INTERNAL AND STRAIGHTENING STRESSES IN NEW-ROLLED RAILS

When laying a rail in the track it must be assumed that in general with given static/dynamic cases of loading, the fatigue strength of the rail material is affected more or less by the thermal and internal stresses. Whereas with thermal stress a technical solution is possible only by laying the rail at a mean temperature between summer and winter, the results of internal stress measurements in rails of different quality and section show that by suitable choice of section and material a reduction can be achieved in the tensile internal stresses in the longitudinal flange direction, and in the compressive internal stresses in the longitudinal head direction, and hence better utilization of the material in respect of its fatigue strength. The results show in detail that internal stresses in new-rolled rails are caused mainly during straightening and not during cooling, and also as a result of the associated phase change. Their magnitude and distribution over the cross- section depend on the curvature of the rail before strengthening, on the yielding point of the material, and on the rail section. Comparison between measured and calculated internal stress shows that the internal stresses caused by strengthening result not ony from plastic, pure bending of the rail in the strengthing press, but also from the plastic, deformation of the rail in way of the contact points of the strengthing rolls.