It is characterized by linearity, exhibiting material nonlinearity, geometric nonlinearity and nonlinearity of boundary conditions. Its mechanical model is also much more complicated than ordinary helical springs. In this paper, the influence of different rubber materials on the stiffness characteristics of rubber composite springs will be discussed from the perspective of finite element nonlinear large deformation.
There are not only many finished or semi-finished rubbers in rubber materials, but also rubbers that can be specially formulated according to different applications. The axial tensile test curves for three rubbers with different mechanical properties are shown. According to the data obtained by the axial tensile test, the Ogton model constants 1, 1, 2, 2 and K (see) of each rubber material can be calculated by the curve fitting method, wherein the unit dimensions of the material constants 1 and 2 are First, the units of 1, 2 and K are MPa. Here, the Oggton model with N=2 is chosen because it is found that by selecting the Ogton model with N=2, the above description is well described. The characteristics of the three rubbers, and save finite element calculation workload. In the calculation of the rubber composite spring by the finite element method, the nonlinear finite element software (MARC) provided by MSC was used. The MARC software provides a program interface for fitting the Ogden model constants directly from the experimental data. In addition, it can be seen that the bulk modulus of the above three rubber materials is not large, because the overall stiffness characteristics of the rubber composite spring are taken into account, that is, when the rubber composite spring is compressed to a certain extent, the spring colloid and the spring When the skirt is in contact, the stiffness characteristics of the rubber composite spring are not too stiff. Starting with the spring skirt, the rubber composite spring outer unit and the spring skirt and spring cap are defined as contact bodies. Therefore, the analysis and calculation of the overall stiffness characteristics of the rubber composite spring is actually a multi-body contact problem.
In the finite element hexahedral mesh division and unit definition of the rubber composite spring, not only the influence of the material model on the overall stiffness characteristics of the composite spring, but also the shape characteristics of each elastic body or contact body must be fully considered. And the influence of the mutual relationship of the contact bodies on the overall stiffness characteristics. Therefore, in the computer modeling and finite element unit division, the model can not be simplified at random, the size should be as precise as possible, and the degree of density and the number of units of each elastic unit should be sufficient to describe the shape characteristics of each elastic body and their mutual relationship. Finally, a finite element partitioning model of the rubber composite spring is obtained (as shown). The rubber body portion is composed of 29,964 hexahedral Hermann units, and the coil spring is composed of 9522 hexahedral units. The total number of units in the model is 39,486 and the number of nodes is 43,207. According to the composition of the rubber composite spring and the characteristics of its service process, the spring top cover is moved downward at a constant speed for a stroke (such as 60mm), and the stroke is divided into several incremental steps (such as 50 steps), and then begins. Calculate the force of each incremental step spring cover on the rubber spring and the displacement of the spring in the vertical direction. The load of the spring top cover on the rubber spring is P, and the displacement of the top layer of the spring in the vertical direction is u.
The overall stiffness of the composite spring, which reflects the overall stiffness characteristics of the rubber composite spring. As a verification, the test points of the type 3 rubber composite spring were also marked. It can be seen that when the displacement of the spring in the vertical direction reaches u0, the slope of the curve Pu suddenly increases. This is due to the fact that the spring colloid is in contact with the spring skirt, resulting in a significant increase in the overall stiffness of the rubber spring. For this reason, the vertical displacement u0 of the spring when the stiffness of the rubber composite spring is significantly increased is the critical displacement. The critical displacement u0 of the three rubber composite springs is about 51mm, which indicates that u0 has little relationship with the mechanical properties of the rubber material, and has a direct relationship with the lateral clearance of the spring skirt.
Conclusion The variety of rubber material types determines the diversity of mechanical properties of rubber materials. This allows rubber-composite springs with rubber as the elastomer filler to have a wider range of mechanical properties. In view of the material diversity characteristics of rubber composite springs, non-linear finite element contact model calculation or computer simulation is used on the basis of the basic mechanical properties of rubber materials measured by simple mechanical tests when designing rubber composite springs for different purposes. It can greatly shorten its research cycle and reduce research costs.
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