Proceedings of SerbiaTrib '13

Measuring system with experimental samples isshown in Figure 5.Figure 5. Measuring systemSamples used in this experimental investigationare with following characteristics: Footwear sole samples (sample A) areprism shaped and formed of soles cutoutglued on a piece of chipboard. Nominalcontact area is 30mmx30mm=900mm 2 . Forthis investigation there are four solesamples: new rubber with relief, worn(used) rubber with texture, new flat rubberand leather. For floor samples (sample B) are usedplates of laminate, rough ceramic tile andsmooth ceramic tile. Dimensions of platesare 60mmx75mm according the measuringdevice.Before testing all contact surfaces are cleanedwith acetone.Floor samples surface roughness was measured byroughness measuring device Mitutoyo Surftest SJ-301. Roughness measuring gave the following results:1. Laminate plate: Ra=0,9µm, R max =4,98µm,R z =3,25µm,2. Rough ceramic tile: Ra=12,85µm,R max =59,04µm, R z =43,93µm,3. Smooth ceramic tile: Ra=0,53µm,R max =3,44µm, R z =2,24µm.Measurements are done with weight (normalforce) variations so that contact pressure was:45kPa, 79kPa and 142kPa.Force sensor is produced by HBM, maximumforce which can be measured is 500N and samplerate is 100Hz. For each contact combination fivemeasuring were done.Contact surfaces are prepared in three ways: drycondition, wet condition and soap lubricated.Tables 1, 2 and 3 show measuring results forstatic friction coefficient for different materialcombination and lubricating. Marks in the tablesare: U1-new rubber with relief, U2-worn rubberwith texture, U3-new flat rubber, U4-leather, P1-laminate plate, P2-rough ceramic tile and P3-smooth ceramic tile.Table 1. Static friction coefficient of footwear solesamples and laminate floor sample (P1)µ U1/P1 U2/P1 U3/P1 U4/P1dry 0,54 0,83 0,96 0,52wet 0,39 0,66 0,67 0,65soap 0,43 0,60 0,46 0,70Table 2. Static friction coefficient of footwear solesamples and rough ceramic tile sample (P2)µ U1/P2 U2/P2 U3/P2 U4/P2dry 0,52 0,47 0,54 0,63wet 0,46 0,40 0,58 0,79soap 0,38 0,54 0,39 0,77Table 3. Static friction coefficient of footwear samplessole and smooth ceramic tile sample (P3)µ U1/P3 U2/P3 U3/P3 U4/P3dry 0,25 0,69 0,44 0,47wet 0,19 0,53 0,42 0,52soap 0,11 0,22 0,13 0,50Performed experiment shows that values of staticfriction coefficient are very unpredictable and random.Static friction coefficient of leather sample (U4) withpresence of lubricants (water, soap) increases that isopposed of rubber samples with lubricants wherecoefficient of friction decreases. Very interesting resultswere in combination of rubber sample with relief (U4)and smooth ceramic tile, respectively measured staticfriction coefficient is very small (0,25 in dry conditionuntil 0,11 lubricated with soap). That can be explainedwith small real contact area. Also, it can be concludethat for smooth ceramic tile coefficient of static frictionis smallest for each sample.Force (N)65605550454035302520151050Experimental test U3P3M3s5 5,2 5,4 5,6 5,8 6 6,2 6,4 6,6 6,8 7Time (s)Figure 6. Friction force-time diagram for flat rubber andsmooth ceramic tile (normal load 131N, dry condition)Force (N)Experimental test U4P3M2v40353025201510501,5 1,7 1,9 2,1 2,3 2,5 2,7 2,9 3,1 3,3 3,5Time (s)Figure 7. Friction force-time diagram for leather andsmooth ceramic tile (normal load 72,28N, wet condition)306 13 th International Conference on Tribology – Serbiatrib’13