PARAMETRIC STUDY AND EXPERIMENTAL EVALUATION … · PARAMETRIC STUDY AND EXPERIMENTAL EVALUATION OF...

221

Int. J. Mech. Eng. & Rob. Res. 2013 Virkar D S and Thombare D G, 2013

PARAMETRIC STUDY AND EXPERIMENTALEVALUATION OF VEHICLE TIRE PERFORMANCE

Virkar D S1* and Thombare D G1

*Corresponding Author: Virkar D S,[email protected]

The purpose of this review paper is to study of effect of the different tire operating parameters ontire performance and review of testing setup to test these tire performance parameters. Thetesting of tire performance parameters by experimentally is help to designer to correlate therelationships of parameters and to design the tire, hence it is need to testing of tire. Knowledgeabout dynamic properties of tires is an essential for any kind of research and developmentactivities on vehicle dynamics. The main purpose of laboratory testing is to separate the propertiesof the tire from the vehicle, achieve high rate of reproducibility and to optimize the cost. Thisreview paper gives the information regarding of different researcher’s works on inter laboratorytire testing setup for measuring tire performance parameters and also this review paper helpsto understand the factors on which tire performance parameters is depends.

Keywords: Inter laboratory, Review, Tire parameters, Tire performance

INTRODUCTIONThe pneumatic tire plays an increasinglyimportant role in the vehicle performance ofroad. However, this status is achieved becauseof more than one hundred years’ tire evolutionsince the initial invention of the pneumatic tireby John Boyd Dunlop around 1888. Tires arerequired to produce the forces necessary tocontrol the vehicle. As we know that the tire isthe only means of contact between the roadand the vehicle but they are at the heart ofvehicle handling and performance (Nicholas,

ISSN 2278 – 0149 www.ijmerr.comVol. 2, No. 2, April 2013

© 2013 IJMERR. All Rights Reserved

Int. J. Mech. Eng. & Rob. Res. 2013

1 Department of Automobile Engineering, R I T Sakharale 415414, Sangli, Maharashtra, India.

2004). The inflated rubber structure providescomfortable ride for transportation. With thegrowing demand for the pneumatic tire, manyimprovements have been made based on theinitial conception, such as the reinforcementcords, the beads, the vulcanization, thematerials and the introduction of the tubelesstire. The relationship between human and tireand environmental surrounding play animportant role for developing of tire technology.These concerns include traffic accidentscaused by tire failure, the waste of energy due

Review Article

222


to bad tire conditions, the pollution through theemission of harmful compounds by tires, andthe degradation of road surfaces related to tireperformance, etc.

Tire as one of the most importantcomponents of vehicles requires to fulfill afundamental set of functions are to provideload-carrying capacity, to provide cushioningand dampening against the road surface, totransmit driving and braking torque, to providecornering force, to provide dimensionalstability, to resist abrasion (Mir Hamid, 2008).Tires have ability to resist the longitudinal,lateral, and vertical reaction forces from theroad surface without severe deformation orfailure. Tire performance is depends on the tirerolling resistance, cornering properties, tiretraction, tire wear, tire temperature, tire noise,tire handling and characteristics, etc. There arevarious losses associated with the vehicle thataffect its fuel economy as it is being operated.These losses include engine, driveline,aerodynamic and rolling losses, while therolling loss is associated with the vehicle tires.This papers tells about the theoretical studyabout the tire background, tire axisterminology, tire performance parameters,experimental setup available for thisparameters, and survey on tire testing setupsavailable for tire testing.

TIRE AXIS TERMINOLOGYIt is need to understand some of the basicterminology for tire, especially regarding thesystems of coordinates, orientations,velocities, forces, moments. Nomenclature anddefinitions based on the SAE standard asshown in Figure 1 X-axis is the intersection ofthe wheel plane and the road plane with

positive direction forward. The Z-axisperpendicular to the road plane with positivedirection downward. The Y-axis in the roadplane, its direction being chosen to make theaxis system orthogonal and right hand. Thereare several forces, moments and angles thatprove to be very important in tire behavior. Allthese forces can be seen as the forces andmoments acting on the tire from the road. First,there are two main angles to consider, thecamber angle and the slip angle. The camberangle is the inclination angle from its verticalposition while the slip angle is the differencein wheel heading and direction.

