Study On The Reinforcement And Blend Dependence Of Hyperelasticity Of Tire Rubbers Under The Moderate Finite Deformation

Designing the rubber materials to meet the performance demand of various advanced tires is an important engineering purpose in the tire industry. To achieve above engineering goal, since past decades, people have realized that it is necessary to develop the theory on reinforcement and blend dependence of hyperelasticity of rubbers, which is also one of the frontier research directions in tire engineering and academic community. Based on the practical moderate finite deformation (MFD) case of tire rubbers, the study on reinforcement and blend dependence of hyperelasticity of rubbers is systematically carried out in this dissertation, by using the method of combining experimental research with numerical analysis.Based on the Automated Grid Method (AGM) testing system, the uniaxial tension tests of three typical kinds of Carbon-Black (CB) filled rubbers with different elastomer matrix (NR, SBR and BR) are conducted under MFD. The CB reinforcement dependence of hyperelastic properties of rubbers is revealed. Along with the increase of filler content, the stress-strain curve rises up, the "S" shaped feature of the curve becomes more obvious, and the stress at certain stretch increases nonlinearly. Fitting results show that the Modified8-Chains (M8C) model has good suitability for characterization of the hyperelasticity of filled rubbers with different filler content and different elastomer matrix. At the mean time, quantitatively relationship between the parameters of M8C model and filler content is established, which is able to explicitly predict the reinforcement dependence of hyperelasticity of rubber materials.By applying AGM system with a temperature box, the uniaxial tension tests of NR with different filler content (including unfilled NR) are conducted at different temperature. The temperature dependence of hyperelastic properties of rubbers is revealed. The filled rubber has a tendency first to become soft and then to become stiff through its "critical temperature", while the unfilled natural rubber directly becomes stiff with temperature rising. Based on the test results, the changing trend of "energy elasticity" with environmental temperature is concluded by introducing the concept of "corrected stress". Thus, from the viewpoint of temperature dependence of "energy elasticity" and in conjunction with the classical "entropy elasticity" theory, these above temperature dependent characteristics of filled and unfilled rubbers could be interpreted more specifically and rationally. Besides, fitting results show that the M8C model is suitable in characterizing the hyperelasticity of rubbers at different temperatures. Recruiting to the energy and entropy elasticity theory, the explicit expression of temperature dependent M8C model is obtained, which can predict well the temperature effect on hyperelasticity of rubbers and corresponding "critical temperature".Based on the consideration of spherical symmetry of CB particles of filled rubber, a "basic cell with24-faces" and another "basic cell with48-faces" are presented, and the corresponding Representative Volume Element (RVE) models are respectively constructed by using these two kinds of basic cells, in which the filler particles randomly distributed in elastomer matrix. With these two multi-particulate numerical models, the computational hyperelastic stress-strain relationship for filled rubbers with different reinforcement volume fraction are obtained, which indicates that the RVE model consisting of "basic cell with48-faces" is superior to "basic cell with24-faces", and superior to "basic cell with12-faces" reported by current references, namely the simulation with polyhedron shaped "basic cell" being more approximate to sphere produce better predictions for the hyperelastic behavior of reinforced rubbers. The calculated stress contour plots of RVEs also reveal the features of local stress distribution of filled rubbers during deformation. Very highly stress concentration phenomenon is observed in those matrix areas connecting the CB fillers, and with more CB filler content, the rubber matrix has a larger maximum stress concentration coefficient.By modifying the shape of "basic cell with48-faces", the "basic cell without radial angle" is proposed. And by introducing the cohesive element, the RVE random numerical model which can take into account decohesion in the particle/matrix interface is established, in which the interface strength is determined by trial calculation and the two other relevant parameters are obtained by referring literatures. This model is used to simulate the uniaxial tension process of NR with20.3filler volume fraction, and the computational curve is in good agreement with the test curve (namely eliminating the "turn up" phenomenon of the simulation data without decohesion considered), which primary shows that this method is efficient. Additionally, the numerical simulation results also primary demonstrate the mesoscopic mechanism of decohesion. During the deformation of rubber materials, the stress concentration is most severe in those neck parts of matrix between adjacent particles and along with tensile direction, which results in the onset of cavity in the interface. With deformation increasing, the size of the interface cavity increases, namely decohesion is a revolution process of cavity from nucleation to growth.The uniaxial tension tests of two typical kinds of blended (NR/BR and NR/SBR) pure rubbers and filled rubbers are carried out under MFD. Test results prove that the mixture rule of hyperelastic properties can be applied to pure blend rubbers, but can not applied to filled blend rubbers, which implies that the blending mechanism of filled rubber is different from the pure rubber. The hyperelastic mixture rules employing M8C model and Yoeh model are corresponding used to predict the hyperelastic properties of tested rubbers. Comparison results illustrate that the one using M8C model can produce better prediction effect, which also verify that the choose of appropriate strain energy density function is essential to predict the hyperelastic blending characteristic of rubbers.The final part concludes all the works of this dissertation, and presents the prospect of future work.