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Stanovení kritické hodnoty pro šíření trhliny z ostrého v-vrubu
Majer, Zdeněk ; Hutař, Pavel ; Náhlík, Luboš ; Knésl, Zdeněk
The aim of this paper is to investigate the beginnings of crack propagation from sharp V-notches. Stress distribution around the tip of a V-notch is described on the basis of linear-elastic fracture mechanics. The V-notch is a singular stress concentrator with a singularity exponent dependent on the V-notch opening angle. The stability criteria are generalized for a stress singularity different from 0,5. Using FEM analysis the critical stress for crack initiation was estimated as a function of the V-notch angle. The results of numerical calculations were compared with experiments taken from the literature.
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Vliv rohové singularity na chování trhliny
Hutař, Pavel ; Náhlík, Luboš
The influence of corner singularity on crack behaviour for a threedimensional structure is described in this paper. The distribution of stress singularity through the thickness of a specimen provides us with an indication of crack behaviour close to a free surface. A decrease in fatigue crack propagation rate in the area influenced by the free surface was carried out. The change of fatigue crack propagation rate in the boundary layer, leads to different intersecting angles between crack front and free surface as a function of Poisson’s ratio.
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Reologická charakterizace LDPE materiálů pomocí diferenciálních konstitučních rovnic
Pivokonský, Radek ; Zatloukal, M. ; Filip, Petr
For rheological description of branched LDPE melts (Escorene LD165BW1 a Bralen RB0323) the following differential constitutive equations were used: eXtended Pom-Pom, Phan Thien-Tanner-XPP, and modified Leonov models. There was carried out quantitative and qualitative comparison of efficiency of the predictions determined by these models with the experimental data measured at 200oC. For both materials there were measured linear viscoelastic properties, shear and uniaxial extensional viscosities.
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Empirický model zohledňující lokální extrém průběhu viskozity
Filip, Petr ; David, Jiří ; Pivokonský, Radek
Almost all empirical models dealing with the flow curves of non- Newtonian fluids can be applied only in the case of monotonous course of these curves. Exceptionally it is possible to model viscosity behaviour of rheologically more complex materials if there appears, in the course of a flow curve, a global extreme. The 8-parameter model proposed enables a description of viscosity behaviour in dependence on shear rate or shear stress also for the case when an extreme (maximum or minimum) is only local.
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Vliv intensity míchání na filtrační cykly při úpravě vody
Pivokonský, Martin ; Pivokonská, Lenka ; Švec, Martin
The aim of this contribution is to investigate aggregation efficiencies when high (G= 260 s-1) and low (G= 60 s-1) intensity agitation is applied for a treatment of surface water with high content of humic substances in a pilot size operation. It was established that high intensity agitation represented by a fluid layer of granular material (FLGM) can be more effective for an aggregation agitation than low intensity agitation with the help of the perforated baffles (PB). The FLGM improves performance of the filters because the filtration runs in the technological arrangement with FLGM took longer periods compared with low intensity agitation.
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Vliv gradientu rychlosti na morfologické vlastnosti aggregátů
Pivokonský, Martin ; Kysela, Bohuš ; Chára, Zdeněk
This paper summarises the preliminary results concerning an influence of the agitation conditions on the aggregation processes. The properties of formed aggregates affecting the efficiency of separation processes are studied as well. The results show that the applied velocity gradient G, the period of its action T and the distribution of velocity field in an agitated volume of water significantly influence the number of aggregates, their size and shape. Smaller and denser aggregates of a homogeneous size and more resistant to breakage are formed under a higher velocity gradient.
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Influence of Bi-material Interface on Crack Propagation Direction in Multilayer Composite
Šestáková, Lucie ; Náhlík, Luboš ; Hutař, Pavel
A substantial number of experimentally based works indicate the changes in crack propagation direction on bi-material interface in composite laminate materials. The paper is focused on estimation of crack propagation direction after its passage through the interface between two materials. For determination of the consequent propagation direction the minimal strain energy density criterion was employed. More accurate results were obtained by means of jointed numerical and analytical solution. The values of crack propagation directions obtained for layered composite were compared with experimental data.
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