Theoretical And Experimental Study On Tire Wear And Temperature Field

Wear is a gradual loss of material due to mechanical or chemical reaction on the contactsurface.Wear takes place in the process of interaction between any two objects in the presence of friction,and the two contact surfaces have the change of material loss and geometry,which is a dynamic process with time-varying characteristics.The friction between the tire and the ground and the transmission of the force provides all the forces and moments needed for the vehicle movement,and tire wear is inevitable during the driving course.The tire is a shell structure composed of rubber and fiber or steel wire reinforced material,which has the characteristics of viscoelasticity,large deformation,nonlinearity,temperature,deformation and velocity sensitivity.So tire wear is a rather complicated process.At present,the research on tire wear is still lack of systematically theoretical achievements and faces many challenges.The reasearch focused on the key issues of tire wear and was performed by means of several theoreticaland experimental methods.The systematicallyanalytical methods of tire wear were developed from the analysis of factors affecting the friction and wear of rubber,mathematical modeling,the thermodynamic analysis of tire and the iterative calculation of wear.1.Analysis of influencing factors on rubber wearThe dependence of tread rubber wear on slip angle,velocity and load was studied by LAT100 wear tester.It is a power function relationship between wear and load.There are two different function relationships between wear and slip angle: a power function relationship exists between wear and slip angleat small slip angles,and it is an exponential function relationshipat large slip angles.It demonstrates wear has a strong dependence on slip angle.The effect of rotating speed on wear is related to temperature.Temperature has an important influence on wear,and the impact of velocity on wear is mainly reflected in the temperature.The test device heating the rubber wheel for high temperature wear was developed.The impact of temperature on rubber wear was studied and characterized by quadratic polynomial.Rubber wear is a complicated process of interaction bewteen angle,temperature,load and velocity.It is difficult to establish a comprehensive analytical formularelated to the above multi-factor.And the importance of each factor to wear is always a fascinating and confusing problem.Therefore,more than 1000 groups of data of TBR tread rubber tested by LAT100 were analyzed by means of data mining algorithm of ‘xgboost'.The influencing weight of five factors including angle,temperature,velocity,load andtread rubberformula on wearwas described quantitatively.2.Friction properties of rubberThe friction coefficient of the different pavement and load is tested and analyzed by the test equipment of friction coefficient and a variety of road surface.Load has little effect on the friction coefficient of rubber on the rough surface.The friction coefficientrelevance to load,angle,temperature and velocity was studied byLAT100 test data.Load has little influence on friction coefficient,which is consistent with the test results at the low velocity.The impact of temperature and velocity on friction coefficient can be represented by the comprehensive variable of logaTV.It is thequadratic polynomial relation between friction coefficient and logaTV.Within a certain temperature range(e.g.the normal temperature of tire),friction coefficient is not very sensitive to temperature and velocity,which is contrary to the views that friction coefficient is very sensitive to temperature and velocity.However,coefficient of friction is very sensitive to slip angle,which is due to the interaction between the adhesion and sliding of the ground area caused by slip angle.Thereby,a new parameter of adhesion coefficient is introduced to achieve the characterization of ship angle by friction coefficient.3.Rubber wear model(1)Thermal-mechanical coupling modelThe relationship between load,angle and wear can be characterized by friction energy.The effect of temperature and velocity on wear can be represented by temperature.It is power function relationship between wear and friction energy.Wear tests were conductedby LAT100 wear test machine.Friction energy under the different working conditions was simulated by finite element method.Power function,power exponent and relation constant for the relationshipbetween wear and friction energy were obtained.It isquadratic polynomial relationship between wear and temperature.The wear at high temperature can be represented by two variables of temperature and friction energy.The thermal-mechanical coupling model considering the impact of temperature on friction energy was obtained.The wear caused by the lagging heat of rubber can be defined as the rolling wear of rubber.Therefore,rubber wear can be regarded as the result of a combination of sliding wear and rolling wear.