940030Paper No.PREPRINTDuplication of this preprint for publication or saleis strictly prohibited without prior written permissionof the Transportation Research Board.Title: THE Y-M TEXTURE-FRICTION METERMARK 2(New Title: The Prediction ofTire-Road Friction from TextureMeasurements)Author($): William O.YANDELL & S.SAWYERTransportation Research Board73rdAnnual MeetingJanuary 9-13,1994Washington, D.C
MEETINGANNUALRESEARCHBOARDTRANSPORTATIONTHEWASHINGTONDCUSA9-13JAN1994The Prediction of Tyre-Road FrictionfromTextureMeasurementsbyW.O.Yandell and S. Sawyer4School of Civil EngineeringUniversity of NewSouth WalesP.O. Box 1, Kensington, N.S.W. 2033,Australia
SUMMARYFor the past two decades the author and his research students have been working on apurely theoretical means for predicting tyre-road friction.It is based on a faithfulsimulation of a pneumatic tyre sliding over the wet texture of the road surface. Thisinvolved the stress-gross strain analysis of the tread rubber, the effect of shear rate,heat and lubrication. A device called the Yandell-Mee Texture Friction Meter isdescribed here and is the end product of this research. If when placed on a roadsurface it samples a 60 cm long total texture profile to an accuracy of 0.05 mm andpredicts side force and locked wheel wet friction for three speeds in seconds. Sincethe result only varies with texture changes this is an excellent control tool forpavementengineers.1.INTRODUCTIONThe author and his colleges have been studying the part played by surface texture ontyre-road friction since 1968 (see references 1 to 12). Much of the work wasinfluenced by that of Tabor [13] and Kummer and Meyer [14]. It was assumed thattyre-road friction was due to hysteretic energy loss in the tread rubber as it flowedover the road surface texture and inter molecular adhesion would not occur on wetroads. Yandell [3] summarised some of the basic elements involved in hystereticsliding friction and the change in micro topology of road surfaces in service. Theauthor [3] set out the principles of the mechano-lattice stress-strain analysis for grossdeformations used in the prediction of hysteretic friction from one texture parameterthe average absolute slope. It was also shown how the friction of small stone surfaceslubricated with liquids of various viscosities sliding on tread rubber could be predictedinthelaboratory
Before the mechano-lattice stress-strain analysis can be used the damping and resilientproperties of the tread rubber as they vary with strain, rate of strain and temperaturemust be known. This work was performed by Zankin [ll] using a temperaturecontrolled apparatus capable of measuring damping in rubber sliding at up to80 km/hr. Taneerananon [10] modified Reynold's equations for sliding and sinkageto use with the mechano lattice stress-strain analysis so that masking water filmthicknessescouldbedetermined.The author's friction prediction was based on the concept that a profile of the roadsurface texture could be broken up into a number of components ranging from courseto fine. While large volumes of rubber were expending energy as they flowed overthe coarsest scales, smaller shallower volumes of rubber simultaneously expendedenergy as they flowed overthe finer scales of texture.The total hysteretic friction wasthe sum of frictions generated on each scale of texture.The friction on a scale was afunction of the effectivedamping factor of the rubber and the average absolute slopeof that scale.Thedampingfactor is the energylost divided bythe energyapplied indeforming rubber in a load-unload operation [3]. The average absolute slope is afunctionoftextureroughness.The next stage in the development of a system for predicting wet friction from roadsurface texture involved measuring the texture of a number of roads of diverse surfacetexture with either bituminous or concrete surfacing [12]. The coarse texture wasmeasured with a profile former (row of needles) the fine by Ziess light sectionmicroscope.The total texture was divided into four scales. The dry hysteretic frictionwas determined from the average absolute slope of that scale of texture and thedamping factor of the tread rubber using the mechano-lattice analysis [12]. Thecoefficients of wet sideways force and locked wheel braking friction for speeds of16,48 and 80km/hrwere computed and compared withpredicted values measured
by a multi-mode friction measuring truck. An example of a correlation for lockedwheel braking is shown in figure 1. The R-squared was 0.7.The above process though reasonably accurate was clumsy and time consuming.Accordingly the author devised a portable device that would do the same job inseconds. It was called the Yandell-Mee Texture Friction Meter. Dr Mee designed thecircuit boards and wrote the Pascal programs that controlled the original meter'soperation. The meter simulates the behaviour of a smooth pneumatic passenger cartyre travelling on a wet pavement. A later version (mk 2) of the Y-M Texture FrictionMeter was developed with the assistance of S. Sawyer and will now be described2.THEYANDELL-MEETEXTUREFRICTIONMETERMARKIThe first portable YM Texture Friction Meter was built under the sponsorship ofPavement Management Services Ltd in Sydney.They incorporated it in theirAustralian Road Evaluation Vehicle (AREV) where friction measurements were madesimultaneously with other pavement characteristics in Australia and Indonesia. TheYM Texture Friction Meter Mark II was developed from the Mark I model at theUniversity of N.S.W. with the N.S.W. State Road Authority's financial support.Mark II is superior to Mark Iin that it is operator independent, has a 60 cm longtexture profile sample, is surface brightness independent and is faster.2.1.GeneralDescriptionThe portable instrument has two main components -the compact surface texturemeasuring unit and the P.C. with screen that controls the entire operation.Figure 2 isa very much summarised flow chart showing the operation of the device