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Flange tip lift crossings are widely utilized in modern tramlines to replace traditional crossings to enhance commuters' comfort and prevent crossing nose failures. However, due to altered contact conditions between wheel flanges and ramps of crossings, the use of flange tip lift crossing has led to the critical issue of ramp wear. To resolve this issue, this paper investigated the dynamic contact response of a ramp during in-service loading, as well as the resultant wear of the ramp. With a dynamic finite element model, the local contact pressure and local sliding distance were computed and subsequently applied in a local contact-based wear model to evaluate the nominal wear of the ramp. Our findings indicate that under typical in-service loading conditions, the ramp exhibited up to 120 times more wear than the rail head, owing to increased contact pressure and reduced contact area during the ramp contact. To mitigate this issue, a design change of a gentler ramp inclination from the default 1:100 ramp to a 1:150 ramp could provide approximately 10% wear reduction. In addition, increasing the flange radius by 1 mm could reduce the wear by up to 13%. Conversely, increasing the speed to 45 km/h from the recommended 15 km/h speed may cause up to 5 times more wear. Furthermore, an empty tram showed 56% less wear on the ramp when compared to the condition of the maximum allowable axle load. These results offer an insight into the detrimental wear of ramps used in flange tip lift crossings of tramlines and can assist in the development of new designs and operating guidelines to mitigate ramp wear. • Ramp wear of a tram crossing was investigated using dynamic finite element simulation and a local contact-based wear model. • The wear of the ramp was found to be up to 120 times greater than that on the rail head of tram rails. • Gentler ramp inclination, increased flange radius, reduced vehicle speed and lower axle load can reduce the wear of the ramp. [ABSTRACT FROM AUTHOR]

• A first study of the effect of full creepage on RCF crack growth behaviour. • Predicted crack growth directions show a good agreement with field observation. • Lateral and spin creepages can significantly affect K II and K III evolutions. • Increase in spin creepage is more detrimental to RCF crack driving force. In heavy-haul railway systems, the experience of high traction force of rails in curved tracks significantly accelerates the rolling contact fatigue crack growth. The overall level of traction force and its detailed distribution within a contact patch can be determined by the extent of wheel slips in different directions, also referred to as creepage. However, few studies have focused on quantifying the influence of creepage on rolling contact fatigue crack growth behaviour. In this paper, a numerical method is proposed to investigate the non-proportional mixed-mode rolling contact fatigue crack growth behaviour in the presence of severe longitudinal, lateral and spin creepages. To partially validate the proposed numerical method, the predicted crack growth directions on the rail surface are compared with the cracking patterns obtained from field observations. A parametric study is also conducted to further quantify the influence of different creepage combinations on the evolution of stress intensity factors at the crack front. Results show that both lateral and spin creepages can significantly affect the phase and maximum magnitude of K II and K III during one complete loading cycle. Moreover, the increase of spin creepage is found to have a more detrimental effect on overall RCF crack driving force than the increase of the other two creepage components. [ABSTRACT FROM AUTHOR]

• A ratcheting mechanism-based numerical model was applied to predict damage initiation in twin-disc tests of premium rail steels. • Wear- and RCF-dominated damages are distinguished by the depth of the ratcheting mechanism-based damage initiation locations. • A higher creepage results in a shallower damage initiation location and a shorter damage initiation life. • The initial wear rate increases with a higher creepage for wear-dominated damage. • HE2 rail steel presents the longest damage initiation life and the lowest initial wear rate compared to HE1 and LAHT. This work presents a ratcheting mechanism-based numerical model to study the initiation location and initiation life of rolling contact fatigue (RCF) or wear damage and the initial wear rate of premium rail steels under the laboratory twin-disc test conditions. Twin-disc tests are widely used in the studies of rail steels due to their ability to reproduce critical aspects of full-scale wheel-on-rail contact under controlled conditions and a relatively short test period compared to field tests. This study introduces a computational model to simulate the cyclic rolling contact for three premium rail steels (HE1, HE2, and LAHT) against wheel steel AAR Class-C under twin-disc test conditions. The cyclic rolling contact is achieved by repeatedly moving a non-Hertzian distribution of contact pressure and the calculated longitudinal surface traction upon a segment of the circumferential surface of the lower disc until a stabilized maximum ratcheting strain rate is reached. The RCF or wear damage initiation location is determined by the location showing the stabilized maximum ratcheting strain rate, and the damage initiation life is estimated by applying the ratcheting failure mechanism. Wear and RCF damages are distinguished by the depth of the damage initiation location. Wear damage is dominant when the location is near the surface. Otherwise, the damage will be RCF-dominated. The initial wear rate due to wear-dominated damage is estimated by identifying a critical profile and affected volume of worn material within the ratcheting strain rate field. The predicted initial wear rate is compared with the experimental result of the examined contact pair. This research can assist in a more profound understanding of the experiment results of a twin-disc test and provide a numerical basis for an experimental twin-disc test design. Furthermore, it may provide significant references for choosing rail steels. [ABSTRACT FROM AUTHOR]

