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Y. Ma
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1
During the last decades, asphalt concrete has been introduced in both ballast and ballastless track (including but not limited to slab track) systems. The use of asphalt concrete provides better damping and waterproofing performance. For this reason, a supporting layer of asphalt concrete (ASL) was introduced to the latest Chinese slab track system. In this paper, an in-depth study of the dynamic behavior of ASL was presented using modelling and in-situ measurement approaches. In the FE model, the train load was simplified to be a time series of concentrated load on rail nodes, and asphalt concrete was modeled as viscoelastic material by Prony series. The FE model was validated against in-situ measurement on a test section, in which a monitoring system was setup during construction. A series of transient analysis were conducted to obtain the dynamic responses of ASL under moving train load. The parametric effects of thickness of ASL was also studied with respect to the dynamic responses of superstructure and substructure, as well as the stability and durability of ASL. The results showed that, under moving bogie load, the reach of the dynamic responses in ASL is about 7.5 m in the longitudinal direction, and the maximum values occur at the position beneath the rails. A thicker ASL is more favorable to ride comfort and structural stability of high-speed railway track system. However, considering the economic and construction factors, an optimal thickness range of 7–10 cm is suggested for ASL in CRTS III slab track.
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During the last decades, asphalt concrete has been introduced in both ballast and ballastless track (including but not limited to slab track) systems. The use of asphalt concrete provides better damping and waterproofing performance. For this reason, a supporting layer of asphalt concrete (ASL) was introduced to the latest Chinese slab track system. In this paper, an in-depth study of the dynamic behavior of ASL was presented using modelling and in-situ measurement approaches. In the FE model, the train load was simplified to be a time series of concentrated load on rail nodes, and asphalt concrete was modeled as viscoelastic material by Prony series. The FE model was validated against in-situ measurement on a test section, in which a monitoring system was setup during construction. A series of transient analysis were conducted to obtain the dynamic responses of ASL under moving train load. The parametric effects of thickness of ASL was also studied with respect to the dynamic responses of superstructure and substructure, as well as the stability and durability of ASL. The results showed that, under moving bogie load, the reach of the dynamic responses in ASL is about 7.5 m in the longitudinal direction, and the maximum values occur at the position beneath the rails. A thicker ASL is more favorable to ride comfort and structural stability of high-speed railway track system. However, considering the economic and construction factors, an optimal thickness range of 7–10 cm is suggested for ASL in CRTS III slab track.
Wheel-Rail Interaction
Enhanced explicit finite element modelling, verification and validation
Nowadays, wheel-rail (W/R) interfaces are suffering from the practical problems (e.g. wear, rolling contact defects) with the increase of train speed and traffic density. For accurate prediction of wear and/or growth of rolling contact defects, rapid determination of detailed contact responses (i.e. contact stresses & strains) using numerical methods, is necessary. As one of the numerical methods, the explicit finite element (FE) method has been increasingly used due to its striking versatility (i.e., the consideration of dynamic effects, material and geometrical non-linearities). But there are still several FE modelling challenges to be addressed. First, the calculation accuracy & efficiency of the FE method can not be automatically guaranteed. Second, the default values of the interface parameters provided in the commercial FE packages are not always suitable for the modelling of W/R rolling contact. Third, the detailed verification & validation methods/procedures for the FE model of W/R interaction are still in demand. It is thus motivated to perform an in-depth study on the performance (i.e. accuracy and efficiency) of the explicit FE method applied to the analysis of the dynamic W/R frictional rolling contact behaviour. Through this study, it is aimed to enrich the detailed knowledge of W/R interaction, and help the researchers in the field of railway engineering to judge the benefits and drawbacks of explicit FE simulations. The dissertation is divided into four parts, in which four research problems are addressed...
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Nowadays, wheel-rail (W/R) interfaces are suffering from the practical problems (e.g. wear, rolling contact defects) with the increase of train speed and traffic density. For accurate prediction of wear and/or growth of rolling contact defects, rapid determination of detailed contact responses (i.e. contact stresses & strains) using numerical methods, is necessary. As one of the numerical methods, the explicit finite element (FE) method has been increasingly used due to its striking versatility (i.e., the consideration of dynamic effects, material and geometrical non-linearities). But there are still several FE modelling challenges to be addressed. First, the calculation accuracy & efficiency of the FE method can not be automatically guaranteed. Second, the default values of the interface parameters provided in the commercial FE packages are not always suitable for the modelling of W/R rolling contact. Third, the detailed verification & validation methods/procedures for the FE model of W/R interaction are still in demand. It is thus motivated to perform an in-depth study on the performance (i.e. accuracy and efficiency) of the explicit FE method applied to the analysis of the dynamic W/R frictional rolling contact behaviour. Through this study, it is aimed to enrich the detailed knowledge of W/R interaction, and help the researchers in the field of railway engineering to judge the benefits and drawbacks of explicit FE simulations. The dissertation is divided into four parts, in which four research problems are addressed...
