Materials Structure & Micromechanics of Fracture

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Authors: O. Kubová, Lucie Bačáková, Václav Švorčík
Abstract: Polymers with modified surface structure are useful for medicine applications. This study is focused on the surface properties of polymers with carbon layers and their biocompatibility. For experiments was used polyethyleneterephtalate (PET). We used magnetron sputtering for producing of the carbon layers. Raman spectroscopy, goniometry, AFM – microscopy, X-ray diffraction and infrared spectroscopy were used in our experiments to describe the physicochemical properties of modified polymers. Biocompatibility of structure polymer-carbon layers was studied with method in vitro. We investigated adhesion of mouse 3T3-fibroblasts. The carbon layers have positive influence on biocompatibility.
Authors: Regina Mikulíková, Kateřina Kolářová, Lucie Bačáková, Václav Švorčík
Abstract: Physical and chemical properties of polyethylene (PE) films doped with calcium salt of oxycellulose (Ca-oxy) and its interaction with cells in culture conditions were studied. The samples with various concentrations of Ca-oxy (0-20 %) were prepared. Samples were tested by goniometer measurements, X-ray diffraction, FTIR spectroscopy and SEM. Sample weight changes during boil sterilization and adhesion and proliferation of tissue cells (3T3 mouse fibroblasts) were studied. It was found that wetting angle of the doped films decreased with increasing Ca-oxy concentration to up to 10% and then increased again. Both film surfaces had different amount of crystalline phase, thereby different surface roughness. Due to a smaller surface roughness, cell growth was much better on the inner surface of the film than on the outer one. Cells adhered better to samples with 1% of Ca-oxy and with a higher content of oxycellulose over 7%. Cell proliferation was the best on samples with 1-5% Ca-oxy. Samples were polished to modify their surface roughness. Polishing increased cell proliferation especially on samples with a lower Ca-oxy concentration (1-5%).
Authors: Gianni Nicoletto, Luca Collini, Radomila Konečná, P. Bujnová
Abstract: Fracture mechanisms of ferritic/pearlitic nodular cast iron are influenced by the heterogeneous matrix microstructure. This contribution is aimed at understanding the role of a heterogeneous matrix on the localization of damage due to mechanical loading. Therefore, bend specimens made of different nodular cast iron were plastically deformed and the degree of strain heterogeneity determined by comparison with a homogenized response. To address these observations elastic-plastic finite element models of local microstructures were developed. Computed strain maps are examined to understand the link between microstructural features and conditions for damage localization.
Authors: Hynek Lauschmann, Filip Šiška, Ivan Nedbal
Abstract: A new concept of counting time at fatigue processes is proposed, aimed to reach fractographic compatibility in cases of different loading sequences. Values of cycle effectivity are summarized to give the new reference time. The improvement is shown in application - textural fractography of three specimens loaded by constant cycle, constant cycle with periodic overloading, and a random block, respectively. In contrast to the conventional crack growth rate, the reference crack growth rate is related to common morphologic features of all fracture surfaces.
Authors: Karel Slámečka, Jaroslav Pokluda
Abstract: The paper deals with a profile analysis of the fracture surface generated by pure cyclic torsion. Roughness and fractal characteristics studied in two mutually perpendicular directions were found to be sensitive to the crack front position. The investigation of surface topography revealed the presence of the opening Mode I in all investigated crack front locations.
Authors: Petr Lukáš, Ludvík Kunz, Milan Svoboda, J. Čadek
Abstract: Creep behaviour of two types of superalloy single crystals of the orientation <001> was studied at 850 °C in air to assess their relative suitability for turbine blade applications: CMSX-4 and its potential low cost alternative, CM186LC. The chemical composition of these two superalloys is similar, their microstructure, especially g/g’ distribution, differs substantially. At the same applied stress, the time to failure of CM186LC is shorter than that of CMSX-4. Simultaneously, the creep rate of CM186LC is higher than that of CMSX-4 for the whole lifetime. This is attributed to easier activation of dislocation sources within large g’particles present in CM186LC crystals.
Authors: Hajo Dieringa, Amanda L. Bowles, Norbert Hort, Karl Ulrich Kainer
Authors: Vlastimil Vodárek, Gabriela Rožnovská, Jaromír Sobotka
Abstract: The long-term creep rupture tests have been carried out on three casts of a type AISI 316LN steel at 600 and 650°C. Two of the casts investigated contained additions of 0.1 and 0.3 wt.% of niobium. The growing niobium content strongly reduced the minimum creep rate and prolonged the time to the onset of the tertiary stage of creep and also shortened this stage. The enhanced creep resistance of niobium containing steels is not accompanied by the longer creep life that might have been expected. At both temperatures of creep exposure the niobium-bearing casts displayed an inferior creep ductility. Microstructural investigations revealed that niobium provoked significant grain size refinement and the formation of Z-phase. Particles of this phase were considerably dimensionally stable. Furthermore, niobium accelerated the formation and coarsening of s-phase, h-Laves and M6(C,N). The coarse intergranular particles facilitated the formation of cavities which resulted in intergranular failure mode.
Authors: Margarita Slámová, P. Sláma, Petr Homola, Miroslav Karlík
Abstract: Inner panels of modern ecological cars are nowadays manufactured from Al-Mg alloys. Continuously twin-roll cast sheets are a cost effective substitution for direct-chill cast sheets. The effect of composition and down-stream processing on sheet properties should be well understood in order to produce high quality products, which exhibit good formability and high strength. Finegrained microstructure and well-balanced texture are the necessary pre-requisites. Results of the investigation of twin-roll cast AlMg2Mn0.8 and AlMg3 alloys are reported. Sheets of 1.0 mm gauge were prepared using different processing routes. The route involving homogenisation results in grain coarsening and anisotropy, however, deep-drawing ability is affected only a little.
Authors: Kyohei Kawamoto, Y. Aoki, Yasuji Oda, Takeshi Yoshimura, Hiroshi Noguchi, Kenji Higashida
Abstract: In order to clarify the effects of hydrogen on the fatigue characteristics of an austenitic stainless steel, bending fatigue tests were conducted in air, in a hydrogen gas and in a nitrogen gas. Main results obtained are as follows. Effects of hydrogen gas environment are not clearly seen on the strain range - fatigue life diagram, because there are opposite effects to crack propagation and to crack initiation; accelerates crack propagation, but retards crack initiation. Striation spacing or in-situ observation confirms the acceleration. The retardation seems to be attributed to the absence of oxygen or water vapor in the hydrogen gas.

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