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Kinetics of Short - crack Growth in Superduplex Steel
Bártová, Lenka ; Pantělejev, Libor (referee) ; Polák, Jaroslav (advisor)
The fatigue life and the kinetics of short crack growth in specimen of austenitic-ferritic duplex steel cycled with constant stress amplitude and different mean stresses is studied. Fatigue life was determined on smooth cylindrical specimens. Strain amplitude and mean strain were recorded. Short crack growth was studied in cylindrical specimens with a shallow notch. Cyclic straining was interrupted and crack length was measured using an optical microscope mounted on the testing machine. Crack length and crack growth rates were evaluated. The effect of the mean stress on the rate of short cracks and fatigue life were discussed.
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Fatigue Properties of Ultra-fine Grain Copper Produced by ECAP Method
Navrátilová, Lucie ; Němec, Karel (referee) ; Pantělejev, Libor (advisor)
This diploma thesis describes properties of ultra-fine grain Cu prepared via ECAP procedure. The influence of fatigue loading with positive mean stress on S-N curve (i.e. fatigue life), cyclic plastic behaviour and grain size was investigated. It was found that tensile mean stress leads to shorter lifetime in comparison with fatigue loading with zero mean stress. During main part of the lifetime, significant hardening of UFG Cu was observed. There is no distinct effect on microstructural orientation and stability.
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Kinetics of Short - crack Growth in Superduplex Steel
Bártová, Lenka ; Pantělejev, Libor (referee) ; Polák, Jaroslav (advisor)
The fatigue life and the kinetics of short crack growth in specimen of austenitic-ferritic duplex steel cycled with constant stress amplitude and different mean stresses is studied. Fatigue life was determined on smooth cylindrical specimens. Strain amplitude and mean strain were recorded. Short crack growth was studied in cylindrical specimens with a shallow notch. Cyclic straining was interrupted and crack length was measured using an optical microscope mounted on the testing machine. Crack length and crack growth rates were evaluated. The effect of the mean stress on the rate of short cracks and fatigue life were discussed.
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Fatigue Properties of Ultra-fine Grain Copper Produced by ECAP Method
Navrátilová, Lucie ; Němec, Karel (referee) ; Pantělejev, Libor (advisor)
This diploma thesis describes properties of ultra-fine grain Cu prepared via ECAP procedure. The influence of fatigue loading with positive mean stress on S-N curve (i.e. fatigue life), cyclic plastic behaviour and grain size was investigated. It was found that tensile mean stress leads to shorter lifetime in comparison with fatigue loading with zero mean stress. During main part of the lifetime, significant hardening of UFG Cu was observed. There is no distinct effect on microstructural orientation and stability.
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An influence of prestress by combined random loading
Svoboda, Jaroslav ; Balda, Miroslav ; Fröhlich, Vladislav
The contribution deals with findings concerning an influence of static load in combination with random dynamic torgue on fatigue life of tube specimens made out of the steel ČSN 411523.1. A generalized formula has been found for fatigue life expressed in a number of loading blocks of torgue process as a function of its standard deviation. It joins both components of the combined loading in one expression. The formula yields very precise estimates of fatigue lives.
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