Research On Loosening Phenomenon Of Bolted Joint Structure And The Effect Of Temperature On The Loosening

For the connection structure,the loose failure of the bolt connection is one of the most common failure modes.In engineering practice,bolt loosening failure often occurs earlier than fatigue fracture,and along with this process,the bolt pre-tightening force gradually decreases.In the early stage,the bolts and nuts in the bolted connection structure showed slight sliding,which did not significantly reduce the working performance of the overall structural system.However,as the working time increases,the bolt tension will be further reduced,which will lead to a series of problems,such as poor sealing,and even fatigue fracture.Therefore,the analysis of the internal causes of the loosening of the bolted connection structure can provide theoretical basis and technical support for preventing the loosening of the bolted connection structure.This paper establishes a finite element model to investigate the loosening of bolted structures under lateral displacement excitation,and conducts experimental verification to analyze the influence of temperature on the loosening of bolted structures.The main research contents are:(1)Summarize the research status of bolt connection,introduce the method of bolt connection anti-loosening in actual engineering and the corresponding principle;give the mechanical theory basis of bolt connection,analyze the calculation of thread torque,thread tooth deformation and thread tooth axial force distribution Process,study the distribution of thread bearing capacity.(2)Based on the mathematical function expression of the thread geometry,the finite element model of the three-dimensional bolt connection structure is established,and the bolt loosening under the horizontal harmonic load is numerically simulated,and the vibration amplitude,initial preload,friction coefficient,The influence of vibration frequency and other factors on bolt loosening.The results show that increasing the initial preload has a better suppression effect on loosening;the larger the friction coefficient or the reduction of the amplitude,it is also helpful to prevent loosening;while changing the vibration frequency has no obvious effect on the decrease of preload.(3)Conduct an experimental study on the bolted connection structure,investigate the attenuation of the pre-tightening force of the bolted connection structure under the condition of cyclic lateral displacement and the influence of factors such as pre-tightening force,amplitude,and number of disassembly on the loosening of the connection structure.Compare the test results with The finite element calculation results verify the validity of the finite element calculation results.(4)Study the effect of axial thermal expansion caused by temperature changes on the loosening of bolted connections,and investigate the changing law of the pre-tightening force of bolted connections under temperature changes;it is found that the loosening is more sensitive to the effect of different thermal expansion coefficients,and the initial pre-tightening force is relatively high.When it is high,it decreases significantly with temperature changes;and the higher the temperature amplitude is,the faster the pre-tightening force decreases.Establish a mathematical model of thread loosening caused by radial expansion caused by temperature change,apply this mathematical model to analyze the force of the bolt connection contact surface,calculate the friction torque when the temperature rises and fall,and investigate the change of the pre-tightening force under the cycle temperature;Investigate the influence of factors such as friction coefficient,temperature peak,and initial tension on bolt loosening.The results show that whether the bolt connection is loosened is mainly due to the relationship between the friction torque of the thread surface and the loosening torque;the friction coefficient increases,the less the temperature causes the loosening;the higher the temperature amplitude,the faster the pre-tightening force decreases;the initial pre-tightening force is increased,The pre-tightening force decreases.