Research On Stochastic Evolution Of Corrosion Fatigue Damage Of Transmission Tower System

The construction of ultra-high voltage transmission tower systems,as the development trend of China’s power system,has made the use of Q420 and other highstrength steel more and more prevalent.In the service environment,transmission towers may suffer from long-term acid rain corrosion and wind-induced fatigue,resulting in material damage and structural weakening,and even leading to collapse accidents.To prevent the accidents,it is important to understand and master the damage evolution law inside the steel of transmission towers in service.For this purpose,this paper conducted research mainly concerning corrosion fatigue tests and corrosion fatigue damage evolution model for Q420 B steel,higher-order analysis for structural hybrid random vibration problems,time-domain and frequency-domain analysis based on nonlinear corrosion fatigue damage models,and structural multi-scale finite element simulation for large structural systems.Then finally a frequency-domain simplified method and a timedomain meticulous method for corrosion fatigue damage random evolution of transmission tower systems are proposed.This study mainly contains the following aspects:(1)The corrosion fatigue crack initiation and growth tests for Q420 B high strength steel in acid rain environment were conducted and corresponding models were proposed.First,laws of the corrosion fatigue crack initiation life,corrosion fatigue damage evolution,corrosion fatigue crack growth rate,and the influence of p H value of corrosive solution,spray methods and stress ratio on the crack growth rate were studied.Second,with reference to the continuous-damage-mechanics-based high-cycle fatigue damage evolution model and the fracture-mechanics-based pit-to-crack model,the pitting corrosion fatigue crack initiation criterion was proposed,and the fully continuousdamage-mechanics-based corrosion fatigue damage evolution model was established.Third,the validity of the proposed model was verified by using two types of material test data.Finally,the corrosion fatigue damage evolution model for Q420 B steel was fitted using the aforementioned corrosion fatigue crack initiation test data.(2)Higher-order analysis methods for hybrid random vibration problem under stationary Gaussian excitations were proposed.First,the concept of conditional expectation was introduced to separate randomness of the structural parameters from that of Gaussian excitation processes.Second,a higher-order analysis method for hybrid random vibration problem under stationary Gaussian excitations was proposed based on the pseudo excitation method and a decomposition method of multi-point Gaussian vector process;then the higher-order spectral density formula under single-point excitation was also given.Third,the computational accuracy and efficiency of the proposed method were verified by numerical examples.(3)A frequency-domain analysis method for fatigue or corrosion fatigue damage based on nonlinear damage models was proposed.First,the concept of block cycle jump technique used in time-domain fatigue analysis methods was introduced to linearize the nonlinear fatigue damage evolution process in segments.Second,the assumption of independence of loading order was introduced for each linear segment;and the nonlinear fatigue or corrosion fatigue damage evolution models were combined with Dirlik’s PDF of rain-flow stress range;then the frequency-domain method for fatigue or corrosion fatigue damage based on nonlinear damage evolution models was proposed.Finally,the proposed method was verified by using test data of two materials and numerical simulations.(4)The frequency-domain simplified analysis and time-domain meticulous analysis of the random evolution of corrosion fatigue damage of multi-scale transmission tower system were established.First,based on the proposed Bayesian updated point estimation method,the power spectrum model of conductor hanging point load and the frequencydomain fatigue method for nonlinear damage,a frequency-domain simplified analysis strategy was proposed.Second,based on the proposed improved Bayesian updated probability density evolution method and time-domain fatigue damage analysis method,a time-domain meticulous analysis strategy was proposed.Third,the hierarchicalconcurrent multiscale finite element modeling and its validation were carried out for an actual engineering project of ultra-high voltage transmission tower system.Finally,acidrain corrosion fatigue damage evolution problem of the multiscale finite element model of the transmission tower system was analyzed by both the frequency-domain strategy and time-domain one.The results of the two proposed analysis strategies were fully illustrated.