Application of Magnetoelastic Technology to the Measurement of Stresses in Rails for High-Speed Trains

Abstract

Abstract On high-speed railroad lines, several dozens of standard rails have to be welded together to make a very long seamless rail. When put into service, owing to the resistance effect of the fasteners and the crossties, such a seamless rail is allowed to expand with heat and contract with cold only within 100 m of its two ends. Thus, huge longitudinal stresses may accumulate inside the rails when the temperature of the rails changes. In a rail, the cross-sectional area of which is 77.45 cm2, and the weight of which is 60 kg per meter, 2.5 MPa of stress will be generated as the temperature of the rail changes 1°C. In a hot summer, if the daily change of the temperature of the rails is 50°C, the stress in the rails will change 75 MPa. Such a large stress in the rails can cause catastrophes. Thus, a technology for the measurement of the stresses inside such a rail in service is urgently needed. The magnetoelastic wave is a physical effect caused by the sudden irreversible movement of the domain walls inside a ferromagnetic material when it is locally magnetized by an alternating magnetic field. This effect is strongly dependent upon many characteristics, such as mechanical, physical, and chemical, of the material. Based on this effect, an instrument for the measurement of the longitudinal stresses in seamless rails has been developed. Its principle and structure are introduced in this paper and a test is described.