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A rail section that failed due to fatigue showed a smooth surface with well-developed conchoidal markings. This indicated successive stages of crack propagation, characteristic of fatigue failure. The crack was one of several which developed in the sections of curved rail which formed the lower roller path on which the superstructure of a walking drag-line excavator slewed. The cracking, which ran horizontally, developed at the junction of the underside of the rail head with the web and originated at surface defects in the form of grooves present on the castings. It was concluded that the cracking was caused by lateral deflection of the rails under in-service loads. The web of a rail would normally be loaded in compression but, should lateral movements occur, then it would be subjected to bending stresses and fatigue cracks could break out in regions where excessive tensile components predominated.

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