• The FaStrip algorithm is modified to estimate elastic-plastic traction distribution. • Softened zones of rail welds experience the highest ratcheting strain rate. • Ratcheting strain rates in the sampled 2000 m radius curved track are higher than those in the sampled tangent track. • The RCF initiation location is highly dependent on the magnitude and pattern of traction distribution. Ratcheting at the rail heads due to cyclic rolling contact stresses is often observed in heavy haul railways, especially when there are large steering forces developed in low-radius curves. Additionally, ratcheting behaviour can be exacerbated when associated with material strength loss in the heat affected zones of rail welds. However, the numerical evaluation of this failure mode requires a sophisticated representation of elastic–plastic contact pressures and traction distributions, which, to the best of the authors' knowledge, cannot be directly measured by any existing tools. In this paper, in order to accurately evaluate the ratcheting performance at rail welds in curved tracks, attempts were conducted to modify the FaStrip algorithm to analytically estimate the traction distributions based on contact pressures and creepages obtained from static finite element analysis and multi-body dynamic simulations, respectively. Cyclic rolling contact was then simulated by repeatedly applying contact pressure and traction on the rail surface consisting of both the rail weld and the parent rail regions. The weld region was divided into 23 sub-zones in the rolling direction to represent the material inhomogeneity within the heat affected zones. Cases on a 2000 m radius curved track and a tangent track were studied for comparison. It was found that the ratcheting strain rate in curved tracks can be significantly elevated due to the higher magnitude of traction, and the location of the elements with the highest ratcheting strain rate was dependent on the traction distribution patterns. The proposed method provides a general tool for predicting rolling contact fatigue initiation life and location, which will benefit the maintenance efficiency of heavy haul rail welds in curved track. [ABSTRACT FROM AUTHOR]

• A first approach to evaluate ratcheting performance of rail flash butt welds is presented. • The numerical study combined a dynamic wheel–rail weld rolling contact simulation, multiple quasi-static wheel–rail weld contact simulations and a cyclic loading simulation. • The weld region was divided into 23 zones due to various mechanical properties across the rail weld. • The region with the lowest hardness in the softened zone has the shortest RCF initiation life. • RCF is likely to initiate more deeply in the softened zone than the parent rail and the region around the bond line. The ratcheting performance of a new R400HT rail flash butt weld was numerically evaluated under a typical heavy haul in-service condition. Due to varying mechanical properties across the rail weld, the weld region was divided into 23 zones in the numerical study. A dynamic finite element simulation of wheel–rail weld rolling contact was first carried out to obtain the total vertical contact force and its variation along rolling distance. Multiple quasi-static wheel–rail weld contact simulations were then performed by applying the total vertical contact force to determine the non-Hertzian contact pressure distribution when the wheel was located at different positions across the weld in the rolling direction. Based on each normal contact pressure distribution, the Haines and Ollerton's strip theory and Carter's theory were employed to estimate the corresponding longitudinal surface tangential traction distribution. Finally, a cyclic loading simulation was conducted to evaluate the ratcheting performance of the rail weld in terms of RCF initiation life by repeatedly translating these normal contact pressure and longitudinal tangential traction distributions on the running surface. The results reveal that the subzone with the lowest hardness in the softened zone has the shortest RCF initiation life among the weld region, followed by the region around the bond line. The parent rail provides the longest RCF initiation life and therefore has the best resistance to RCF. Additionally, the existence of the softened zone can shorten the RCF initiation life of the parent rail and the bond line section, particularly the regions located adjacent to the softened zone. The possible location of RCF initiation in the softened zone of the rail head can reach deeper than those in the parent rail and the region around the bond line. The results can help us understand the failure of flash butt rail welds in heavy haul operations and the numerical method can be applied to study different rail welds and rail welds under different conditions such as in a curved track. [Display omitted] [ABSTRACT FROM AUTHOR]

