An Investigation On Calculation And Modeling Methods For Static Properties Of A Rubber Isolator

With the rapid improvement of the vehicle industry, people pay more and more attentionto improve the NVH performance of the automobile. Automobile power-train is the mainsource of vibration and noise in automobiles, which has great effect on comfortability. Theengine mounting system, which is designed to isolate the vibration between the engine andthe chassis, plays an important role in avoiding the vibrations of the engine from the body.Rubber isolators are the major component of the Engine Mounting System. Using the finiteelement analyzing method to do the static characteristics analysis and optimize the design ofthe engine mount system, can avoid the vibrations from the body effectively and improve theautomobile comfortableness.In this paper, the static properties of two different kinds of rubber isolators areinvestigated using the finite element analyzing method. The contents of this dissertation are:1. The developing history of the engine mounting system and the rubber isolators areillustrated after reading large quantities of papers. The static properties calculation methods ofrubber isolators are summarized. The structure type and applied range of rubber isolators arepresented in this dissertation.2. The experimental method and hyperelastic constitute models of rubber material arediscussed, under the statistical thermodynamics and phenomenological theory. The stressversus strain relation of a rubber material, which can be used to obtain constitute constants,under simple tension, pure shear and equi-biaxial tension stress versus strain conditions aremeasured.3. The finite element modes (FEM) of two rubber isolators are created by usingHyperMesh. Then import the FEM to ABAQUS to calculate the force versus displacementrelations in three vertical directions. According to the actual working load of rubber isolator,the experimental stiffness is combined by the testing force and displacement in the MTS833three axial elastomeric testing systems.4. The experimental stiffness and the finite element simulation results are compared toanalyze the factors which would affect the accuracy of the estimated stiffness. It is known thatthe different stress versus strain conditions plays an important role in the force versusdisplacement relations. The estimated stiffness that calculated by using the constituteconstants under three kinds of stress versus strain conditions is more accurate than it onlyunder simple tension stress versus strain condition, when the mount is tension type mount. Onthe contrary, the estimated stiffness that calculated by using the constitute constants only under pure shear stress versus strain condition is more accurate than it under three kinds ofstress versus strain conditions.5. The reasonable selection of Rubber material constitutive model is also an importantfactor to guarantee the accuracy of the estimated stiffness. For common rubber isolators,Mooney-Rivlin model has the highest calculation precision, whose relative errors are less than10%. Then is Arruda-Boyce model, Ogden model and Yeoh model. The calculation relativeerrors of Marlow and Van der Waals model are larger than others. In practical engineeringapplication, the most suitable constitutive model should be selected according to rubberisolator’s structure characteristic and loading conditions.6. The Mullins effect has great influence on three-way static stiffness calculation resultsof rubber isolator. Therefore, in the stress-strain test about rubber material, the Mullins effectinfluence on test results should be eliminated as far as possible. Rubber material is definedwith incompressibility generally because of its little impact on calculation results.