Figure 1: Tire Axis Terminology

Forces include the longitudinal force in theX direction, the lateral force in the Y directionand the normal force in the Z direction.Longitudinal force (F

x) is the result of the tire

exerting force on the road and becomesnegative during braking. The lateral force (F

y)

is the resultant of the forces produced by a non-zero camber angle and by a non-zero slipangle during cornering. Normal force (F

z) can

also be viewed as the negative of the upwardvertical force. Moments include the overturningmoment, the rolling resistance moment, thewheel torque and the aligning moment. The

223


overturning moment (Mx) is caused by a lateral

shift of the vertical load during cornering.Rolling resistance (M

y) is created by various

factors that lead to a loss of energy. Thealigning moment (M

z) also known as the self-

aligning torque, produces a restoring momenton the tire to realign the direction of travel withthe direction of heading when the slip angle isnon-zero. It should also be noted that there isalso a moment produced by the axle on thewheel (Nicholas, 2004).

PERFORMANCEPARAMETERSTire performance is affected by the rollingresistance, tire wear, tire noise, tiretemperature, cornering properties.

Rolling Resistance

When a tire rolls on the road, mechanicalenergy is converted to heat as a result of thephenomenon referred to as rolling resistance.Effectively, the tire consumes a portion of thepower transmitted to the wheels, thus leavingless energy available for moving the vehicleforward. Rolling resistance therefore plays animportant part in increasing vehicle fuelconsumption. The rolling resistance of tires onhard surfaces is primarily caused by thehysteresis in tire materials due to the deflectionof the carcass while rolling. Friction betweenthe tire and the road caused by sliding, theresistance due to air circulating inside the tireand the fan effect of the rotating tire on thesurrounding air also contribute to the rollingresistance of the tire, but they are of secondaryimportance (Berng, 2011). Availableexperimental results give a data of tire lossesin the speed range 128-152 km/h (80-95 mph)as 90-95% due to internal hysteresis losses

in the tire, 2-10% due to friction between thetire and the ground, and 1.5-3.5% due to airresistance. Fuel consumption is the mostimportant topic of discussion in the automotiveindustry today. Tire energy losses areresponsible for about 25% of the total fuelconsumption of a typical passenger car. Thecoefficient of rolling resistance of the first tiresin 1900 was approximately 0.025. This valuewas reduced by 50% to 0.013 with theintroduction of radial tires in 1946. Theintroduction of silica fillers in 1992 furtherreduced resistance to 0.008. Rollingresistance is the effort required to keep a giventire rolling. Its magnitude depends on the tireused, the nature of the surface on which it rolls,and the operating conditions inflation pressure,load and speed. Rolling resistance hashistorically been treated as a force opposingthe direction of travel, like a frictional force. Amore general concept is in terms of the energyconsumed by a rolling tire. Driving resistancescan be divided into two categories one issteady-state resistances and second isdynamic resistances. Steady-state resistancesoccur when a vehicle is running at a constantspeed, rolling resistance, aerodynamic dragand climbing resistance fall in to thiscategories. Dynamic resistance occurs whenvehicle is accelerating, this type of resistanceoccurs due to the vehicle inertia (Berng, 2011).The rolling resistance of a wheel (F

R) is made

up of four components. The sum of thesecomponents is equal to the total rollingresistance Components such as Tire rollingresistance (F

R, T),Road rolling

FR = F

R, T + F

R, Tr + F

R, + F

R, fr ...(1)

Resistance (FR, Tr) Resistance due to tire

slip angle (FR, ) Resistance due to bearing

224


friction and residual braking (FR, fr) (Berng,

2011). Tire rolling resistance is depends uponthe following parameters.

Tire Temperature

The temperature of the tire has significanteffect on rolling resistance of tire. Increasingof rolling resistance of tire is due to thedeflection and energy loss in the material.

Tire Inflation Pressure and Load

Tire inflation pressure determines the tireelasticity and combination with load,determines the deflection in the sidewallsand contact region. The overall effect ofroll ing resistance is depends on theelasticity of the ground. On the soft surfaceslike sand, high inflation pressure results inincreased ground penetration work andtherefore higher coefficients while the lowerinflation pressure decreasing groundpenetration. Thus the optimum pressuredepends on the surface deformationcharacteristics.

