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A possible approach for assessment of general singular stress concentrators on the basis of linear elastic fracture mechanics
Náhlík, Luboš
This paper studies a stress distribution around a general singular stress concentrator tip on the basis of linear elastic fracture mechanics. A procedure for development of stability criteria of general singular stress concentrators is shown. Three different methods for determination of an essential critical stress for crack propagation from the stress concentrator tip are introduced. Each of used method is useful for different mechanism of crack propagation. The described procedures are based on three dissimilar physical basis: on the energetic ground – the generalized strain energy density factor is mentioned, on the failure stress of material grain ahead of concentrator tip and on the size of plastic zone in front of concentrator tip. The numerical results can contribute to better understanding of general stress concentrators behaviour and can be used for design of engineering structures with mentioned type of stress concentrator
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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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An analysis of stress distribution around singular stress concentrators
Knésl, Zdeněk ; Náhlík, Luboš ; Hutař, Pavel
Problems of determination of stress distribution around singular stress concentrators are discussed in the paper. Procedure for dependable estimation of stress field in the vicinity of singular stress concentrator is suggested. The procedure is based on combination of numerical (FEM) and analytical approaches. Presented procedure facilitates appraisal of influence of the singular stress concentrators on lifetime of engineering structures.
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Interakce trhliny a kovového substrátu v plasmových keramických nástřicích
Náhlík, Luboš ; Knésl, Zdeněk ; Kroupa, František
Plasma-sprayed ceramic coatings contain a high density of intrasplat microcracks which are responsible for small YoungŽs moduli and low fracture toughness. The extension of an initial surface crack in the direction to the interface, where the crack is repelled by the metal substrate with higher YoungŽs modulus, is studied using the methods of fracture mechanics. It is shown that high tensile stresses induced by the crack in the interface can lead to a local decohesion along the interface so that the crack can deviate into the interface
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Vliv rozhraní mezí matricí a inkluzí na šíření únavových trhlin
Náhlík, Luboš
The interaction between an inhomogeneity and a crack propagating near the circular inhomogeneity is studied under the assumptions of linear elastic fracture mechanics (LEFM). Three cases are considered: a crack located in front of the inhomogeneity, a crack situated arbitrarily near the inhomogeneity, and a special case when the crack tip lies at the interface between the matrix and the inhomogeneity. The main purpose of this paper is to find the most often configurations in materials with inhomogeneities
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Modelling of crack propagation through bi-material interface
Náhlík, Luboš
Under conditions of Linear Elastic Fracture Mechanics is studied crack behaviour in front of circular particle. The typical behaviour of crack approaching the interface between matrix and particle is showen. Results of numerical calculations and applications of earlier suggested tentative fracture criteria for crack terminating at the bi-material interface are presented.
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Interaction of crack and aggregate in concrete
Keršner, Z. ; Náhlík, Luboš ; Knésl, Zdeněk
Concrete is represented as a two-phase material in this paper. Behaviour of a single macrocrack approaching to the interface between hardened cement paste (matrix) and aggregate (particle) is modelled. It is shown that in the case of where Young modulus of cement paste is greater then those of aggregates, the effective fracture toughness of concrete is predominantly given by fracture properties of aggregates.
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Interaction between crack and circular inclusion
Náhlík, Luboš
The interaction between an inhomogeneity and a crack propagating near the circular inhomogeneity is studied under the assumptions of linear elastic fracture mechanics (LEFM) (we assume elastic behaviour of the matrix and the inhomogeneity as well). Three cases are considered: a crack located in front of the inhomogeneity, a crack situated arbitrarily near the inhomogeneity, and a special case when the crack tip lies at the interface between the matrix and the inhomogeneity . The main purpose of this paper is to find the most often configurations in materials with inhomogeneities.
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