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Numerical Analysis of the Thickness Influence on the Stress Field at Crack Tip for Different Poisson´s Ratios
Seitl, Stanislav ; Hanzlovský, Radovan ; Fernandez, C.
The influence of in- and out- of plane constraints on the behaviour of cracks under mode- I loading condition is studied. The independence of the stress intensity tensor structure, with respect to the specimen thickness B shows that under loss of constraint conditions higher order tensor members of the Williams expansion must be considered to characterize the singular stress field, and to explain the increasing apparent fracture toughness resulting experimentally for decreasing specimen thickness. A numerical study of the effect of Poisson’s ratio on stationary mode I crack tip fields is presented in the contribution. Finite element calculations for two-dimensional (v =0) and three-dimensional bodies are performed and compared. Further, the stress intensity tensor K, and the elastic txx and tzz components of the tij constraint tensor in the middle of a three-dimensional crack front are determined using direct methods for the same level of loading.
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The influence of residual stresses on the polymer pipe lifetime
Luky, R. ; Zouhar, Michal ; Hutař, Pavel
The aim of this article is study the influence of residual stresses on the pipe lifetime. The two dimensional numerical model of the pipe with inner crack was created and the creep crack growth in the pipe with and without residual stress is modelled. The results of K-kalibration curves are presented. After that the Paris law is used for solving the lifetime. The results of time to failure in dependency on the hoop stress for pipe with and without residual stress were compared. The existence of residual stresses decrease the lifetime of the pipe. Combination of the creep crack growth tests and numerical simulations can be a very powerful tool for lifetime estimation of plastic pipes under different loading conditions.
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Methods for evaluation of stability of crack between two isotropic/orthotropic materials
Damborský, Petr
This article deal with problems of cracks in bodies with bimaterial interface. The approaches based on the stress intensity factor (SIF) and the energy release rate (ERR) concepts are presented for isotropic and orthotropic materials. A relation between the mixity of the two fracture modes (I and II) in accordance with the two approaches mentioned is presented. The last part deals with the use two states ψ- integral to determine generalized stress intensity factor.
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Influence of point load on crack shape in polymeric pipe
Ševčík, Martin ; Hutař, Pavel ; Náhlík, Luboš ; Pinter, G. ; Frank, A.
The aim of this work was to develop an easy applicable algorithm of numerical model creation simulating a cracked polymeric pipe under various combination of loading. Proposed algorithm is able to find a real crack front shape using iterative procedure. The main aim was to study the effect of the point load and its consequences on the crack front shape. It was numerically confirmed that point loading causes grater crack extension in axial direction than in the case of pipe loaded by pure inner pressure. This results leads to higher stress intensity factor and lower residual life-time of the pipe system.
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TWO-PARAMETER DESCRIPTION OF CRACKS IN THE VICINITY OF INHOMOGENEITY
Seitl, Stanislav ; Knésl, Zdeněk
In case of two-parameter linear fracture mechanics a study of inhomogeneity influence on behaviour of short cracks is performed. The values of stress intensity factor (KI), T-stress and strain energy density (SED) are shown as a function of material constants of both components. The calculation of numerical values of mechanical parameters is accomplished by using finite element method ANSYS.
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Influence of bi-materials interface on crack interaction
Seitl, Stanislav
Existence of the interface between regions with different elastic properties has a pronounced influence on the behaviour of cracks. The aim of the present contribution are a modelling and analysis of two perpendiculars cracks growing in a vicinity of the interface between two different elastic materials. The dependence of stress intensity factor for mod I (KI) on the distance of a crack with respect to the interface is studied. The results contribute to better understanding of crack's behaviour in relation to microstructure of material.
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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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