National Repository of Grey Literature 69 records found  beginprevious56 - 65next  jump to record: Search took 0.01 seconds. 
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.
Velikost lomové procesní zóny a disipační energie během šíření trhliny v kvazi křehkém materiálu
Řoutil, L. ; Veselý, V. ; Keršner, Z. ; Seitl, Stanislav ; Knésl, Zdeněk
The paper presents a numerical analysis of fracture processes in testing specimen configurations with substantially different crack tip stress constraint levels. Specimens of several sizes and relative notch lengths are taken into account. The features of the distribution of current/cumulative value of fracture energy along the specimen ligament are discussed and related to estimations of fracture process zone (FPZ) size and shape, in which the energy is dissipated. Significant effect of the stress constraint on the size/shape of the FPZ, and consequently the energy dissipated within it, is reported.
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.
Aspects of fatigue and fracture of advanced building materials
Keršner, Z. ; Veselý, V. ; Seitl, Stanislav ; Pukl, R.
The paper is focused on ideas about subject-matter of the project Basic fatigue characteristic and fracture of advanced building materials. The effort of this grant is to gain new pieces of knowledge about behaviour of advanced building materials through the effective application of till this time not used methods of complex determining of physical-mechanical and performance qualities. These are predetermined to describe fatigue, fracture and microstructural characteristics. Mentioned qualities will be modelled on the level of continuum/multiphase composite. There is presumption that will be gained results describing fatigue behaviour of studied materials, especially for application in construction with demands for high durability, it is necessary to follow initiation and propagation of microcracks complexly.
Vliv šířky zářezu na lomovou odezvu ohýbaných betonových vzorků
Veselý, V. ; Keršner, Z. ; Seitl, Stanislav ; Klusák, Jan
An influence of the test specimen’s preparation – shape and width of a stress concentrator – on the values of parameters of nonlinear fracture models of quasi-brittle cement-based composites is analyses in the paper presented. The parameters – e.g. effective crack extension, effective fracture toughness, and specific fracture energy – can be calculated from results of loading tests performed on notched three point bend specimens. The effects are investigated by means of a comparison of numerically simulated fracture process in the cracked specimen with the specimens with the double V-notch. The numerical simulations of the fracture according to the linear elastic fracture mechanics were performed by using finite element method programs (ANSYS, and FRANC2D). The influence on the load-carrying capacity and the initial compliance of the cracked specimen are introduced and discussed.
Influence of notch width and length on crack initiation in 3PB specimens
Seitl, Stanislav ; Klusák, Jan ; Keršner, Z.
The paper presents the influence of the various notch depths for the range of starting notch width on a crack initiation in three-point bending specimens. These specimens are the most frequently used for fracture laboratory testing, especially of quasi-brittle cement-based composites. It is shown that the values of fracture toughness obtained from the tests of specimens with larger widths with various length of the starting notch can be overestimated.
Evaluation of notch geometry effect on behaviour of fracture toughness testing specimen
Seitl, Stanislav ; Klusák, Jan ; Keršner, Z. ; Knésl, Zdeněk
The basic fracture properties of cement-based composite are ascertained on the basis of test evaluations of the specimens in suitable test configurations. Three-point bending specimens with a central starting notch are the most frequently used specimen for laboratory testing. Through models of equivalent elastic cracks the critical crack length and effective fracture toughness (or toughness) can be calculated. The influence of the geometry of the starting notch in a three-point bend specimen on the resulting values of critical applied force and fracture toughness is studied in this paper. To this end, a crack initiation at the notch tip is numerically simulated. It is shown that the values of fracture toughness obtained for specimens with larger widths of starting notch can be overestimated.
Fracture toughness of quasi-brittle specimens using three-point bending test: Correction with respect to notch width
Frantík, P. ; Keršner, Z. ; Klusák, Jan ; Seitl, Stanislav
The paper introduce the influence of the starting notch width on a crack growth in three-point bending specimens that are the most frequently used specimens for fracture laboratory testing, especially of quasi-brittle cement-based composites. There are analyses of three geometrically different configurations of the specimens. It is shown that the values of fracture toughness obtained from the tests of specimens with larger widths of the starting notch can be overestimated. Correction functions for selected testing configurations are presented.
Influence of interfacial transition zone of cement paste-aggregate on crack propagation: finite element modelling
Keršner, Z. ; Náhlík, Luboš ; Knésl, Zdeněk
Concrete is represented as a three-phase material in this paper. Behaviour of a single macrocrack approaching to the interface between hardened cement paste (matrix) and aggregate (particle) is modelled and interfacial transition zone is taken into account. Results of these analyses are useful for description of fracture behaviour of macrocrack propagation with respect to material parameters of matrix, interfacial transition zone and particle. FEM is used in this study.
INFLUENCE OF DEGRADATION OF HARDENED CEMENT PASTE ON FRACTURE BEHAVIOUR OF CONCRETE
Náhlík, Luboš ; Keršner, Z. ; Knésl, Zdeněk
Fracture behaviour of concrete is studied using two-phase material model. Propagation of a single macrocrack in hardened cement paste (matrix) and aggregate (particle) is modelled. Influence of carbonation of matrix on crack propagation in composite is assessed and discussed in this paper: degradation of hardened cement paste is important aspect of fracture behaviour of concrete.

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