Research On Experiment And Calculation Method Of Dynamic Characteristics Of Mechanical Joint Surface

In Mechanical Structure, the surface between two components is defined as 'Mechanical Joint Surface'. Because of exist of the mechanical joint surface, the machinery is not an continuous structure. So the joint surface exerts a tremendous influence on the dynamic characteristics of the mechanical structure. Studies have shown that joint surfaces usually become the weak part of the mechanical structure. So the joint surfaces must be concerned in the research of the machinery dynamic characteristics. The joint dynamic characteristics are concluded as two joint parameters-Contact Stiffness and Contact Damping, according to its feature (there are both elasticity and damping). Yet the joint parameters can be used in the whole machine modeling. The identification of the dynamic joint parameters becomes the key issue of the joint research therefore. This paper presents methods to identify the dynamic characteristic parameters of bolt-joint and shrink-fit interface, and to use the parameters in the FE-modeling (finite-element-modeling) of a typical motor frame.For bolt-joint surface, the joint parameters identified under a certain situation (including the number, the layout form and the pretightening force of bolts) are not universally applicable. Not limited to the specific mechanical structure, an experiment platform is specially designed, the test system is set up, and the kinetic model of the joint surface is derived. The contact stiffness and contact damping per unit area of the joint surface are acquired by the test system. The joint parameters in different joint conditions can be got by adjusting the experiment platform and replacing the specimens. In this way, the parameters identified are versatile. On the basis of the experiment results, the variation rules of the contact stiffness and contact damping with changing of pre-load, exciting frequency and surface roughness are summarized, and the mechanism is analyzed.For shrink-fit interface, it has difficulty in identifying the joint parameters by experiment. The FEA (Finite Element Analysis) method is utilized therefore:the FE-model of the shrink-fit assembly is built in ANSYS. The boundary conditions are applied on the FE-model. Parameters of nodes and elements on the interface are extracted after simulation to calculate the contact stiffness and contact damping. Theoretical model of the shrink-fit assembly is derived by using receptance coupling method, while the contact stiffness and contact damping are added in. Then the FRF (frequency response function) on one end of the shrink-fit assembly is calculated. At last, the calculated FRF is compared with the experimental one to verify the shrink-fit interface parameters.The contact stiffness and contact damping identified by experiment are applied on FE-modeling of the mechanical structure. A typical motor frame is chosen as the study object. In the FE-modeling, the spring-damping elements are built on the bolt-joint surface. The mode analysis is completed. The result is contrasted to the experimental one to verify the FE-model. Accordingly a method dealing with the joint surface in the FE-modeling is raised.