Abstract
When a rubber block is squeezed against a nominal flat but rough surface, the rubber bottom surface will penetrate into the substrate roughness profile. The relation between penetration depth \(w\) (or the average interfacial separation \(\bar{u}\)) and the applied squeezing pressure \(p\) determines the (perpendicular) contact stiffness \(K=\hbox {d}p/\hbox {d}w=-\hbox {d}p/\hbox {d}\bar{u}\), which is important for many applications. We have measured the relation between \(p\) and \(\bar{u}\) for a rubber block squeezed against 28 different concrete and asphalt road surfaces. We find a linear relation between \({\mathrm{log}}p\) and \(\bar{u}\), in agreement with theory predictions. The measured stiffness values correlate rather well with the theory prediction.
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Notes
The filled rubber compound we use exhibits strain softening with an elastic modulus which decreases from \(\approx 12 \ {\mathrm{MPa}}\) to \(\approx 4 \ {\mathrm{MPa}}\) as the strain increases from 0.1 to 10 %. The rubber strain in the asperity contact regions is approximately independent of the nominal contact pressure and relative large so the large strain \(E\)-module is most relevant and we take \(E\approx 4 \ {\mathrm{MPa}}\). The effective modulus for the confined rubber disk is approximately given by the equation derived by Gent and Lindley (see Ref. [16]): \(E_{\mathrm{eff}} \approx E(1+2 S^2)\) where \(S=D/4d \approx 2.5\) (where \(D\approx 10 \, {\mathrm{cm}}\) is the diameter of the disk and \(d=1 \, {\mathrm{cm}}\) the thickness of the disk). Thus, we get \(E_{\mathrm{eff}} \approx 13.5 E \approx 54 \, {\mathrm{MPa}}\).
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Acknowledgments
The work underlying this report was commissioned by the Federal Ministry of Transport, Building and Housing under FE SV.0003/2009, by the Federal Ministry of Economics and Technology under 19 S 11002 and on behalf of the German Research Foundation. We thank Stephan Westermann (Goodyear, Luxenburg) and Boris Lorenz for comments on the manuscript.
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Wang, D., Ueckermann, A., Schacht, A. et al. Tire–Road Contact Stiffness. Tribol Lett 56, 397–402 (2014). https://doi.org/10.1007/s11249-014-0417-x
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DOI: https://doi.org/10.1007/s11249-014-0417-x