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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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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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Calculation of residual fatigue life of railway set
Náhlík, Luboš ; Hutař, Pavel ; Knésl, Zdeněk ; Matušek, P.
The calculation of residual fatigue life of railway set is described in the contribution. The initial defect is modeled as a semicircular crack, which propagates preferentially in normal mode of loading perpendicularly on the axis of the axle. The conservative approach based on linear elastic fracture mechanics was chosen for residual fatigue life prediction. The aim of calculation is to determine number of loading cycles, which permits safe run of the railway axle, i.e. the dependence of crack depth on number of loading cycles for given loading spectrum.
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Crack propagation through a material interface
Náhlík, Luboš
This paper describes a study of the fatigue crack propagation through a material interface of two different elastic materials under assumptions of linear elastic fracture mechanics. Two procedures for estimation of threshold value for further crack propagation from bi-material interface to the second material are suggested. Special attention is devoted to crack perpendicularly oriented to the bi-material interface. The first one is based on modified Sih?s strain energy density concept and the second one on the size of area of the plastic zone in front of the crack tip. It is shown that the corresponding fatigue threshold value is strongly influenced by the existence of an interface between two materials. As a numerical example the procedures are in applied on body with protective layer. The calculation of the corresponding threshold values and comparison of both suggested procedures is performed. Both procedures make it possible to decide whether the crack will stop at the interface or will continue growing into the second material. The results generally contribute to a better understanding of the failure of structures with protective layers.
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Crack propagation through a material interface
Náhlík, Luboš
This paper describes a study of the fatigue crack propagation through a material interface of two different elastic materials under assumptions of linear elastic fracture mechanics. Two procedures for estimation of threshold value for further crack propagation from bi-material interface to the second material are suggested. Special attention is devoted to crack perpendicularly oriented to the bi-material interface. The first one is based on modified Sih?s strain energy density concept and the second one on the size of area of the plastic zone in front of the crack tip. It is shown that the corresponding fatigue threshold value is strongly influenced by the existence of an interface between two materials. As a numerical example the procedures are in applied on body with protective layer. The calculation of the corresponding threshold values and comparison of both suggested procedures is performed. Both procedures make it possible to decide whether the crack will stop at the interface or will continue growing into the second material. The results generally contribute to a better understanding of the failure of structures with protective layers.
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Influence of material characteristics on the fatigue crack growth through bi-material interface
Náhlík, Luboš
This contribution describes a study of the behaviour of a fatigue crack growing in one material and penetrating through the bi-material interface into a second material. Dependence of the stress singularity exponent on Poisson's ratio of both materials is studied. The study especially aims to quantify the influence of the interface on the values of fatigue threshold. It is suggested that the controlling variable for the behaviour of a crack approaching to the interface is the size of the plastic zone existing near the tip of the crack. The results of the contribution makes it possible to decide whether the crack will stop at the interface or continue growing into the second material. The results contribute to a better understanding of the damage of composite materials.
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