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Luboš Náhlík - One of the best experts on this subject based on the ideXlab platform.
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fatigue lifetime estimation of railway Axles
Engineering Failure Analysis, 2017Co-Authors: Rostislav Fajkos, Petr Matušek, Martin Sevcik, Luboš Náhlík, Pavel Pokorný, Pavel HutarAbstract:Abstract The railway Axles are subjected to cyclic loading during their operation. Their load is of long-term nature, therefore a real risk of fatigue failure exists. This failure could lead to derailment of the whole train with serious consequences. To prevent such scenario, the railway Axles have to be safely removed from operation before their final failure occurs. This paper presents methodology for the residual fatigue lifetime prediction of the railway axle based on the linear elastic fracture mechanics concept. The methodology contains estimation of the critical position of initial crack, prediction of the fatigue crack front shape development during crack propagation, separation of the bending and press-fitting contributions to the axle load, experimental measurement of the crack growth kinetics of EA4T steel and subsequent estimation of the residual fatigue lifetime of railway axle. Part of the presented study is also devoted to the probability aspects of determination of material characteristics describing fatigue crack propagation and retardation effects caused by existence of plastic zone ahead of propagating fatigue crack. Described methodology is already applied in the design process of new railway Axles in Bonatrans company.
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fatigue lifetime estimation of railway Axles
Engineering Failure Analysis, 2017Co-Authors: Rostislav Fajkos, Petr Matušek, Martin Sevcik, Luboš Náhlík, Pavel Pokorný, Pavel HutařAbstract:Abstract The railway Axles are subjected to cyclic loading during their operation. Their load is of long-term nature, therefore a real risk of fatigue failure exists. This failure could lead to derailment of the whole train with serious consequences. To prevent such scenario, the railway Axles have to be safely removed from operation before their final failure occurs. This paper presents methodology for the residual fatigue lifetime prediction of the railway axle based on the linear elastic fracture mechanics concept. The methodology contains estimation of the critical position of initial crack, prediction of the fatigue crack front shape development during crack propagation, separation of the bending and press-fitting contributions to the axle load, experimental measurement of the crack growth kinetics of EA4T steel and subsequent estimation of the residual fatigue lifetime of railway axle. Part of the presented study is also devoted to the probability aspects of determination of material characteristics describing fatigue crack propagation and retardation effects caused by existence of plastic zone ahead of propagating fatigue crack. Described methodology is already applied in the design process of new railway Axles in Bonatrans company.
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effect of residual stresses on the fatigue lifetime of railway axle
Procedia structural integrity, 2017Co-Authors: Pavel Hutar, Rostislav Fajkos, Jan Poduška, Pavel Pokorný, Luboš NáhlíkAbstract:Abstract The operation of railway Axles should fulfill at least two main demands: safety and low operation costs. A significant part of operation costs is given by the length of regular inspection intervals which should reveal potential fatigue cracks in railway axle. The detection of cracks is of a probabilistic nature, therefore their detection is not ensured in all cases. For the safe operation of trains, an existence of potential initial crack should be considered on the axle surface and residual fatigue lifetime should be conservatively determined for this case. Reliable procedure of residual fatigue lifetime estimation should take into account real axle geometry, material characteristics and loading of the railway axle. This paper shows methodology for determination of residual fatigue lifetime (RFL) based on the fracture mechanics approach, taking into account real spectrum of the loading cycles, existence of press-fitted wheels and surface residual stresses given by the thermo-mechanical surface treatment of the railway axle. It is demonstrated that the effect of the residual stresses is significant and should not be neglected in the numerical estimation of residual fatigue lifetime of the axle.
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Crack closure in near-threshold fatigue crack propagation in railway axle steel EA4T
Engineering Fracture Mechanics, 2017Co-Authors: Pavel Pokorný, Luboš Náhlík, Tomáš Vojtek, Pavel HutařAbstract:Abstract The paper is focused on fatigue crack propagation in the threshold area of the EA4T railway axle steel. Railway Axles represent one of the most critical components for safety of trains. The main aim of this paper is to describe fatigue crack closure mechanisms in EA4T, which significantly influence the threshold value – a crucial parameter for determination of residual fatigue lifetime of railway Axles. Investigated fatigue crack closure mechanisms are: plasticity induced crack closure, roughness-induced crack closure and oxide-induced crack closure. One part of this paper is focused on comparison of crack closure determined by NASGRO relationship (including plasticity induced crack closure mechanism only) with the experimentally obtained one. Difference between these two approaches is explained by presence of roughness and oxide induced crack closure. Based on theoretical models different sources of fatigue crack closure mechanisms was separated and evaluated. The significance of oxide-induced crack closure was confirmed based on experimental measurement of fatigue crack propagation in low humidity air. Finally, the effect of a reduced threshold value in low-humidity air on residual fatigue lifetime of railway Axles is demonstrated.
