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O navrhování v geotechnice podle residuální smykové pevnosti
Koudelka, Petr
2015 - český
Příspěvek hodnotí možnosti a efektivitu nové koncepce navrhování na základě reziduální smykové pevnosti. Koncepce návrhů podle reziduální nebo kritické smykové pevnosti není vyzkoušená. K tomu, aby mohla být vyzkoušena a používána, je třeba znalost hodnot residuální smykové pevnosti. V současné době se residuální ani kritické hodnoty v běžné praxi téměř nevyšetřují, i když\njejich znalost může přispět ke spolehlivosti a hospodárnosti návrhů a všeobecně jsou\nprojekčním přínosem. Při návrhu svahů podle residuálních hodnot smykové pevnost, které jsou nejspolehlivější, bude možné stupeň bezpečnosti/součinitele odporu podstatně snížit oproti jeho hodnotám používaným při uvažování vrcholových/efektivních hodnotách. Doporučení jsou součástí tohoto příspěvku. The paper consider on possibility and effectivity of a new concept of ULS design on residual shear strength based. Values of residual shear strength are the most reliable and in opposite, applied peak values of shear strength are the most favorable and applicable for states of small deformations only. The paper presents results of a prior analysis of slope stability and compares designs applying values of residual shear strength and peak shear strength. Some recommendations are included.
Klíčová slova:
residual shear strength; slope stability; peak shear strength
Dokument je dostupný na externích webových stránkách.
O navrhování v geotechnice podle residuální smykové pevnosti
Příspěvek hodnotí možnosti a efektivitu nové koncepce navrhování na základě reziduální smykové pevnosti. Koncepce návrhů podle reziduální nebo kritické smykové pevnosti není vyzkoušená. K tomu, aby ...
Numerical modelling of a bridge subjected to simultaneous effect of a moving load and a vertical seismic ground excitation
Fischer, Cyril; Fischer, Ondřej; Frýba, Ladislav
2015 - anglický
A simple beam subjected to a row of regularly distributed moving forces and simultaneous vertical motions of its supports is described using a simplied theoretical model and a nite dierences approach. Several levels of simplication of the structure and input data are supposed. Numerical results conrm legitimacy of the assumptions.
Klíčová slova:
numerical modelling; seismic excitation; moving load
Plné texty jsou dostupné v digitálním repozitáři Akademie Věd.
Numerical modelling of a bridge subjected to simultaneous effect of a moving load and a vertical seismic ground excitation
A simple beam subjected to a row of regularly distributed moving forces and simultaneous vertical motions of its supports is described using a simplied theoretical model and a nite dierences ...
Changes in dislocation substructure of S235JR steel during fatigue loading
Jandová, D.; Gajdoš, Lubomír; Šperl, Martin; Kaiser, J.
2014 - anglický
Changes in dislocation substructure were studied in normalized and annealed S235JR steel in relation to the number of symmetrical reversed stress cycles with the amplitude σa = 242 MPa and corresponding mean life Nf = 17,950 cycles. The microstructure of the steel consisted of ferrite with a small amount of pearlite. The substructure was observed in as received condition and after application of various relative numbers of cycles n/Nf, these being 0.25, 0.50 and 0.75. An irregular dislocation net occurred in the virgin specimen, however, during cyclic loading the dislocations started to accumulate gradually in slip bands and to form a cell substructure in grains of favourable crystallographic orientations. Total dislocation density, dislocation density in slip bands and inter-band distance were measured using transmission electron microscopy (TEM). The total dislocation density was found to slightly decrease and the density in slip bands to increase with increasing number of cycles. The results concerning the dislocation density were compared with changes in the microplastic limit (MPL) which were determined by the measurement of the inductance of the “specimen - coil” system. They consisted in a rapid initial decrease at the first stage of the fatigue process and in a gradual increase during the major part of the life. These changes can be interpreted on the basis of changes in dislocation density as was verified independently by X-ray diffraction and nanoindentation tests. On the basis of the measurement of dislocation density by TEM it appears that changes in MPL can be connected with the dislocation density in slip bands rather than with the total dislocation density.
