A MECHANICAL MODEL FOR THE PREDICTION OF THE TIRE/ROAD FRICTION
The viscoelastic deformation of tire rubber by road surface asperities was modeled by the rolling contact between a Kelvin solid and a surface motif, which is the part of surface profiles between two peaks. Stress and strain calculations showed that contact losses might occur locally, depending on the rolling speed, the viscoelastic properties of the Kelvin solid and the geometry of the motif. Mean vertical and horizontal forces were calculated, from which a coefficient of friction was derived. The model was successfully coupled with a profile analysis method to predict tire/road friction at low speed from road surface microtexture. The contribution of various texture scales to friction was emphasized. For the covering abstract see ITRD E118503.
Friction of Different Surface Layer of Pavements in Contact With a Rubber
We analyse the physical mechanisms taking place in unlubricated friction between surface layer of pavements and a piece of rubber at low sliding speeds < 200 mm/s. This analysis is based on extensive experimental investigations of the load and velocity dependences of dynamic friction forces. The dynamical behaviour caused by dry friction is studied for a rubber-block system pulled with constant velocity over a surface layer of pavements. The dynamical consequences of a general type of phenomenological friction law (stick-time dependent static friction, velocity-dependent kinetic friction) are investigated. Three types of motion are possible: stick-slip motion, continuous sliding, and oscillations without sticking events. In the last case, we propose values of friction coefficient of different surface layer of pavements.© 2005 ASME
Chemosymbiotic bivalves and stable carbon isotopes indicate hydrocarbon seepage at four unusual Cenozoic fossil localities
Four unusual Cenozoic fossil localities are identified here as ancient hydrocarbon seep sites using palaeontological, petrological, and stable carbon isotope data. Late Eocene carbonate-cemented sandstone bodies in the Wagonwheel Mountains in California were previously suspected to represent ancient hydrocarbon seep sites, but the relatively high δ13Ccarbonate values (−12.2 to −5.0‰) suggest oil rather than methane seepage. The Oligocene fauna of the Elmira asphalt mine, Cuba, was previously interpreted as a mix of freshwater and marine taxa, but all species are here identified as belonging to marine groups, including the bivalve families Lucinidae and Vesicomyidae, whose extant members live largely in symbiosis with chemoautotrophic endosymbionts. A carbonate concretion from this site showed δ13Ccarbonate values as low as −32.2‰, which most likely indicates methane seepage. A previously unpublished Oligocene fossil locality in Atlantico, northern Colombia, is dominated by large solemyid, mytilid, lucinid, and vesicomyid bivalves, which most likely lived with chemotrophic endosymbionts. Seepage of biogenic methane without a significant contribution of thermogenic methane is indicated by δ13Ccarbonate values as low as −51.3‰. We confirm that the Pleurophopsis-dominated sites of the Heath Shale and Lomitos Chert in northern Peru are ancient seep sites, although the previous identification of Pleurophopsis peruviana as a vesicomyid is doubtful.