Research On The Transient Thermo-mechanical Coupling Characteristics And Thermal Buckling Deformation Of Hydro-viscous Drive During Soft Start

The hydro-viscous drive is widely used in the soft start of scraper conveyors and belt conveyors and step-less speed regulation of fans and water pumps,with the advantages of energy saving,high efficiency,and high reliability.The friction pairs are the core component of hydro-viscous drive.During the soft start of the scraper conveyor,a large amount of frictional heat is produced due to the relative sliding of friction pairs for a long time,which often leads to the ablation and spalling of the friction materials,buckling deformation of the steel disc,and other problems caused by local high temperature.These will cause the thermal failure of friction pairs,which directly affects the working performance,reliability,and service life of hydro-viscous drive.Therefore,it is necessary to investigate the transient thermal-mechanical coupling characteristic and thermal buckling deformation of friction pairs during the soft start process.Taking the soft start process of hydro-viscous drive as the research object,the models of oil film shear torque and asperity contact torque were established.Based on the dynamic equilibrium relationship between friction torque and load torque,the oil film thickness,oil film pressure,and asperity contact pressure during the soft start process were solved.And the dynamic variation of the contact pressure of friction pairs was obtained.The results show that when the start speed follows the S-curve,the oil film thickness decreases gradually according to the inverse S-curve,and the contact pressure increases according to the S-curve,which provide the necessary boundary conditions for the prediction of the temperature field of friction pairs.In order to explore the thermal characteristics of friction pairs during the soft start process,the transient heat transfer model of friction pairs was established considering the time-varying contact pressure and relative speed.The dynamic distribution of non-uniform temperature of friction pairs during the soft start process was obtained.On this basis,the influence of soft start time on thermal characteristics was studied in depth.The results show that the temperature of the steel disc first rises slowly with the start time,then rises rapidly,and then decreases gradually after reaching the maximum value.The temperature of the friction disc reaches the maximum value at the end of soft start,and the temperature of the central region for each rhombus are higher than those of the surrounding area.The longer the start time is,the higher is the generated temperature,and the greater is the radial temperature gradient.The research results can provide a basis for the subsequent study of thermomechanical coupling characteristics and thermal buckling deformation.In order to reveal the coupling relationship among temperature,stress,and strain combined the thermal and mechanical loads,the transient thermomechanical coupling model of friction pairs was established based on the dynamic distribution characteristics of non-uniform temperature field.The distribution of stress and strain field during the soft start process was analyzed,and the influence of radial displacement constraint position on the thermoelastoplastic deformation was clarified.The results show that the stress of the steel disc rises first and then decreases along the inner diameter to outer diameter.The circumferential stress is determined to be the most important stress component,and can thus be used as a basis for judging whether plastic deformation will occur.Moreover,the thermal load and radial displacement constraint position are found to crucially affect the stress and strain distributions.For the thermal buckling behavior of friction pairs,a buckling finite element model was established based on the nonlinear radial temperature distribution of friction pairs.The thermal buckling deformation law of friction pairs was revealed,and the eigenvalue value,critical buckling temperature,and corresponding deformation mode were obtained.Moreover,the main factors affecting the ability to resist buckling deformation were investigated.The results show that the coning mode deformation and potato chip mode deformation are two common deformation modes in friction pairs with failure.Under the free boundary condition,the critical buckling temperature and the thickness are approximately quadratic.The coefficient of thermal expansion is a key factor in the study of thermal buckling.The larger the coefficient of thermal expansion is,the greater the possibility of thermal buckling is.According to the requirements of the thermal characteristics test of friction pairs,a special comprehensive test bench for friction pairs of hydro-viscous drive was developed.The dynamic variation of temperature of friction pairs during the soft start process was measured.The influence of the contact pressure,relative speed,and lubricating oil flow rate on temperature was revealed.The simulation results are in good agreement with the experimental results,which verifies the accuracy of the numerical simulation model and indicates that the simulation model can be used to accurately predict the actual temperature of friction pairs.