Klíčová slova:
carbon steel; cyclic loading; transmission electron microscopy; dislocation; inductance
Dokument je dostupný na externích webových stránkách.
Changes in dislocation substructure of S235JR steel during fatigue loading
Changes in dislocation substructure were studied in normalized and annealed S235JR steel in relation to the number of symmetrical reversed stress cycles with the amplitude σa = 242 MPa and ...
Assessment of damage propagation in carbon-fibre composite under cyclic loading
Šleichrt, J.; Fíla, T.; Šperl, Martin; Kytýř, Daniel
2014 - anglický
Carbon-fibre composite is very popular material in aircraft industry. Application of this material is limited by low fragility and low impact resistance. In flight airplane can be initialy damaged by hailstorm or bird strikes. Vibrations of the engine and turbulence during flight may cause propagation of this damage. This study describes the of laser profilometry to investigate post damage under cycling loading.
Klíčová slova:
carbon-fibre composite; damage propagation; laser profilometry
Dokument je dostupný na externích webových stránkách.
Assessment of damage propagation in carbon-fibre composite under cyclic loading
Carbon-fibre composite is very popular material in aircraft industry. Application of this material is limited by low fragility and low impact resistance. In flight airplane can be initialy damaged ...
On the X-ray micro-tomography measurements of biological samples under compressive loading
Fíla, T.; Kumpová, Ivana; Zlámal, Petr; Kytýř, Daniel; Koudelka_ml., Petr; Doktor, Tomáš; Jiroušek, Ondřej
2014 - anglický
In this paper, compact loading device for micro-CT measurements under applied load was used in a series of instrumented compressive test of bone sample. Tested bone samples were loaded in several deformation steps and micro-CT scanning was carried out in each step. Reconstructed three-dimensional data of intact bone sample were used to develop 3D model of the specimen. Data from each deformation step were processed by DVC method for identification of displacement and strain fields and thus for evaluation of deformation response of human trabecular bone sample.
Klíčová slova:
micro-tomography; trabecular bone; compressive test; medical imaging; finite element modelling
Dokument je dostupný na externích webových stránkách.
On the X-ray micro-tomography measurements of biological samples under compressive loading
In this paper, compact loading device for micro-CT measurements under applied load was used in a series of instrumented compressive test of bone sample. Tested bone samples were loaded in several ...
Calibration of an image processing tool for analysis of fibre orientation in fibre reinforced composites
Hos, J.; Doktor, T.; Petráňová, Veronika; Kytýř, Daniel
2014 - anglický
This paper deals with calculation of fibre orientation distribution (FOD) in fibre reinforced composite. The calculation was based on image analysis algorithm applied on image acquired by scanning electron microscope. A composite with oriented fibres was selected to be enable calibration of the algorithm by comparison of the obtained results with FOD declared by the manufacturer.
Klíčová slova:
C/PPS; fibre orientation; SEM; composite
Dokument je dostupný na externích webových stránkách.
Calibration of an image processing tool for analysis of fibre orientation in fibre reinforced composites
This paper deals with calculation of fibre orientation distribution (FOD) in fibre reinforced composite. The calculation was based on image analysis algorithm applied on image acquired by scanning ...
New devices for diagnostics of historical structures
Hasníková, Hana; Kloiber, Michal; Zíma, Pavel
2014 - anglický
Two new devices developed at ITAM AS CR for non-destructive testing of materials, especially from historical structures, are presented below. So called microtube is a semi-automatic portable tool for water absorption measurements. The natural stones, mortars and other porous materials can be measured and it is very useful to assess the efficiency of various hydrophobic treatments used within the restoration also. The diagnostic device for in-situ assessment of timber enables direct determination of conventional compressive strength and modulus of deformation in arbitrary depth along timber profile. The semi-destructive method causes a very gentle damage on the structural members.