(2)Microscopic mechanism and constitutive characterization of rubber wearThe origin of wear pattern is due to the aggregation of tearing energy and the resulting crack propagation.The box-counting method in fractal geometry is used to describe the characteristics of rubber wear patterns.A new model of rubber wearwas put forward based on the analysis for the characteristics of the existing microscopic analytical models.The comprehensive formula between modulus,heat generation,fracture energy,friction coefficient and wear strength was established.4.Thermal-mechanical analysis of tireThe shear stress and sliding displacement of each element on the gound area of tire can be obtained by the mechanicalanalysis,then friction energy can be calculated.The temperature of each element of the ground area can be obtained by the FEA of tire temperature field.Wear loss and wear height of tire can be obtained by the thermal-mechanical coupling model of rubber wear.The reliability and precision of thermal-mechanical calculation directly affect the analytical results of wear,and is an important part of tire wear analysis.The key problems of the theory and application of thermal-mechanical simulation,such as the precision of material and theoretical model,the testing accuracy of material and the optimization methods of productwere studied and explored.(1)Structural mechanics analysisA set of testing system for rubber mechanical property is established,by which the material properties of tire rubber can be obtained.It includes the experimental design,CCD image processing,design of test vulcanization mould for rubber material,testing of rubber material and steel wire.The test platform and test data are used to the accuracy of the different material models are evaluated and optimized based on the testing system and test data.Finite element analysis and evaluation criteria is established based on the structural mechanics analysis software TYSYS developed by the enterprise and the university,which includes the theory of minimum strain capacity,the minimum amplitude of stress and strain,the best ground shape,the best strain energy cycle,the best rolling contour.These methods have obtained a number of scientific and technological achievements and produced huge economic benefits.(2)Thermal analysisThe model of the key thermal parameters of rubber material(single rubber and rubber / steel wire single layer material)is untangled and refined,and the temperature dependence of loss factor and thermal conductivity was characterized according to a large number of test data.The theoretical solution of the steady-state nonlinear temperature field is derived considering the nonlinearity of loss factor and thermal conductivity.5.Tire wear analysisBased on the thermo-mechanical coupling analysis of tire and the rubber wear model,the impact of velocity and load on the profile and wear of tire was studied by means of the iterative calculation method.The impact of velocity on wear is mainly reflected by the hysteresis heat and temperature rise of tire that has an important influence on wear.Therefore,it is very important to establish a comprehensive model aboutthe friction energy and temperature of wear,also called the thermo-mechanical coupling model.The increase of load will lead to the increase of ground pressure,friction force and the variation of stress distribution.the increase of load,the wear profile shows a trend of decreasing in the centre and increasing in the shoulders.It is the relation of power function between wear loss and load.The load and temperature have an important influence on wear.The influencing law is consistent with the experemental results of LAT100 wear,which indicates that the simulation results are reasonable.The research on tire pressure imprint is of great practical significance,and is also the research basis of wear.It has a direct impact on the wear resistance of the tire,and is closely related to the uneven wear of tire.The measurement and evaluation method of tire pressure imprint is established by the TV7101 test and analysis system for tire ground pressure distribution.This method gives the definition and calculation equation of some parameters such as rectangular coefficient,inhomogeneity,pressure gradient,load rate,area occupancyand so on,can realize the detailed quantitative evaluation to the pressure imprint.At present,it has been used and form the technological standards by enterprise.Tire pressure imprint can be improved by the parameter optimization of the structure design.The evaluation of the pressure imprint and the finite element analysis provide the means for the optimization of the structure design of tire.Taking the improvement of 12R22.5 product as an example,the improving process of the wear resistance by the optimization of thepressure imprint is described by the improvement of 12R22.5.The experiments show: the average ground pressure of tire is reduced by 7.802%,the wear resistance of road mileage test isincreased by 20%,and it is basically up to 2.5 times compared with unimproved tire.The experimental results is well consistent with the theoretical analysis.