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THE INFLUENCE OF T-STRESS FOR RELATIONSHIP BETWEEN CTOD AND J
Hutař, Pavel ; Knésl, Zdeněk
Relations between crack opening displacement (CTOD) and other fracture mechanics parameters are of a great importance in fracture mechanics. The basic aim of this paper is to describe an influence of T-stress on the plastic eta factors, plastic rotation factor and proporcional factor, i.e. the factors correlating J-integral and CTOD. Specimens with different values of T-stress (compact tension,three point bend and single edge cracked tension) are analysed by finite element method, the factors are calculated as functions of corresponding crack length and results obtained are discussed from the point of view of two-parameter fracture mechanics.
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Two paramether description of crack opening displacement
Hutař, Pavel
The basic aim of this paper is to describe the influence of T-stress on a crack profile, crack tip opening displacement CTOD and crack mouth opening displacement CMOD. Different methods of determination CTOD values are discussed. Numerical analysis of specimens is made by finite element method (Ansys). These result are compared with values determinated by modified boundary layer model MBLM.
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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 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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Two-Parameter Approach for Short Cracks at Notches
Seitl, Stanislav ; Hutař, Pavel ; Knésl, Zdeněk
A two parameter constraint-based fracture mechanics method is applied to the behavior of microstructurally and mechanically short fatigue cracks. A short crack in the vicinity of a grain boundary and a crack which is engulfed by the plastic strain field of a notch are studied as examples. The different levels of stress constraint are quantified by using the T-stress and the Q parameter. The corresponding calculations are performed by using a finite element method (ANSYS system). The influence of the T values on the propagation of short fatigue cracks is analyzed. The size of the plastic zone and the crack closure are significantly affected by the level of constraint. The influence of constraint on small fatigue crack growth kinetic is studied under the assumption that the controlling variable for the rate of propagation of the fatigue crack is the size of the plastic zone.
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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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Evaluation of the T-stress by the quarter-point elements
Hutař, Pavel
The three-dimensional (3D) finite element model of center cracked plate, CT-specimen... is used to study evaluation of T-stress along the crack front. $T$ is evaluated by direct methods and from wedge quarter-point element nodal dispacement. Results are compared and discussed from point of view of using in three-dimensional finite element models. This paper contains summary of relations for T-stress evaluation for quarter-point element nodal.
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