Speed of Vehicle

The rolling resistance is directly proportionalto speed because of increasing of flexingwork and vibration in the tire body. Influenceof speed becomes more important whencombines with lower inflation pressure.

Tire Material Design

The material and thickness of both the tiresidewalls and the tread determines thestiffness and energy losses in the rolling tire.The cord material in the sidewall has only asmall effect, but the cord angle and tire beltproperties have significant influence on rollingresistance of tire.

Tire Slip Angle

Wheels Tractive and braking forces showshigher effects on rolling resistance due to thewheel slip angle. At a few degree of slip therolling resistance coefficient may nearly doublein the magnitude (Thomas, 1992).

Tire Wear

The wear performance of a tire is its ability toreach high mileages. One way of evaluatingthis wear performance is consider the durationof tire service life, which is the mileage afterwhich a point on the tread has reached thelegal limit of the wear indicator. The durationof a tire’s Service life depends on the massloss from the tread, which is usually expressedin g/100 km, and by the transverse worn profilewhich enables the wear shape of the tread tobe qualified. The duration of a tire’s servicelife depends on the condition in which the tireis used, that is the type of driver and thegeographical area. Wear is depend upon manyparameters, which gives designer tomodification tire force applied on tire orchanges in rubber or ground surface (Olivieret al., 1998).

Road Surface and Styles of Driving

Depending upon the route and the style ofdriving, the acceleration levels reached by thevehicle may vary. These acceleration levelsmodify the forces applied to the tire. Thesystem of loads causing wear in the contactpatch (sliding, stresses) is directlyproportional to these forces. The effect of thestyle of driving can be quantified by measuringthe tire wear on the same vehicle driven bydifferent drivers over the same course (Olivieret al., 1998).

225


Tire

The tire is the link between the vehicle and theground and therefore has a major effect onwear. The most important tire parametersacting on wear are the first one is to differentstiffness which determine the shape, stressand slip in the contact patch second one is therubber volume available for wear, which iscorrelated to geometrical characteristics ofboth tire (width, diameter) and tread (rubberthickness and the tread pattern percentage)and third one is the material characteristics ofthe tread such as friction and abrasion. Hence,the facts that tire size choice and inflationpressure are first order parameters for the wearperformance of the tire. This difference is dueto the variation in rubber volume and stiffnessbetween the two tires. The inflation pressureof the tires also has a great influence on wearand worn profile. It acts on the shape of thecontact patch and on the tire’s stiffness (Olivieret al., 1998).

Seasonal Effects

Environmental parameters such astemperature and humidity are very season-dependent. These parameters have a verysubstantial influence on the rubber/groundinterface characteristics and therefore on wear(Olivier et al., 1998).

Vehicle Weight

When the vehicle is travelling on the roadweight of the vehicle is acts as force and itdirectly applied on tire. The average life of tiremay vary within the range of 50% or thedepending upon the vehicle characteristics.The vehicle characteristics of the greatestinfluence are weight, suspension and steeringgeometry. The axle geometry factor such as

toe and camber angle is influence on massloss and worn profile of tire (Olivier et al.,1998).

Tire Noise

When the tread of a tire rolls into contact thevoid areas in the tread pattern compress andair force out of the voids take place, when thetread element leave contact the voids expandsand air rushes in back in due to this repetitivecompression and expansions of the treadvoids known as air pumping and it can causesignificant tire noise. Tire or road noisecontributes the maximum percentage of noiseis 30% after the engine noise 34%. It isunderstand that the effect of roughness of roadsurface, effects of exciting force due to patternsuch as lug grooves in tread surface, effectsof driving torque of tires under an acceleratingperiod etc. are considered as the exciting forcegenerating tire/road noise (KejirioIiwao andIchiro, 1996). It is found the sound pressurelevel is depends upon roughness of the roadsurface. Tire/road noise dependant not onlyupon exciting force due to the tread patternand roughness of the road surface, but alsolargely depends upon the structure of tire suchas thickness of the tread blocks (KejirioIiwaoand Ichiro, 1996).

