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Determination of T stress for arbitrary oriented crack terminating at interface between two dissimilar materials
Gröger, Roman
The most important factors describing the fracture-mechanics behavior of layered structures are the generalized stress intensity factor and also T stress describing the amplitude of the stress field independent on the radial distance from the crack tip.. Direct methods of the calculation of such parameters are well known and their accuracy is critically assessed by the experimental measurements. The present work proposes an alternative method of determining of the elastic T stress based on the validity of the reciprocal work theorem using the integration of the strain energy along a circular path surrounding the crack tip. The results obtained from a model of a crack terminating at interface between two dissimilar elastic materials are compared with the usually used direct approach. It is shown that such this term is not negligible and generally need to be taken into account in the considerations on the stability of layered materials.
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Comparison of fracture behaviour of cracks and sharp notches
Klusák, Jan ; Knésl, Zdeněk
The theoretical background of linear elastic fracture mechanics of V-notches is presented. A crack is considered as a special case of the V-notch with zero open angle. Conditions for stability of a general singular stress concentrator are formulated. Based on results obtained a fracture behaviour of notches and cracks is compared.
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The effect of V-notch on the propagation rate of fatigue crack
Hutař, Pavel ; Knésl, Zdeněk
The rate of a fatigue crack propagating in a vicinity of a V-notch is studied. To assess the influence of the constraint on the rate of the propagation, two parameter constraint based linear elastic fracture mechanics is used. The corresponding values of the T-stress are calculated and values of the effective stress intensity factor Keff controlling the rate of a crack propagation are estimated as a function of the V-notch opening angle. The results obtained are compared with those for a crack emanating from nonsingular U- notch concentrator.
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Problems of determination of a Q-parameter
Hutař, Pavel
The basic thema of this paper is to the determinate Q-parameter. In two parameter description for larger plastic zone Q-parameter is used. It is two ways how determinate Q: the HRR (Hutchinson, Rice, Rosengreen) reference field or MBLM (modified boundery layer model) can used. These methods are compared. Aim of this paper is to refer to same problems of Q determination.
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The influence of T-stress on the characteristics of a fatigue crack
Hutař, Pavel
The influence of the T-stress values on the propagation of fatigue cracks is analyzed. The parameters of the plastic zone are studied at two levels of applied stress, i.e. loading and unloading. The CTOD parameter and rp (plastic zone size) in the crack grow direction are discussed as a driving parameter of a fatigue crack propagation rate. The three ways of determination of propagation rate of a fatigue cracks are compared. Recommendations for applications of these methods are discussed.
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Calculation of fracture parameters for the cracked bodies strengthened by circular patches
Gröger, Roman
The present article yields a quantitative characterization of the influence of geometry and material properties on the values of fracture parameters. Both the cracked sheets with single and double circular patches are used for the analysis. The desired value of elastic T stress is obtained using the conservation M integral resulting from the Eshelby integral concept. For the SIF calculation, the indirect method of J integral is used and the general concept for the SIF separation in case of a mixed mode of loading is discussed here. The reduction effect is specified by the ratios of SIF and T stress. The method of stiffening the region surrounding the crack tip can be used as an alternative method of the lifetime prolongation, but cannot be used in all cases. Sometimes the usual method of the crack tip singularity cancellation is the only one to repair the structure.
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Calculation of the fracture parameters for a crack growing from the tip of a V-notch
Gröger, Roman ; Hutař, Pavel
This article yields a comparison of two principles for caculation of the fracture parameters - the direct finite element method and hybrid element method. The stress intensity factor and the T stress for a crack growing from the tip of a nonsingular stress concentrator for a large variety of notch angles is obtained. It is discussed the sensitivity of each parameter on the ratio of crack length to the width of the specimen. The obtained results can contribute to more precise characterisation of the crack instability state in a case of the combination V-notch + crack.
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Comparison of fracture behaviour of notches and cracks
Klusák, Jan ; Knésl, Zdeněk
The theoretical background of linear elastic fracture mechanics of V-notches is presented. A crack is considered as a special case of the V-notch with zero open angle. Conditions for stability of a general singular stress concentrator are formulated. Based on results obtained a fracture behaviour of notches and cracks is compared.
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