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FE model termomechanické interakce pryžového bloku při cyklickém dynamickém zatížení
Pešek, Luděk ; Šulc, Petr
The COMSOL code based on weak formulation of PDE’s problem was used at a solution of feedback thermo-mechanical interaction in pre-pressed rubber block used for resilient elements of the composed tram wheels. The structural motion and heat conduction equations are solved interactively as time dependent problems. The equality of heat energy density and dissipation energy density realizes the coupling between the equations. The dissipation energy density is computed according to the assumed proportional damping model. In the paper the results of thermo-mechanical processes in cases of a plane strain and 3D space deformation under static pre-pressed and cyclic dynamic loading are presented and analyzed.
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Epitaxial rectrystalization of the Ni/MgO(001)interface
Vacík, Jiří ; Naramoto, H. ; Yamamoto, S. ; Narumi, K. ; Havránek, Vladimír
Process of recrystallization of the epitaxially grown Ni layer deposited on the MgO(001) single crystal is studied. Thin Ni layer prepared by the vapor deposition of Ni on the MgO substrate kept were annealed between 500 and 1000 0C and systematically analyzed by Rutherford backscattering, X-ray diffraction and atomic force microscopy. Dramatic change in evolution of the crystalline quality was observed during the thermal treatment. The strain and defect density gradually decreased and at the temperature 1000 0C the strain-free Ni/MgO(001) interface was obtained.
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CYCLIC PLASTICITY AND DISLOCATION SUBSTRUCTURE OF ferritic STAINLESS STEEL
Petrenec, Martin ; Polák, Jaroslav
The cyclic plastic response of polycrystalline ferritic stainless steel with b.c.c. structure is analysed in terms of the general statistical theory of the hysteresis loop and cycled in the magnetic field. Simultaneously, the internal dislocation substructure developed in the material during cyclic straining is studied using transmission electron microscopy and Kikuchi lines. The inhomogeneous distribution of dislocations into the persistent slip bands can be correlated with the localization of the cyclic plastic strain. The analysis of the loop shape by plotting the first and the second derivative of the half-loop allows determining the effective stress and the probability density function of the critical internal stresses. Extra peak of the second derivative of the half-loop was explained by the inverse magneto-elastic effect.
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Deformation Behaviour of Advenced Magnesium and Aluminium Alloys
Jäger, Aleš
Aluminum and magnesium alloys are often considered as promising materials due to high strength/density ratio. In general, light alloys are very attractive structural materials for applications where environmental protection or weight reduction play essential role. Therefore, it is of interest to investigate microstrucrure and its changes during plastic deformation because it helps to understand the nature of solute effect and processes taking place during plastic deformation. The aim of this work is to reveal microstructures, deformation characteristics and micromechanisms of plastic deformation at different strain rates and temperatures in selected light alloys. Two commercially available alloys were used in this work: AZ31 rolled magnesium alloy and AA6082 extruded aluminium alloy. These alloys were studied with the help of various experimental techniques such as tensile testing, light microscopy, electron backscatter diffraction (EBSD) and X-ray diffraction. Abstrakt Hlinikove a horcikove slitiny jsou povazovany za vysoce perspektivni materialy, protoze nabizeji velmi dobry pomer pevnosti k hustote. Tyto lehke slitiny nalezaji uplatneni pfedevsim v aplikacich, kde je kladen duraz na ochranu zivotniho prostredi a nebo snizeni hmotnosti. Detailni studium jejich mikrostruktury a deformacniho...
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Use of X-ray computed tomography for construction of FE models of bones
Jiroušek, Ondřej ; Jírová, Jitka ; Máca, J.
The article reports on procedures used for development of FE models of bones on basis of data obtained from series of computed tomography (CT) scans. These models include mechanical properties reflecting the bone inhomogeneity through apparent density which can be easily retrieved from the CT scans. Experimental procedures used for evaluation of mechanical properties of cancellous bone using small samples of cylindrical shape were designed in such a way, which allows for determination of the viscoelastic properties of cancellous bone. Both compressive and tensile specimens are tested while for the strain measurement an optical method utilizing CCD camera of high resolution is used. Relationship between the apparent density and mechanical properties of cancellous bone in a power-law form is proposed.
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Experimentální vyšetřování závislosti mezi mechanickými vlastnostmi spongiózní kosti a její relativní hustotou
Jiroušek, Ondřej ; Jírová, Jitka ; Jíra, J.
Finite element models of parts of human skeletal system are nowadays constructed on basis of data obtained from Computed Tomography or Magnetic Resonance images. Material properties of cancellous bone have been found to be strongly dependent on apparent density of the tissue. Experimental procedures used for evaluation of mechanical properties of cancellous bone using small samples of cylindrical shape will be described and relationship between the apparent density and Young's modulus of elasticity as well as ultimate strength are proposed. Compressive and tensile specimens are used while for the strains are measured using an optical method utilizing CCD camera of high resolution
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Lasery s tenkými InAs vrstvami v GaAs - absorpce a elektroluminiscence
Mačkal, Adam
Contribution presents the electroluminescence, photoabsorption and polarization properties of semiconductor lasers with thin strained InAs layers in GaAs at elevated temperature (above 25.sup.o./sup.C). The lasers exhibit high optical recombination efficiency, low threshold current density and wide temperature operation range
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