The economic importance of railways has generated more studies regarding improvements in this modal. The rail is the component responsible for guiding the rail vehicles and this contact with the rail generates service stresses that, added to the residual stresses, can cause the rail to collapse. The regions close to the welds are, in general, the most fragile regions and more susceptible to macro and micro structural defects that may or may not generate more residual stresses. The present work aimed to determine the acoustoelastic constant in the regions of HAZ and CS of a rail with TR68 profile, welded by electric butt welding with sparking (Flash Butt Welding-FBW). And later quantify the difference of residual tension (σ1-σ2) existing in these regions. Specimens were sectioned and then subjected to subcritical annealing heat treatment for stress relief. A tensile test was performed to determine the yield stress, the initial birefringence of the material was determined, a fractional loading test was performed to simultaneously determine the birefringences in each load, which generated linear curves in the load x birefringence graphs, where the slope is the acoustoelastic constant. Finally, the residual voltage difference is calculated. It was observed that the difference in residual stresses in the HAZ region of the head for the two welded rails (J1 and J3) are compressive, as well as in the HAZ of the web, with maximum magnitudes of 40.2 MPa and 30.6 MPa.
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