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RESIDUAL FATIGUE LIFETIME OF RAILWAY AXLES
Pokorný, Pavel ; Fajkoš,, Rostislav (referee) ; Materna, Aleš (referee) ; Náhlík, Luboš (advisor)
This Ph.D. thesis deals with methodology for determination of residual fatigue lifetime of railway axles based on damage tolerance approach. This approach accepts an existence of potential defect, which could lead to fatigue failure of whole axle. The behavior of crack in railway axle is described by approaches of linear elastic fracture mechanics. There are plenty of factors, which more or less influence determined residual fatigue lifetime. The aim of this thesis is to quantify effects of these factors. The first part of Ph.D. thesis represents overview of studied problems relating to fatigue damage of railway axles. This part is focused on parameters, which influence fatigue crack growth in railway axle materials. The second part of thesis shows procedure for determination of residual fatigue lifetime, which was developed at the Institute of Physics of Materials of the Academy of Sciences of the Czech Republic. The main aim of this thesis was to improve current procedure for more precise estimation of residual fatigue lifetime. Significant part of this work is determination of significance of studied factors, which influencing calculated residual fatigue lifetime of railway axles (e.g. effect of threshold value, load spectrum, retardation effects, residual stress, axle geometry, material of axle etc.). The procedures described and results obtained can be also used for determination of residual fatigue lifetime of general mechanical component (not only railway axles). Therefore, results obtained in this Ph.D. thesis can be used e.g. for assessment of regular inspection intervals of cyclically loaded general mechanical parts.
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Determination of residual fatigue lifetime of railway axle after surface treatment
Pánek, Ondřej ; Poduška, Jan (referee) ; Náhlík, Luboš (advisor)
This master thesis deals with prediction of residual fatigue lifetime of railway axle. In the first part of this thesis, theoretical introduction to the issue based on research of available literature is elaborated. The second part is dedicated to numerical modelling of actual railway axle with crack, which serves to obtain the necessary parameters entering estimation of the residual fatigue lifetime. At first, a finite element model of cylindrical body with crack loaded by bending moment was created and compared with analytical solution for verification purposes. The second step was the creation of separate models of railway axle with crack for three types of loading – bending moment, press fit of wheel and residual stresses, respectively. Furthermore, the shape of various crack propagation stages was determined, according to the methodology developed at IPM CAS. Using the determined crack shape, stress intensity factors were calculated separately from all types of loads for various crack depths. Dependence of stress intensity factor on the crack length was then used to calculate residual fatigue life for real loading spectrum.
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RESIDUAL FATIGUE LIFETIME OF RAILWAY AXLES
Pokorný, Pavel ; Fajkoš,, Rostislav (referee) ; Materna, Aleš (referee) ; Náhlík, Luboš (advisor)
This Ph.D. thesis deals with methodology for determination of residual fatigue lifetime of railway axles based on damage tolerance approach. This approach accepts an existence of potential defect, which could lead to fatigue failure of whole axle. The behavior of crack in railway axle is described by approaches of linear elastic fracture mechanics. There are plenty of factors, which more or less influence determined residual fatigue lifetime. The aim of this thesis is to quantify effects of these factors. The first part of Ph.D. thesis represents overview of studied problems relating to fatigue damage of railway axles. This part is focused on parameters, which influence fatigue crack growth in railway axle materials. The second part of thesis shows procedure for determination of residual fatigue lifetime, which was developed at the Institute of Physics of Materials of the Academy of Sciences of the Czech Republic. The main aim of this thesis was to improve current procedure for more precise estimation of residual fatigue lifetime. Significant part of this work is determination of significance of studied factors, which influencing calculated residual fatigue lifetime of railway axles (e.g. effect of threshold value, load spectrum, retardation effects, residual stress, axle geometry, material of axle etc.). The procedures described and results obtained can be also used for determination of residual fatigue lifetime of general mechanical component (not only railway axles). Therefore, results obtained in this Ph.D. thesis can be used e.g. for assessment of regular inspection intervals of cyclically loaded general mechanical parts.
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Procedure of residual fatigue lifetime assesment of railway axle
Scholz, David ; Seitl, Stanislav (referee) ; Náhlík, Luboš (advisor)
The goal of the bachelor's thesis is to present options to calculate residual life of a railway axle from more sophisticated points of view. These methods are requested by railway operators to ensure higher safety of train traffic. The main issue is the perspective of fracture mechanic, considering railway axle as a component with an initial crack or other defect. The theoretical part deals with basic definitions of fracture mechanics and processes describing crack propagation, using conception of stress intensity factor, which is the most used nowadays. Following part also describes a fatique life estimation process in real. This process is demon-strated using an example after that.
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Determination of residual fatigue lifetime of railway axle after surface treatment
Pánek, Ondřej ; Poduška, Jan (referee) ; Náhlík, Luboš (advisor)
This master thesis deals with prediction of residual fatigue lifetime of railway axle. In the first part of this thesis, theoretical introduction to the issue based on research of available literature is elaborated. The second part is dedicated to numerical modelling of actual railway axle with crack, which serves to obtain the necessary parameters entering estimation of the residual fatigue lifetime. At first, a finite element model of cylindrical body with crack loaded by bending moment was created and compared with analytical solution for verification purposes. The second step was the creation of separate models of railway axle with crack for three types of loading – bending moment, press fit of wheel and residual stresses, respectively. Furthermore, the shape of various crack propagation stages was determined, according to the methodology developed at IPM CAS. Using the determined crack shape, stress intensity factors were calculated separately from all types of loads for various crack depths. Dependence of stress intensity factor on the crack length was then used to calculate residual fatigue life for real loading spectrum.
