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Estimation of Anisotropy of Creep Properties in Al and Mg Alloys by Means of Small Punch Test
Dobeš, Ferdinand; Dymáček, Petr
2017 - anglický
Small punch test was used to determine the properties of light alloys and composites in various directions. Three different materials were studied:\n(i) magnesium alloy WE54 prepared by a powder metallurgical route with final hot extrusion,\n(ii) aluminium alloy reinforced with 20 vol. % of Saffil fibres with planar orientation, and\n(iii) Al-Al4C3 composite prepared by mechanical alloying and subjected to equal channel angularpressing as a final step.\nSmall punch tests were performed under constant force at elevated temperatures. The observed orientation dependence of creep properties is strongly material dependent. The results confirm the feasibility of the small punch test for determination of anisotropy of mechanical properties.
Klíčová slova:
creep; small punch test; aluminium composite
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Estimation of Anisotropy of Creep Properties in Al and Mg Alloys by Means of Small Punch Test
Small punch test was used to determine the properties of light alloys and composites in various directions. Three different materials were studied:\n(i) magnesium alloy WE54 prepared by a powder ...
High cycle fatigue life of Ti6Al4V alloy produced by direct metal laser sintering
Konečná, R.; Nicoletto, G.; Bača, A.; Kunz, Ludvík
2017 - anglický
High cycle fatigue life of Ti6Al4V alloy specimens manufactured by Direct Metal Laser Sintering (DMLS) was experimentally determined. The DMLS fabrication process was characterized by a 400 W laser power and 50 micrometer layer melted thickness. Post-fabrication heat treatment consisted in stress relieving for 3 h at 720 °C in vacuum with subsequent cooling in argon atmosphere. Fatigue testing of specimens oriented in three different directions with respect to the material build direction was performed with the aim to examine the influence of the layered microstructure on the fatigue behavior. Results of measurement of surface roughness, metallographic examinations of the layered material and fractographic investigation of the fatigue fracture surfaces were employed in the discussion of fatigue crack initiation in DMLS fabricated Ti6Al4V alloy.
Klíčová slova:
Additive Manufacturing; Fatigue Life; Laser Powder Melting; Titanium Alloy
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
High cycle fatigue life of Ti6Al4V alloy produced by direct metal laser sintering
High cycle fatigue life of Ti6Al4V alloy specimens manufactured by Direct Metal Laser Sintering (DMLS) was experimentally determined. The DMLS fabrication process was characterized by a 400 W laser ...
Assessment of Crack Stability in a Quasi-brittle Particle Composite
Malíková, Lucie; Klusák, Jan; Keršner, Z.
2017 - anglický
Fracture behaviour of a crack in a particle (silicate based) composite is studied. The crack propagation depends not only on mutual elastic mismatch of matrix and aggregate but also the influence of the interfacial transition zone (ITZ) between the matrix and the aggregate is discussed. Various combinations of materials and geometry of matrix, aggregate and ITZ can improve or degrade fracture properties of the composite. Extensive numerical simulations on a basic 3-point-bending cracked specimen via the finite element method are performed in order to analyze the stress field near the crack tip. Linear elastic fracture mechanics approach is utilized in order to assess the crack stability and summarize several conclusions.
Klíčová slova:
Stress intensity factor; Particle composite; Interfacial transition zone; Crack stability
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Assessment of Crack Stability in a Quasi-brittle Particle Composite
Fracture behaviour of a crack in a particle (silicate based) composite is studied. The crack propagation depends not only on mutual elastic mismatch of matrix and aggregate but also the influence of ...
W-B-C Nanostructured Layers - Microstructure and Mechanical Properties
Buršík, Jiří; Kuběna, Ivo; Buršíková, V.; Souček, P.; Zábranský, L.; Mirzaei, S.; Vašina, P.
2017 - anglický
Several W-B-C layers were prepared by magnetron sputtering. The microstructure of thin layers was observed by means of scanning and transmission electron microscopy on cross sections prepared using a focused ion beam. Both undisturbed layers and the volume under indentation prints were inspected.
