The circumstances giving rise to the incipient derailment of a railway wheel-set under steady-state rolling conditions are re-examined in the light of recent developments in rolling-contact theory. It is found that the problem can be stated in a form which avoids difficulties inherent in most earlier treatments. However, a quantitative solution requires data relating tangential force to creepage and spin in a parameter region previously unexplored. New experimental results are presented which partially correct this lack of data, but more work, both theoretical and experimental, is required. One outcome of the new study is the establishment of the region of applicability of Nadal's classical formula. It shows it to be highly relevant for practical decision-making.

An integrated design methodology has been developed for the fatigue life evaluation of railway vehicle bogies. In principle, there are five parts in the procedure: specijkation and measurement of track irregularities; modelling a railway vehicle and description of rail-wheel profiles: obtaining the railway vehicle suspension load histories; dynamic analysis and stress evaluation of the bogie p a m e ; fatigue li&e evaluation of the bogie. The whole procedure has been applied to a typical London Underground railway vehicle. The theoretical results have been validated against field test data and fatigue calculations have indicated good agreement with operational data from the actual vehicles. I t has been shown that a design methodology for railway vehicle bogies based on the track profiles on which they will run and on their own structural characteristics is possible and can be used at an appropriate stage in the design process.

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