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influence of extension of load spectrum on estimation of residual fatigue lifetime of railway axle
Solid State Phenomena, 2016Co-Authors: Pavel Pokorný, Pavel Hutař, Luboš NáhlíkAbstract:Railway Axles are subjected to cyclic amplitude loading which can lead to fatigue failure. For safe operation of railway Axles a damage tolerance approach taking into account a possible defect in railway axle is often required. Because of different operation regimes of trains (fast/slow ride, ride on straight track, on curved track, over switches etc.) the load amplitude of axle is not constant. The variability of load is defined by a load spectrum, which is determined experimentally by measuring of load in service conditions. Even though the load spectrum is measured on several hundreds or thousands of operation kilometres, the railway Axles are in operation much longer time (often tens of years). Therefore, some load amplitudes higher than ones measured in the test can occur during a long-term axle service. The contribution presented deals with the effect of extension of load spectrum by rare high load amplitudes, which can occur during long-term operation, on residual fatigue lifetime of railway Axles.
Pavel Pokorný - One of the best experts on this subject based on the ideXlab platform.
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fatigue lifetime estimation of railway Axles
Engineering Failure Analysis, 2017Co-Authors: Rostislav Fajkos, Petr Matušek, Martin Sevcik, Luboš Náhlík, Pavel Pokorný, Pavel HutarAbstract:Abstract The railway Axles are subjected to cyclic loading during their operation. Their load is of long-term nature, therefore a real risk of fatigue failure exists. This failure could lead to derailment of the whole train with serious consequences. To prevent such scenario, the railway Axles have to be safely removed from operation before their final failure occurs. This paper presents methodology for the residual fatigue lifetime prediction of the railway axle based on the linear elastic fracture mechanics concept. The methodology contains estimation of the critical position of initial crack, prediction of the fatigue crack front shape development during crack propagation, separation of the bending and press-fitting contributions to the axle load, experimental measurement of the crack growth kinetics of EA4T steel and subsequent estimation of the residual fatigue lifetime of railway axle. Part of the presented study is also devoted to the probability aspects of determination of material characteristics describing fatigue crack propagation and retardation effects caused by existence of plastic zone ahead of propagating fatigue crack. Described methodology is already applied in the design process of new railway Axles in Bonatrans company.
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fatigue lifetime estimation of railway Axles
Engineering Failure Analysis, 2017Co-Authors: Rostislav Fajkos, Petr Matušek, Martin Sevcik, Luboš Náhlík, Pavel Pokorný, Pavel HutařAbstract:Abstract The railway Axles are subjected to cyclic loading during their operation. Their load is of long-term nature, therefore a real risk of fatigue failure exists. This failure could lead to derailment of the whole train with serious consequences. To prevent such scenario, the railway Axles have to be safely removed from operation before their final failure occurs. This paper presents methodology for the residual fatigue lifetime prediction of the railway axle based on the linear elastic fracture mechanics concept. The methodology contains estimation of the critical position of initial crack, prediction of the fatigue crack front shape development during crack propagation, separation of the bending and press-fitting contributions to the axle load, experimental measurement of the crack growth kinetics of EA4T steel and subsequent estimation of the residual fatigue lifetime of railway axle. Part of the presented study is also devoted to the probability aspects of determination of material characteristics describing fatigue crack propagation and retardation effects caused by existence of plastic zone ahead of propagating fatigue crack. Described methodology is already applied in the design process of new railway Axles in Bonatrans company.
