Study On Contact Stiffness Modeling And Equivalent Method Of Generalized Clearance Of Fixed Joint Surface

The machine joint surfaces exist extensively in assembling machinery parts. It plays an important role to transfer movement, load and energy in the normal operation of mechanical system. The joint surfaces’ material and contact interface parameters affect the stiffness, damping, machining accuracy and stability of the whole mechanism. Studies on joint surfaces’ dynamic characteristic aims at exploring the mechanism of affecting mechanical dynamic performance, hence for providing theoretical basis for design material selection, maching of part’s face, assembly of mechanical parts and error compensation of mechanical processing. Thus, by developing this research, it has important significance on theory and practical applications.The joint surface of composite beams with bolt tightening is taken as the study subject, and the combination of theoretical derivation and experimental verification is taken as the research method. This thesis mainly studies the influence of elastic-plastic deformation, modeling of joint surfaces’ contact stiffness, the generalized clearance equivalent method processing and modal test. The tasks are listed out mainly on the below several aspects:(1) The fractal modal of normal contact stiffness and tangential contact stiffness are established considering the influence of elastic-plastic deformation, and the influence of relevant parameters is revealed. Based on fractal contact theory, the M-B fractal contact model is modified. Considering the influence of elastic-plastic deformation, the fractal modal of normal contact stiffness and tangential contact stiffness are established. With the research of numerical simulation, the influence of normal load, fractal dimension, fractal scale parameters and material characteristic parameters on contact stiffness are revealed.(2) The fractal dimension D and the fractal scale parameters G of structure surface are measured. Based on the fractal properties of surface micro-morpholog of component, the fractal dimension D and the fractal scale parameters G of composite beam’s joint surface under different processing precision are measured with roughness measuring instrument, which can provide data support for the posterior research of the influence of micro-morpholog on the natural frequencies of composite beams.(3) Based on the established "solid-generalized clearance-solid" system, the generalized clearance equivalent method of composite beams is researched, and the finite element modal analysis is carried out. The composite beams and their joint surface are reconstructed as a "solid-generalized clearance-solid" system. That is, the joint surface is regarded as the generalized clearance. Then, the generalized clearance equivalent model is established by making equal of the contact stiffness fractal model and the strain energy of the material. By infite element analysis, the influence of micro-morpholog on the natural frequencies of composite beams is researched.(4) The experimental verification of generalized clearance equivalent method is completed. First-5natural frequencies of composite beams’ bending vibration is obtained by modal test. Through the error analysis of generalized clearance equivalent method results and modal test results, the generalized clearance equivalent method is verified feasible.