Research On The Moving Mechanism Of Wetting Contact Line And Wet Skid Resistance For Tire-Road

Wetting refers to the dynamic process that one fluid replaces another immiscible fluid on the solid substrate,and the most common wetting phenomenon is the gas being replaced by the liquid on the surface.Wettability is one of the important characteristics of the solid surface,and it directly affects the spreading and phase transition of the fluid in the contact interface.There are many engineering technologies related to the wettability,such as vehicle driving on the wetting road,the design of windscreen wiper,rubber sealing and so on.As the traditional wetting theory mainly contains the models of contact angle,and these wetting parameters have limitations when they are used to describe the dynamic spreading behavior of fluid.It is difficult to explain the reason of tire hydroplaning after raining through the traditional wetting theory,because it lacks of theoretical basis when they are used to construct the relationship between the wettability and friction property.As the moving mechanism of triple contact line has a natural theoretical advantage to describe the spreading behavior of the fluid on the solid surface,therefore the wetting and spreading mechanism of contact line is explored from the physical and mechanical mechanism of triple contact line in the present study.And the wet skid resistance between the road and the tire is also studied on the basis of the spreading mechanism of contact line.It not only has significant theoretical meaning,but also has important practical engineering value for the designing of tire patterns and pavement texture.First of all,according to the lubrication approximation theory and Navier-Stokes equation,a general nonlinear evolution equation of film thickness were derived.Numerical methods is adopoted to solve these equations through writing simulation programs,and the relevancy between film thickness,spreading radius,speed of wetting contact line and time is also quantitatively analyzed in detail.Results show that spreading process is mainly divided into two phases:expansion phase and contraction phase,and the spreading process is along with mutual transformation among surface energy,kinetic energy and different kinds of potential energy.The "collapse effect" is concerned with Laplace pressure of curved liquid surface,and the final spreading radius of droplet is determined by the inherent wettability of solid surface.Next,on the basis of mumerical simulation and wetting experiment,liquid spreading and wetting behavior have been studied quantitatively from the physical and mechanical mechanism of moving contact line.The quantitative description of triple contact line and its influence on the contact interface were also discussed.The results shows that Laplace pressure inner the droplet provides excess driving force and accelerate the liquid as it approaches.Droplet spreading process on the smooth and textured surfaces respectively meets two regimes:R?t1/4 for the textured surface and R?t1/7 for the smooth surface.The dynamic balance between sliding force(caused by Laplace pressure and droplet gravity)and viscous resistance(caused by surface roughness)is the main reason for the occurrence of contact angle hesteresis(CAH).CAH is closely bounded up with surface topography,and CAH on the substrates with same roughness but different surface topography shows a great difference.Lastly,the tribological properties of rubber sliding interface and road/tire interface have been studied by experiment based on the independently developed linear reciprocating tribotester and viscoelastic tribotester.Experimental results show that the contact angle of lubricant on the solid surface gradually decreases and the static friction coefficient increases with the decrease of additive ratio.The contact angle of lubricant is linear with static friction coefficient.The depth of water-film has a distinct effect on the braking friction coefficient,the vehicle has a great chance to lose control on the road with thin water-film because of high slip ratio.Especially in the sharp braking process,the tire tends to slip on the road and gets a lower braking friction coefficient,which has a significant effect on the driving safety.