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Effect of residual stresses on the fatigue lifetime of railway axle
Hutař, Pavel ; Pokorný, Pavel ; Poduška, Jan ; Fajkoš, R. ; Náhlík, Luboš
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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Influence of Extension of Load Spectrum on Estimation of Residual\nFatigue Lifetime of Railway Axle
Pokorný, Pavel ; Hutař, Pavel ; Náhlík, Luboš
Railway axles are subjected to cyclic amplitude loading which can lead to fatigue failure.\nFor safe operation of railway axles a damage tolerance approach taking into account a possible\ndefect in railway axle is often required. Because of different operation regimes of trains (fast/slow\nride, ride on straight track, on curved track, over switches etc.) the load amplitude of axle is not\nconstant. The variability of load is defined by a load spectrum, which is determined experimentally\nby measuring of load in service conditions. Even though the load spectrum is measured on several\nhundreds or thousands of operation kilometres, the railway axles are in operation much longer time\n(often tens of years). Therefore, some load amplitudes higher than ones measured in the test can\noccur during a long-term axle service. The contribution presented deals with the effect of extension\nof load spectrum by rare high load amplitudes, which can occur during long-term operation, on\nresidual fatigue lifetime of railway axles.
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RESIDUAL FATIGUE LIFETIME OF RAILWAY AXLES
Pokorný, Pavel ; Fajkoš,, Rostislav (referee) ; Materna, Aleš (referee) ; Náhlík, Luboš (advisor)
This Ph.D. thesis deals with methodology for determination of residual fatigue lifetime of railway axles based on damage tolerance approach. This approach accepts an existence of potential defect, which could lead to fatigue failure of whole axle. The behavior of crack in railway axle is described by approaches of linear elastic fracture mechanics. There are plenty of factors, which more or less influence determined residual fatigue lifetime. The aim of this thesis is to quantify effects of these factors. The first part of Ph.D. thesis represents overview of studied problems relating to fatigue damage of railway axles. This part is focused on parameters, which influence fatigue crack growth in railway axle materials. The second part of thesis shows procedure for determination of residual fatigue lifetime, which was developed at the Institute of Physics of Materials of the Academy of Sciences of the Czech Republic. The main aim of this thesis was to improve current procedure for more precise estimation of residual fatigue lifetime. Significant part of this work is determination of significance of studied factors, which influencing calculated residual fatigue lifetime of railway axles (e.g. effect of threshold value, load spectrum, retardation effects, residual stress, axle geometry, material of axle etc.). The procedures described and results obtained can be also used for determination of residual fatigue lifetime of general mechanical component (not only railway axles). Therefore, results obtained in this Ph.D. thesis can be used e.g. for assessment of regular inspection intervals of cyclically loaded general mechanical parts.
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RESIDUAL FATIGUE LIFETIME OF RAILWAY AXLES
Pokorný, Pavel ; Fajkoš,, Rostislav (referee) ; Materna, Aleš (referee) ; Náhlík, Luboš (advisor)
This Ph.D. thesis deals with methodology for determination of residual fatigue lifetime of railway axles based on damage tolerance approach. This approach accepts an existence of potential defect, which could lead to fatigue failure of whole axle. The behavior of crack in railway axle is described by approaches of linear elastic fracture mechanics. There are plenty of factors, which more or less influence determined residual fatigue lifetime. The aim of this thesis is to quantify effects of these factors. The first part of Ph.D. thesis represents overview of studied problems relating to fatigue damage of railway axles. This part is focused on parameters, which influence fatigue crack growth in railway axle materials. The second part of thesis shows procedure for determination of residual fatigue lifetime, which was developed at the Institute of Physics of Materials of the Academy of Sciences of the Czech Republic. The main aim of this thesis was to improve current procedure for more precise estimation of residual fatigue lifetime. Significant part of this work is determination of significance of studied factors, which influencing calculated residual fatigue lifetime of railway axles (e.g. effect of threshold value, load spectrum, retardation effects, residual stress, axle geometry, material of axle etc.). The procedures described and results obtained can be also used for determination of residual fatigue lifetime of general mechanical component (not only railway axles). Therefore, results obtained in this Ph.D. thesis can be used e.g. for assessment of regular inspection intervals of cyclically loaded general mechanical parts.
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Procedure of residual fatigue lifetime assesment of railway axle
Scholz, David ; Seitl, Stanislav (referee) ; Náhlík, Luboš (advisor)
The goal of the bachelor's thesis is to present options to calculate residual life of a railway axle from more sophisticated points of view. These methods are requested by railway operators to ensure higher safety of train traffic. The main issue is the perspective of fracture mechanic, considering railway axle as a component with an initial crack or other defect. The theoretical part deals with basic definitions of fracture mechanics and processes describing crack propagation, using conception of stress intensity factor, which is the most used nowadays. Following part also describes a fatique life estimation process in real. This process is demon-strated using an example after that.
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