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The influence of specimen geometry on plasticity induced crack closure
Náhlík, Luboš ; Hutař, Pavel
The paper investigates the effect of in-plane constraint on plasticity induced crack closure under conditions of small scale yielding. The growth of a sharp straight crack in middle tension specimen (MT) and compact tension (CT) specimen, under constant amplitude of cyclic loading, was analyzed with help of finite element method. The material constitutive behavior was represented by a purely kinematic hardening law. Obtained results are discussed from point of view of the influence of T-stress on plasticity induced crack closure. Significant difference between opening values for CT and MT specimens was found under conditions of plane strain.
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Resistance of HDPE materials against crack propagation from two-parametric fracture mechanics point of view
Bareš, Pavel ; Fiedler, L.
The influence of geometry constraint on the resulting values of fracture characteristics of HDPE material is analysed. To this aim the crack growth resistance (J-R) curves and the initial fracture toughness values for HDPE material were experimentally determined for an arc-shaped test specimen with and without protective layer. Two parameter fracture mechanics is applied and transferability of the experimental data to the two-layer pipe used in praxis is discussed. Finite element calculations were used for the investigation. It is concluded that the estimation of the service life of pipes based on the approach is conservative.
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Critical stress for crack propagation in concrete
Náhlík, Luboš ; Knésl, Zdeněk
Concrete is modelled as a two-phase material. Behaviour of a crack with its tip on the interface between two different materials - hardened cement paste (matrix) and aggregate (particle) - is studied. In contrast to cracks in homogeneous materials the stress singularity for a crack terminating at the interface is of the type r -lambda, where the value of the stress singularity exponent, lambda, is in the interval 0 < lambda < 1. Than classical fracture mechanics theory and criterion cannot be applied. In the paper a new stability criterion is used to estimate the critical stress for the intersection of coarse aggregate particles.
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Determination of a crack propagation direction initiated at the bi-material interface
Náhlík, Luboš
The strain energy density distribution in the vicinity of a crack with its tip at the bi-material interface and the generalized strain energy factor is calculated. The crack orientated arbitrarily with respect to the interface and both cases of stress singularities around the crack tip, corresponding to normal and shear modes of loading, are taken into account. The problem is solved by a combination of analytical and numerical calculations. To estimate the crack propagation direction, the generalized strain energy criterion is used. A numerical example is presented.
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Crack propagation analysis in multilayered pipes
Bareš, Pavel
The fracture behavior of multilayered pipes applied for water and gas distribution is analyzed in this paper. The attention is focused on numerical modeling of crack propagation through twolayered pipe. Special attention is paid to the influence of interface between the layers on fatigue crack growth. The analysis is performed under the assumption of validity of linear-elastic fracture mechanic. Numerical calculations are performed by finite element method (system ANSYS).
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