Research On Contact Characteristics And Modeling Method Of Bolt Rough Interfaces

Bolted connection has the advantages of convenient installation and disassembly.It is widely used in aviation and aerospace,high-grade CNC machine tools and other mechanical equipment.Since bolted connection forms a contact interface,the micro roughness of the interface results in complex contact stiffness and damping of the interface,leading to complex dynamic performance of mechanical equipment.The contact characteristics of the interface are affected by the micro morphology of the interface,especially the micro roughness makes the contact characteristics of the interface more complex.Therefore,it is urgent to study the contact characteristics and laws of the bolt interface with micro roughness,establish an accurate contact stiffness model of the bolt interface,and set up a calculation model of the dynamic characteristics of bolted structure,thereby providing technical support for the bolted structure design of aviation and aerospace,high-grade CNC machine tools and other mechanical equipment.Taking the bolt contact interface as the research object,this thesis investigates the influence of micro roughness on the interface contact characteristics and the influence of micro roughness on the dynamic characteristics of bolted structure and reveals the influence of interface micro morphology parameters and interface attribute parameters on the contact characteristics of the contact interface and the modal frequency of the bolted structure are revealed.This thesis establishes an interface contact model with micro roughness and the equivalent model of dynamic characteristics of bolted structure considering the influence of micro roughness,which solves the problem that the current modeling technology cannot accurately obtain the modal frequency of bolted equipment due to the influence of micro roughness of the interface,and provides a theoretical foundation and method reference for the accurate prediction of static and dynamic performance of mechanical equipment,thereby providing a theoretical basis for improving the dynamic service performance and working reliability of mechanical equipment.The main achievements made in this thesis include:(1)The interface contact models of positive contact and side contact of micro convex body considering the micro rough morphology and texture direction of interface are established.With respect to the limitations of the current mechanical contact model hypothesis of micro convex body and according to the measurement results of the micro morphology of the interface surface and the hypothesis that the height distribution of micro convex body obeys Gaussian distribution,this thesis conducts the mechanical analysis of the positive contact of micro convex body and establishes the interface normal contact stiffness model based on statistical theory.This thesis builds an explicit analytical expression of the normal contact load on the contact deformation,which overcomes the disadvantage that the existing model parameter expression can only obtain the numerical solution.Based on the mechanical analysis of the lateral contact micro convex body,it decomposes the contact force on the micro convex body into the normal component perpendicular to the ideal plane and the tangential component parallel to the ideal plane and establishes the interface normal contact stiffness model considering the lateral contact of the micro convex body.The results show that the contact force,contact area and contact stiffness increase nonlinearly with the decrease of the average contact spacing of the contact interface.(2)This thesis proposed a method to study the contact area and contact pressure distribution of bolt interface,thereby laying a foundation for establishing the equivalent model of dynamic characteristics of bolted structure.In view of the problem that it is difficult to determine the thickness and elastic modulus of the virtual material layer at the bolt contact interface and based on the analysis of the micro roughness characteristics of the interface surface,this thesis proposes a method to determine the thickness and elastic modulus of the virtual material layer at the interface.In view of the problem that it is difficult to determine the contact area and contact pressure distribution of bolt interface,this thesis proposes a method to investigate the contact characteristics of bolt interface based on virtual material layer method,with which it determines the contact area of bolt interface by finite element method,and then carries out the experiment research and verification of the determination results obtained with this method.Then,this thesis finds out the law of the influence of the micro roughness on the real contact area of the bolt interface.The research shows that the micro roughness increases the distribution range of the real contact area of the bolt interface.Given the same other parameters and without considering the influence of the contact boundary conditions on the contact pressure area,the contact area of the interface decreases gradually with the increase of the elastic modulus of the virtual material layer.(3)This thesis establishes a semi-analytical theoretical model of multi-interface bolted stiffness considering the distribution law of interface contact pressure.In view of the problem that it is difficult to accurately establish the calculation model of the stiffness characteristics of bolted structure,firstly,this thesis investigates the law about the influence of the micro roughness of the contact interface on bolted stiffness.Based on the analysis of the influence of each single factor on the bolted stiffness of the smooth contact interface and the mapping relationship between the parameters,this thesis uses the Levenberg-Marquardt intelligent algorithm for optimal fitting,obtaining the semi-analytical theoretical calculation model of the bolt head smooth contact interface connection stiffness and the semi-analytical theoretical calculation model of the connected part stiffness.Based on the investigation into the contact pressure distribution law of bolt single interface,considering the influence of smooth surface interface and the characteristics of uneven interface pressure distribution,this thesis establishes a semi-analytical theoretical model of bolted stiffness considering the influence of micro roughness of contact interface,and constructs a calculation method of multi-interface bolted stiffness,thereby solving the problem of large error of current calculation methods.(4)This thesis establishes an equivalent model of dynamic characteristics of bolted connections considering the influence of multiple rough surface interfaces.Based on the theoretical model of normal contact stiffness of contact interface as established,which considers micro roughness,this thesis investigates the contact area and pressure distribution of the given bolt structure and establishes an equivalent model of dynamic characteristics of bolted spring damping considering the influence of micro roughness of contact interface.Such model overcomes the disadvantage of not considering the influence of micro roughness of contact interface in the past and solves the problem that the previous model ignores the influence of the micro roughness of the contact interface on the contact area.