Research On The Contact Mechanics Characteristics And Relative Aspects Of A Wire Race Ball Bearing

In recent 10 years, the wire race ball bearing has been extensively used, including in the field of weapon equipments, like the big antenna of radar and the aircraft simulating rotary table; the field of numerical control slewing machines, the field of building machineries, the medical apparatus and instruments, and the field of the textile industry. It has been regarded as a technique of the supporting system with high ratio of stiffness to inertia and high resistance capability to overturning moment. It has become the optimal proposal for solving the engineering design and manufacture problem with limitation in spatial dimension, and with restriction in mass and inertia. This kind of bearing can simultaneously support axial loads, radial loads, overturning moment and compound loads. However, the alternating stress and the residual unbalanced moment often result in fatigue, wear and pitting corrosion on contacting surfaces of wires. They have significant effects on the precision and dynamic stability of the system. No effective method has been reported. Hence, we present that this problem can be treated as a contact problem. According to the corresponding theories of contact mechanics, tribology and material science, by the analytical method, elastic-plastic finite element method and experiments, with taking the geometric nonlinearity, the material nonlinearity, the compound load distribution and the friction into account, the preload of the wire race ball bearing, the supporting stiffness and the contact failure were investigated in detail.Reasonable preload can improve the supporting stiffness; while excessive preload results in plastic deformation and contact failure. Therefore, the research on preload is critical.In order to eliminate the problem of the traditional method for adjusting the preload which relies heavily on personal experience of engineers, the mechanical equilibrium conditions were analyzed firstly. Then, the preload mathematical model of a wire race ball bearing was built based on the non-conforming Hertz contact theory. And a numerical method was developed in MATLAB?. The normal contact forces, contact deformation, contact pressure distribution and the semi axes of the contact ellipse were obtained. Further, the appropriate range of preload for a wire race ball bearing was achieved. Finally, the preload measuring system was constructed by employing an example of a wire race ball bearing with a diameter of 1000 mm used in a certain type of aircraft simulating rotary table. The experimental results are in good agreement with the theoretical results.To exactly determine the preload magnitude of the wire race ball bearing, in the present dissertation, the mathematical model of the relationship between the starting torque and the preload magnitude was built, based on the analysis of the spatial force system, Coulomb's law, the law of rolling resistance and the theorem of equivalent spatial couple. The theoretical curve of the above model was obtained by the numerical solution in MATLAB?. Finally, the experiments were performed to validate the theoretical results. It shows that the theoretical and experimental results are very close. The investigation provides an effective method for the adjusting and controlling of preload in a wire race ball bearing in practice.It is paramount that the stiffness characteristic should be exactly described for being the foundation of the vibration theory and the structure stability analysis. Hence, firstly, the load distribution of the wire race ball bearing was analyzed. According to the non-conforming Hertz contact theory, the principle of virtual displacement, the cosine law, L'Hospital's rule and the definition of stiffness and flexibility and Stribeck's load distribution, the mathematical models of the axial supporting stiffness, the radial supporting stiffness and the overturning supporting stiffness were developed. Finally, the loading mechanisms were designed. The measuring systems of the above supporting stiffness were built. The experimental results are in good agreement with the theoretical results, which demonstrates the validity of the above supporting stiffness mathematical models. It provides basis for the contact dynamics analysis and parametric support for engineering application of the wire race ball bearing.The solution of contact problems is highly nonlinear and requires significant computer resources. The conventional contact analysis is mainly based on the classical Hertz elastic contact theory and the geometric and material nonlinearity are not considered. Hence, firstly, the geometric and material nonlinearity of 2 kinds of wires named No. I and No. II were taken into account by using the real stress-strain curve of the wire tested on the Instron-5569 universal electron tension tester. Secondly, the ANSYS Parameter Design Language (APDL) was used to model and solve the contact analysis of 4 kinds of 3-D contact sub-models, namely steel ball-wire race of No. I, steel ball-wire race of No. II, Si3N4 ceramic ball-wire race of No. I and Si3N4 ceramic ball-wire race of No. II. The von Mises stresses, the elastic strain, the plastic strain and the shape and sizes of contact ellipses were achieved. Finally, comparison between the elastic-plastic contact analysis and the elastic contact analysis shows that the elastic-plastic contact analysis is exacter and closer to the fact in practice; and the sub-modeling technology and the multi-size mesh method greatly contribute to the saving of the computing cost, and the improvement of the computational efficiency and precision.In addition, the influences of the contact load, the geometric parameters and the material property parameters on the contact characteristic are not clear. Furthermore, the characteristic, regularity and mechanism on wear and pitting corrosion are ambiguous. Therefore, firstly, the influnces of the contact load, the geometric parameters and the material property parameters on the contact characteristic were analyzed theoretically. Secondly, the contact failure experiments for the 4 types of contact, namely steel ball-wire race of No. I, steel ball-wire race of No. II, Si3N4 ceramic ball-wire race of No. I and Si3N4 ceramic ball-wire race of No. II were carried out. Finally, the contact zones of the contact bodies were characterized by the scanning electronic microscopy (SEM). The results reveal the characteristic, regularity and mechanism on contact failure. The present work provides theory and technology for effectively preventing the wire from contact failure and studying on the new material and the novel processing.