• Uniaxial and biaxial stress-controlled cyclic tests were performed to investigate the ratcheting behaviour of flash butt welds in a heat-treated hypereutectoid steel rail. • The distribution of ratcheting strain can be correlated to the longitudinal hardness profile within the heat-affected zone of the weld. • At a same cyclic stress level, the softened zone exhibits a highest ratcheting strain, followed by the parent rail and the region near the bond line. • At the initial stage of cyclic loading tests, the softened zone exhibits cyclic hardening while the region near the bond line exhibits cyclic softening. • The spheroidised microstructure present in the softened zone significantly reduces its hardness and ratcheting resistance. Experimental study consisting of both uniaxial and biaxial stress-controlled cyclic tests was performed to investigate the ratcheting behaviour of new flash butt welds in a heat-treated hypereutectoid steel rail used in Australian heavy haul railways. Digital image correlation technology was applied to capture the heterogeneous strain field and its evolution at every point on the surface of the weld specimen. The results show that the softened zone with a significant hardness drop is more sensitive to plastic deformation and results in a higher ratcheting strain than the region around the bond line. Moreover, the distribution of ratcheting strain can be correlated to the longitudinal hardness profile within the heat-affected zone of the weld. At the initial stage of cyclic tests, the softened zone tends to exhibit cyclic hardening while the region around the bond line is more likely to exhibit cyclic softening. Compared with the parent rail, the softened zone shows much worse ratcheting resistance, while the region around the bond line demonstrates slightly better ratcheting resistance. Metallographic analysis indicates that the microstructure and resulting ratcheting resistance of the weld vary with the longitudinal position. High ratcheting strain in the softened zone is mainly attributed to the existence of the spheroidised microstructure with a high amount of ferrite. The outcomes of this study can provide valuable information for further establishing the constitutive models to quantify the heterogeneous ratcheting of rail welds under practical wheel-rail contact situations by finite element simulations. Image, graphical abstract [ABSTRACT FROM AUTHOR]

The ratcheting performance of heavy haul rails in curved tracks under different in-service loading conditions was numerically evaluated by using a recently developed approach. The wheel–high rail cyclic rolling contact was simulated by translating the non-Hertzian contact pressure distribution and the estimated longitudinal tangential traction repeatedly on the running surface of the high rail. The maximum ratcheting strain rate of the rail target section was obtained in each loading cycle. Based on the known ductility limit of the rail steel and the obtained maximum stabilized ratcheting strain rate, the crack initiation life of the rail was predicted in each case. The results indicate that the crack initiation life for all the three rail steel grades investigated decreases with the increase of the tangential traction coefficient, the friction coefficient, the ratio of lateral/vertical load and the axle load. Under the same in-service loading conditions, the ratcheting performance of the rails in curved tracks is worse than the one in tangent tracks. For instance, the crack initiation life of the low alloy heat-treated steel installed in the high rails is reduced by approximately 80% with the axle load of 35 t, the lateral/vertical load ratio of 0.3, the friction coefficient of 0.4 and the tangential traction coefficient of 0.5. The hypereutectoid steel rail with a lower carbon content always shows the best ratcheting performance and is likely to be the most reliable choice for the high rails in curved tracks. Moreover, the crack is predicted to initiate around 1 mm beneath from the top initial contact point. As the traction conditions become more severe, the location of crack initiation will shift from the subsurface to the running surface. The results can provide valuable information to assist rail operators in the selection of rail steel grades and the development of rail maintenance strategies. • The ratcheting performance of high strength rail steels installed in high rails is worse than that in tangent tracks. • Initiation of RCF may shift from the sub-surface to the surface of high rail gauge corner with severer loading conditions. • The hypereutectoid steel with a lower carbon content shows the best ratcheting performance. [ABSTRACT FROM AUTHOR]