| Joint interfaces are widely used in machine tools and other mechanical structures.Contact characteristics of joint interface such as contact load,contact area,contact stiffness,contact damping,friction and so on have an important influence on the static and dynamic characteristics of mechanical structures,and it is of great significance to carry out the modeling and experimental research on the contact characteristics.In view of the shortcomings of existing studies,this dissertation firstly studies the contact characteristic modeling of multiscale asperity during loading and unloading process of the joint interface based on the important characteristics of multiscale contact of the joint interface,and the change of hardness of the asperity with elastic-plastic deformation and the influence of friction factor are considered respectively.On this basis,based on the multiscale contact fractal theory of the joint interface,the multiscale fractal model of the contact characteristics of the joint interface considering the influence of hardness changes and the multiscale fractal model of the contact characteristics of the joint interface considering the influence of friction factors were established respectively,and the corresponding simulation analysis was carried out.Furthermore,the correctness and feasibility of the models are verified by the experimental modal analysis of the linear rail sliding table.The main research contents and innovations of this dissertation are as follows:1.Defined the critical deformation of multiscale asperity in each deformation stage,and researched on the elastic and plastic deformation contact characteristics of multiscale asperity during loading and unloading process.A theoretical model of loading and unloading process of multiscale asperity without considering the influence of hardness change and friction factors is established.2.The limit mean geometric hardness function based on the first and second elastic-plastic deformation mechanism of the asperity is constructed.The theoretical models of contact area,normal contact load and contact stiffness of multiscale asperity were established considering the change of contact surface hardness.Then the multiscale fractal theoretical models were established considering the change of contact surface hardness,and simulation analysis was carried out to obtain the influence of fractal parameters,material properties and deformation on the contact characteristics of the loading process of the joint interface.3.The limit mean geometric hardness coefficient and deformation ratio W in the unloading process of the multiscale asperity were introduced to study the relationship between them in each deformation stage.The theoretical models of contact area,normal contact load and normal contact stiffness of multiscale asperity during unloading process considering the change of contact surface hardness were studied,and the corresponding results were compared and analyzed with the corresponding results without considering the change of hardness.The distribution density function correction coefficient and contact load correction coefficient considering hardness change during unloading process are studied.Furthermore,the multiscale fractal theoretical models of joint interface during unloading process were established considering the change of contact surface hardness,and simulation analysis was carried out to obtain the influencing factors of joint interface contact characteristics of unloading process.4.The contact characteristics of the multiscale asperity during loading and unloading process with the influence of friction factors were studied and the fractal theoretical models were established.The influence of friction coefficient and fractal parameters on the normal contact load and contact stiffness of a multiscale asperity was studied.On this basis,according to the range of different scale series,the contact load correction coefficients considering the influence of friction factors at each deformation stage of unloading process of joint interface are introduced.Furthermore,the multiscale fractal theoretical models of contact area,normal contact load and contact stiffness during loading and unloading process of joint interface considering the influence of friction factors were established and simulated.5.The changes of normal contact load and contact stress of a single asperity during loading and unloading were obtained by using finite element analysis software.At the same time,the plastic properties of asperity materials are introduced into the solution by multi-linear follow-up strengthening model.The results were compared with three kinds of fractal theoretical models of contact load of a single asperity established in this paper,and the rationality of the contact load model of a single asperity given in this paper considering hardness changes and friction factors was verified.6.According to the two normal contact stiffness theoretical models of the joint interface established in this paper,the simplified model of the JNYOLRS250 series of linear rail sliding table with the model of LRS250×560 is established by using finite element analysis software and the finite element modal analysis is carried out to obtain the first 14 order modes of the two groups of modal analysis of the slide table.The first 8 modes were obtained through modal tests on the rail sliding table.The theoretical and experimental modes are compared to verify the correctness of the fractal theoretical models of normal contact stiffness of the joint interface,which were established in this paper respectively considering hardness changes and friction factors.The multiscale fractal theory models of contact of joint interface in loading-unloading process established in this dissertation can provide theoretical basis for the study of contact and friction of joint interface,and it is of great significance to describe the contact state of joint interface scientifically and reasonably and to establish more accurate dynamic model of joint interface. |
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