Research On Natural Rubber Constitutive Model And Tire Forming Simulation

With the improvement of computer operation speed and ability,finite element analysis technology(CAE)has become an effective way to solve complex engineering problems.Carrying out the computer simulation of the tire building process can explore the influence of various process conditions on tire building,analyze the mechanism of pressure and temperature on the flow of natural rubber melt,determine the influence of the structure,shape,and material characteristics of the tire on the shaping effect,and reveal the internal connection between flow deformation and process conditions driven by high-pressure hot water,and then optimize the capsule structure and process parameters before the test,avoid the waste of materials,energy,time and molding defects caused by repeated tests,and improve the design efficiency.To obtain more accurate tire simulation results,rheological experiments and constitutive models of unvulcanized natural rubber melt were carried out in this paper.A modified Phan-Thien-Tanner(PTT)model was proposed to describe its rheological characteristics.Eight hyperelastic constitutive models and Prony series were evaluated based on Abaqus software and tensile and relaxation experiments.Based on the established material model,the molding simulation of rubber tire is carried out on the Abaqus software,and the applicability of the model is verified.The main research work is as follows:(1)The shear rheological experiment of unvulcanized natural rubber melt was carried out.Based on the experimental results,a modified PTT model was proposed to describe the shear rheological characteristics,which was compared with the Cross-Williams-Landel-Ferry(Cross-WLF)viscosity model,the simulation accuracy of the modified PTT model in the low shear region(shear rate less than 0.1 s^-1)and high shear region(shear rate greater than 10 s^-1)is improved by 34.4%on average,compared with the original PTT model,The simulation accuracy of the modified PTT model in the high-shear region increased by 26.2%on average,indicating that the modified PTT model can more accurately describe the rheological properties of the experimental rubber melt.(2)The normal temperature uniaxial tensile test and plane tensile test are carried out.According to the property evaluation function of the Abaqus software,eight commonly used hyperelastic constitutive models,such as Yeoh,are evaluated.The results show that the Ogden3,Yeoh and Van der Waals models have little error in fitting the experimental data.And uniaxial and planar tensile finite element simulation of rubber based on Abaqus software was implemented,the results showed that the Ogden3model is the most suitable hyperelastic constitutive model for numerical simulation.The stress relaxation test at room temperature was carried out and the experimental data were evaluated by using the Prony series built in the Abaqus.The results show that the Prony series can accurately describe the relaxation characteristics of the experimental rubber.(3)The mechanical properties of rubber under cyclic loading were explored by dynamic tensile experiments.The stress-strain curves of the loading section,unloading section and plastic deformation stage were described by Ogden3,Mullins and Plastic-Model models respectively.The constitutive parameters of the Mullins model were obtained by combined Abaqus and Isight softwares.The temperature rise curve of rubber is obtained by dynamic small rotation oscillation test,and the inelastic heat fraction of rubber is obtained by thermal-mechanical coupling simulation.(4)Based on modified PTT model and Abaqus software was used to carry out tire building simulation.For two tires with different structures,smooth tires and longitudinal tread tires,the effects of temperature and pressure on rubber internal stress and belt cord force were analyzed.As well as the deformation state of the rubber material and the belt layer during the molding process,the reliability of the quasi-static analysis is verified by comparing the ratio of the kinetic energy to the internal energy of the entire system during the molding process.