Dynamic Stiffness Analysis of Rubber Mounting
With the improvement of people's requirements for automobile comfort, major engine manufacturers have put forward dynamic stiffness requirements to improve the vibration isolation rate of the mounting system. The usual requirement is that the dynamic stiffness at full throttle is less than a certain value. Therefore, the prediction of dynamic stiffness of common structures is of great significance in the development of rubber mounts.
Many scholars at home and abroad have used experimental or computational methods or a combination of the two to predict the dynamic stiffness of rubber parts. In the case of large deformation, the increasing trend of dynamic stiffness is different from that in small deformation. Build a chassis bushing model that simulates stiffness and damping behavior under a wide range of static and dynamic loads. Assume that the dynamic-to-static ratio at a certain frequency is constant, and use the test data of the rubber suspension test column at a certain frequency and strain level to determine the dynamic-to-static ratio of the rubber material at the specified frequency and strain level, and use the dynamic-to-static ratio Predict the dynamic stiffness of rubber parts. Dean and G studied the dynamic stiffness of carbon black filled rubber under small strain as a function of frequency, strain amplitude and temperature. The effects of preload force, amplitude and frequency on the dynamic stiffness of rubber were studied through experiments. The influence of rubber formulation on the dynamic and static ratio of rubber was studied. method to test the dynamic parameters of materials under high frequency pre-shear and pre-compression, and it is pointed out that the influence of pre-compression on dynamic performance is much greater than that of pre-shear. Due to the geometrical dependencies of empirical models, extensive testing is still required when the geometry of rubber parts changes. Using the combination of finite element method and empirical model, the dynamic stiffness of rubber bushings under excitation frequencies of 0~50Hz and different amplitudes is predicted, which greatly reduces the number of tests and calculation costs.
The challenges of predicting the dynamic behavior of preloaded rubber mounts are:
1) Viscoelasticity and nonlinear properties of rubber materials.
2) The initial deformation caused by the preload will affect the dynamic characteristics of the rubber mount.
3) Geometric correlation of dynamic characteristics. Through experiments and simulation calculations, the dynamic stiffness prediction methods of two common structural types below 300 Hz under the action of small amplitude and large preload are studied.
Correlation test and analysis of dynamic stiffness and frequency:
To investigate the general relationship between dynamic stiffness and frequency, the dynamic stiffness of specimens and typical parts were tested with amplitudes of ±0.01 mm and frequencies from 1 to 700 Hz, respectively. For the sample model, one end of the metal plate in the middle of the sample is fixed, and the excitation force F is applied to the other end. For the cross-rib bushing model used in the test, the outer ring of the part was fixed and an excitation amplitude was applied inside the core to test its dynamic stiffness.
The correlation between dynamic stiffness and preload:
In order to study the relationship between dynamic stiffness and preload, the dynamic stiffness of two common preloads at a fixed frequency was tested. They are part 1 and part 2 models tested separately. These two components have low static stiffness and low dynamic-to-static ratio under a preload of about 5000n. It can be seen from the test results that the influence of preload on the dynamic-to-static ratio fluctuates, but the general trend is that the greater the preload, the greater the dynamic-to-static ratio.
In order to further study the effect of preload on the dynamic-to-static ratio, a finite element model was established to analyze the stress-strain distribution under the action of large preload. The results show that the influence of medium pressure strain on dynamic characteristics is much greater than that of shear strain.