Research On Fretting Fatigue Test And Life Model Of Friction Type High-strength Bolted Joints

Fretting fatigue is a kind of special fatigue phenomenon which is obviously different from others and widely found in all kinds of metal joints with contact.Because of friction type high strength bolt is very reasonable and easy installation,So it is widely used in all kinds of steel structure connection.When the friction type high-strength bolted joint is subjected to cyclic loading,Fretting fatigue is easy to produce.In this paper,we based on the fretting fatigue test of friction type high strength bolted joints.Combinate to the classical fatigue life model,a critical plane life model with fretting fatigue parameters is developed.The parameters of the new fretting fatigue life model are identified by experimental data and The influence of relative parameters on fretting fatigue life is analyzed.Specific contents are as follows:(1)Based on different stress amplitude Fretting fatigue test of friction type high strength bolted joints.Through fracture morphology and fracture analysis,the fretting fatigue fracture surface was determined.Then the fretting fatigue life was fitted by the three parameter power function method with FFD crack location parameters.We obtained the FFD-N fretting fatigue life formulation.The results are compared with the commonly S-N curves,the FFD-N life model is more accurate.(2)Based on the concept of critical plane,A life prediction model based on parametric representation is proposed.Compared with the experimental results,It is found that W,FFD and SWT multiaxial fatigue parameters can be used to predict the crack location of two dimensional bridge specimens.For the friction type high-strength bolted joints,FFD and W can also be used to predict the crack location.By changing the parameters of the specimen under different stress amplitude,a new W-N fretting fatigue life relationship is proposed.(3)Based on FFD-N formulation,the effects of the friction coefficient of the contact surface,the bolt pretension force,the size of the gasket,the strength of the bolt and the diameter of the bolt on the fretting fatigue life of the friction type high-strength bolts were investigated.The results show that the friction coefficient is reduced,the bolt pretightening force is insufficient,the size of the gasket reduced,the bolt grade reduced and the bolt diameter reduced,they will lead to the increase of the FFD parameters of the contact surface,which will reduce the fretting fatigue life of the friction type highstrength bolted joints.(4)Based on W-N life relationship,the friction coefficient of the contact surface,the pre tightening force of the bolt and the size of the gasket changed were analyzed.We found that the decrease of the friction coefficient,the lack of pre tightening force and the decrease of gasket size will lead to the decrease of fretting fatigue life.The predicted results are the same as those of FFD-N life model.