Research On Fatigue Damage Assessment And Life Prediction Method Of Pitting High-Strength Steel Wire

Cables and suspension rods are subjected to the combined effects of corrosion environment and fatigue loading during service.The corrosion environment can cause pitting corrosion in the internal steel wires,thereby reducing the fatigue performance of the components,and the resulting fatigue damage directly affects the safety of the bridge structure system.Therefore,it is necessary to study the fatigue life and damage evolution law of pitted steel wires under fatigue loading.In this paper,fatigue tests of pitted steel wires considering the pitting corrosion coefficient were conducted,and a plasticity-based fatigue damage model was established using the continuum damage mechanics(CDM)and introduced into the secondary development platform(UMAT)of ABABQUS to predict the fatigue life.The damage and stress evolution of pitted steel wires were analyzed,the magnetic signals during the fatigue process of pitted steel wires were detected based on the weak magnetic effect,and the relationship between the magnetic signal and the fracture mechanics crack propagation model parameters was studied.The effectiveness of the proposed method was verified through experimental results.The main research contents and achievements of this paper are as follows:(1)In order to study the effect of pitting corrosion on the fatigue properties of high-strength steel wires,the uniaxial tensile fatigue tests of 5 non-corroded steel wires and 25 pitting high-strength steel wires made by accelerated corrosion method were carried out.The results show that the fatigue fracture of high strength steel wire occurs at the corrosion pit due to the decrease of cross-sectional area and the concentration of corrosion pit stress.The influence of pitting on the fatigue life of steel wire is mainly manifested as the downward shift and attenuation rate change of S-N curve.Based on the influence law of stress amplitude and pitting,a unified S-N_ccurve equation of pitting high strength steel wire modified by exponential function is established.The results show that the model has good adaptability in relatively low fatigue life,and the error is basically within±30%.(2)In order to study the fatigue performance and damage evolution of pitting high-strength steel wire,the fatigue life test of steel wire was carried out.The continuum damage mechanics was introduced through the UMAT secondary development of ABAQUS platform,and the finite element model for predicting fatigue life was established.The results show that the error between the predicted fatigue life and the experimental value is within±20%.The stress and damage evolution results of CDM simulation show that in the early and middle stages of fatigue life,the stress is concentrated at the bottom of the corrosion pit,and the damage first appears in the stress concentration area.At the end of fatigue life development,the material at the bottom of the corrosion pit is damaged and the stress redistribution occurs around the corrosion pit.The results are consistent with the experimental phenomena.The crack propagation zone of the specimen section appears at the bottom of the corrosion pit,and the sudden fatigue fracture of the pitting steel wire occurs at the corrosion pit.(3)The weak magnetic signal was detected during the fatigue test of pitting high-strength steel wire,and the change rule of weak magnetic signal in the fatigue process of pitting steel wire was analyzed,and compared with the prediction results of crack propagation model of fracture mechanics.The results show that the characteristic parameters of weak magnetic signal can effectively reflect the process of fatigue damage to fatigue fracture failure of pitting steel wire,and have obvious correlation with the parameters in the crack propagation model of fracture mechanics.According to the correlation,the quantitative relationship between weak magnetic parameters and crack propagation parameters is established.Based on the above relationship,the process of weak magnetic signal evaluating the fatigue crack propagation of pitting steel wire is proposed.The experimental results show that the weak magnetic signal can better characterize the crack propagation behavior.