# Rubber Creep Model and Its Influence on Mounting Stiffness
## 4 Influence of Rubber Creep on Static and Dynamic Characteristics of Mount  
### Influence of Rubber Creep on Static Characteristics of Engine-Mounted Main Spring  
The static characteristics of the suspended rubber main spring were simulated and analyzed based on different creep models, and the geometric models without creep, 2.98 mm creep and 3.83 mm creep were established. The static characteristics of the suspended rubber main spring were analyzed based on the creep. Considering that there would be errors in solving different models, the three 3D models with different creep were divided into grid cells of the same size to eliminate the errors in the calculation results caused by grid reasons, and then the divided grid models were imported into ABAQUS for simulation calculation respectively. Simulation analysis steps: Just set a static analysis step, fix the lower end of the main spring, set coupling constraints in the middle loading position of the main spring, concentrate the six degrees of freedom of all nodes at the loading position to a single point, and apply a load of 1000 N in the -Y direction, as shown in Figure 6.  
The resulting data were extracted and the corresponding force-displacement curves drawn, as shown in Figure 7. Generally, the static stiffness of the suspended main spring can be obtained by the slope of the linear section of the curve. Therefore, the static stiffness corresponding to the non-creep, 2.98 mm creep and 3.83 mm creep are 201.8 N/mm, 253.3 N/mm and 269.6 N/mm, respectively, after calculation. The error between numerical simulation results and experimental results is small. The reliability of the numerical model is verified. It can be used for simulation calculation.  
Figure 6: Finite element model of mounting main spring.  
Figure 7: Static stiffness curve after suspension creep.  
When the creep increases from 0 to 2.98 mm, the static stiffness of the suspended main spring increases by 51.5 N/mm, while when the creep increases from 2.98 mm to 3.83 mm the static stiffness of the suspended main spring increases by 16.3 N/mm. The variation of the static stiffness of the suspended main spring is greatly affected by the creep. As can be seen from the stress cloud diagram of the suspended main spring in Figure 8, for different degrees of creep, the shape variable of the suspended main spring under the same load changes very significantly. As the load increases, the size of the suspended main spring is compressed less in the same time.  
The engine is mounted in a left-right symmetric structure. While the axial static stiffness is calculated, the radial static stiffness of the suspended main spring is also simulated and analyzed. Figure 9 shows the force-displacement curves of the calculated results of three creep models, namely, non-creep, 2.98 mm creep and 3.83 mm creep. The radial static stiffness values are 133.4 N/mm, 144.2 N/mm and 157.5 N/mm, respectively. From the change of radial static stiffness, it can be concluded that when the creep increases from 0 to 2.98 mm, the stiffness value increases by 10.8 n/mm, and when the creep increases from 2.98 mm to 3.83 mm, the stiffness value increases by 13.3 N/mm.  
Figure 8: Finite element model of suspended main spring. (**a**) Mises stress cloud map of static stiffness without creep. (**b**) Mises stress map of 2.98 mm creep stiffness. (**c**) 3.83 mm misses.  
In the analysis of the axial and radial static stiffness of the main suspension spring of rubber creep, the axial and radial static stiffness of the main suspension spring increase with the increase of the creep. Moreover, axial stiffness is more affected by creep than radial stiffness.