Národní úložiště šedé literatury Nalezeno 70 záznamů.  1 - 10dalšíkonec  přejít na záznam: Hledání trvalo 0.00 vteřin. 
Application of the Williams expansion near a bi-material interface
Malíková, Lucie ; Seitl, Stanislav
A simplified model of a crack approaching a bi-material interface is modelled by means of the finite element method in order to investigate the significance of the higher-order terms of the Williams expansion for the proper approximation of the opening crack-tip stress near the bi-material interface. The discussion on results is presented and the importance of the higher-order terms proved.
Comparison of calibration functions for short edge cracks under selected loads
Seitl, Stanislav ; Miarka, Petr ; Malíková, Lucie ; Krejsa, M.
Attention to the fatigue cracks in steel structures and bridges has been paid for long time. In spite to efforts to eliminate the creation and propagation of fatigue cracks throughout the designed service life, cracks are still revealed during inspections. Note, that depending on location of initial crack, the crack may propagate from the edge or from the surface. The theoretical model of fatigue crack progression is based on linear fracture mechanics. Steel specimens are subjected to various load (tension, three- and four-point bending, pure bending etc.). The calibration functions for short edge cracks are compared for various load and the discrepancies are discussed.
Effect of the load eccentricity on fracture behaviour of cementitious materials subjected to the modified compact tension test
Seitl, Stanislav ; Ríos, J. D. ; Cifuentes, H. ; Veselý, V.
Fracture properties of quasi-brittle cementitious composites are typically determined from the load–displacement response recorded during a fracture test by using the work-of-fracture method or possibly other relevant fracture models. Our contribution is focused on a set of experimental tests which are used to study the fracture behaviour on notched dog-bone-shaped specimens made of cementitious materials. These specimens are subjected to modified compact tension (ModCT) test under a specific range of eccentricity of the tensile load. This type of test generates a stress state in the specimen ligament which combines a direct tension with a defined level of bending due to eccentricity of the tensile load. Several values of relative notch length are also considered. While the crack propagates, a variety of stress states, resulting in variations in the crack-tip stress and deformation constraint, appears in the ligament zone because of the changes in the eccentricity of the applied load, which influences the fracture behaviour of the investigated specimens. The K-calibration, T-stress, CMOD and COD curves for ModCT specimens are introduced and variations of these curves with varying load eccentricity are discussed.
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.
Fracture Analysis of Cube- and Cylinder-shaped WST Specimens Made of Cementitious Composites with Various Characteristic Length
Řoutil, L. ; Veselý, V. ; Seitl, Stanislav
The paper is focused on finding reasonable proportions for both cube-shaped and cylinder-shaped silicate-based composite specimens subjected to wedge-splitting tests. The analysis is conducted using finite element method code with an implemented cohesive crack model. The aspect of the material's brittleness, related to the heterogeneity of the material and described by what is termed as the characteristic length of quasi-brittle material, is accented. The results yield some recommendations for the determination of parameters of nonlinear fracture models for cementitious composites by means of wedge splitting tests of laboratory specimens of the two standard shapes.
Fatigue damage prediction of short edge crack under various load: Direct Optimized Probabilistic Calculation
Krejsa, M. ; Seitl, Stanislav ; Brožovský, J. ; Lehnert, P.
Fatigue crack propagation depends on a number and value of stress range cycles. This is a time factor in the course of reliability for the entire designed service life. Three sizes are important for the characteristics of the propagation of fatigue cracks - initial size, detectable size and acceptable size. The theoretical model of a fatigue crack progression can be based on a linear elastic fracture mechanics (uses Paris-Erdogan law). Depending on location of an initial crack, the crack may propagate in structural element (e.g. from the edge or from the surface under various load) that could be described by calibration functions. When determining the required degree of reliability, it is possible to specify the time of the first inspection of the construction which will focus on the fatigue damage. Using a conditional probability and Bayesian approach, times for subsequent inspections can be determined based on the results of the previous inspection. For probabilistic modelling of a fatigue crack progression was used the original and a new probabilistic method - the Direct Optimized Probabilistic Calculation ('DOProC'), which uses a purely numerical approach without any simulation techniques or approximation approach based on optimized numerical integration. Compared to conventional simulation techniques is characterized by greater accuracy and efficiency of the computation.
A numerical investigation of the stress intensity factor for a bent chevron notched specimen: Comparison of 2D and 3D solutions
Seitl, Stanislav ; Miarka, Petr ; Sobek, J. ; Klusák, Jan
In the contribution, normalized stress intensity factors for three- and four-point bending specimens with a chevron notch is introduced by varying the chevron notch angle and length. The three- and two-dimensional models of bent chevron notched specimens in the software ANSYS were prepared by using possible symmetrical conditions. The 2D model was used with variable thicknesses of the layers representing the characteristic shape of the chevron notch (with the plane stress boundary condition). The numerically obtained results from the 2D and 3D solutions are compared with data from literature.
Effect of rivet holes on calibration curves for edge cracks under various loading types in steel bridge structure
Seitl, Stanislav ; Miarka, Petr ; Kala, Z. ; Klusák, Jan
Attention has been paid to fatigue cracks in steel structures and bridges for a long time. In spite of efforts to eliminate the creation and propagation of fatigue cracks throughout the designed service life, cracks are still revealed during inspections. There is some limitation of crack sizes which are detectable on structure (from 2 up to 10 mm). Note that depending on the location of the initial crack, the crack may dominantly propagate from the edge or from the surface. The theoretical model of fatigue crack progress is based on linear elastic fracture mechanics. Steel specimens are subjected to various load types (tension, three- and four-point bending, pure bending etc.). The calibration functions for short edge cracks that are near the hole for a rivet or bolt are compared for various loads and the discrepancies are discussed.
CORRECTION OF FATIGUE PARAMETER VALUES OF CONCRETE USING APPROXIMATION OF MECHANICAL-FRACTURE PARAMETER VALUES IN TIME
Simonová, H. ; Kersner, Z. ; Seitl, Stanislav
Selected approximation curves of mechanical-fracture parameter values modulus of elasticity, effective fracture toughness, specific fracture energy, compressive cube strength, splitting tensile strength, maximum load force in time are used to determine the most accurate fatigue parameter values corresponding to the age of specimens when dynamic tests were performed.
Numerical study of thin HPC overlay for orthotropic bridge deck
Miarka, Petr ; Šimonová, Hana (oponent) ; Novák, Drahomír (oponent) ; Seitl, Stanislav (vedoucí práce)
Diplomová práce porovnává tři různé betonové směsi pro celkové ztužení ortotropní mostovky a zkoumá jejich vliv na redukci napětí ve zvoleném svarovém přípoji. Práce uvažuje se standartní zatěžovací situaci mostu, ale také situaci s přetížením mostu. Byla také provedena parametrová studie různých materiálových modelů použitého betonu pro zachycení vlivu napětí ve svarovém přípoji.

Národní úložiště šedé literatury : Nalezeno 70 záznamů.   1 - 10dalšíkonec  přejít na záznam:
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