This paper reviews the experience in London Transport of fatigue cracking in railway axles, and presents the results of laboratory fatigue tests on full-scale axle specimens under simulated rotating bending. The investigation was undertaken with the aim of entirely eliminating fatigue cracking and fretting under the press fits of wheel-axle sets. Whilst cold rolling of wheel seats, which is standard L.T. practice, strongly inhibits the propagation of such fatigue cracks, it does not prevent their initiation. The introduction of a stress-relieving groove, such that the edge of the press fit overhangs the groove, leads to a marked reduction in fretting and increase in life of test specimens, and the results of a limited service test suggest that the presence of such a groove reduces the stresses under the wheel hubs to a level at which cracking is eliminated. Since the presence of a press fit near to a groove increases the stress level at the root of the groove it is desirable to cold-roll the grooves, and a suitable rolling technique employing three rollers of slightly different profile radii has been developed.
