Rolling-sliding laboratory tests of friction modifiers in leaf contaminated wheel-rail contacts

Leaf-related adhesion problems have been present in many railway networks all over the world in the last few decades. Since the early 1970s many measures have been undertaken in order to mitigate the problem. One of the measures adopted by many railway networks is the use of friction modifiers. However, the low adhesion problem still persists. Furthermore, the effectiveness of these friction modifiers has not well proven yet due to the lack of research in controlled conditions. Consequently, the rolling stock operators and infrastructure managers do not clearly understand the performance and side effects of the friction modifiers used on their networks. In this paper, an investigation of the performance of two existent friction modifiers in controlled laboratory conditions is presented. These friction modifiers have been used or tested in several railway networks. A twin-disk roller rig has been used to study their performance in leaf contaminated contacts. The adhesion characteristics of both friction modifiers are examined for different slip ratios. The constituents of the friction modifiers are identified and the solid components are analyzed. In addition, damage that these friction modifiers may cause to wheel and rail is also discussed.