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effect of residual stresses on the fatigue lifetime of railway axle
Procedia structural integrity, 2017Co-Authors: Pavel Hutar, Rostislav Fajkos, Jan Poduška, Pavel Pokorný, Luboš NáhlíkAbstract:Abstract The operation of railway Axles should fulfill at least two main demands: safety and low operation costs. A significant part of operation costs is given by the length of regular inspection intervals which should reveal potential fatigue cracks in railway axle. The detection of cracks is of a probabilistic nature, therefore their detection is not ensured in all cases. For the safe operation of trains, an existence of potential initial crack should be considered on the axle surface and residual fatigue lifetime should be conservatively determined for this case. Reliable procedure of residual fatigue lifetime estimation should take into account real axle geometry, material characteristics and loading of the railway axle. This paper shows methodology for determination of residual fatigue lifetime (RFL) based on the fracture mechanics approach, taking into account real spectrum of the loading cycles, existence of press-fitted wheels and surface residual stresses given by the thermo-mechanical surface treatment of the railway axle. It is demonstrated that the effect of the residual stresses is significant and should not be neglected in the numerical estimation of residual fatigue lifetime of the axle.
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Crack closure in near-threshold fatigue crack propagation in railway axle steel EA4T
Engineering Fracture Mechanics, 2017Co-Authors: Pavel Pokorný, Luboš Náhlík, Tomáš Vojtek, Pavel HutařAbstract:Abstract The paper is focused on fatigue crack propagation in the threshold area of the EA4T railway axle steel. Railway Axles represent one of the most critical components for safety of trains. The main aim of this paper is to describe fatigue crack closure mechanisms in EA4T, which significantly influence the threshold value – a crucial parameter for determination of residual fatigue lifetime of railway Axles. Investigated fatigue crack closure mechanisms are: plasticity induced crack closure, roughness-induced crack closure and oxide-induced crack closure. One part of this paper is focused on comparison of crack closure determined by NASGRO relationship (including plasticity induced crack closure mechanism only) with the experimentally obtained one. Difference between these two approaches is explained by presence of roughness and oxide induced crack closure. Based on theoretical models different sources of fatigue crack closure mechanisms was separated and evaluated. The significance of oxide-induced crack closure was confirmed based on experimental measurement of fatigue crack propagation in low humidity air. Finally, the effect of a reduced threshold value in low-humidity air on residual fatigue lifetime of railway Axles is demonstrated.
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influence of extension of load spectrum on estimation of residual fatigue lifetime of railway axle
Solid State Phenomena, 2016Co-Authors: Pavel Pokorný, Pavel Hutař, Luboš NáhlíkAbstract:Railway Axles are subjected to cyclic amplitude loading which can lead to fatigue failure. For safe operation of railway Axles a damage tolerance approach taking into account a possible defect in railway axle is often required. Because of different operation regimes of trains (fast/slow ride, ride on straight track, on curved track, over switches etc.) the load amplitude of axle is not constant. The variability of load is defined by a load spectrum, which is determined experimentally by measuring of load in service conditions. Even though the load spectrum is measured on several hundreds or thousands of operation kilometres, the railway Axles are in operation much longer time (often tens of years). Therefore, some load amplitudes higher than ones measured in the test can occur during a long-term axle service. The contribution presented deals with the effect of extension of load spectrum by rare high load amplitudes, which can occur during long-term operation, on residual fatigue lifetime of railway Axles.
Pavel Hutar - One of the best experts on this subject based on the ideXlab platform.
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fatigue lifetime estimation of railway Axles
Engineering Failure Analysis, 2017Co-Authors: Rostislav Fajkos, Petr Matušek, Martin Sevcik, Luboš Náhlík, Pavel Pokorný, Pavel HutarAbstract:Abstract The railway Axles are subjected to cyclic loading during their operation. Their load is of long-term nature, therefore a real risk of fatigue failure exists. This failure could lead to derailment of the whole train with serious consequences. To prevent such scenario, the railway Axles have to be safely removed from operation before their final failure occurs. This paper presents methodology for the residual fatigue lifetime prediction of the railway axle based on the linear elastic fracture mechanics concept. The methodology contains estimation of the critical position of initial crack, prediction of the fatigue crack front shape development during crack propagation, separation of the bending and press-fitting contributions to the axle load, experimental measurement of the crack growth kinetics of EA4T steel and subsequent estimation of the residual fatigue lifetime of railway axle. Part of the presented study is also devoted to the probability aspects of determination of material characteristics describing fatigue crack propagation and retardation effects caused by existence of plastic zone ahead of propagating fatigue crack. Described methodology is already applied in the design process of new railway Axles in Bonatrans company.
