Research On The Deformation Coordination Mechanism Of Bolt Under Tightening Load And The Evolution Law Of Bolt Stress

With the rapid development of modern manufacture,mechanical equipment has gradually developed towards precision,complexity and intelligence.As the "meter of industry",bolts play very important role in the manufacture industry.Particular,the crucial connection parts of many major mechanical equipment are connected by bolts and fasteners.Whether the quality of the bolt connection is good will be directly related to the structural stability of the assembled components during working,as well as the durability and fatigue life of the assembled components.At present,when tightening bolts in the construction machinery,the utilization rate of torque for tightening is low.Among the input tightening torques,50%of the torque is used to overcome the friction under the bolt head,40%of the torque is used to overcome the friction of the thread.In other words,up to 90%of the torque is used to generate the shear stress of the bolt in the tightening stage,which is ineffective for bolt tightening.And only 10%of the torque is used to generate the bolt normal stress that is effective for bolt tightening.Thus the bolt pre-tightening force is insufficient,but the bolt stress is relatively large,which ultimately affects the bolt tightening performance.If the tightening performance does not meet the standard,it will lead to the bolt pre-tightening force degradation and bolt loosening,which will bring about major hidden dangers for the safe and stable use of mechanical equipment,and even cause major accidents.Research on the bolt assembly process that can reduce the bolt shear stress generated by the bolt tightening process,improve the utilization rate of the bolt,and improve the bolt tightening performance,and the coordination mechanism of bolt deformation and the evolution law of the stress field are urgent and have very important engineering significance.Aiming at the typical bolt connection structure widely used in construction machinery,the deformation coordination process of bolts,nuts,and connected parts in the bolt tightening assembly process with the back-tightening stage is explored.From the perspective of theoretical analysis,it reveals that the back-tightening stage is effective in reducing the shear stress of the bolts and improving bolt utilization.The finite element simulation model of the bolted connection structure was established using ANSYS Workbench,and the evolution law of the bolt stress field in the bolted connection structure under tightening load was analyzed,and the effect of geometric parameters,friction coefficient,material characteristics,and tightening load on the evolution of the bolt stress was revealed,especially on the shear stress release of the bolt in the back-tightening stage.Finally,a single bolt tightening test is used to verify the release effect of the bolt shear stress in the back-tightening stage.It mainly uses a combination method of theoretical analysis,finite element simulation,and experimental verification to explore the deformation coordination mechanism and stress field evolution of the bolt tightening assembly process including the back-tightening stage,and clarifies the importance of the research of the bolt stress and bolt utilization rate in the back-tightening stage.