چكيده به لاتين
The rails are the most important part of the railroad and are directly connected to the train wheels, so the quality and efficiency of the rails is very important. Welding rails create a more sensitive area along the rails due to the thermal stresses experienced during welding. Therefore, because welds must have a lifespan equal to the life of the rail, mechanical tests, metallurgy, fracture mechanics, and the phenomenon of rail and weld fatigue make us choose and ensure the quality of the welds performed and select the appropriate and reliable welding method and Reliability of domestic and foreign purchased railways helps. In this dissertation, the fracture mechanical properties of rail thermite welds in Iranian railways were investigated by performing a fracture toughness test and a fatigue crack growth rate test in the form of three-point bending test. And the modeling of these tests was performed in the software of limited components ABAQUS and FRANC3D. The failure level due to fatigue loading was examined by SEM fractographic examination. the obtained results are compared with the allowed values of the regulations and the values obtained by other researchers. Finally, using the fracture toughness value and the relationship between the fatigue crack growth rate for thermite welding, the fatigue test of full-scale thermite railweld with a small surface defect common in rail welding (semicircular crack in the center of rail foot) It was simulated with EN 14587-2 and EN 14730-1 standards until the welding failure. The value of fracture toughness of the seam thermite weld specimen according to the ASTM E399 standard, 43 Mpa.m1/2 , and according to the numerical modeling results, the value of fracture toughness for rail seam termite welding, the value of 44.4 MPa.m0.5 obtained. And according to the experiments to determine the growth rate of fatigue cracks in the weld sample, the parameters c and m of the Paris relationship, the rate of fatigue crack growth in mm / cycle, respectively, equal to 4.5271×10-12 and 5.9861 were obtained. Fractographic examination of the failure level of the fatigue test showed brittle failure of the sample.
