Investigation On Fracture Failure Behavior And Machanism Of Flow Booster Coupling Tail Bracket

A fracture occurred on a flow booster coupling bracket of a sewage treatment plant,which caused serious economic loss to the enterprise.The failure behavior analysis and mechanism research of the coupling bracket may help to find out the root causes of the incident,and to prevent the similar failure,and to promote the safety production of the enterprise.The objective of this paper is the fractured coupling bracket connection bolts.The fracture failure behavior and mechanism of coupling bracket joint bolt were investigated based on physical and chemical properties tests,strength analysis,contact finite element numerical simulation analysis,and fatigue characteristic.The main contents of this paper are as follows:(1)The physical and chemical properties of the fracture bolts and flange of the coupling bracket were examined,including macroscopic and microscopic observation of the fracture,chemical composition analysis,mechanical property tests and metallographic analysis.Through a series of tests,the failure mode is determined and the intrinsic causes of the coupling bracket fracture are found.(2)The connection bolts are regarded as an elastic system,and the mechanical properties under preloading and external loading are analyzed.Then the Yamamoto analytical solution of bolt axial load distribution is obtained by Yamamoto method for bolt load distribution.By checking the static strength of the bolts,thread strength of the bolts,the contact strength of flange bolt holes and fatigue strength of the bolts,the results are used to verify if the bolt and the flange bolt holes are overloaded or with insufficient fatigue strength.(3)The ANSYS software is adopted to conduct the contact finite element analysis,and to simulate the actual operating conditions of the joint bolts.The stress distribution is obtained for the mechanical factors of the fracture bolts and flange and the possible crack initiation position.The simulation results are verified by comparing the simulated solution and the analytical solution of the axial load distribution.In addition,the effect of the rim radius at the root of the thread,the pre-tightening torque and the vibration on the fatigue life of the bolts are discussed,and the optimal design is carried out.(4)The fatigue strength limit and S-N curve expression of the bolts are obtained through fatigue test of the bolt samples.Then the fatigue design of the bolts are based on S-N curve,and the maximum stress amplitude that the bolts might withstand under working conditions are obtained.Finally,the fatigue life of the bolts is simulated with nCode Fatigue-Life fatigue analysis software,and the fatigue life contours and fatigue damage contours of the bolts are obtained,and the fatigue properties of bolts is analyzed.(5)The causes for the fracture of coupling bracket joint bolt are comprehensively analyzed,and corresponding improvement measures are put forward according to the factors including material,strength,stress concentration and operation conditions.