The steady state abrasion of rubber: Why are the weakest rubber compounds so good in abrasion?

This paper examines the blade abrasion of four different rubber materials, unfilled natural rubber (NR), unfilled styrene butadiene rubber (SBR), unfilled butadiene rubber (BR) and carbon black filled styrene butadiene rubber. Each is abraded until the steady state abrasion pattern is developed on the surface of moulded rubber wheels. The steady state conditions are measured using the weight loss per revolution of the wheel. The abraded surface is cut to examine the typical asperity profile. Each profile is modelled using finite element analysis to calculate the stored energy release rate for each combination of material and test condition. The stored energy release rate when combined with an independent measure of the rate of crack growth measured using a fatigue crack growth test gives a reasonable prediction of the abrasion rate for both SBR materials as well as the BR. However, the NR materials appear to be about 30 times worse in abrasion than would be expected from the cyclic fatigue crack growth measurements. This is most likely to result from the strain induced crystallisation being suppressed by the very rapid loading rates that are encountered during blade abrasion. It is apparent that the low strength of the BR material results in much smaller asperities being formed under steady state abrasion. When these asperities are modelled they create very low values of strain energy release rate which results in a much slower abrasion rate. Conversely the strongest material NR has the longest tongue on the asperity and this in turn generates much larger values for the tearing energy at the tip of the asperity and this contributes to its poor abrasion resistance. (c) 2009 Elsevier B.V. All rights reserved.