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Estimation of crack propagation direction in structures with material interface
Šestáková, Lucie ; Náhlík, Luboš ; Hutař, Pavel
The aim of the paper is to develop a procedure, which makes it possible to estimate crack propagation direction after its pass through the bimaterial interface between two elastic materials. For numerical calculations the finite element method is used. Conditions of linear elastic fracture mechanics are considered in the paper. The results obtained can help to better understanding of crack propagation in structures with material interface and for more reliable estimation of their service life.
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Vliv rohové singularity na tvar únavové trhliny
Hutař, Pavel ; Náhlík, Luboš ; Knésl, Zdeněk ; Seitl, Stanislav
Due to the existence of vertex singularity at the point where the crack intersects the free surface, stress distribution around the crack tip and the type of the singularity is changed. In the interior of the specimen the classical singular behaviour of the crack is dominant and can be described using generally known analytic equations. Contrary to this, at the free surface or in the boundary layer close to the free surface the vertex singularity is significant. The influence of vertex singularity on crack behaviour and crack shape for a three-dimensional structure is described in this paper. To estimate the influence of the free surface on fatigue crack growth rate the model of a general singular stress concentrator was applied. The estimated fatigue crack shape can help to provide a more reliable estimation of the fatigue life of the structures considered.
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Odhad zdánlivé lomové houževnatosti keramických laminátů založený na zobecněném faktoru hustoty deformační energie
Náhlík, Luboš ; Šestáková, Lucie ; Hutař, Pavel
The paper presented deals with fracture behavior of ceramic laminates. Assumptions of the linear elastic fracture mechanics and small scale yielding are considered. In this frame the residual stresses in individual layers of Al2O3/5vol.%t-ZrO2 (ATZ) and Al2O3/30vol.%m-ZrO2 (AMZ) are determined. The procedure based on generalization of Sih's strain energy density factor to the case of a crack touching the interfaces between two dissimilar materials is used for determination of effective values of stress intensity factor at material interfaces.Important increase of the fracture toughness at AMZ/ATZ interface was predicted in comparison to the fracture toughness of individual material components. Predicted values were compared with data available in literature and mutual good agreement was found. Procedure suggested can be used for estimation of resistance to crack propagation of multilayered structures and its design.
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Šíření trhliny v okolí bi-materiálového rozhraní: aplikace na vícevrstvé trubky
Šestáková, Lucie ; Náhlík, Luboš ; Hutař, Pavel ; Knésl, Zdeněk
Layered materials are often used in praxis, primarily because of their better mechanical properties in comparison with properties of individual materials components. During the crack propagation process a configuration of a crack with its tip at the bi-material interface in the structure can occur. It is important to decide if the crack propagates into the second material in this case or not. The step change of material properties at bi-material interface causes that the classical linear elastic fracture mechanics cannot be used. A generalized approach has to be applied. It is to find suitable criteria for determination of the effective values of stress intensity factor for the crack terminating at bi-material interface. Knowledge of these values is important for assessment of service life time such structures.
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