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Smyková pevnost písku při velmi malém normálovém zatížení
Hudek, J.; Koudelka, Petr
2014 - Czech
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.
Keywords:
shear strength; sand; low normal load
Fulltext is available at external website.
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 - English
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.
Keywords:
aluminium foam; high strain-rate compression; finite element modelling
Fulltext is available at external website.
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 - English
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.
Keywords:
surface; reflectance; photometry
Fulltext is available at external website.
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 ...
Post-critical multi-modal vibration of a continuous inverse pendulum type system
Náprstek, Jiří; Fischer, Cyril
2014 - English
Auto-parametric effects are processes endangering structures during a seismic attack. Tall structures exposed to a strong vertical component of an earthquake excitation nearby the epicenter can collapse due to auto-parametric resonance effect. Vertical and horizontal response components being independent in the linear regime get into a complex interaction due to non-linear terms in post-critical regime. Two generally different types of the post-critical regimes are presented: (i) post-critical state with possible recovery; (ii) exponentially rising horizontal response leading to a collapse. A special attention is paid to processes of transition from semi-trivial to post-critical state in case of time limited excitation period as it concerns the seismic processes. Solution method combining analytical and numerical approaches is developed and used. Its applicability and shortcomings are commented. A few hints for engineering applications are given.
Keywords:
auto-parametric systems; dynamic stability; semi-trivial solution; multi-modal vibration
Available in digital repository of the ASCR
Post-critical multi-modal vibration of a continuous inverse pendulum type system
Auto-parametric effects are processes endangering structures during a seismic attack. Tall structures exposed to a strong vertical component of an earthquake excitation nearby the epicenter can ...
Investigation of deformation behaviour of aluminium foam under high-strain rate loading and comparison with conventional energy absorbing material
Zlámal, P.; Fíla, Tomáš; Jiroušek, O.; Králík, V.
2014 - English
The aim of this study is proper description of stress-strain behaviour of the metal foam structure Alporas under high-strain rate loading. Stress-strain response of Alporas specimens is measured during an impact test using a drop tower experiment. Strain of the specimens is evaluated by two independent approaches: i) double numerical integration of acceleration data and ii) digital image correlation technique. Thus, experimental setup is equipped with triaxial accelerometer and high speed camera. Resulting stress-strain curves are compared with behaviour of polystyrene material samples (polystyrene material is commonly used as a shock absorber) obtained from the same testing procedure and with stress-strain function determined from Alporas quasi-static compression testing.
Keywords:
digital image correlation; impact test; polystyrene; metal foam
Fulltext is available at external website.
Investigation of deformation behaviour of aluminium foam under high-strain rate loading and comparison with conventional energy absorbing material
The aim of this study is proper description of stress-strain behaviour of the metal foam structure Alporas under high-strain rate loading. Stress-strain response of Alporas specimens is measured ...
Metody hodnocení důlkového korozního napadení
Kreislová, K.; Nováková, R.; Majtás, Dušan
2014 - Czech
Článek popisuje metody měření hloubky důlkového korozního napadení. Použití digitální mikroskopie je porovnáno se standardním metalografickým hodnocením výbrusu. The article describes methods for measuring the depth of pitting corrosion attack. Comparison of digital microscopy and common metallography on sample crossection is made.
Keywords:
pitting corrosion evaluation; 3D microscopy; depth of pits; aluminium
Available in digital repository of the ASCR
Metody hodnocení důlkového korozního napadení
Článek popisuje metody měření hloubky důlkového korozního napadení. Použití digitální mikroskopie je porovnáno se standardním metalografickým hodnocením výbrusu....
Determination of drift distortion in SEM micrographs acquired at different magnifications and acquisition times
Petráňová, Veronika; Koudelka_ml., Petr; Valach, Jaroslav
2014 - English
In the experimental mechanics wide variety of optical methods including measurement of deformation at reduced length scales using combination of computer vision and scanning electron microscopy (SEM) have been recently applied. One of suitable methods for in-plane measurement of displacements and deformations in the micrographs obtained by SEM is the 2D digital image correlation. In contrast to images obtained in visible spectrum by classical optical devices temporally-varying distortions known as drift distortion are present in the SEM micrographs. These distortions are caused by positional errors of electron beam during scanning process. Magnitude of this effect decreases with higher conductivity of the sample and is also influenced by magnification and scanning time. For this purpose measurement of distortion was performed on a series of micrographs of conductive samples acquired at different magnifications and acquisition times. Surface of each sample was covered with liquid silver to ensure adequate contrast pattern necessary for determination of distortion’s magnitude and distortion magnitudes were assessed.
Keywords:
scanning electron microscopy; digital image correlation; drift distortion
Fulltext is available at external website.
Determination of drift distortion in SEM micrographs acquired at different magnifications and acquisition times
In the experimental mechanics wide variety of optical methods including measurement of deformation at reduced length scales using combination of computer vision and scanning electron microscopy ...
Experimental study of tile grout material behavior
Kumpová, Ivana; Kloiber, Michal; Ševčík, Radek; Kytýř, Daniel
2014 - English
Study provides preliminary results of experimental study of tile grout material behavior. Experiments were performed with the use of microCT, three point bending test and methods for chemical analysis. It was proven that material behave very elastic and the suitability of the combination of used methods.
Keywords:
grout; three point bending test; microtomography; X-ray diffraction; FTIR
Fulltext is available at external website.
Experimental study of tile grout material behavior
Study provides preliminary results of experimental study of tile grout material behavior. Experiments were performed with the use of microCT, three point bending test and methods for chemical ...
Aeroelastic divergence modeled by means of the stochastic resonance
Náprstek, Jiří; Pospíšil, Stanislav
2014 - English
The divergence is one of the most important and dangerous phenomenon of aeroelastic post-critical states occurring at a prismatic slender beam in a cross-flow. This phenomenon manifests by stable periodic hopping between two nearly constant limits perturbed by random noises. Experimental observation and numerical simulation motivates an idea to model this process as the effect of the stochastic resonance. Being observed and practically used in a number of disciplines in physics (optics, plasma physics, atd.) its mathematical basis follows in the most simple case from properties of the Duffing equation with negative linear part of the stiffness. The occurrence of this phenomenon depends on certain combinations of input parameters, which can be determined theoretically and verified experimentally in the wind tunnel.
Keywords:
stochastic resonance; interwell hopping; non-linear vibration; aeroelastic divergence
Available in digital repository of the ASCR
Aeroelastic divergence modeled by means of the stochastic resonance
The divergence is one of the most important and dangerous phenomenon of aeroelastic post-critical states occurring at a prismatic slender beam in a cross-flow. This phenomenon manifests by stable ...
Influence of geometric parameters on the stiffness of traditional dovetail timber joint
Kunecký, Jiří; Cacciotti, Riccardo; Kloiber, Michal
2012 - English
The paper presents the development of numerical modeling for a traditional dovetail timber joint. The objective is to find the influence of its geometrical properties on the mechanical stiffness of the joint as well as to assess the main problems and limitations faced during the numerical modeling of the structure. An experiment with a replicated timber joint was used to validate the model. Material properties were ascertained and contact adjustment was made. Parametric study was performed: two angles of the joint beams were varied. Suitable ranges of the angles for each type of loading were found. Main limitations and problems present in the modeling are depicted in the discussion.
Keywords:
timber joint; numerical modeling; dovetail
Available in digital repository of the ASCR
Influence of geometric parameters on the stiffness of traditional dovetail timber joint
The paper presents the development of numerical modeling for a traditional dovetail timber joint. The objective is to find the influence of its geometrical properties on the mechanical stiffness of ...
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