| The structural style of flange-bolt connections is widely used in civil engineering.Under cyclic load and corrosive environment,corrosion fatigue is the main failure mode.Different from general fatigue,the damage of lightning rod structure is often attributed to corrosion fatigue of flange-bolt connection structure.Corrosion fatigue refers to the fatigue with corrosion damage,and the corrosion fatigue life is much lower than ordinary fatigue life.The flange-bolt connection structure depends on the bolt preload and friction of contact surface to resist the external load.In corrosive environment,when the external load is the dynamic load,the part will be the first to crack,and then expand,resulting in the destruction of the connection structure.In order to get the corrosion fatigue life of lightning rod flange-bolt connection structure,the predecessors have carried out engineering examples and determine the position of crack initiation.On the basis of the above work,the corrosion fatigue crack process is analyzed from two aspects.The main work is as follows:(1)The FEM of crack propagation was established,and the automatic expansion of the initial crack was realized based on the fracture mechanics and the Python language,the fatigue crack extension life and extensions path were obtained.Based on the influence of different Na Cl concentrations on the fatigue life of the structure,the fatigue life of flange-bolt connections decreases gradually with the increase of corrosion degree.Based on the results of finite element simulation and actual bolt damage,the general failure mode of the lightning rod structure can be inferred.The failure accident caused by bolt corrosion fatigue fracture of lightning rod structure under the combined action of corrosion and wind load is reasonably explained.(2)The model of crack extension life was established based on the XFEM.Firstly,the failure section of engineering bolt is analyzed,and the simulation results in(1),and the finite element model of the experiment was established.The simulated crack propagation path can be compared with the crack trend in the failure section of engineering bolts.The results show that the simulated crack propagation is closer to the real crack propagation,and the obtained crack propagation life has a good agreement with the calculated crack model.(3)In general,the fatigue load of lightning rod is not easy to obtain,and the flangebolt connection parameters vary greatly.In order to consider the influence of such factors,the parameters of the wind load were analyzed.Based on the quasi-dynamic crack propagation life model,the influence of wind load,friction coefficient and bolt pretension on the fatigue life of flange-bolt joints were analyzed.The results show that the reduction of wind load can lead to an increase in the corrosion fatigue crack growth life of the structure;the decrease of the bolt pretension and the decrease of the friction coefficient can lead to the decrease of the corrosion fatigue life of the structure. |
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