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Analýza rozdělení napětí pro trhlinu s vrcholem na rozhraní dvou materiálů
Náhlík, Luboš
The problem of arbitrarily oriented crack terminating at the boundary of two bonded materials is studied from the point of view of linear elastic fracture mechanics. The nature of the stress singularity for the crack terminating at the interface is different from 1/ square root of r and thus current fracture mechanics criteria cannot be adopted. The values of stress singularity exponent for selected ratio of elasticity modulus of both applied materials in dependency on orientation of crack and interface are calculated.
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Influence of grain orientation on threshold values of short fatigue cracks
Náhlík, Luboš ; Knésl, Zdeněk
The influence of a grain boundary on the propagation of a fatigue crack is studied. To this aim the grain boundary is considered as an interface between two different materials with their elastic constants depending on the orientation of the adjacent grains. The main goal is to estimate the threshold value of a microstructurally short fatigue crack propagating through the grain boundary. The corresponding threshold values are calculated as a function of material parameters of grains. Corresponding modelling have been performed by combination of analytical and numerical approach. For numerical calculations the finite element system ANSYS has been used. The model describes only one of many aspects of short fatigue crack behaviour and the results obtained contribute to a better understanding of microstuctural aspects of short fatigue crack growth.
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Estimation of the Critical Stress for Failure of a Protective Layer
Náhlík, Luboš ; Knésl, Zdeněk
This contribution describes a study of the behaviour of a crack growing in a protective layer and penetrating through an interface into a substrate. Special attention is devoted to a crack touching the interface. Conditions for the stability of a crack terminating at the interface between two materials are analyzed. The problem is studied under the assumptions of linear-elastic fracture mechanics. A new tentative criterion of stability based on application of the strain energy density concept is formulated and applied to the problem. The suggested criterion is used to estimate the critical applied stress for the failure of a substrate caused by a crack growing through the protective layer. It is shown that the critical stress may strongly depend on the fracture toughness of the substrate and on the bi-material parameters.
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