Vibration Fatigue And Damage Detection Of Bolted Joints

Joints are the essential part in most engineering equipments.They are widely used in various industrial fields such as aerospace and transportation.These joints very often work in a very complex vibrational environment.The main failure mode is caused by fatigue fracture.Thus,it has practical application value and important theoretical significance to carry out research on vibration fatigue and damage detection of bolted joints in depth and systematically.The main contributions of the present work are as follows:Firstly,the influence of pretightening force on the surface morphology of boltedjoint interfaces is examined.The surface morphology is assessed using optical microscopy and 3D optical profilometer,and is characterized using seven most commonly used surface roughness parameters.Besides,a 3D elasto-plastic finite element contact model is established by considering the asperity of bolted-joint interfaces.The established model is capable of reflecting the measured 3D surface morphology of the bolted-joint interfaces,implying thus a high accuracy surface modeling method.The model,based on the contact analysis approach,can also be used to predict the 3D morphology,surface roughness value,contact area,contact stress and contact pressure of the bolted-joint interfaces when the bolted joints are subjected to various different bolt pretightening forces.Secondly,the testing scheme for bolted joints is determined based on the modal simulation combined with vibration test.Ncode simulation software is used to analyze the resonance fatigue life of bolted joints,and detect damage and failure location of the bolted joints.Vibration fatigue tests are then carried out on the bolted joints previously preloaded with various different pretightening forces using electromagnetic shaker.The vibration fatigue test results show that the vibration fatigue life of the bolted joints is the highest when the bolt is preloaded with a pretightening force of 10N·m.Finally,the acceleration signal data collected in the resonance fatigue test are processed and analyzed by using the programmed transmissibility function and the operational modal analysis algorithm,and the evolution law of vibration fatigue damage of bolted joints is studied.The results show that the natural frequency and the pole frequency of the high frequency transmissibility function are effective parameters to evaluate the accumulation of fatigue damage.The failure mechanism of vibration fatigue is studied by the failure analysis of bolt joints.The results show that the stress concentration induced by bolt pretightening force leads to crack initiation.The bolt preload can restrain the crack growth,but too high preload will produce more crack sources and accelerate the fatigue failure.The research method relating to vibration fatigue established in the present work can thereby provide a guideline for the future research work on vibrational fatigue of structural parts.The experimental results verify the effectiveness of the damage detection methods based on the transmissibility function and the operational modal analysis method,which provides an effective way for the fatigue damage detection of large-scale engineering equipment.