Materials Structure & Micromechanics of Fracture V

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Authors: Jakub Siegel, Petr Slepička, Vladimír Kotál, Miroslava Novotná, Olga Bláhová, Václav Švorčík
Abstract: Ablation, water etching and gold coating were studied on poly(ethyleneterephtalate) (PET) exposed to DC Ar plasma for 240 s at 8.3 W power. Au layers were sputtered on pristine and modified PET and their adhesion and topography were investigated. The roughness and changes of topography after plasma treatment, subsequent water etching and gold coating were followed using AFM microscopy. The thicknesses of ablated layer and water dissolved layer were determined using gravimetry. A nanoindentor was used to perform microstratch tests of sputtered layers. Water dissolving of thin layer after plasma treatment was confirmed by FTIR spectroscopy. We have found that under the present experimental conditions ca 30 nm thick layer of PET is plasma ablated. The surface topography changes dramatically and surface roughness increases. Another ca 16 nm thick layer was removed under present laboratory conditions after 24hour water etching. Subsequent coating with 50 nm thick gold layer increases surface roughness in all cases of surface modification.
Authors: Kateřina Kolářová, Nikola Kasálková, Barbora Dvořánková, Jiří Michálek, Václav Švorčík
Abstract: Polymer hydrogels have many different functions in the field of tissue engineering and medicine. Modification of 2-hydroxy-ethyl-methacrylate (HEMA) and 2-ethyl-oxy-ethylmethacrylate (EOEMA) by plasma treatment performed in Ar atmosphere at RT for 0-400 s was studied using different techniques. Sample ablation was determined by gravimetry, surface wettability and aging by goniometry, chemical structure by FTIR spectroscopy and surface morphology by AFM microscopy. The plasma modification changes the sample surface morphology. In vitro cultivation shows that the plasma treatment changes the proliferation of human LEP cells.
Authors: Nikola Kasálková, Kateřina Kolářová, Lucie Bačáková, Martin Pařízek, Anna Macková, Václav Švorčík
Abstract: The interaction of cells with polymers is important for their potential applications in medicine and various areas of biotechnology. Their physico-chemical surface properties strongly influence the cell morphology, adhesion and growth. Physical and chemical properties of pristine and modified polyethylene (PE) films were studied. PE was modified by Ar plasma (0–400 s, 2.0 W) and than grafted with amino acid (glycine). Structural and morphological changes of polymer were studied by goniometry and Rutherford back-scattering (RBS). The interaction of these samples with vascular smooth muscle cell (VSMC) from the rat aorta was studied. Number and morphology of the adhered and proliferated cell on the pristine and modified PE was studied in vitro method. It was found that wetting angle of the modified films decreased with exposure time. Experiments in vitro indicated that the adhesion and proliferation of VSMC is increasing function of degradation time and glycine grafting.
Authors: Simona Hutařová, Tomás Vlasák, Tomáš Podrábský, Jan Hakl, Martin Juliš
Abstract: High-temperature constructional parts of aircraft engines and energy units are exposed to high dynamic stress (fatigue processes and creep) and various temperatures in dioxide-corrosion condition (hot corrosion, oxidation and erosion). The improvement of aero-engine and turbine efficiency is possible through the increase of temperature in front of turbine. This requires the use of heat-resistant and creep-resistant materials, especially nickel-base superalloys which resist mentioned effects for a limited period of time. A deposition of protective layers should improve hot corrosion resistance. This paper is focused on microstructure of protective layers created by codeposition of Al and Si on nickel-base superalloys INCO 713 LC and INCO 738 LC after thermal and thermal-stress exposition and on microstructure of basic materials (substrates). The contribution also shows creep tests results for both superalloys with and without a protective layer.
Authors: Pavel Lejček, Jaromír Kopeček
Abstract: Well-characterised samples such as single crystals, bi-, tri- or multicrystals are needed for basic studies of properties of solids. Growth of such metallic structures by means of the floatingzone melting technique is demonstrated for iron base alloys, FeAl intermetallics and NiTi shape memory alloy.
Authors: Petr Ponížil, Ivan Saxl, Jaroslav Procházka
Abstract: In an analogy to the 3D tool of tessellation classification – w−s diagram, a similar graphical device is proposed for 2D tessellations. Any tessellation is represented by a point in the Cartesian coordinate system with the axes Ep (the mean cell perimeter) and CV a (the coefficient of cell area variation). Images of tessellations and p−CV a diagrams for selected tessellations with low and high values of CV a are shown as examples.
Authors: Jaroslav Procházka, Petr Ponížil, Ivan Saxl
Abstract: The estimation of grain size (volume) by using computer database of tessellations is explained and demonstrated. As model material was selected an anisotropic material formed by compression-moulded pellets of PVC. The pellets were first covered with carbon paste to highlight borders of grains in final specimen and then moulded; their volumes were exactly known. Standard profile and intercept counts were carried out on the planar sections of the specimen and used to estimate the grain size by means of computer database. The obtained estimates were then compared with the known pellet characteristics. The estimation of grain volume and of other suitable characteristics by inspection of section planes is necessary in opaque materials (e.g. metal alloys, crystalline polymers, ceramics), where their values are inaccessible by direct measurements. The aim of this work is show that the standard approaches can be improved with the help of a suitably prepared computer database.
Authors: Marina Davydova, Denis Davydov
Abstract: In the present work, the statistics of fragmentation is being studied in experiments with thin glass plates under uniformly distributed quasi-static loads. For this purpose the original pneumatic setup was manufactured. The glass plate is placed into a "sandwich" in order to fix the fragmentation pattern after unloading and to photograph it by a digital camera. A photoimaging and computer processing technique are used to assess the fragment areas and the total crack length.
Authors: Ludvík Kunz, Petr Lukáš, Rastilav Mintách
Abstract: The lifetime of superalloy single crystals CMSX-4 and CM186LC subjected to tensile mean stress with vibrations at high temperatures has been experimentally studied. Both beneficial and detrimental effect of cyclic stress component has been observed. An increase of lifetime due to superposition of cyclic component on the mean stress is explained by reduction of creep rate due to vibrations. The onset of decrease of lifetime with increasing stress amplitude is observed when the fatigue damage due to initiation and propagation of fatigue crack overbalances the beneficial influence of high frequency cycling.
Authors: Yoshimasa Takahashi, Hiroyuki Hirakata, Takayuki Kitamura
Abstract: The plasticity of a copper (Cu) nano-component is experimentally evaluated by a cantilever specimen with multi-layered structure. The cantilever is monotonically loaded by a diamond tip and the deflection at the free-end is precisely measured by a transmission electron microscope (TEM). The plastic deformation of the Cu nano-component is successfully monitored through the non-linear behavior of applied load, P, and cantilever deflection, δ. The plastic constitutive quation of the Cu component is inversely analyzed by finite element method (FEM) assuming that the component obeys the Ramberg-Osgood law. The parameters in the R-O law (σ0, n and α) are optimally fitted to reproduce the experimentally evaluated P-δ relation. The resultant parameter set is derived as (σ0, n, α) = (345 MPa, 3.2, 1.25). The Cu nano-component has a much higher yield stress and a hardening rate compared with the ones in a bulk Cu.

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