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Transient Vibration of Thin Rectangular Elastic and Viscoelastic Isotropic and Orthotropic Plate
Soukup, J. ; Trnka, Jan ; Valeš, František ; Volek, J.
The article is a part of the systematic analisys of assumption effects on the transient vibration of isotropic or orhotropic elastic and viscoelastic thin 2D plate. Several deformation models - according to Kirchhoff, Rayleigh, Flügge, Mindlin - were applied. The linear models of material rheologic properties were applied according to Hook, Voigt-Kelvin, Maxwell, Zener models. The results obtained by FEM methods and experiments are mutually compared.
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Determination of mechanical properties of thin films by nanocompresion
Kuběna, Ivo ; Hutař, Pavel ; Náhlík, Luboš ; Kruml, Tomáš
Measurements of mechanical properties of objects with micrometric (or even smaller) dimensions is still not a common task. In this paper, the possibility of evaluation basic mechanical properties of a thin film by nanocompression is demonstrated. Cylindrical specimens with the axis normal to the film plane, attached by the bottom to the substrate, are prepared by the focused ion beam technique. Such pillars are deformed by a nanoindenter outfitted by a flat diamond punch. An equivalent of compression curve is obtained. It is possible to measure directly parameters as the yield stress, stress at a chosen strain level or work hardening rate. Finite elements modelling is necessary for the Young modulus evaluation. It is shown that the Young modulus can be evaluated quite precisely, even if the geometry of the pillar is not perfect.
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Lomová analýza epoxido-hliníkových spojů vystavených teplotnímu a strukturnímu zatížení
Korbel, J. ; Klusák, Jan ; Knésl, Zdeněk
The paper presents a fracture mechanics approach to estimation of critical load (thermal or structural) of adhesive joints. Attention is focused on failure of test specimens prepared by gluing aluminum plates with a commercial thermosetting adhesive. Residual stresses caused by differences of thermal expansion of the adhesive and adherent are also examined. Classical fracture mechanics does not deal with behavior of a bi-material interface, and therefore an approach based on a generalized stress intensity factor and generalized fracture toughness is employed.
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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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Růst krátkých trhlin ve feriticko-perliticko-bainitické oceli
Polák, Jaroslav
The initiation and the growth of short cracks were studied in ferritic-pearlitic-bainitic steel. Short cracks initiate preferably in persistent slip markings in areas of proeutectoid ferrite. The kinetics of short crack growth is characterized by exponential growth. Crack growth coefficient was found to be a function of plastic strain amplitude. The comparison of the short crack growth kinetics with Coffin-Manson law allows determining the parameters of the short crack growth law from the low cycle fatigue experiments
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Limit žhavení pro vyhodnocení rychlosti pomocí CTA termoanemometru
Antoš, Pavel
Paper deals with the velocity measurement by means of the CTA. Hot-wire anemometry is based on the heat transfer from the hot wire to the fluid. Limit of overheating is dependent on the probe geometry. The use of generalized form of the Collis-Williams law for common probes at low overheats has been discussed in detail.
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Transition from the saltation mode of bed load transport to the rolling mode
Lukerchenko, Nikolay ; Ivanova, Irina ; Chára, Zdeněk ; Vlasák, Pavel
The paper deals with the sediment transport of sand particles conveyed by water in an open channel. A 3D numerical model developed by the authors was used for simulation of the sand particles movement in the channel with rough bed. Similarly to Shields theory of sediment transport incipient motion of the bed load particles the shear stress for the transition process from saltation mode to rolling mode can be defined. The shear stress value can be determined as a function of two dimensionless parameters, particle parameter and equivalent bed roughness. The particle parameter is a function of the particle size and density, and the carrier liquid density and viscosity. The presented numerical solution reveals that the shear stress for the transition process from saltation mode to rolling mode is less than the shear stress for the incipient sediment motion and depends on channel bed roughness.
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Flow behaviour of highly concentrated slurries
Vlasák, Pavel ; Chára, Zdeněk
The paper describes results of experimental investigation of the highly concentrated fine-grained slurry. The flow behaviour of the slurry was experimentally investigated for the laminar and turbulent regimes with respect to the effect of solid concentration and flow velocity. The re-circulation pipe loop with smooth stainless steel pipe of the inner diameter D = 17.5 mm was used. Stony dust from Mistrovice quarry (d50 = 8 μm, ρs = 2 701 kg/m3) was used as a solid phase, water was used as a carrier liquid. Volumetric concentration and slurry velocity reached up to 44% and 6 m/s, respectively.
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