| The structural style of bolted connection is widely used in civil engineering;Under dynamic load,fatigue is the main failure mode.Different from general fatigue,the fatigue of friction type high-strength bolt connection is attributed to the fretting fatigue of the connecting plate.Fretting fatigue refers to the fatigue with fretting wear,and the fretting fatigue life is much lower than ordinary fatigue life.The friction type bolt connection structure depends on the friction resistance of the contact surface to resist the external load.When the external load is the dynamic load,the contact surface will inevitably continue to misbehave each other,and the most serious part will be the first to crack,and then expand,resulting in the destruction of the connection structure.In order to get the fretting fatigue life of friction type high-strength bolt connections,the predecessors have carried out the friction coupling structure fatigue tests,fracture electron microscope scanning test and determine the position of crack initiation.On the basis of the above work,the fatigue process is divided into two stages:fatigue crack initiation and crack propagation.The main work is as follows:（1）The FEM of three dimensional crack propagation was established,and the automatic expansion of the initial crack was realized based on the fracture mechanics and the Python language,and the fatigue crack extension life was obtained.The initiation life was identified in terms of the total fatigue life and propagation life.Based on the result of the initiation life and finite element analysis,the parameters of FFDmax-Ni were identified,and the crack initiation life model was established.Thereby,a method for predicting fatigue life of friction type high strength bolts connection was developed,the predicted fatigue lives were in reasonable agreement with the experimental results in the range of error less than two times of deviation.（2）In order to verify the validity of the above prediction crack propagation life method,the model of scanning crack extension life was established based on the profile data of the specimen.Firstly,the fatigue fracture of the specimen was scanned,and the test crack was modeled based on the scanning data,and the finite el ement model of the experiment was established.The simulated crack propagation path can be compared with the brightness in the scanning results of electron microscopy.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）Based on the two-stage prediction fatigue life method,the influence of friction coefficient and bolt pretension on the fretting fatigue life of friction type high-strength bolt was analyzed.The results show that the decrease of friction coefficient and the shortage of bolt pretension can lead to the decrease of the total life span of the fretting fatigue. |
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