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Vliv plasticky indukovaného zavírání trhliny a bi-materiálového rozhraní na prahové hodnoty
Náhlík, Luboš ; Hutař, Pavel
The paper is devoted to fatigue crack propagation in layered materials. The influence of plasticity induced crack closure on threshold values for fatigue crack propagation through interfaces between different materials layers is studied. The main aim was to estimate the influence of the loading ratio R on threshold values for crack propagation through a bi-material interface as a function of the elastic mismatch of both materials. The finite element method (FEM) is used for numerical calculations. Results obtained for different loading ratios, materials, boundary conditions and magnitude of applied loading can be generalized and used for the design of composite bodies with different material layers.
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Influence of Bi-material Interface on Crack Propagation Direction in Multilayer Composite
Šestáková, Lucie ; Náhlík, Luboš ; Hutař, Pavel
A substantial number of experimentally based works indicate the changes in crack propagation direction on bi-material interface in composite laminate materials. The paper is focused on estimation of crack propagation direction after its passage through the interface between two materials. For determination of the consequent propagation direction the minimal strain energy density criterion was employed. More accurate results were obtained by means of jointed numerical and analytical solution. The values of crack propagation directions obtained for layered composite were compared with experimental data.
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The Influence of Multilayer Composite Interface on Crack Propagation Direction
Šestáková, Lucie ; Náhlík, Luboš ; Hutař, Pavel
The paper deals with crack propagation in multilayer composites. A substantial number of experimentally based works have indicated the changes in crack propagation direction on multilayer composite interfaces. Changes of this kind are mostly desirable for composite technical life extension. Crack direction modification in the composite interface is investigated through a numerical simulation of this problem. For determination of the consequent propagation direction the minimal strain energy density criterion is employed. The ascertained propagation direction of the crack in the multilayer composite is compared with experimental results.
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Numerical analysis of a surface crack in protective layers
Šestáková, Lucie ; Majer, Zdeněk ; Náhlík, Luboš ; Knésl, Zdeněk
Two elastic plane strain problems relevant to the cracking of protective layers bonded to dissimilar semi-infinite substrate materials are solved. In the first case a crack initiated at the free surface of the layer and propagating within the film is considered and the influence of its original orientation on cracking mode of the layer is studied. The second problem is that of the crack in the layer oriented perpendicularly to the layer/substrate interface and its influence on a debonding of the layer/substrate system is analysed. In both cases the influence of elastic mismatch of both components on the crack behaviour is discussed. The results provide the details making it possible to solve practical problems connected with damage of bodies with protective layers.
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Numerical analysis of a surface crack propagation in protective layers
Majer, Zdeněk
The paper contains a numerical analysis of a surface crack propagation in an elastic surface layer. It was analysed an influence of elastic material parameters of both system components, initial length and orientation of crack on fatigue crack propagation direction. The typical behaviour of crack propagation in thin layers was described. The finite element method for determination of the direction of the farther crack propagation was used.
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Determination of threshold values of components with protective layers
Náhlík, Luboš ; Bareš, Pavel
The contribution is focused on the influence of existing fatigue cracks in protective layers on fatigue life of structures with protective layers. The problem is solved under conditions of linear elastic fracture mechanics with help of finite element method. Is shown, that in the case of the hard protective layer on the ductile substrate represents existing crack with its tip on the bi-material interface dangerous singular stress concentrator, because of decrease of threshold values of applied loading necessary for crack propagation. Knowledge of crack propagation in protective film is of paramount importance when studying potential failure of the substrate.
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