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Influence of notches under cyclic high-frequency fatigue loading
Kozáková, Kamila ; Ševeček, Oldřich (referee) ; Klusák, Jan (advisor)
The diploma thesis deals with the evaluation of the lifetimes of smooth and notched specimens. The comparison of their lifetimes is focused on the case of high-frequency cyclic loading in the area of high-cycle and gigacycle fatigue of materials. The theory of critical distances is used to evaluate and recalculate the life curves of the notched specimens. The effect of the notch is quantified using the Line method. The critical length parameter is determined so that the life curve of the notched specimens corresponds to the curve measured on smooth specimens. The result is the dependence of the critical length parameter on the number of cycles to fracture. Knowledge of critical length parameters can be used to determine the lifetime of notched specimens as well as real notched components using the results of fatigue tests of smooth specimens.
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Influence of notches under cyclic high-frequency fatigue loading
Kozáková, Kamila ; Ševeček, Oldřich (referee) ; Klusák, Jan (advisor)
The diploma thesis deals with the evaluation of the lifetimes of smooth and notched specimens. The comparison of their lifetimes is focused on the case of high-frequency cyclic loading in the area of high-cycle and gigacycle fatigue of materials. The theory of critical distances is used to evaluate and recalculate the life curves of the notched specimens. The effect of the notch is quantified using the Line method. The critical length parameter is determined so that the life curve of the notched specimens corresponds to the curve measured on smooth specimens. The result is the dependence of the critical length parameter on the number of cycles to fracture. Knowledge of critical length parameters can be used to determine the lifetime of notched specimens as well as real notched components using the results of fatigue tests of smooth specimens.
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Fracture behaviour of the short crack near the stress concentrator
Hutař, Pavel ; Knésl, Zdeněk
A two-parameter fracture mechanics method is applied to small cracks near a stress concentrator. The small crack in the present contribution is considered as crack influenced by the stress concentrator. The sharp V-noch or V-noch with radius $R$ are studieded here. The effect of V-notch geometry on the small crack fracture parameters is analysed. The necessary calculations are performed by using a finite element method (system Ansys). Obtained results are discussed from point of view of the small crack behavior. The small fatigue crack growth is especially influenced by the constraint level. The results improve the quality of fatigue life estimation of structure with concentrators.
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Two-Parameter Approach for Short Cracks at Notches
Seitl, Stanislav ; Hutař, Pavel ; Knésl, Zdeněk
A two parameter constraint-based fracture mechanics method is applied to the behavior of microstructurally and mechanically short fatigue cracks. A short crack in the vicinity of a grain boundary and a crack which is engulfed by the plastic strain field of a notch are studied as examples. The different levels of stress constraint are quantified by using the T-stress and the Q parameter. The corresponding calculations are performed by using a finite element method (ANSYS system). The influence of the T values on the propagation of short fatigue cracks is analyzed. The size of the plastic zone and the crack closure are significantly affected by the level of constraint. The influence of constraint on small fatigue crack growth kinetic is studied under the assumption that the controlling variable for the rate of propagation of the fatigue crack is the size of the plastic zone.
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