G. Jayasree Krishnan
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4 records found
1
Stick–slip is considered the root cause of railway engineering phenomena such as squeal noise and corrugation. Little consensus regarding the actual physical description of stick–slip has been achieved because its manifestations cannot be explained by a single underlying mechanism. To investigate the generation mechanisms of stick–slip contact, this study reproduced wheel-rail stick–slip experimentally with an in-house test rig—V-Track and numerically with an explicit finite element method (FEM). The V-Track is capable of reproducing realistic wheel-rail dynamic interactions under well-controlled lab conditions, while the explicit FEM has been proven to be suitable for the simulation of dynamic contact and frictional instability. Crucial influential factors including wheel-rail lateral creepage, friction levels, and friction characteristics were varied in the experiments and simulations to examine their impacts on the occurrence of stick–slip. The study shows that the creepage level needs to be sufficiently high to generate stick–slip. Stick–slip can be eliminated by reducing friction to a very low level, whereas changing the friction characteristics from negative to positive may not work for stick–slip mitigation. Moreover, wheel-rail friction conditions cannot be sufficiently represented by a single parameter, i.e. coefficient of friction.
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Stick–slip is considered the root cause of railway engineering phenomena such as squeal noise and corrugation. Little consensus regarding the actual physical description of stick–slip has been achieved because its manifestations cannot be explained by a single underlying mechanism. To investigate the generation mechanisms of stick–slip contact, this study reproduced wheel-rail stick–slip experimentally with an in-house test rig—V-Track and numerically with an explicit finite element method (FEM). The V-Track is capable of reproducing realistic wheel-rail dynamic interactions under well-controlled lab conditions, while the explicit FEM has been proven to be suitable for the simulation of dynamic contact and frictional instability. Crucial influential factors including wheel-rail lateral creepage, friction levels, and friction characteristics were varied in the experiments and simulations to examine their impacts on the occurrence of stick–slip. The study shows that the creepage level needs to be sufficiently high to generate stick–slip. Stick–slip can be eliminated by reducing friction to a very low level, whereas changing the friction characteristics from negative to positive may not work for stick–slip mitigation. Moreover, wheel-rail friction conditions cannot be sufficiently represented by a single parameter, i.e. coefficient of friction.
Friction behaviour at the wheel–rail interface is of critical importance for railway operations and maintenance and is generally characterised by creep curves. The V-Track test rig was used in this study to measure both the lateral and longitudinal creep curves with uncontaminated dry interface conditions, utilising contact pressures representative of operational railway wheel–rail systems. The novelties of this study are threefold. 1. With proper representations of train/track components, the V-Track tests revealed the effects of structural dynamics on measuring wheel–rail creep curves in real life. 2. Pure lateral and longitudinal creepage conditions were produced with two distinct experimental principles—displacement- and force-controlled—on the V-Track, i.e., by carefully controlling the angle of attack and the traction/braking torque, respectively, and thus the coefficient of friction from lateral and longitudinal creep curves measured on the same platform could be cross-checked. 3. The uncertainties in the measured creep curves were analysed, which was rarely addressed in previous studies on creep curve measurements. In addition, the measured creep curves were compared against the theoretical creep curves obtained from Kalker’s CONTACT. The influence of wheel rolling speed and torque direction on the creep curve characteristics was then investigated. The measurement results and findings demonstrate the reliability of the V-Track to measure wheel–rail creep curves and study the wheel–rail frictional rolling contact.