Klíčová slova:
historical structures; water absorption measurement; timber assessment
Dokument je dostupný na externích webových stránkách.
New devices for diagnostics of historical structures
Two new devices developed at ITAM AS CR for non-destructive testing of materials, especially from historical structures, are presented below. So called microtube is a semi-automatic portable tool for ...
Smyková pevnost písku při velmi malém normálovém zatížení
Hudek, J.; Koudelka, Petr
2014 - český
Příspěvek se zabývá výsledky smykových zkoušek velni suchého (ideálně nesoudržného) křemičitého písku střední zrnitosti při velmi malém normálovém zatížení ve škále do 25 kPa. Výsledky srovnává se smykovými zkouškami stejného materiálu ve škále 63 – 163 kPa. Solutions of some extraordinary geotechnical problems need knowledge of shear strength in a scale of very low normal stress. An example is physical modelling of soil mass behaviour using medium or little samples. The paper deals with results of testing a very dry uniform quartz sand of medium size. Resulting values of effective shear strength for the normal stress scale till of 25 kPa are compared with former testing of the same material in other scale of 63 – 163 kPa.
Klíčová slova:
shear strength; sand; low normal load
Dokument je dostupný na externích webových stránkách.
Smyková pevnost písku při velmi malém normálovém zatížení
Příspěvek se zabývá výsledky smykových zkoušek velni suchého (ideálně nesoudržného) křemičitého písku střední zrnitosti při velmi malém normálovém zatížení ve škále do 25 kPa. Výsledky srovnává se ...
On the modelling of compressive response of closed-cell aluminium foams under high-strain rate loading
Koudelka_ml., P.; Zlámal, Petr; Fíla, Tomáš
2014 - anglický
Porous metals and particularly aluminium foams are attractive materials for crash applications where constructional elements have to be able to absorb considerable amount of deformation energy while having as low weight as possible. Compressive behaviour for medium impact velocities can be experimentally assessed from a series of droptower impact tests instrumented with accelerometer and high-speed camera. However to predict such behaviour a proper modelling scheme has to be developed. In this paper droptower impact tests of Alporas aluminium foam were used for development of a material model for explicit finite element simulations of high-strain rate deformation process using LS-DYNA simulation environment. From the material models available low density foam, Fu-Chang’s foam, crushable foam and modified crushable foam models were selected for simulations using smoothed-particle hydrodynamics and solid formulations respectively. Numerical simulations were performed in order to assess constitutive parameters of these models and identify material model describing deformation behaviour of Alporas with the best accuracy.
Klíčová slova:
aluminium foam; high strain-rate compression; finite element modelling
Dokument je dostupný na externích webových stránkách.
On the modelling of compressive response of closed-cell aluminium foams under high-strain rate loading
Porous metals and particularly aluminium foams are attractive materials for crash applications where constructional elements have to be able to absorb considerable amount of deformation energy while ...
Semiautomatic Surface Reflectance Measurement for Monitoring of Material Weathering
Kocour, Vladimír; Valach, Jaroslav
2014 - anglický
We present a device for measurement of surface reflectance in dependence on incidence angle and reflectance angle. This measurement enables us to quantitatively determine how much the surface is glossy or matt. The device is programmable, which enables us to choose non-equidistant steps of angles, and study special situations more in detail. It can be used for monitoring of material weathering or other types of degradation as weathering usually causes that the surface becomes more matt.
Klíčová slova:
surface; reflectance; photometry
Dokument je dostupný na externích webových stránkách.
Semiautomatic Surface Reflectance Measurement for Monitoring of Material Weathering
We present a device for measurement of surface reflectance in dependence on incidence angle and reflectance angle. This measurement enables us to quantitatively determine how much the surface is ...
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