. Steel rails; their history, properties, strength and manufacture, with notes on the principles of rolling stock and track design . Fig. 198. — Polished Surface with Small Cracks. (J. W. Ewing and J. C. W. Humfrey.) 276 STEEL RAILS The effect of this repeated &hding or grinding is seen at the pohshedsurface of the specimen by the production of a burr or rough and jagged irregu-lar edge, broadening the slip band, and suggesting the accumulation of the crystal this repeated grinding tends to destroy the cohesion of themetal across the surface of the slip, and in certain cases this
. Steel rails; their history, properties, strength and manufacture, with notes on the principles of rolling stock and track design . Fig. 198. — Polished Surface with Small Cracks. (J. W. Ewing and J. C. W. Humfrey.) 276 STEEL RAILS The effect of this repeated &hding or grinding is seen at the pohshedsurface of the specimen by the production of a burr or rough and jagged irregu-lar edge, broadening the slip band, and suggesting the accumulation of the crystal this repeated grinding tends to destroy the cohesion of themetal across the surface of the slip, and in certain cases this develops into a crack. Once the crack is formed, it quickly grows in a well-known manner,by tearing at the edges, in consequence of the concentration of stress which. Fig. 199. — Polished Surface with Large Cracks. (J. W. Evving and J. C. W. Humfrey.) results from lack of continuity. The experiments throw light on the knownfact that fracture by repeated reversals or alternations of stress resemblesfracture resulting from creeping flaw in its abruptness, and in the absenceof local drawing out, or other deformation of shape. * The rupture of steel is not caused by the gradual growth of the crystal-line structure of the metal under the influence of shocks and vibrations. Thebreaking down is due to fatigue. When fatigued, the metal breaks more , when subjected to sudden shock, the metal has no time to flow. The * P. Kreuzpointer, Journ. Franklin Inst., 153, 233, 1902. J. A. Ewiiig, Nadirc, 70, 1S7, Hrcuil, Suppl. Journ. I. & S. Inst., 1904. STRENGTH OF THE RAIL 277 slipping of the crystal planes, or the plasticity of the metal, has no time to comeinto play. The metal, in consequence, appears to be abnormally brittle. * The ex
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