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Initiation of stable crack propagation of selected building composites
Majtánová, Romana Viktória ; Veselý, Václav (referee) ; Keršner, Zbyněk (advisor)
The purpose of my bachelor’s thesis is study of the effects of fibres in normal-weight concrete and light-weight concrete. Specimens were prepared from concrete with polypropylene fibres FORTA FERRO of three different lengths – 19, 38 and 54 mm – and also reference concrete (without fibres) was prepared. This thesis contains gradual evaluation of fracture tests on specimens from mentioned materials. The used fracture test was a three–point bending fracture test on beams with a central notch. From the measured load–deflection in the middle of span and load–crack mouth opening displacement diagrams were determined values of modulus of elasticity, unstable fracture toughness, initiation part of fracture toughness and also load level for beginning of stable crack propagation composites. For determination was used „double–K“ fracture model. For illustration is described evaluation using the effective crack model.
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Study of influence of input parameters for the numerical modeling of the compression test
Polách, Marek ; Keršner, Zbyněk (referee) ; Lehký, David (advisor)
The thesis analyses influence of input parametres of the 3D Non Linear Cementitious 2 material model for the numerical modeling of compression test performed in ATENA 2D and ATENA 3D software. The aim is to identify parametres with considerable influence and subsequently replicate the load-deflection curve obtained from laboratory compression test by numerical modeling. The effects of selected model and material model settings are studied on three kind of models in total. As tools for analyzing the effects, deterministic and statistic sensitivity analyses were chosen. Parametres with significant influence will be highlighted and added to the group of parametres obtained from numerical modeling of three-point bending test. This will create a set of parametres of considerable influence when it comes to modeling advanced structures with different types of stresses.
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Probabilistic description of the S–N field of concrete using Weibull and Gumbel fatigue software
Przybilla, C. ; Seitl, Stanislav ; Keršner, Z. ; Canteli, A.
While the problem of deciding which statistical model is the “true one” in fatigue studies has occupied investigators for many years, only the analysis of the lower tail of the fatigue lifetime distribution, i.e. the distribution of minima values, is relevant for design purposes. Accordingly, in this work a probabilistic fatigue model for analysis of the S–N field is suggested after justification of Weibull or Gumbel domains of attraction, and the consequences of its extension to other cases are discussed. Finally, the ProFatigue software is applied for assessment of selected concrete fatigue data.
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Únavové parametry betonu pro předepjaté vzorky
Seitl, Stanislav ; Juřinová, E. ; Keršner, Z. ; Bílek, V.
The paper presents values of basic fatigue parameters measured on three-point bending specimens of concrete for pre-stressed elements. These specimens are the most frequently used for fracture laboratory testing, especially of quasi-brittle cement-based composites. According to the regression technique, pilot Wöhler curve for predicting the fatigue life of pres-stressed concrete element is suggested. Keywords of the paper are fatigue/fracture parameters and cement-based composite
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Influence of stress concentrator geometry on fracture parameters values of quasi-brittle materials
Frantík, P. ; Keršner, Z. ; Klusák, Jan ; Řoutil, L. ; Seitl, Stanislav ; Veselý, V.
To assess the reliability of building structures, values of fracture mechanical properties of their materials have to be known. In the case of cement-based composite types the basic parameters are ascertained on the basis of evaluation of the response of specimens conducted to a test in a suitable testing configuration. Three-point bending specimens with a central starting notch are the most frequently used specimens for laboratory testing. The influence of the stress concentrator – starting central edge notch – in a three point bend specimen on the resulting values of fracture toughness was studied in author’s papers: a crack initiation at the notch tip was numerically simulated. It was shown that the values of fracture toughness obtained for specimens with larger widths of starting notch can be overestimated.
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Únavové parametry vybraných vlaknových compozitůpři tříbodovém testu
Seitl, Stanislav ; Keršner, Z. ; Bílek, V.
The paper presents the influence of the various concrete mixtures on fatigue parameters measured on three-point bending specimens. These specimens are the most frequently used for fracture laboratory testing, especially of quasibrittle cement-based composites. From the test results, the effects of the fibre type and the fibre content on concrete fatigue behaviour are studied. According to the regression technique, Wöhler curve for predicting the fatigue life of each concrete mixture are suggested. Keywords of the paper are fatigue/fracture parameters and fibre reinforced cement-based composites.
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Fatigue parameters of cement based composited: measuring and modeling
Keršner, Z. ; Seitl, Stanislav ; Pukl, R.
This paper introduces the basic fracture mechanics parameters of advanced building materials –selected glass fibers reinforced cement based composites and their fracture and fatigue behavior is investigated. Specimens tested were prepared as high performance concrete/mortar developed by ZPSV, a.s. company for production of thin-walled panels/elements. The dosage of cement CEM I 42.5R Mokra was 1000 kg per m3 of fresh mixture, water to cement ratio was 0.28, superplasticizer Spolostan; sand aggregates of 4 mm maximum size were used. . Alkali-resistant glass fibers (glass with high content of zirconium oxide) are applied with a dosage of 5 kg per m3. The introductory study was introduced by the authors, the study is performing in matter of the project Basic fatigue characteristic and fracture of advanced building materials.
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