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INFLUENCE OF BOUNDARY CONDITIONS ON HIGHER ORDER TERMS OF NEAR-CRACK-TIP STRESS FIELD IN A WST SPECIMEN
Veselý, V. ; Šestáková, L. ; Seitl, Stanislav
A precise description of the stress and deformation fields in a cracked body is provided using multi-parameter fracture mechanics based on the approximation of the fields by means of the Williams' power series. This paper presents a detailed analysis of the stress field in a wedge-splitting test geometry specimen aimed at the calculation of coefficients of the higher order terms (up to 14) of the Williams' expansion. The numerical study is conducted with the use of a conventional finite element package; however, for processing of the results an over-deterministic method is employed. Special attention is paid to the influence of boundary conditions of the test geometry on the values of the coefficients of the higher order terms of the Williams' series. The results are compared to data from the literature; a strong effect of the boundary conditions is observed.
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Recovery of arrears on local charges
ŠESTÁKOVÁ, Lenka
Local charges are written in Act no 565/1990 of Collection about local charges, which currently includes 9 local charges. The municipal council decides, which charges will be collect and their amount. The local charges are then introduced by a generally binding public notice. Options recover arrears by Act no 280/2009 of Collection tax code, which is effective from 1 January 2011. Municipalities have the option to recover the arrears on their own, a tax execution, or may use the services of an executor. The offices used to recover arrears of tax execution. Most often there are the execution of tax deductions from wages, tax execution commandment receivable account with the payment services and tax execution commandments other monetary claims.
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Estimation of crack propagation direction in structures with material interface
Šestáková, Lucie ; Náhlík, Luboš ; Hutař, Pavel
The aim of the paper is to develop a procedure, which makes it possible to estimate crack propagation direction after its pass through the bimaterial interface between two elastic materials. For numerical calculations the finite element method is used. Conditions of linear elastic fracture mechanics are considered in the paper. The results obtained can help to better understanding of crack propagation in structures with material interface and for more reliable estimation of their service life.
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Odhad zdánlivé lomové houževnatosti keramických laminátů založený na zobecněném faktoru hustoty deformační energie
Náhlík, Luboš ; Šestáková, Lucie ; Hutař, Pavel
The paper presented deals with fracture behavior of ceramic laminates. Assumptions of the linear elastic fracture mechanics and small scale yielding are considered. In this frame the residual stresses in individual layers of Al2O3/5vol.%t-ZrO2 (ATZ) and Al2O3/30vol.%m-ZrO2 (AMZ) are determined. The procedure based on generalization of Sih's strain energy density factor to the case of a crack touching the interfaces between two dissimilar materials is used for determination of effective values of stress intensity factor at material interfaces.Important increase of the fracture toughness at AMZ/ATZ interface was predicted in comparison to the fracture toughness of individual material components. Predicted values were compared with data available in literature and mutual good agreement was found. Procedure suggested can be used for estimation of resistance to crack propagation of multilayered structures and its design.
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Šíření trhliny v okolí bi-materiálového rozhraní: aplikace na vícevrstvé trubky
Šestáková, Lucie ; Náhlík, Luboš ; Hutař, Pavel ; Knésl, Zdeněk
Layered materials are often used in praxis, primarily because of their better mechanical properties in comparison with properties of individual materials components. During the crack propagation process a configuration of a crack with its tip at the bi-material interface in the structure can occur. It is important to decide if the crack propagates into the second material in this case or not. The step change of material properties at bi-material interface causes that the classical linear elastic fracture mechanics cannot be used. A generalized approach has to be applied. It is to find suitable criteria for determination of the effective values of stress intensity factor for the crack terminating at bi-material interface. Knowledge of these values is important for assessment of service life time such structures.
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Cracks propagation in multilayer composites
Šestáková, Lucie
The paper deals with the investigation of the direction of a further crack propagation from the interface between two elastic materials. The purely numerical solution showed to be disadvantageous and therefore a new approach was proposed. This method follows from theory that is valid for crack propagation in homogenous body. The ratio of stress intensity factors for individual modes of loading was considered as the key-quantity for the crack propagation direction from the interface between two materials. Good agreement between experimental observation and estimation of crack propagation direction by means of jointed numerical and analytical solution was found. The potential difference can be caused by using of simplified 2D model.
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Fracture mechanics parameters of bi-material body
Šestáková, Lucie
Multilayer pipes consisting of different materials are frequently used in praxis because of partial improvement of the properties of pipe systems. To estimate their service life the basic fracture parameters have to be determined. In this work finite element calculations are applied in order to estimate the stress intensity factor K and T-stress values. Transferability of the fracture mechanics parameters obtained from two proposed C-type specimens to pipe systems was discussed using a constraint-based two-parameter fracture mechanics approach.
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Influence of Bi-material Interface on Crack Propagation Direction in Multilayer Composite
Šestáková, Lucie ; Náhlík, Luboš ; Hutař, Pavel
A substantial number of experimentally based works indicate the changes in crack propagation direction on bi-material interface in composite laminate materials. The paper is focused on estimation of crack propagation direction after its passage through the interface between two materials. For determination of the consequent propagation direction the minimal strain energy density criterion was employed. More accurate results were obtained by means of jointed numerical and analytical solution. The values of crack propagation directions obtained for layered composite were compared with experimental data.
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