Testing And Modeling Of Mechanical Behaviors Of Uncured Rubbers And Simulation Of Tire Building And Shaping Processes

Tire building and shaping are very critical processes in tire production.In tire building process,a variety of semifinished components are assembled to form a green tire through differents steps.Subsequently,the green tire is vulcanized to obtain a finished tire through the tire shaping process.During the tire building and shaping process,the rubber components and the cord reinforcements will be significantly deformed,which will affect the structure of the finished tire,reduce its performance,and even lead to tire production defects in some cases.Due to the complexity,there are few studies on the tire building process.While the studies on the tire shaping process mainly focus on the temperature field.The deformation of different components is also rarely studied.In recent years,with the improvement of tire manufacturing quality requirements,it is becoming more essential to conduct in-depth research on the tire building and shaping processes.In this context,this paper tests and characterizes the mechanical properties of the uncured rubber from different component,and presents a research on the tire building and shaping processes using the finite element method to establish a complete simulation scheme,and explore the influence of some key parameters on the final tire stracture.The tensile mechanical behaviors of the uncured rubber from tire 12R22.5(GAL836)were tested in the strain rates ranging from 0.001/s to 0.1/s.Under the requirements of material stability,material uniformity and dimensional accuracy,a preparation method of the specimen of the uncured rubber was developed.The Automatic Grid Method,a non-contact deformation measurement method,was adopted to accurately obtain the full-field deformation of the specimen during experments.Through tensile tests under different tension modes(monotonic tension,cyclic loading and unloading,relaxation,and multistep tensile relaxation tests)at different strain rates,the tensile mechanical characteristics of the uncured rubber from different components were systematically obtained.The experimental results show that the uncured rubber,which could be regarded as an incompressible material,has highly rate-dependent mechanical behaviors.With strain rate increasing,the tensile stress increases,the hysteresis increases,and the plasticity level decreases.The Mullins effect can be observes at every strain rate.And the viscoplastic flow rate of the uncured rubber is not a constant,but has a complex nonlinear feature.To further study the temperature dependence of the mechanical properties,the tensile mechanical behaviors of the tread rubber at different temperatures(25℃,50℃,75℃,100℃)were investigated.The test results show that with the increase of temperature,the elasticity of the tread rubber decreases and the viscoplasticity increases.Under the same strain value,the stress level decreases by about 50%for every 25℃ increase in temperature.According to the complex nonlinear mechanical behaviors of the uncured rubber,an isothermal three-network viscoelastic-plastic constitutive model(TN model)was firstly proposed to characterize its mechanical behaviors at room temperature.The model is composed of a hyperelastic network and two nonlinear viscoplastic networks.And the nonlinear viscoplastic flow and the Mullins effect are comprehensively considered.The constitutive model can well characterize the nonlinear deformation behaviors of the uncured rubber.After that,to further characterize the temperature dependence of the mechanical behaviors,a temperature dependent three network constitutive model(TTN model)which can better characterize the temperature-rate dependent mechanical behaviors of the uncured rubber was proposed.In the TTN model,the Ogden Roxburgh damage model in the original TN model is replaced by the damage laws based on molecular evolution theory.At the same time,to characterize the temperature effect on the hyperelastic stress level and viscoplastic flow rate,two temperature correction terms are introduced into the eight-chain model and bergstrom-boyce flow respectively.Finally,the finite element implementation of the above constitutive model was completed and verified numerically.Using the obtained TN model,the finite element method for the tire building process was established,and the complete numerical simulation of the building process including components winding,rubber bladder inflation,components stitching and carcass band folding-back was realized.The deformation and stress distribution on each rubber component and the tensile force and angle changes of the cord reinforcements were obtained.From simulation,it can be obsevered that the chafer is severely deformed during the tire building process,and both the stress and angle of cord have changed significantly.The maximum tensile force is about 200N,and the angle decreases about 23°.Compared to chafer,the tensile force and angle changes of the cord in the belts and carcass are relatively small.The tensile force is genrally less than 100N.The simulated green tire profile was compared with the actual green tire profile obtained through 3D scanning.The two profiles are in good agreement.The thickness of the simulated green tire is basically consistent with the actual one,and the difference of rubber thickness at each point is less than 10%,which verifies the effectiveness of the simulation strategy.The section cutting experiment of the green tire was carried out using a water jet.It was found that there is little air traped in the green tire,which is also consistent with the simulation results.This further verifies the reliability of the simulation.Based on the tire building simulation results,the finite element model of the green tire for the the shaping simulation was established,and the whole shaping process including tire installing,tire setting,mold closing and vulcanization was realized.The stress and deformation of each component during the shaping process were obtained systematically.The results indicate that the stress level at the beads and the belt ends is generally higher,and the strain level at the groove,sidewall and bead is probably higher.The tensile force of each belt cord varies greatly.The maximum tension is about 750N,while some cords are under pressure during the shaping process.The angle variation of each belt cord is usually within 5°.After the simulation strategy from the semifinished components to the final tire structure was obtained,the effects of different process parameters(including the ring segment,belt strength,drum width)on the tire building and shaping processes were studied.The simulation results show that if the bead setter fails to firmly lock the bead in the tire building process,the defects of shoulder flection and tread unevenness may be caused.When the 0° winding belt is too strong,more severe tread unevenness defects will happen.The increase of the drum width will also lead to tread unevenness and shoulder flection defects.To verify the effectiveness of the simulation results,The experimental verification with drum width increased by 10 mm was carried out.It is found that the shoulder flection happened after the increase of the drum width,which is consistent with the simulation results.