Studies On Dynamic Modeling Of Bolted Joints Based On Fractal Theory

As is known to all, a complete machinary is constituted of various parts according to design requirement, expecially the large-sacle equipment, and the bolted joints are widely used in the machinary. Because the influence of joints, the whole mechanical system no longer continous, and the ′contact surfaces′ are formed between the parts. The friction and wear of contact surfaces have an signification influence on the dynamic characteristic of mechanical assenbly, so it is important that research the dynamic characteristic of contact surfaces.Based on the fractal theory, the micro-contact mechanism of joint surfaces are analysed, the micrograph of joint surface is characterizatied, and the three-dimensional stiffness model of normal and tangentia contact are established, then theoretical analysis and experiments are executed.The specific research contents are as follows:Firstly, as the specialty of joint surfaces, the research background and meaning are illustrated of this paper, then the fractal theory is introduced, and the micro-contact mechanism of joint surfaces is analysed, the three-dimensional contact fractal model of joint surfaces is disscussed in a single spheroid asperity, the normal contact load and the real contact area, after that, the influence factors of contact stiffness are analysed.Next, based on deformation features( elastic contact deformation, elastic-plastic contact deformation and plastic contact deformation), the highly nonlinear three-dimensional fractal model are established of normal contact stiffness and tangential stiffness, then the different parameters on the impact of contact stiffness areanalysed, such as fractal dimension, fractal roughness and external load. Research shows that the non-dimension normal and tangential stiffness are positive relation to the load, the stiffness increased with increasing D and decreased with increasing G*.Finally, based on the fractal function, the single spheroid asperity model is established, the three-dimensional model and the contact model by use of MATLAB and Pro/E, then the models analysed by used of ANSYS and gain the function between external load and deformation, an exponential relationship(K=mPn) model between normal/tangential stiffness and pressure is achieved by differential method, with the increasing of D, the coefficient m is increased and n is decreased. The validity of the model was verified with an example.