Cornering Properties

One of very important function of a tire is todevelop the lateral forces necessary to controlthe direction of the vehicle, generate lateralacceleration in corner or for lane changes, andto resist the external force such as wind energyand road cross-slope. These forces aregenerated either by lateral slip (slip angle) ofthe tire, by lateral inclination (camber angle)or the combination of two angles. When a

226


rolling tire is subjected to a lateral force, thetire will drift to the side so therefore there anglewill be created between the direction of tireheading and the direction of travel this angleis known as a “slip angle”. When the tire travelsforward tread of tire come in contact with theroad but they are undeflected from their normalposition and therefore it unable to developinglateral force. But as tire travels forward at someangle direction of travel, the tread elementsremain in the position of their original contactwith the road and therefore deflected sidewayswith respect to the tire, by this process thelateral force is developed. The lateral forcebehavior of rolling tire is characterized only inthe steady state that is at constant load andslip angle. When the slip angle is zero thelateral force is zero, at the slip angle is goingto increase the lateral force developing rapidlyand linearly. At the large slip angle behavior ofwheel is locked, which has a lateral force equalto the sine angle resultant of the slidingcoefficient friction (

s), times the vertical load

(FZ). The ratio of lateral force (F

Y) to the slip

angle () is called the “cornering stiffness”.

YFC ...(2)

From the following equation we get thecentral to drag force ratio which reduces withslip angle, higher cornering stiffness is. Thereason for this is that a given central force willbe achieved at smaller slip angles andtherefore results in lower tire drag force. Thecentral/drag ratio is given as follows:

sin

cos

CF

C

Fd

Fs

VR...(3)

Cornering force at the given slip angle riseswith the vertical loading on tire but It’s doesn’t

rise proportionately with load while, themaximum cornering force per unit load occursat the lightest loads. Due to inflation pressurecarcass stiffness is increases butsimultaneously reduces the contact length ofthe tire it influences on cornering stiffness oftire. Tread rubber acts as a series spring inthe generation of lateral force with respect toslip angle. Therefore tread design has apotential influence on cornering stiffness.Cornering stiffness is influenced by one factoris “aspect ratio” is nothing but the sectionheight to section width, as the increasing thewidth and decreasing the height of the tire thereis increasing cornering stiffness is proved byexperimentally in currently used tire. Thecornering stiffness is dependent upon on manyvariables like tire size and type, number ofplies, cord angle, wheel width, and treaddesign (Thomas, 1992).

Tire TemperatureTire behavior is largely dependent upon tiretemperature. Temperature of tire is affect ontire’s adhesion, ride comfort, wear, and rollingresistance, hence it is important to measuretire temperature during testing and includetemperature effects in any simulations of tirebehavior. There is also a direct relationshipbetween tire temperature and the power lossin the tire. The effects listed above dependmainly on the temperature of the rubber in thetire’s tread surfaces. This temperature can bemeasured using various methods ranging fromsimple insertion measurements at the end ofa test run to complex high speed infraredcameras. Another temperature measurementtechnology, developed at TUV Sud Automotiveand known as T3M, uses a microsensorembedded in the rubber of the tire’s tread

227


surface. These measured values can beevaluated and modeled with respect to thetire’s adhesion, durability, and wear properties(Berng, 2011).

EXPERIMENTAL SETUP FORTESTING TIRE PARAMETERSDifferent research centers and researchershave used following tire test machine formeasuring tire forces and moments, rollingresistance, braking and traction efforts, andcornering characteristics.

Flat Bed Tire Testing Machine

The test surface is travelling table. Due tolimited stroke, the test speed is considerablylower than actual tire operating speed and thesteady state working conditions cannot beachieved as seen following Figure 2. Thisconstruction is very useful in determination ofthe static elastic properties of tires and is usedby researcher for years (Ergin and Samim,2001).

generated by the test tire, a bearing to supportthe belt used. To control the belt tension andposition one of the drum carrying the belt ispositioned by a feedback control system.Some flat surface test machine may reachroad speeds of 0-250 km/h, and the surfacecoating and temperature may be controlled tosimulate different road condition. Flat surfacetest setup is used to test parameters like rollingresistance, tire wear, tire temperature, tirenoise, cornering stiffness of tire (Ergin andSamim, 2001).

Drum Type Tire Testing Machine

Due to the complexity of flat surface testmachine there is development of drum typetire testing machine as seen Figure 4. Thetest surface is either internal or externalsurface of drum. In both case contact patchis distribution is different than flat surface testmachine. The test results are comparativeamong different tires and mostly cannot beextrapolated to flat surface. Drum type testmachines are used to test the parameters likerolling resistance, tire wear, tire temperature,tire noise, cornering stiffness of tire (Ergin andSamim, 2001).