To improve the understanding of dynamic impact in 1:9 crossing panel, which is suffering from rapid surface degradation, detailed modelling and experimental studies are performed. A three-dimensional explicit finite element (FE) model of a wheel rolling over a crossing rail, that has an adaptive mesh refinement procedure coupled with two-dimensional geometrical contact analyses, is developed. It is demonstrated that this modelling strategy performs much better than the ‘conventional’ FE modelling approach. Also, the experimental validations show that the FE results agree reasonably well with the field measurements. Using the validated FE model, the tribological behaviour of contact surfaces is studied. The results indicate that the proposed modelling strategy is a promising tool for addressing the problems of wheel-crossing dynamic impact.
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To improve the understanding of dynamic impact in 1:9 crossing panel, which is suffering from rapid surface degradation, detailed modelling and experimental studies are performed. A three-dimensional explicit finite element (FE) model of a wheel rolling over a crossing rail, that has an adaptive mesh refinement procedure coupled with two-dimensional geometrical contact analyses, is developed. It is demonstrated that this modelling strategy performs much better than the ‘conventional’ FE modelling approach. Also, the experimental validations show that the FE results agree reasonably well with the field measurements. Using the validated FE model, the tribological behaviour of contact surfaces is studied. The results indicate that the proposed modelling strategy is a promising tool for addressing the problems of wheel-crossing dynamic impact.
It is widely recognized that the accuracy of explicit finite element simulations is sensitive to the choice of interface parameters (i.e. contact stiffness/damping, mesh generation, etc.) and time step sizes. Yet, the effect of these interface parameters on the explicit finite element based solutions of wheel–rail interaction has not been discussed sufficiently in literature. In this paper, the relation between interface parameters and the accuracy of contact solutions is studied. It shows that the wrong choice of these parameters, such as too high/low contact stiffness, coarse mesh, or wrong combination of them, can negatively affect the solution of wheel–rail interactions which manifest in the amplification of contact forces and/or inaccurate contact responses (here called “contact instability”). The phenomena of “contact (in)stabilities” are studied using an explicit finite element model of a wheel rolling over a rail. The accuracy of contact solutions is assessed by analyzing the area of contact patches and the distribution of normal pressure. Also, the guidelines for selections of optimum interface parameters, which guarantee the contact stability and therefore provide an accurate solution, are proposed. The effectiveness of the selected interface parameters is demonstrated through a series of simulations. The results of these simulations are presented and discussed.
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It is widely recognized that the accuracy of explicit finite element simulations is sensitive to the choice of interface parameters (i.e. contact stiffness/damping, mesh generation, etc.) and time step sizes. Yet, the effect of these interface parameters on the explicit finite element based solutions of wheel–rail interaction has not been discussed sufficiently in literature. In this paper, the relation between interface parameters and the accuracy of contact solutions is studied. It shows that the wrong choice of these parameters, such as too high/low contact stiffness, coarse mesh, or wrong combination of them, can negatively affect the solution of wheel–rail interactions which manifest in the amplification of contact forces and/or inaccurate contact responses (here called “contact instability”). The phenomena of “contact (in)stabilities” are studied using an explicit finite element model of a wheel rolling over a rail. The accuracy of contact solutions is assessed by analyzing the area of contact patches and the distribution of normal pressure. Also, the guidelines for selections of optimum interface parameters, which guarantee the contact stability and therefore provide an accurate solution, are proposed. The effectiveness of the selected interface parameters is demonstrated through a series of simulations. The results of these simulations are presented and discussed.
Over the past few years, a number of implicit/explicit finite element models have been introduced for the purpose of tackling the problems of wheel–rail interaction. Yet, most of those finite element models encounter common numerical difficulties. For instance, initial gaps/penetrations between two contact bodies, which easily occur when realistic wheel–rail profiles are accounted for, would trigger the problems of divergence in implicit finite element simulations. Also, redundant, insufficient or mismatched mesh refinements in the vicinity of areas in contact can lead to either prohibitive calculation expenses or inaccurate implicit/explicit finite element solutions. To address the abovementioned problems and to improve the performance of finite element simulations, a novel modelling strategy has been proposed. In this strategy, the three-dimensional explicit finite element analysis is seamlessly coupled with the two-dimensional geometrical contact analysis. The contact properties in the three-dimensional finite element analyses, such as the initial “Just-in-contact” point, the exact wheel local rolling radius, etc., which are usually a priori unknown, are determined using the two-dimensional geometrical contact model. As part of the coupling strategy, a technique has been developed for adaptive mesh refinement. The mesh and mesh density of wheel–rail finite element models change adaptively depending on the exact location of the contact areas and the local geometry of contact bodies. By this means, a good balance between the calculation efficiency and accuracy can be achieved. Last, but not least, the advantage of the coupling strategy has been demonstrated in studies on the relationship between the initial slips and the steady frictional rolling state. Finally, the results of the simulations are presented and discussed.
