| Friction-type high-strength bolt connections are widely used in civil engineering.When the structure is subjected to cyclic external loads for a long time,the effect of fatigue on the structure needs to be considered.Fatigue failure of friction-type high-strength bolted structures is often attributed to fretting fatigue failure of the connection plate.Unlike ordinary fatigue,fretting fatigue bears the combined effects of cyclic load and fretting,and fretting action will reduce the fatigue life of components.In this paper,the fretting fatigue life and fracture morphology of eight one-sided joints made of Q460C steel and Grade 10.9 frictional high strength bolts were tested.In order to establish the fretting fatigue crack life model,the total fatigue life was divided into crack initiation life and propagation life.By establishing a finite element model,the fatigue analysis of high-strength steel connectors was performed,and the effect of contact surface roughness on fretting fatigue was considered.The main work is as follows:(1)The fatigue life and fracture morphology were obtained through the fatigue test of frictional high-strength bolts with one-sided overlap connection.By analyzing the pictures obtained by scanning electron microscope,it can be judged that they are fretting fatigue failure,and the path of crack growth is obtained.(2)Firstly,the 3D fracture surfaces were numerically modeled based on laser scanning data of the fatigue fracture surfaces,which were imported into ABAQUS to establish the extended finite element model considering the realistic crack path.Based on the model,the crack propagation life and crack propagation path are obtained by Python.(3)The roughness parameter R_a was estimated according to the measured data of the contact surface near the crack initiation zone,and parameters of the roughness-based crack initiation life R_a-N_i model were identified based on the estimated roughness parameter and crack initiation life by subtracting the crack growth life from the experimental total life.The predicted total life based on the proposed model is in reasonable agreement with the experimental results,in range of error less than two times of deviation.(4)In order to consider the influence of rough surface factors on the fatigue life of cracks,a two-dimensional sliding friction micro-model of rough surfaces was established.Considering the effects of elastoplastic deformation,damage failure,and adhesion of the material during sliding,ABAQUS was used to analyze the force on the contact surface,and the friction coefficient was obtained by considering the adhesion and deformation effects.By substituting this friction coefficient into the crack growth life model and crack initiation life model in the paper,the crack growth life and initiation life considering the influence of rough surface can be obtained.It was found that the total life calculated by considering the influence of the rough surface is closer to the total life of the test than the total life calculated by not considering the influence of the rough surface. |
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