Dynamic Wheel-Rail Force-Based Track-Irregularity Evaluation for Ballasted Track on Serviced Railway by Adjacent Excavation

This study investigates a load-based, track-irregularity-analysis technique for ballasted tracks on a serviced railway line with respect to excavation work conducted in adjacent sites. A numerical analysis and field measurements (railbed-settlement-monitoring sensor, track-geometry-measurement system, wheel-load measurements) were analyzed comparatively to demonstrate the correlation between the track irregularities and the Wheel-Rail interaction force. In this way, we highlight the necessity for load-based track-irregularity-management methods. The analyzed results show that the maximum dynamic wheel load was measured in the range of approximately 10 m before and after the location where the maximum track irregularities occurred, and that even if the maintenance criteria of track irregularities were satisfied, the design dynamic wheel load could still be exceeded depending on the train speed, thus indicating that track damage can be caused by the impact load.

Monitoring and Evaluation of the Lateral Stability of CWR Track

Continuous welded rail (CWR) track has great advantages of low-cost maintenance, environmental influence, and ride comfort. However, the CWR track is subjected to the longitudinal stresses in rails due to temperature influence as well the inhomogeneous stress accumulation due to train loadings. The stresses cause the accelerated track lateral irregularity accumulation that without timely maintenance can cause track buckling. The present paper present a method of the CWR track lateral stability estimation during its lifecycle using the track geometry monitoring information from the track measurement cars. The methods proposes a systematic approach of track stability evaluation based on multiple criteria of track stability evaluation. It takes into account the lateral resistance of the track, actual temperatures, and the lateral geometry condition of the track. The presented case study of a half-year track geometry monitoring and the track stability evaluation in a track curve shows the practical possibility of the recent detection of the track sections with low lateral stability and buckling prevention.

Modelling of Railway Sleeper Settlement under Cyclic Loading Using a Hysteretic Ballast Contact Model

Ballasted tracks are common in the railway system as a means of providing the necessary support for the sleepers and the rails. To keep them operational, tamping and other maintenance actions are performed based on track geometry measurements. Ballast particle rearrangement, which is caused by train load, is one of the most important factors leading to track degradation. As a result, when planning maintenance, it is vital to predict the behaviour of the ballast under cyclic loading. Since ballast is a granular matter with a nonlinear and discontinuous mechanical behaviour, the discrete element method (DEM) was used in this paper to model the ballast particle rearrangement under cyclic loading. We studied the performance of linear and nonlinear models in simulating the settlement of the sleeper, the lateral deformation of the ballast shoulder and the porosity changes under the sleeper. The models were evaluated based on their ability to mimic the ballast degradation pattern in vertical and lateral direction. The linear contact model and the hysteretic contact model were used in the simulations, and the effect of the friction coefficient and different damping models on the simulations was assessed. An outcome of this study was that a nonlinear model was proposed in which both the linear and the hysteretic contact models are combined. The simulation of the sleeper settlement and the changes in the porosity under the sleeper improved in the proposed nonlinear model, while the computation time required for the proposed model decreased compared to that required for the linear model.

An efficient physical-based method for predicting the long-term evolution of vertical railway track geometries

The dynamic wheel-rail contact forces resulting from the interaction between vehicle and track are responsible for the local track settlement. If these local settlements vary along the track, geometric irregularities develop further amplifying the dynamic loading of the track caused by the interaction between the vehicle and track. In this work, an efficient vehicle-track interaction (VTI) model is presented for predicting the long-term evolution of vertical track settlement during operation. The VTI model has two interacting components – vehicle and track. The vehicle model describes the vertical dynamics of an 8th of a car. The track model considers an elastic rail on discrete (sleeper) supports. Each sleeper location can have its own stiffness, relative height and settlement characteristics. Dependent on the distribution of stiffness and settlement behaviour along the track together with the initial track geometry, each sleeper settles dependent on the number of load cycles (vehicle passes). The track model is initialized with measured vertical track geometry data and static track deflection data at the beginning (day 0) for two types of track sections in the field, a track section where concrete sleepers with Under Sleeper Pads (USP) are used and a track section where only concrete sleepers are used. Using the same settlement model parameters (constant along the track) for the two tracks, the physical-based VTI model can predict the different track geometry quality evolution for both tracks over 350 days. Finally, the VTI model is used to assess the track geometry deterioration when the track/vehicle properties are changed. The prediction strength of the fast VTI model based on the physical understanding can assist in designing and optimizing tracks and in supporting of maintenance activities.

Parametric studies on laser additive manufacturing of copper on stainless steel

Laser additive manufacturing using directed energy deposition (LAM-DED) technique is one of the recent techniques for fabricating engineering components directly from 3D CAD model data using high power lasers. In this respect, LAM-DED of copper (Cu) and stainless steel (SS) is an enduring research area. However, LAM-DED of Cu is challenging due to higher thermal conductivity, lower absorption to infrared radiation and oxide formation tendency. The present work reports an experimental investigation to evaluate the effect of process parameters on the track geometry, contact angle, inter-diffusion and micro-hardness of Cu tracks deposited on SS 304L substrate using LAM-DED. Analysis of variance is used to estimate the contribution percentage of process parameters on the track geometry. Further, Cu bulk structures are deposited at an identified combination of process parameters and they are subjected to optical microscopy for microstructural characterisation. Further, finite-element-based numerical simulation is performed to understand the temperature distribution during the processing of Cu bulk structures on SS304L and the temperature results are co-related with the microstructural transformation during the processing. This investigation paves a way to understand the effect of processing parameters for building Cu bulk structures on SS Substrate using LAM-DED.