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Kinetics of fatigue crack growth in Eurofer 97 steel
Kruml, Tomáš ; Hutař, Pavel ; Náhlík, Luboš ; Seitl, Stanislav ; Polák, Jaroslav
The fatigue crack growth rate in the Eurofer 97 steel was measured by two different methodologies. Small crack growth data were obtained using cylindrical specimens with a shallow notch. No artificial crack starters were used. The growth of semicircular cracks of length between 10 – 2000 m were measured in symmetrical tension-compression cycling with constant strain amplitude (R = -1). Long crack data were measured using standard CT specimen and ASTM methodology in stress control with R = 0.1. The growth of fatigue cracks with length in the range of 10 – 30 mm was determined. It is shown that the crack growth rate of both types of cracks are in a very good agreement if J-integral rep-resentation is used and reasonable assumptions of the crack closure effects are taken into account.
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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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Influence of vertical compresive force on level of constraint in cubical specimen for wedge splitting test
Seitl, Stanislav ; Klusák, Jan ; Dymáček, Petr ; Řoutil, L. ; Veselý, V.
The subject of the contribution is to gain new aspects of knowledge about the fracture behaviour of cementitious building materials by the wedge splitting test (WST). The particularly, the paper investigates the influence of the vertical compressive force Pv, that represents a reaction of the bottom support of the specimen, on the fracture parameters via tools of the two-parameter fracture mechanics. The effects of the vertical compressive force, Pv, on the plastic and fracture process zones are examined.
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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 properties of Eurofer steel developed for fusion application
Kuběna, Ivo ; Kruml, Tomáš ; Hutař, Pavel ; Náhlík, Luboš ; Seitl, Stanislav ; Polák, Jaroslav
In this study fatigue properties of Eurofer 97 steel in room temperatures were measured. Fatigue parameters of the cyclic stress - strain curve and fatigue life curves (Coffin-Manson curve and derived Wöhler curve) were evaluated. Major attention was given to the measurement of kinetics of fatigue crack growth by two different methods. The initiation sites of fatigue cracks and short crack growth were observed and measured on cylindrical specimens with shallow notch. These cracks had a length from 20 micrometers to 1 mm. Kinetics of growth of long cracks with the length 15-30 mm was measured on CT specimens. It was found that results obtained by the both methods are in a good agreement if the J-integral is used. It was possible to determine the threshold values of J-integral and stress intensity factor and to calculate the Paris law parameters.
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Vliv rohové singularity na tvar únavové trhliny
Hutař, Pavel ; Náhlík, Luboš ; Knésl, Zdeněk ; Seitl, Stanislav
Due to the existence of vertex singularity at the point where the crack intersects the free surface, stress distribution around the crack tip and the type of the singularity is changed. In the interior of the specimen the classical singular behaviour of the crack is dominant and can be described using generally known analytic equations. Contrary to this, at the free surface or in the boundary layer close to the free surface the vertex singularity is significant. The influence of vertex singularity on crack behaviour and crack shape for a three-dimensional structure is described in this paper. To estimate the influence of the free surface on fatigue crack growth rate the model of a general singular stress concentrator was applied. The estimated fatigue crack shape can help to provide a more reliable estimation of the fatigue life of the structures considered.
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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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