coupling behavior between corrosion and fatigue is further analyzed.Firstly,the corrosion rate under different stress states was measured by using the Tafel linear extrapolation method to evaluate the effect of fatigue stress on corrosion behavior.It is found that the corrosion tendency of steel wire under fatigue stress is more obvious,and the corrosion rate will be further increased with the stress amplitude.Secondly,the fatigue fracture photographs of corroded steel wire are obtained by using the industrial camera,and the influence of corrosion pits on crack initiation and propagation behavior is analyzed according to its morphological characteristics.The EIFS model was used to quantitatively analyze the fatigue life of corroded steel wires in different stages under corrosion pits.Thirdly,the corrosion fatigue tests of corroded steel wires in chloride salt environment and DC environment were conducted,furthermore,the fracture morphology and plane strain fracture toughness under corrosion fatigue and mechanical fatigue are compared.The life calculation model of steel wire with unilateral crack is used to analyze the effect of different corrosion levels on fatigue life.Based on the series-parallel fiber bundle model,the life-cycle calculation model of parallel steel cables is presented.Taking Runyang suspension bridge as an example,the parametric analysis of corrosion fatigue life of suspension cables is conducted by measuring the stress-time response of suspension cables,and four types of wire breaking mechanism of corroded steel wire are considered.The effects of different stress amplitudes,initial defects,ambient temperature and humidity on corrosion fatigue life of suspension cables are takne into account.The calculation results show that in normal corrosion environment,the traffic load would not lead to the fracture of the steel wire in the design period,but the steel wire with initial defects is likely to fracture during this period,and the corrosion fatigue coupling effect would further shorten its life;In high temperature and humidity environment,even under the effect of small stress amplitude,the suspender could still break within a relatively short time. |
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