Figure 2: Flat Bed Tire Testing Machine

Flat Surface Tire Testing Machine

Flat bed tire testing machine is probablycaused by limited stroke of the table toovercome this problem there is use of infinitebelt as seen Figure 3. Due to the high force

Figure 3: Flat Surface Testing Machine

228


Flat Rotating Disc Type TireTesting Machine

To eliminate the effects caused by drumcurvature, a flat rotating disc was used as seenin Figure 5. However, due to the finite width ofthe tire tread, the rotational speeds of the innerand outer tread edges are different, whichresults in slip in the contact area

reproducibility and optimize costs. Laboratorytesting can also be used to conduct tests ofabsolute strength, which cannot be performedduring vehicle testing due to safetyconsiderations. In this paper we discuess thethree methods, these methods includes rollingdrum type testing machine, Flat-Trac rollingmachine and twin rolled test rig.

Ergin and Samim (2001) have studied onprediction of cornering force by finite elementmodeling and analysis. For the prediction oftire cornering force characteristics two distincttype of models analytical and empirical modeland physical tire model have been developed.They observed that lateral cornering forcedeveloped by tire was strongly affected thedirection control and stability of the vehicle,depends upon the slip angle at which tire isoperating, inflation pressure, vertical tireloading. They discuses the methods availablefor tire testing which includes flat bed tiretesting machine, flat surface tire testingmachine and drum type tire test machine. Forthe experimentally verification they tested tireon drum type machine. For testing of tire theychoose brand new tire 155 R13 on which upto 500 N load is applied and this test conduct

Figure 4: (a) Internal Drum Tire Test; (b) External Drum Tire Test

Figure 5: Flat Rotating Disc Type TireTesting Machine

SURVEY ON TIRE TESTINGSETUPThe main purposes of laboratory testing is toseparate the properties of the tire from thoseof the vehicle, achieve a high rate of

229


on 0-60 km/h. Their study says that with thehelp of this finite element model the corneringforce characteristics of a tire can be estimatedwithout going to lengthy and expensive processof prototype manufacturing and testing.

Padmanabha (2004) have studied on effectof overload and inflation pressure on rollingresistance and fuel consumption for truck/bustires. For the experimental verification theyused 1.7 m cylindrical diameter drum androlling resistance were measured accordingto SAE J1269. By adjusting tire load, pressurecondition they finding the rolling resistance.This test is done on SAE J1269 for measuringrolling resistance. Through this research paperthey found that a truck or bus tires carrying100% load consumes more than twice theamount of fuel compared to normal load. Theysuggest the possible method for optimizingfuel consumption by adjusting load andpressure conditions.

Nikola et al. (2011) have studied on finiteelement analysis of a tire steady rolling on thedrum and its results compared withexperimentally. They developed a CAD modelof rolling on the drum which was used to quicklyfind out the optimal tire design parameters.Equipment and methods have been used forexperiment determination of braking andcornering characteristics of the tire as well asfor experimental determination of friction ofcoefficient of tire tread. For experimentaltesting of tire parameters they used drumdiameter 1219 m and uses maximum speedof 150 km/h. For the cornering test they varyslip angle from –10 degree to +10 degree.Through this research paper they found thatthe differences between experimental andnumerical results were decreased after the

calibration of friction has been performed andalso they found that CAD model is help fordesigner to quickly find out the optimal valuesof tire design parameters.

Parmeet and Sid (1999) have studied ontesting of tire rolling resistance according tothe SAE J2452 and to compare results withthe new parameters. The new parameters areMean Equivalent Rolling Force (MERF) andStandard Mean Equivalent Rolling Force(SMERF) are mathematically derived andcomparing with inter laboratory rollingresistance data as per SAE J2452. They toldthat SAE J2452 is the new test method formeasuring rolling resistance on drum machinein the laboratory, this method is able to testrolling resistance at different load, speed andinflation pressure condition. They told thatMERF and SMERF values are helpful tocompare directly for two tire at given load andpressure.

