A novel technique (patent in application) is proposed for the non-destructive measurement of longitudinal stresses in rail which make use of two phenomena known as (1) magne tostriction and (2) skin effect. Magnetostriction is exhibited by ferromagnetic materials such as rail steels and gives rise to a change in the magnetic permeability with applied stress. The skin effect determines the distribution of alt ernating currents near the surface of a conductor (hence, resistance according to the magnetic permeability and electrical conductivity of the material as well as the fre frequency of the alternating current. The electrical re resistance of a given section of rail is measured using di direct current and alternating currents of several frequencies and current amplitudes. As a result of the skineffect, the resistance of therail measured using an alter nating current of frequency, f, will depend on the permeab eability, thereby, providing an indirect measurement of the longitudinal stresses within the rail since the permeabilityof steels increases rodecreases with the application of tension or compression.
