Estudo da vida em fadiga de trilhos ferroviários sob solicitações de rolamento aleatórias

Abstract

The current work presents a study of fatigue life of rails by applying multiaxial fatigue models, considering the residual stresses due to the cyclical wheel loads in different positions and directions. For that, a rail of heavy haul railway applications used in in Brazil was modeled using the finite element method and ABAQUS ® software. A model was developed by applying nodal forces obtained analytically with the theories of contact of both Hertz and Linear of Kalker. The nodal forces patch represents the rolling passes of the wheel along the rail in different straight lines and directions. For purposes of comparison, a model with pure rolling was also analyzed, in this case always passing in a straight line along the rail. To obtain the nodal forces, the finite element mesh generated in the ABAQUS ® software was imported by a program in MATLAB ® , where the efforts were calculated at each moment, associated with the node, and exported again for the ABAQUS ® as an input. Static analyzes were then made, simulating successive load applications during the rolling of a wheel on the rail. The stresses and strains variation in elements of a cross section of the rail were then analyzed aiming to identify the elastic shakedown phenomenon, since the presence or not of this phenomenon will guide the study of the life under fatigue. The stress and strain tensors, which are inputs to the fatigue criteria implemented, were exported back to the program in MATLAB ® . The methodology involved the application of low and high-cycle multiaxial fatigue criteria for a large number of points of a rail cross-section, each analyzed in 144 different planes, followed by the selection of the critical point and plane, according to each criterion. For this point and plane, the number of cycles necessary for crack nucleation was estimated. The results showed that the shakedown is reached after a few cycles. When the direction of the wheel passages is reversed, the shakedown appears again. After eight-wheel passes, the stabilization is once again achieved, remaining unchanged until the end of the simulation, even after further reversals of the wheel passages. Thus, when the rail was requested by loads so that the shakedown regime has already been reached, the stabilization is not affected. Besides, applications with tangential stresses influenced the distribution of equivalent stress and strain. For pure rolling, the distribution of equivalent stresses and strains presents lower stress and strains at the surface, and maximums in depths of about 3 mm. For the case where tangential stresses were considered, the distribution of stresses and strains for all analyzed fatigue criteria, showed an increase close to the surface.