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Fatigue life of crankshaft
Wolf, David ; Kučera, Pavel (referee) ; Vopařil, Jan (advisor)
This thesis is focused on the crankshaft as one of the most dynamically stressed component of internal combustion engines. At the beginning describes in the wider context how is the crankshaft of internal combustion engines strained. Then it considers individual parts of crankshaft, which are affecting its construction in terms of fatigue life. And in the last section describes the different ways to eliminate the damage caused by cyclic loading and modern methods of fatigue life prediction of crankshafts.
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Influence of the Francis turbine stay vane trailing edge shape on generation of Karman vortex street
Novotný, Vojtěch ; Skoták, Aleš (referee) ; Rudolf, Pavel (advisor)
In the flow past bluff bodies for a certain range of velocity a periodical vortex shedding emerges which is known as von Kármán vortex street. This phenomenon causes the periodical alteration of pressure field which affects the body. Should the vortex shedding frequency be similar to the body natural frequency, the amplitude of vibration significantly increases which can lead to fatigue cracking. In the case of water turbines, this phenomenon often affects the stay vanes. Both the vortex shedding frequency and the lift force amplitude can be influenced by the modification of the trailing edge geometry. The aim of this thesis is to use CFD computation in order to find the optimal geometry of the stay vane trailing edge for the specific Francis turbine unit.
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Plasticity induced crack closure effect on fatigue crack growth
Šebík, Marek ; Vojtek, Tomáš (referee) ; Hutař, Pavel (advisor)
This study is focused on plasticity induced crack closure effect on fatigue crack propagation. It utilizes finite element method modeling to evaluate the effect of this phenomenon on crack propagation at a series of MT specimen configurations. The modeling has been done both 2D and 3D. Comparison of computed results with experiments explains effect of the phenomenon at performed experimental measurements. Above all, three-dimensional modeling provides assessment of plasticity induced crack closure through thickness of the object. Thereby it explains shapes of fatigue crack fronts and lays foundations for including plasticity induced crack closure phenomenon to fatigue crack growth predictions in three-dimensional space.
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Plasticity induced crack closure effect on fatigue crack growth
Šebík, Marek ; Vojtek, Tomáš (referee) ; Hutař, Pavel (advisor)
This study is focused on plasticity induced crack closure effect on fatigue crack propagation. It utilizes finite element method modeling to evaluate the effect of this phenomenon on crack propagation at a series of MT specimen configurations. The modeling has been done both 2D and 3D. Comparison of computed results with experiments explains effect of the phenomenon at performed experimental measurements. Above all, three-dimensional modeling provides assessment of plasticity induced crack closure through thickness of the object. Thereby it explains shapes of fatigue crack fronts and lays foundations for including plasticity induced crack closure phenomenon to fatigue crack growth predictions in three-dimensional space.
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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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Influence of the Francis turbine stay vane trailing edge shape on generation of Karman vortex street
Novotný, Vojtěch ; Skoták, Aleš (referee) ; Rudolf, Pavel (advisor)
In the flow past bluff bodies for a certain range of velocity a periodical vortex shedding emerges which is known as von Kármán vortex street. This phenomenon causes the periodical alteration of pressure field which affects the body. Should the vortex shedding frequency be similar to the body natural frequency, the amplitude of vibration significantly increases which can lead to fatigue cracking. In the case of water turbines, this phenomenon often affects the stay vanes. Both the vortex shedding frequency and the lift force amplitude can be influenced by the modification of the trailing edge geometry. The aim of this thesis is to use CFD computation in order to find the optimal geometry of the stay vane trailing edge for the specific Francis turbine unit.
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Fatigue life of crankshaft
Wolf, David ; Kučera, Pavel (referee) ; Vopařil, Jan (advisor)
This thesis is focused on the crankshaft as one of the most dynamically stressed component of internal combustion engines. At the beginning describes in the wider context how is the crankshaft of internal combustion engines strained. Then it considers individual parts of crankshaft, which are affecting its construction in terms of fatigue life. And in the last section describes the different ways to eliminate the damage caused by cyclic loading and modern methods of fatigue life prediction of crankshafts.
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THE EFFECT OF THRESHOLD VALUE ON THE RESIDUAL FATIGUE LIFETIME OF RAILWAY AXLES
Pokorný, Pavel ; Náhlík, Luboš ; Hutař, Pavel
The fatigue failure of railway axles could have unaccepted consequences. Because of safe operation, it is important to determine the residual fatigue lifetime. The railway axle could contain some cracks either from manufacturing process or from previous service operation. Present defectoscopy can reliably detect only relatively long cracks (longer than 2 mm), see [1]. In other words, there is a risk that the existing crack is not detected by defectoscopy. For conservative establishment of the residual fatigue lifetime the crack, which could be not detected by defectoscopy, must be considered. This paper deals with an effect of the threshold value of fatigue crack propagation on the residual fatigue lifetime of railway axles. Two very commonly used materials for railway axles EA1N and EA4T steels are considered. The results of this paper could be used for safer operation of railway axles.
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