Relationship between the dynamic softening transition and wet sliding friction of elastomer compounds

Abstract

For properly chosen elastomer compounds, thermorheological characterization is combined with an examination of the variation of the wet sliding friction with temperature. A conceptual argument leads to the assumption that the wet sliding friction should maximize at the energy dissipation peak associated with the dynamic softening transition at a characteristic frequency determined by the sliding speed and the effective smallest surface asperity scale. The dynamic softening transition is characterized with the peak in tan δ/G′n, where tan δ is the loss tangent, G′ is the elastic modulus, and n is a constant between 0 and 1. The William–Landel–Ferry transform is uncritically applied for extrapolating the position of the peak in tan δ/G′n at high frequencies. Even based on the criterion of tan δ, the results obtained on a concrete surface indicate that the effective smallest asperity scale is of order of 100 μm. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2467–2478, 2004

Significance of Tuning Bulk Viscoelasticity via Polymer Molecular Design on Wet Sliding Friction of Elastomer Compounds

“…Crosslinking density is examined with the method of equilibrium swelling in toluene [13]. The volume fraction of polymer (including filler) in the network at equilibrium swelling, V R , is listed in table 4 for each compound.…”

“…The torsion rectangular geometry is employed for testing with ARES while the parallel plate geometry is employed for testing with ARES-HT. The testing protocols are similar to those described previously [13,14]. For tests of strain sweep and time sweep, all the results presented below are obtained with samples exposed to prior large deformation.…”

“…The setup and procedure for BPST testing have been described earlier [12][13][14]. A Portland cement concrete block provides the road surface.…”

“…Outside the glassy state G 00 increases with increasing f, or equivalently with decreasing l. It is thus reasonable to assume that when testing wet traction at fixed v, the peak in coefficient of friction l as a function of T coincides with the peak in tand(T) obtained at f = v/l where l is now the effectively smallest scale on the testing surface. By using data points for unfilled compounds exhibiting less nonlinear viscoelasticity, it is estimated that the effectively smallest scale for wet sliding on the concrete surface employed is about 200 lm [13]. Asperities at smaller scales are still immersed in water.…”

“…This test is not ideal as v is not constant. However, it clearly demonstrates impacts on wet traction of rubber compounds from a variety of factors [12][13][14].…”