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effect of residual stresses on the fatigue lifetime of railway axle
Procedia structural integrity, 2017Co-Authors: Pavel Hutar, Rostislav Fajkos, Jan Poduška, Pavel Pokorný, Luboš NáhlíkAbstract:Abstract The operation of railway Axles should fulfill at least two main demands: safety and low operation costs. A significant part of operation costs is given by the length of regular inspection intervals which should reveal potential fatigue cracks in railway axle. The detection of cracks is of a probabilistic nature, therefore their detection is not ensured in all cases. For the safe operation of trains, an existence of potential initial crack should be considered on the axle surface and residual fatigue lifetime should be conservatively determined for this case. Reliable procedure of residual fatigue lifetime estimation should take into account real axle geometry, material characteristics and loading of the railway axle. This paper shows methodology for determination of residual fatigue lifetime (RFL) based on the fracture mechanics approach, taking into account real spectrum of the loading cycles, existence of press-fitted wheels and surface residual stresses given by the thermo-mechanical surface treatment of the railway axle. It is demonstrated that the effect of the residual stresses is significant and should not be neglected in the numerical estimation of residual fatigue lifetime of the axle.
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residual fatigue lifetime estimation of railway Axles for various loading spectra
Theoretical and Applied Fracture Mechanics, 2016Co-Authors: Pavel Hutar, Pavel Pokorný, Luboš NáhlíkAbstract:Abstract The knowledge of the residual fatigue lifetime of railway Axles is very important for the safe operation of trains. The railway Axles could include some defects like cracks, scratches or inhomogeneities which could contribute to the fatigue crack initiation and in the final stage to axle failure. The non-destructive testing methods are not reliable for detection of relatively short (circa 1–2 mm), but even dangerous cracks. For conservative estimation of residual fatigue lifetime the railway axle containing initial crack should be considered. The residual fatigue lifetime is given by the number of load cycles for fatigue crack growth from the initial size of the crack up to the critical size with consequent fatigue failure of railway axle. Railway Axles are used in different types of trains which are used under different conditions (regional trains, urban trains, high speed trains, freight trains, etc.). This work is focused on numerical estimation of residual fatigue lifetime of railway axle while several different load spectra taken from the literature are considered in the performed estimations. This paper also shows the influence of the discretization level of the continuous load spectrum and effect of magnification or diminution of load spectrum on the calculated residual fatigue lifetime of the railway axle.
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Influence of Threshold Values on Residual Fatigue Lifetime of Railway Axles under Variable Amplitude Loading
Procedia Engineering, 2015Co-Authors: Pavel Pokorný, Luboš Náhlík, Pavel HutarAbstract:Abstract The paper deals with an estimation of residual fatigue lifetime of railway Axles under real loading spectrum. The residual fatigue lifetime is given by magnitude of fatigue crack propagation rate. This rate depends predominantly on load, geometry and material of the axle. Standard steel EA4T for manufacturing of railway Axles is considered in this paper. The scatter of data in v-K curve could be caused by inaccuracy of experimental measurement or by local change of material properties. The paper shows important differences between obtained residual fatigue lifetime estimations considering scatter in measured material data, especially near the threshold region.
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comparison of different load spectra on residual fatigue lifetime of railway axle
Procedia Engineering, 2014Co-Authors: Pavel Pokorný, Luboš Náhlík, Pavel HutarAbstract:Abstract The railway Axles are subjected to variable amplitude loading. The variability is caused by many different regimes of train operation. The dominant load is caused by the weight of the vehicle, which generates rotary bending during train movement. Nevertheless, there are additional forces, which are generated when train goes through curved track, over crossovers, switches, rail joints etc. Present non-destructive defectoscopy can reliably detect only relatively long cracks (approximately 2 mm long or longer). Hence there is a risk that the existing crack is not detected. Therefore, for conservative estimation of the residual fatigue lifetime the railway axle with a crack should be considered. The behaviour of the crack depends on load spectrum of railway axle. Hence for accurate determination of residual fatigue lifetime of the railway axle is necessary to know representative load spectrum. This paper compares several measured load spectra of railway Axles, which are available in the literature. The effect of different load spectra is shown on two widely used materials for railway Axles: EA1N and EA4T steels. Obtained results could be used for safer operation of railway Axles.
