Micro-vibration exists extensively within high-tech industrial plants, precision laboratories, spacecraft and other structures, and the operation of the precision equipment will be seriously affected. Space micro-vibration will seriously affect the imaging quality of high resolution camera, reduce the hit accuracy of the guided weapon, shorten the service life of the precision instruments and spacecraft, will seriously hinder the development of advanced science and technology. Therefore, the research of micro-vibration suppression is an important and urgent task. At present, for the research on micro-vibration suppression, rich achievements have been gained and various technical means have been proposed. However, there are still some problems, such as additional energy supplies, the interference of magnetic field, time delay effect, which may lead the control system become unstable. These problems will become more prominent on the space micro-vibration control performance. Therefore, it is necessary to further study the micro-vibration control, and propose the more simple, effective and stable vibration control method. Viscoelastic materials and dampers are widely used for vibration controlling in the fields of aerospace, mechanical engineering, civil engineering, vehicle engineering and military facilities owing to their advantages of strong energy consumption, reliable performance, no additional energy, easy manufacture and low cost. A lot of research on viscoelastic dampers for ordinary vibration suppression have been conducted by researchers. These studies are focused on the performance of viscoelastic dampers, mechanical model of the damper and the controlled structures. However, Studies on the application of VE dampers under micro-vibration conditions are rare and have not been reported，especially the vibration mechanism and mechanical properties of viscoelastic materials under micro-vibration need to be further studied.
This paper is aimed at using viscoelastic dampers to suppress micro-vibration. Then, the theoretical and experimental study on micro-vibration damping mechanism of viscoelastic material, mechanical properties and mechanical model of viscoelastic dampers under micro-vibration conditions were carried out. Based on the above studies, a viscoelastic micro-vibration isolation and mitigation platform was designed and was introduced to isolate micro-vibration caused by the spacecraft flywheel. Then, the dynamics model of the coupling system that consists of the platform with flywheel was established. Finally, the numerical simulation analysis of dynamic response and isolation and mitigation effect of the system were analyzed and discussed. The research of this paper is of great significance to promote the development of micro-vibration suppression technology and viscoelastic damping technology. The following is the main content and conclusions of this study:
（1）The molecular chain structure of the matrix rubber was abstractly analyzed. The effects of the structure of the crosslinked network chain and the structure of the free molecular chain on the properties of the viscoelastic material were investigated. The influence of chain length heterogeneity and chain motion constraint on the elastic recovery properties of viscoelastic materials in cross-linked network chains was studied. The effect of chain length heterogeneity of free molecular chain on the energy dissipation of viscoelastic materials was also studied. The results show that the mechanical properties of the matrix rubber are mainly related to the molecular chain structure characteristics, but has no relation with the displacement amplitude, this indicates that the application of viscoelastic materials to micro vibration suppression is feasible.
（2）The effects of the filler-filler interaction and filler-rubber interaction on the mechanical properties and energy dissipation of the viscoelastic materials were studied. The energy dissipation caused by the filler-rubber interaction and the evolution of filler-network were deduced respectively. The results show that the filler structure and volume fraction have a great influence on the energy consumption capacity of viscoelastic materials.
（3）Based on the study of the relationship between microstructure and properties of viscoelastic materials, the micro-vibration damping mechanism of viscoelastic materials was studied by combining the characteristics of micro vibration. The results show that the energy consumption of viscoelastic materials is mainly due to the filler-rubber interaction and the matrix rubber under micro-vibration conditions. This study provides theoretical guidance for the development of high energy consumption viscoelastic micro-vibration suppression materials.
（4）Based on the achievements of study on micro-vibration damping mechanism of viscoelastic materials, micro-vibration suppression viscoelastic materials were developed and made into corresponding viscoelastic dampers. Under the micro-vibration conditions, the experimental study on the developed viscoelastic dampers were conducted at different temperatures, frequencies and amplitudes. Then, the effects of temperature, frequency and amplitude on the viscoelastic dampers were analyzed. The results show that the viscoelastic dampers have better energy dissipation capacity under micro vibration condition, and the temperature and frequency have a great influence on the mechanical properties, while the influence of amplitude is small.
（5）Based on the micro-vibration damping mechanism of viscoelastic materials and the mechanical properties tests of viscoelastic micro-vibration dampers, the microscopic chain structure model of viscoelastic dampers is proposed. By combining with temperature-frequency equivalent principle，the modified microscopic chain model are finally proposed. The results of the tests and the model were compared and it can be found that the two are in good agreement. It is shown that the proposed mechanical model can comprehensively reflect the influence of temperature and frequency on the mechanical properties of viscoelastic materials. At the same time, the microscopic chain model can reflects the relationship between the dynamic mechanical properties and the microstructure of the material. The model parameters are related to the microstructure of the viscoelastic material and have a clear physical meaning.
（6）Based on the analysis of the characteristics of flywheel vibration system and flywheel structure, the scheme of using the viscoelastic vibration isolation device for the vibration reduction of the flywheel system was put forward. The dynamic characteristics of the flywheel system are analyzed, and the influencing factors of the micro-vibration disturbance of the flywheel system are studied. Then, the micro-vibration excitation model of the flywheel system is established. The results show that the micro disturbance caused and transmitted to spacecraft by the flywheel system is closely related to the structure of the flywheel itself, and it is influenced by the modal of the flywheel. The micro-vibration isolation and mitigation platform for flywheel system was designed by using high energy consuming viscoelastic material. The viscoelastic isolation and mitigation element as key components of the platform was studied. It is found that the damping effect of the isolation and mitigation element is better than that of the ordinary vibration isolation device due to the frequency dependence of the viscoelastic material. The coupling dynamic model of the flywheel micro-vibration isolation and mitigation system is established, and the dynamic response and the vibration reduction effect of the isolation and mitigation system are analyzed under different excitation. The results show that the designed isolation and mitigation device can effectively suppress the transmission of micro disturbance from the flywheel to the spacecraft structure, and it has a good isolation effect at the different excitations.
The innovations of this paper are of the followings:
（1）The micro-vibration damping mechanism of viscoelastic materials were studied. The effects of molecular structure, additive effect and filler on the energy dissipation of viscoelastic materials were studied at the microscopic level. The energy dissipation mechanism of viscoelastic materials is studied theoretically, which provides the theoretical basis for the development and application of high performance viscoelastic materials.
（2）The mechanical properties of viscoelastic dampers under micro vibration are experimentally studied, the effect of temperature on the mechanical properties of dampers are especially considered. The influence of ambient temperature, excitation frequency and displacement amplitude on the mechanical properties of viscoelastic dampers under micro vibration condition is studied. Based on the damping mechanism and performance test of viscoelastic materials, a modified microscopic chain structure model which can describe the influence of temperature and frequency on the mechanical properties of viscoelastic dampers is proposed.
（3）The micro-vibration isolation and mitigation platform is designed by using the high energy consumption viscoelastic material. The flywheel system is used as the vibration isolation object, and the flywheel vibration isolation and mitigation system is established. The dynamic response and the vibration reduction effect are analyzed.