This article details the findings of a series of twin disc machine adhesion tests that investigated the effects of oil and water mixtures on adhesion at the wheel/rail interface. Oil was found to have a dominant effect on adhesion in the presence of water. Surfaces coated with oil at 4.7×10−3 g/cm2 and sprayed with water had levels of adhesion similar to those coated by a replenishing supply of oil. The tests showed that drying a wet contact can initially give a reduction in adhesion, that increased roughness results in increased adhesion in the presence of oil, and that increased contact pressure improves adhesion in the presence of oil.

Abstract--Feldspars in granitic saprolite in southwestern Australia have altered to halloysite, kaolinite, and gibbsite with no evidence of noncrystalline material. The secondary minerals are commonly present as intimate mixtures within altered feldspar grains, but discrete zones of gibbsite or halloysite-kaolinite also are present. Variations in the chemical microenvironment within micrometer-size zones in grains apparently controlled the type and distribution of secondary minerals. The alteration of both plagioclase and alkali feldspars involved congruent dissolution by soil solution and crystallization of halloysite, kaolinite, and gibbsite from this solution. Highly altered feldspar grains consist of etched feldspar fragments embedded within a highly porous framework of subhedral to euhedral platy crystals of kaolinite and gibbsite, or of spherical and felted aggregates of halloysite.

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Incidents involving low levels of adhesion between the wheel and rail are a recurrent issue in the rail industry. The problem has been mitigated using friction modifiers and traction enhancers, but a significant number of incidents still occur throughout the year. This study looks at the environmental conditions that surround periods of low adhesion in order to provide an insight into why low adhesion events occur. Network Rail Autumn data, which provided details on the time and location of low adhesion incidents, were compared against weather data on a national and then local scale. Low adhesion incidents have often been attributed to contamination on the rails, such as organic leaf matter, but these incidents also occur when no contamination is visible. The time, date and location of incidents were linked to local weather data to establish any specific weather conditions that could lead to these events. The effects of precipitation, temperature and humidity on rails were analysed in order to further the understanding of low adhesion in the wheel–rail contact, which will lead to adopting better methods of mitigating this problem.

Abstract--Laterite profiles developed from granite in southwestern Australia were studied by scanning electron microscopy. The morphology of soil materials reflects the mineralogy of secondary minerals formed from feldspar. In the saprolite, etched feldspar surfaces are coated with kaolinite or radiating, spherical aggregates of tubular halloysite. In the lower pallid zone these minerals have replaced most of the feldspar. In the upper pallid zone a porous framework has developed consisting mainly of quartz and gibbsite with 5-/xm euhedral gibbsite crystals in voids. Halloysite crystals in the upper pallid zone are partly unrolled and have splayed ends. Differences in mineralogy and morphology between profiles are thought to be due to variations in the intensity of leaching.