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Numerical Modelling of Fatigue Crack Closure
Oplt, Tomáš ; Růžička, Milan (referee) ; Horníková, Jana (referee) ; Hutař, Pavel (advisor)
This Ph.D. thesis was written under the supervision of Assoc. prof. Pavel Hutař, Ph.D., and Assoc. prof. Luboš Náhlík, Ph.D. The thesis is focused on the effect of plasticity induced crack closure, its characteristic and ways of numerical modelling. Premature fatigue crack closure has a significant effect on the fatigue crack propagation rate and therefore on the residual lifetime of a structure. A three-dimensional numerical model allows a detailed look at the stress and strain distribution along the crack front, and particularly it allows a local description of parameters along the crack front which governs the fatigue crack propagation rate. In the first part of the thesis, the study is focused on the influence of a singular stress field at the vicinity of the free surface on the crack front curvature without crack closure being involved. In the second part, a numerical model in 2D of plasticity induced crack closure was created and verified by experimental results. In the final part, a 3D numerical model is used to describe the influence of the crack closure on its fatigue propagation rate and explains typical crack front curvature. The suggested technique allows quantitative accuracy improvement of numerical simulation of the fatigue crack propagation and therefore, more reliable estimation of the residual lifetime of the cracked structure.
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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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Numerical Modelling of Fatigue Crack Closure
Oplt, Tomáš ; Růžička, Milan (referee) ; Horníková, Jana (referee) ; Hutař, Pavel (advisor)
This Ph.D. thesis was written under the supervision of Assoc. prof. Pavel Hutař, Ph.D., and Assoc. prof. Luboš Náhlík, Ph.D. The thesis is focused on the effect of plasticity induced crack closure, its characteristic and ways of numerical modelling. Premature fatigue crack closure has a significant effect on the fatigue crack propagation rate and therefore on the residual lifetime of a structure. A three-dimensional numerical model allows a detailed look at the stress and strain distribution along the crack front, and particularly it allows a local description of parameters along the crack front which governs the fatigue crack propagation rate. In the first part of the thesis, the study is focused on the influence of a singular stress field at the vicinity of the free surface on the crack front curvature without crack closure being involved. In the second part, a numerical model in 2D of plasticity induced crack closure was created and verified by experimental results. In the final part, a 3D numerical model is used to describe the influence of the crack closure on its fatigue propagation rate and explains typical crack front curvature. The suggested technique allows quantitative accuracy improvement of numerical simulation of the fatigue crack propagation and therefore, more reliable estimation of the residual lifetime of the cracked structure.
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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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