| Popis: |
MEASUREMENTS OF SKID RESISTANCE (BRAKING FORCE COEFFICIENT (BFC) HAVE BEEN MADE USING TRAILER AND FRONT WHEEL BRAKING TECHNIQUES. THE FIVE SETS OF SMOOTH TREADED TIRES DIFFERED ONLY IN THE TREAD POLYMERS WHICH WERE CHOSEN TO COVER A RANGE OF PHYSICAL PROPERTIES. THE TIRES WERE TESTED AT SPEEDS RANGING FROM 1 KM/H(0.4 MPH) TO 160 KM/H(100 MPH) ON EIGHT SURFACES HAVING A WIDE RANGE OF TEXTURES. MACROTEXTURE WAS MEASURED BY SANDPATCH "TEXTURE DEPTH" AND STEREOPHOTOGRAMMETRIC "PROFILE RATIO" TECHNIQUES. COMPARSION OF THE MEAN BFC/SPEED CURVES FOR EACH POLYMER SHOWS A SIMILARITY OF SPEED DEPENDENCE, INDICATING THAT ON THE HIGHWAY PENETRATION OF THE WATER, FILM IS THE OVERRIDING FACTOR RATHER THAN A SPEED DEPENDENT VISCOELASTIC EFFECT WHICH HAS BEEN POSTULATED FROM LABORATORY FRICTION MEASUREMENTS. HOWEVER THE ORDER OF THE BFC SHOWS EVIDENCE OF VISCOELASTIC BEHAVIOR, THE MORE RESILIENT POLYMERS GIVING THE LOWER VALUES. A HYPOTHESIS RELATING TO A CHANGE IN THE TIRE/PAVEMENT CONTACT CONDITIONS AT HIGH SPEEDS IS PUT FORWARD THAT THE HIGH VALUES OF BFC ON SURFACES WITH LARGE TEXTURE DEPTH ARE PARTLY DUE TO MODIFICATION OF THE CONTACT CONDITIONS BY CHANGES IN THE VISCOSITY OF THE LUBRICANT BROUGHT ABOUT BY HEATING. /ASTM/ |
