Calculation of Critical Crack Size of Repair Welded Rail

Abstract

Repair of damaged rail surface by overlay welding is the common rail maintenance method. But the discontinuity in material between base and weld brings initiation of cracks and they causes a rail fracture. Unfortunately, such cracks are hard to detect on site because the weld boundary prevents the echo signals penetration by reflection. So estimation of the critical crack size (CCS) has been a critical issue in railroad industry to prevent a rail from sudden fracture. In this study, we calculated the critical size of crack which was initiated and propagated underneath of the overlay welded rail by applying linear elastic fracture mechanics. For this purpose, we measured the maximum load carrying capacities of cracked UIC60 by inverted 3 point bend tests and checked the feasibility of the finite element (FE) analysis procedure. We could find the correlation in crack size between the test and 3D FE analysis results and applied the proposed 3D FE analysis model to calculate the CCS of a rail. We calculated the stress intensity factors on cracked rail by increasing the size of crack until the rail broke. The CCS was calculated as around 30.0 mm under the normal railway service operating condition.