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Friction behaviour at the wheel–rail interface is of critical importance for railway operations and maintenance and is generally characterised by creep curves. The V-Track test rig was used in this study to measure both the lateral and longitudinal creep curves with uncontaminated dry interface conditions, utilising contact pressures representative of operational railway wheel–rail systems. The novelties of this study are threefold. 1. With proper representations of train/track components, the V-Track tests revealed the effects of structural dynamics on measuring wheel–rail creep curves in real life. 2. Pure lateral and longitudinal creepage conditions were produced with two distinct experimental principles—displacement- and force-controlled—on the V-Track, i.e., by carefully controlling the angle of attack and the traction/braking torque, respectively, and thus the coefficient of friction from lateral and longitudinal creep curves measured on the same platform could be cross-checked. 3. The uncertainties in the measured creep curves were analysed, which was rarely addressed in previous studies on creep curve measurements. In addition, the measured creep curves were compared against the theoretical creep curves obtained from Kalker’s CONTACT. The influence of wheel rolling speed and torque direction on the creep curve characteristics was then investigated. The measurement results and findings demonstrate the reliability of the V-Track to measure wheel–rail creep curves and study the wheel–rail frictional rolling contact.
Creep curves characterise the behaviour of frictional forces at the wheel-rail interface. This study used the V-Track test rig to measure lateral and longitudinal creep curves under clean and dry contact conditions with practical wheel-rail contact pressures. The measured lateral and longitudinal creep curves were cross-compared to estimate the coefficient of friction of the V-Track. The measurement results and findings demonstrate the reliability of using the V-Track test rig to study the wheel-rail frictional rolling contact and to accurately measure the coefficient of friction at the wheel-rail interface, highlighting its significance in railway engineering and operational safety studies.
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Creep curves characterise the behaviour of frictional forces at the wheel-rail interface. This study used the V-Track test rig to measure lateral and longitudinal creep curves under clean and dry contact conditions with practical wheel-rail contact pressures. The measured lateral and longitudinal creep curves were cross-compared to estimate the coefficient of friction of the V-Track. The measurement results and findings demonstrate the reliability of using the V-Track test rig to study the wheel-rail frictional rolling contact and to accurately measure the coefficient of friction at the wheel-rail interface, highlighting its significance in railway engineering and operational safety studies.
The Coefficient of Friction (CoF) is an important parameter affecting acceleration and braking behavior of trains, and consequently the inter-train distance and utilization of track. To optimize operation schedules, maximize railway capacity, and realize automatic train operations, reliable measurements of the CoFs experienced by in-service trains are desirable. In this study, a train-borne measurement approach is proposed based on a torque modulation concept. It involves superimposing a small-amplitude sinusoidal signal on the motor torque. Because the wheel-rail friction force acts as variable damping, it causes a phase difference between the angular velocity response of the wheelset and the input modulated torque signal. This phase difference can be used to determine the creep coefficient, i.e., the slope of the creep curve, and then to estimate the CoF in combination with the measured Coefficient of Adhesion (CoA), i.e., the ratio between the wheel-rail friction force and normal load. Simulations of torque modulation with VI-Rail are conducted. Variation of phase difference with the increase of the modulated torque is derived theoretically and compared with numerically obtained results using the VI-Rail multibody dynamics model under different CoF conditions. The good agreement between the results indicates the effectiveness of the proposed measurement concept.
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The Coefficient of Friction (CoF) is an important parameter affecting acceleration and braking behavior of trains, and consequently the inter-train distance and utilization of track. To optimize operation schedules, maximize railway capacity, and realize automatic train operations, reliable measurements of the CoFs experienced by in-service trains are desirable. In this study, a train-borne measurement approach is proposed based on a torque modulation concept. It involves superimposing a small-amplitude sinusoidal signal on the motor torque. Because the wheel-rail friction force acts as variable damping, it causes a phase difference between the angular velocity response of the wheelset and the input modulated torque signal. This phase difference can be used to determine the creep coefficient, i.e., the slope of the creep curve, and then to estimate the CoF in combination with the measured Coefficient of Adhesion (CoA), i.e., the ratio between the wheel-rail friction force and normal load. Simulations of torque modulation with VI-Rail are conducted. Variation of phase difference with the increase of the modulated torque is derived theoretically and compared with numerically obtained results using the VI-Rail multibody dynamics model under different CoF conditions. The good agreement between the results indicates the effectiveness of the proposed measurement concept.