...
Over the past few years, a number of implicit/explicit finite element models have been introduced for the purpose of tackling the problems of wheel–rail interaction. Yet, most of those finite element models encounter common numerical difficulties. For instance, initial gaps/penetrations between two contact bodies, which easily occur when realistic wheel–rail profiles are accounted for, would trigger the problems of divergence in implicit finite element simulations. Also, redundant, insufficient or mismatched mesh refinements in the vicinity of areas in contact can lead to either prohibitive calculation expenses or inaccurate implicit/explicit finite element solutions. To address the abovementioned problems and to improve the performance of finite element simulations, a novel modelling strategy has been proposed. In this strategy, the three-dimensional explicit finite element analysis is seamlessly coupled with the two-dimensional geometrical contact analysis. The contact properties in the three-dimensional finite element analyses, such as the initial “Just-in-contact” point, the exact wheel local rolling radius, etc., which are usually a priori unknown, are determined using the two-dimensional geometrical contact model. As part of the coupling strategy, a technique has been developed for adaptive mesh refinement. The mesh and mesh density of wheel–rail finite element models change adaptively depending on the exact location of the contact areas and the local geometry of contact bodies. By this means, a good balance between the calculation efficiency and accuracy can be achieved. Last, but not least, the advantage of the coupling strategy has been demonstrated in studies on the relationship between the initial slips and the steady frictional rolling state. Finally, the results of the simulations are presented and discussed.
The paper presents an integrated approach for analysis and improvement of performance of railway crossings. The approach consists of a detailed finite element (FE) model of a wheel rolling over a crossing (validated against the measured crossing accelerations) and experimental tools installed on the crossings in situ. The studied crossings are the cast manganese steel 1:9 crossings. This type of crossings suffers from severe plastic deformations and cracks. The presented approach has been applied to improve the performance of these crossings and to assess the effectiveness of the maintenance actions.
The obtained numerical and experimental results have helped to explain the poor performance of the crossings. Moreover, a number of the design improvements have not only been proposed, but also effectiveness of these improvements have been confirmed by the numerical simulations and/or measurement results.
The results are presented and discussed. More details are in the extended version of this paper.
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The paper presents an integrated approach for analysis and improvement of performance of railway crossings. The approach consists of a detailed finite element (FE) model of a wheel rolling over a crossing (validated against the measured crossing accelerations) and experimental tools installed on the crossings in situ. The studied crossings are the cast manganese steel 1:9 crossings. This type of crossings suffers from severe plastic deformations and cracks. The presented approach has been applied to improve the performance of these crossings and to assess the effectiveness of the maintenance actions.
The obtained numerical and experimental results have helped to explain the poor performance of the crossings. Moreover, a number of the design improvements have not only been proposed, but also effectiveness of these improvements have been confirmed by the numerical simulations and/or measurement results.
The results are presented and discussed. More details are in the extended version of this paper.
Verification of the explicit finite element (FE) model with realistic wheel-rail profiles against the CONTACT model, which has not been sufficiently discussed, is performed by comparing the resulting shear stress, slip-adhesion area, etc., obtained from the two models. The follow-up studies using the verified FE model on the influence of the varying operational patterns (such as different friction, traction, etc.) on the surface and subsurface tribological responses of wheel-rail interaction are accomplished through a series of simulations. It can be concluded that the results obtained from most of the explicit FE simulations agree reasonably well with the ones from CONTACT. Also, the increase of the friction and traction can bring the stress concentrations from the subsurface upwards to the surface.
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Verification of the explicit finite element (FE) model with realistic wheel-rail profiles against the CONTACT model, which has not been sufficiently discussed, is performed by comparing the resulting shear stress, slip-adhesion area, etc., obtained from the two models. The follow-up studies using the verified FE model on the influence of the varying operational patterns (such as different friction, traction, etc.) on the surface and subsurface tribological responses of wheel-rail interaction are accomplished through a series of simulations. It can be concluded that the results obtained from most of the explicit FE simulations agree reasonably well with the ones from CONTACT. Also, the increase of the friction and traction can bring the stress concentrations from the subsurface upwards to the surface.