Ratchetting damage of railhead material of gapped rail joints with reference to free rail end effects

Abstract

Free ends of insulated rail joints occur because gaps between the rails and endposts can be created due to pull-apart problems as the rails contract longitudinally in winter and by degradation of railhead material. Dynamic behaviour of gapped rail joints changes adversely compared to that of insulated rail joints. Thus, material degradation and damage of gapped rail joint components such as rail ends, joint bars, etc. are accelerated. Only limited literatures are available addressing the free end of rail effects at rail joints, targeting stress and pressure distributions in the vicinity of the rail joints. To understand clearly the material degradation and delamination process of gapped rail joints, a thorough analysis of failure of both insulated rail joints and gapped rail joints and subsequent damage of the railhead material is necessary to improve the service life of these joints. A new three-dimensional finite element analysis is carried out in this paper to assess damage to railhead material when gapped rail joints form. Both narrow (5 mm) and wide (10 mm) gaps are considered, using a peak vertical pressure load of 2500 MPa applied cyclically at one rail end, forming vertical impacts. Stress distributions and plastic deformations in the vicinity of gapped rail joints are quantified using finite element analysis data and compared with that of the insulated rail joints to show the effects of free rail ends. Residual stress and strain distributions indicate the damage to the railhead material. Equivalent plastic strain (PEEQ) quantifies the progressive damage to the railhead material at the rail ends. The free end of rail effects can be further illustrated by comparing PEEQ for insulated rail joints and gapped rail joints. The railhead material of 5 and 10 mm gapped rail joints is more sensitive to permanent deformation compared to that of the corresponding insulated rail joints. Therefore, free rail end joints pose an increased potential threat to rail operations in relation to crack initiation, damage and premature failure of railhead material.

Investigating the Effect of Some Train and Track Parameters on Contact-impact Forces in the Vicinity of a Rail Breakage

“…The derailment index is calculated based on the ratio of lateral to vertical wheel load. The threshold for this value varies in different standards, from 0.6 to 1.0 [24]. Moreover, in some of the standards, it is stated that derailment occurs only when the derailment index is exceeded for a specific amount of time/distance.…”

Effect of wheel–rail interface parameters on contact stability in explicit finite element analysis

“…5–7 These approaches have been verified and/or validated to be effective and efficient enough for addressing the problems of wheel–rail (W/R) contact in elasticity as well as in the cases of quasi-static and/or low-frequency dynamics. 2,8–12 Regarding the complex problems with both realistic contact geometries and material plasticity considered, finite element (FE) method, as opposed to the aforementioned approaches, appears to be much preferable and powerful for ensuring the desired solutions.…”