INFLUENCE OF SPATIAL VARIATIONS OF RAILROAD TRACK STIFFNESS AND MATERIAL INCLUSIONS ON FATIGUE LIFE

Railroad transportation is very important for economic growth and effective maintenance is one critical factor for its economic sustainability. The high repetitive forces from a moving railcar induce cyclic stresses that lead to rail bending and potential deterioration due to fatigue crack initiation and propagation. Previous research for prediction of fatigue life has been done under the assumptions of a uniform track bed and a homogeneous rail. However the spatial variation of the track stiffness is expected to increase the maximum stresses in the rail and, therefore, accelerate the fatigue process. The research described in this dissertation is focused on the variations of the track modulus as well as the inclusions within the rail and their role on fatigue life. The computational procedure is based on the automated preprocessing and post processing of several hundreds of finite element models of the rail across a set of crossties chosen from a random ensemble with representative statistical variations. The model parameters are estimated from field track deflection dynamic measurement data in comparison with deflection data from FE models. A multiaxial fatigue model is used for the estimation of fatigue cycles to crack initiation while the extended finite element method (XFEM) is used for the computation of the crack propagation directions and the stress intensity factor range as the indicator of the crack propagation rate. The results show that a nonuniform track bed can reduce fatigue life up to 100 times in comparison with the behavior expected for a uniform trackbed. The role of inclusion stiffness relative to the background rail steel and inclusion location are both important for fatigue life. Both effects also influence the direction of the initiated crack propagation. The results of this work are expected to be used for the effective maintenance and scheduling of rail inspection