# Study of the Lifetime Testing of Spherical Rubber Isolators
## 1 Introduction  
With the rapid development of science and technology, various high-tech equipment is confronted with serious vibration isolation and buffering problems in specific environments. Engineering systems such as vehicles, ships, spacecraft, bridges, etc., are often subjected to various excitations, inevitably leading to various vibrations. When the components in the equipment cannot withstand the harsh mechanical environment, vibration isolation or shock absorption is desperately needed. At present, due to the relative flexibility of rubber materials, they can withstand up to 100% deformation and reinstate their original shapes after stress is released [1]. Consequently, they are widely used as vibration damping materials in a range of engineering fields. Notably, rubber isolators play an irreplaceable role as metal isolators especially in environments with special requirements, such as nonmagnetic requirements. Furthermore, modern engineering technology puts forward higher expectations and stricter requirements for solving vibration problems, yearning for thorough investigations of the dynamic characteristics of the rubber isolator.  
Despite the extensive use of rubbers in a variety of fields, the understanding of the characteristics of rubber materials is still relatively limited. Therefore, efforts need to be devoted to the research of the dynamic characteristics and fatigue lifetime of rubber isolators to improve vibration damping performance. The mechanical properties of rubber materials exhibit very complex behaviors, and the behavior under stress and deformation is generally nonlinear. References [2; 3; 4] introduced a detailed explanation of the nonlinear physical mechanism of rubber materials. The performance parameters of rubber isolators mainly refer to dynamic stiffness and dynamic damping, which not only depend on the chemical composition of the rubber material, but also on temperature, humidity, vibration frequency, and vibration amplitude. Of note, the rubber geometry also makes a difference [5; 6; 7]. If theimpact of nonlinearity on the dynamic characteristics of rubber materials could be fully understood, it would be possible to adopt new ways to improve the mechanical properties of rubber materials.  
Due to fatigue, aging, and other factors, the stiffness of the rubber isolator tends to transform with altered dynamic characteristics and load-bearing capacity. Stiffness failure is defined when the stiffness of the rubber isolator transforms by more than 50%. Due to numerous factors affecting the lifetime of rubbers, such as mechanical load (load amplitude, load ratio, load frequency, etc.) and the atmosphere (oxygen, ozone, water vapor, etc.), a comprehensive description of the fatigue characteristics of the rubbers and accurate prediction of the lifetime of the vibration isolator remain as technical barriers [8]. Generally speaking, the increase in the amplitude of a cyclic load leads to a decrease in the activation energy of the chemical reaction in the fatigue process, which makes it easier for the oxidation reaction to proceed and reduces the fatigue lifetime of rubber materials [9; 10; 11]. Therefore, the effect of mechanical vibration on the lifetime of rubber still needs further investigation.  
This paper is mainly divided into three parts to identify the dynamic mechanical properties of a rubber isolator when subjected to vibration excitation and investigate the fatigue lifetime of the rubber isolator. Firstly, the structure of the experimental system is briefly introduced, and the vibration test of the rubber isolator is carried out; then the mechanical model from the system structure is extracted, and the mathematical model of the rubber isolator is established and analyzed based on mechanics theory; finally, a fatigue lifetime prediction model of rubber isolators is established, and the influence of different load masses on the fatigue lifetime of the rubber isolator is explored.