UNDERSTANDING WET SKID RESISTANCE TESTING WITH THE BRITISH PENDULUM SKID TESTER: ANALYSIS OF SLIDING NOISE FROM VARIOUS FILLED COMPOUNDS

The British pendulum skid tester (BPST) has been widely adopted for laboratory characterization of wet skid resistance (WSR) for rubber compounds. However, testing results are not yet well explained with material properties. For filled compounds made of the same styrene-butadiene rubber, on a Portland cement concrete surface wetted with water, WSR for compounds filled with inorganic oxides is higher than WSR for compounds filled with carbon black at the same filler volume fraction. However, such difference in WSR is eliminated under ethanol lubrication. Difference in WSR remains under ethanol lubrication between compounds filled with a reinforcing filler and compounds filled with a nonreinforcing filler. Accepting that dynamic deformation of rubber occurs in the frequency range between 10(3) and 10(6) Hz during testing with the BPST, loss tangent for the compounds is measured at various low temperatures but fails to correlate with WSR detected under water lubrication. Modification of bulk viscoelasticity from ethanol absorption should not be neglected for consideration of WSR under ethanol lubrication. During testing with the BPST, sliding noise generated by the assemblage of the spring and lever system in the pendulum with a rubber slider attached is captured under varied lubrication conditions. Both viscoelastic properties of rubber compounds and lubrication condition significantly affect sliding noise. However, no strict correlation between the intensity of sliding noise and WSR is observed. From frequency domain analysis, major components of the sliding noise lie in the frequency range between 500 and 5000 Hz for most compounds. For better understanding on testing with the BPST, modes of material deformation during dynamic sliding on a wet rough surface need to be further scrutinized.