Clark and Dieter (1998) have studied oninter laboratory test for tire rolling resistance.The major objectives of these test is to examinethe rolling resistance equipment measuringdevice and to study the effect of test wheeldiameter on rolling resistance. The test wereorganized a group of five types of passengercar tires. Texture surface were tested by fourmethods force, power, torque, cost- down time.They use conversion of drum type results in toflat track. They told that drum diameter iseffectively affected on rolling resistance, as thedecreasing the drum diameter rollingresistance is increases. From this experimentthey conclude that tire type and tire pressurehad strong effects on rolling resistance. Thetire were tested on flat surface as well as onvariety of drum and best correlation between

230


rolling resistance and drum diameter wereobtained.

CONCLUSIONFrom the literature survey we observed thattire performance is affected by rollingresistance, tire wear, tire temperature,cornering properties, tire noise, etc., from thisparameters we conclude that rolling resistancehaving the major contribution in the tireperformance and fuel economy of the vehicle.Tire performance parameters we can test bythe drum type, flat-track type, flat bed typetesting rig and flat rotating disc type from thisabove four type we observed that drum type isthe simplest in construction, manufacturing andto design than the other test rig. Reactions atthe tire affects the dynamic performance of thevehicle, hence it is need to test the tireperformance parameters and to optimizethose parameters for improvement in the fueleconomy.

REFERENCES1. Berng Heibing (2011), Chasis Handbook,

ATZ Technology, 1st Edition, pp. 35-50.

2. Clark S K and Dieter J Schuring (1998),“Interlaboratory Tests for Tire RollingResistance”, Journals of SAE, 780636,pp. 1-8.

3. Ergin Tonouk and Samim Unlusoy Y(2001), “Prediction of Automobile TireCornering Force Characterstics by FiniteElement Modeling and Analysis”,Journals of Computers and Structures,Vol. 79, pp. 1219-1232.

4. Hans B Packeja (2005), Tire and VehicleDynamics, 2nd Edition, pp. 472-476, DelftUniversity Technology.

5. KejirioIiwao and Ichiro Yamazaki (1996),“A Study on the Mechanism of Tire/RoadNoise”, Journals of Science Direct, Vol.17, pp. 139-144.

6. Mir Hamid Reza Ghoreishy (2008), “AState of the Art Review of the FiniteElement Modelling of Rolling Tyres”,Iranian Polymer Journal, Vol. 17, No. 8,pp. 571-597.

7. Nicholas D Smith (2004), “UnderstandingParameters Influencing Tire Modeling”,Journals of SAE Dynamics, pp. 1-22.

8. Nikola Korunoviæ, Miroslav Trajanoviæ,Miloš Stojkovic, Dragan Mišiæ and JelenaMilovanovic (2011), “Finite ElementAnalysis of a Tire Steady Rolling on theDrum and Comparison with Experiment”,Journals of Mechanical Engineering,Vol. 57, pp. 888-897.

9. Olivier Le Maitre, Manfred Sussner andCesar Zarak (1998), “Evaluation of TireWear Performance”, Journals of SAE,980256, pp. 43-48.

10. Padmanabha S Pillai (2004), “Effect ofTyre Overload and Inflation Pressure onRolling Loss (Resistance) and FuelConsumption of Automobile Truck/BusTyres”, Indian Journals of Engineeringand Material Science, Vol. 11, October,pp. 406-412.

11. Parmeet S Grover and Sid H Bordelon(1999), “New Parameters for ComparingTire Rolling Resistance”, Journals ofSAE, 1999-01-0787, pp. 1-8.

12. Thomas D Gillespie (1992), Fundamentalsof Vehicle Dynamics, pp. 335-337, Societyof Automotive Engineering.

231


FX

Longitudinal force F Cornering stiffness

FY

Lateral force Slip angle

FZ

Normal force FR

Total rolling resistance

MX

Overturning moment FR,T Tire rolling resistance

MY

Rolling resistance moment FR, Tr Road rolling resistance

MZ

Aligning moment FR, Resistance due to slip angle

FR, fr Resistance due to bearing friction and residual braking Fd Drag force

Fs Force component perpendicular to travel

APPENDIX

Nomenclature

PARAMETRIC STUDY AND EXPERIMENTAL EVALUATION … · PARAMETRIC STUDY AND EXPERIMENTAL EVALUATION OF...

Documents

Transcript of PARAMETRIC STUDY AND EXPERIMENTAL EVALUATION … · PARAMETRIC STUDY AND EXPERIMENTAL EVALUATION OF...