Guozheng Kang - One of the best experts on this subject based on the ideXlab platform.
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probabilistic fatigue assessment for high speed railway Axles due to foreign object damages
International Journal of Fatigue, 2018Co-Authors: Guozheng KangAbstract:Abstract Various surface defects of high-speed railway lightweight hollow Axles made of alloy steel were identified carefully for assessing its operation safety and reliability. Three types of foreign object damages (FOD) from compressed-gas gun device were defined as the corner, edge and plane defects in terms of defect geometry, respectively. The fatigue probabilistic S-N (P-S-N) curves and fatigue limits were acquired for smoothed and FOD-affected specimens. In view of the variations of size and roughness between the full-scale Axles and specimens, the fatigue properties with three defect types were then modified for full-scale Axles. The probabilistic Kitagawa–Takahashi diagram widely used for assessing the FOD in aero-engine was well transferred to the damaged railway Axles. The fatigue limits of an FOD-affected axle with 95% confidence level and 95% reliability level were evaluated to replace that of smoothed specimens, which was suggested to assess the reliability of a damaged axle at the presence of FOD generated at a prospective higher operation speed.
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on the fatigue performance and residual life of intercity railway Axles with inside axle boxes
Engineering Fracture Mechanics, 2018Co-Authors: Y X Liu, Guozheng Kang, S L LiangAbstract:Abstract Railway Axles with inside axle boxes have a great potential in modern urban railway system due to good dynamic performance on small-radius track. However, because of entirely different loading nature from widely-used one, a challenging problem of the fatigue performance and damage endurance arises in the case of defects from various external sources. In this paper, a stepwise fatigue assessment framework composed of safe life as the first level and damage tolerance as the second level was tentatively proposed for the wheelset with inside axle boxes. An assumed load spectrum was employed to estimate the remaining life for a damaged axle made of the EA4T steel. Calculated results show that the critical safety region has been transferred to the axle center in contrast to classical Axles, where a 1.0 mm-depth crack as the inspection limit has less probability to propagate. Besides, the wheelset with inside axle boxes shows the smaller stress value. The analysis from well-known Kitagawa-Takahashi diagram indicates a security risk while only using nominal stress approach.
D. Regazzi - One of the best experts on this subject based on the ideXlab platform.
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Probabilistic fatigue assessment for railway Axles and derivation of a simple format for damage calculations
International Journal of Fatigue, 2016Co-Authors: Stefano Beretta, D. RegazziAbstract:Abstract This paper describes a procedure for the determination of railway axle risk of fatigue failure under service loading for a simple fatigue assessment compliant to modern structural recommendations. After an initial review of reliability assessment under fatigue, a fully probabilistic approach is outlined, whose input data for the fatigue damage obtained with the EURAxles project are briefly summarized. Then, a series of Montecarlo simulations was carried out in order to determine the maximum allowable stress for a given axle made of EA4T and EA1N under service conditions identified by different load spectra from the literature. Results have been obtained in terms of a safety factor for damage calculations that allows designers to adopt a simple semi-probabilistic approach for designing Axles for a target reliability against fatigue. The application of this procedure to a railway axle then shows how safety factors should be have to be further increased for taking into the prospective presence of impact damages.
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fatigue assessment of old design Axles service simulation and life extension
Proceedings of the Institution of Mechanical Engineers Part F: Journal of Rail and Rapid Transit, 2016Co-Authors: Laura Mazzola, D. Regazzi, S Beretta, Stefano BruniAbstract:This paper proposes a damage-tolerant approach for ensuring the safe operation of railway Axles with an old, non-EN-compliant design, until completion of their life cycle. The approach consists in defining a suitable non-destructive testing (NDT) inspection programme, which is based on the precise evaluation of service loads using multi-body simulation and on validated crack propagation models. The application of the proposed approach is presented for two different test cases, both representing old design Axles for urban railway vehicles. It is demonstrated that NDT inspection intervals are highly dependent on the specific axle design and service scenarios, particularly with regard to the effects of braking.