Numerical investigation of the fatigue life of center sill of a BFNSM wagon

Abstract

This paper evaluates the fatigue life of a roll-formed center sill part in a coil-carrying railway wagon underframe assembly. The loading cycles experienced by this rail wagon architecture are taken from a recorded railroad data available in the Association of American Railroads (AAR) Manual of Standards and Recommended Practices. To estimate the fatigue life of the roll-formed center sill under the given loading history, a two-step finite element (FE) analysis is carried out, considering the residual stresses and thinning introduced in the center sill due to roll forming. Firstly, a COPRA^® FEA RF model is used for roll forming analysis to predict the residual stresses in the center sill, followed by modeling of the actual loading history on the wagon underframe and prediction of fatigue life using commercial FE codes ABAQUS and fe-safe. To validate the results from fe-safe, experimental results of the fatigue tests of pre-strained lab-scale tensile specimens are compared with the predicted values obtained from fe-safe. Our prediction of the roll-formed center sill life shows that the residual stresses introduced due to roll forming are locally detrimental, as the fatigue life is reduced compared to the conventional center sill. This proposed method of evaluating the fatigue life of a part using railroad spectrum load data and roll forming residual stresses developed in the process of center sill fabrication, can be effectively used during the design phase of a rail wagon at both the part and assembly levels.