ABSTRACT

Rubber friction is a complex phenomenon that is composed of different contributions. Because it always consists of a friction pairing, the road surface topology has a main impact on the adhesive and sliding characteristics in the rubber-road interaction. New manufacturing processes offer the means to develop specific road surfaces. By using a modified three-dimensional (3D) printing method based on selective laser melting with stainless steel, it is possible to create any desired surface up to a resolution of 20 μm. In this work, several metallic surfaces are built for two separate purposes. First, the rubber-road interaction is analyzed and compared for metal and asphalt. Second, theoretical friction laws are investigated with synthetic surfaces. Toward this aim, the friction coefficients are measured in both dry and wet conditions. A multiscale approach for friction properties on different length scales is implemented to accumulate the micro and mesoscopic friction into a macroscopic friction coefficient. On each length scale, a homogenization procedure generates the friction features as a function of slip velocity and contact pressure for the next coarser scale. Within the multiscale approach, adhesion implemented as nonlinear traction separation law is assumed to act only on microscopic length scales. By using the finite element method, the sensitivity of the influencing factors, such as macroscopic slip and load conditions, is investigated. The friction loss from dry to wet conditions cannot be explained by loss of adhesion alone. Hysteresis has to be affected as well. A possible hypothesis for this is the trapped water pools in the texture. The road surface is effectively smoothed and thus hysteresis reduced. To verify this hypothesis, a hysteretic friction model is calibrated to dry measurements. The cavities in the modeled texture are then filled incrementally to simulate various amounts of trapped water.

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