Klíčová slova:
coating; nanostructure; electron microscopy
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
W-B-C Nanostructured Layers - Microstructure and Mechanical Properties
Several W-B-C layers were prepared by magnetron sputtering. The microstructure of thin layers was observed by means of scanning and transmission electron microscopy on cross sections prepared using a ...
Spin-dependent electrical transport at finite temperatures from the first principles
Wagenknecht, David; Carva, K.; Turek, Ilja
2017 - anglický
A theoretical method for finite-temperature electronic transport properties of metallic systems is presented. The developed formalism is applied to pure platinum and to random Cu-Ni alloys.
Klíčová slova:
elektrical transport; finite temperature; ferromagnetic alloys
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Spin-dependent electrical transport at finite temperatures from the first principles
A theoretical method for finite-temperature electronic transport properties of metallic systems is presented. The developed formalism is applied to pure platinum and to random Cu-Ni alloys.
Quantum-mechanical study of tensorial elastic and high-temperature thermodynamic properties of grain boundary states in superalloy-phase Ni3Al
Friák, Martin; Všianská, Monika; Holec, D.; Šob, Mojmír
2017 - anglický
Grain boundaries (GBs), the most important defects in solids and their properties are crucial for many materials properties including (in-)stability. Quantum-mechanical methods can reliably compute properties of GBs and we use them to analyze (tensorial) anisotropic elastic properties of interface states associated with GBs in one of the most important intermetallic compounds for industrial applications, Ni3Al. Selecting the Sigma 5(210) GBs as a case study because of its significant extra volume, we address the mechanical stability of the GB interface states by checking elasticity-based Born stability criteria. One critically important elastic constant, C 55, is found nearly three times smaller at the GB compared with the bulk, contributing thus to the reduction of the mechanical stability of Ni3Al polycrystals. Next, comparing properties of Sigma 5(210) GB state which is fully relaxed with those of a Sigma 5(210) GB state when the supercell dimensions are kept equal to those in the bulk we conclude that lateral relaxations have only marginal impact on the studied properties. Having the complete elastic tensor of Sigma 5(210) GB states we combine Green's-function based homogenization techniques and an approximative approach to the Debye model to compare thermodynamic properties of a perfect Ni3Al bulk and the Sigma 5(210) GB states. In particular, significant reduction of the melting temperature (to 79-81% of the bulk value) is predicted for nanometer-size grains.
Klíčová slova:
Anisotropic elastic properties; Defects in solids; Elastic tensors
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Quantum-mechanical study of tensorial elastic and high-temperature thermodynamic properties of grain boundary states in superalloy-phase Ni3Al
Grain boundaries (GBs), the most important defects in solids and their properties are crucial for many materials properties including (in-)stability. Quantum-mechanical methods can reliably compute ...
Comparison of calibration functions for short edge cracks under selected loads
Seitl, Stanislav; Miarka, Petr; Malíková, Lucie; Krejsa, M.
2017 - anglický
Attention to the fatigue cracks in steel structures and bridges has been paid for long time. In spite to efforts to eliminate the creation and propagation of fatigue cracks throughout the designed service life, cracks are still revealed during inspections. Note, that depending on location of initial crack, the crack may propagate from the edge or from the surface. The theoretical model of fatigue crack progression is based on linear fracture mechanics. Steel specimens are subjected to various load (tension, three- and four-point bending, pure bending etc.). The calibration functions for short edge cracks are compared for various load and the discrepancies are discussed.
Klíčová slova:
Calibration curve; Edge crack; Fracture mechanics; Paris-erdogan law; Stress intensity factors
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Comparison of calibration functions for short edge cracks under selected loads
Attention to the fatigue cracks in steel structures and bridges has been paid for long time. In spite to efforts to eliminate the creation and propagation of fatigue cracks throughout the designed ...
Fatigue crack initiation and growth in 316L steel in torsional cyclic loading
Karol, Michal; Chlupová, Alice; Mazánová, Veronika; Kruml, Tomáš
2017 - anglický
Fatigue crack initiation and growth study in 316L austenitic stainless steel was made in cyclic\ntorsion. The experiments on hollow cylindrical specimens were performed at room temperature using fully reversed shear strain controlled cycles. The specimens used were polished mechanically and electrolytically to enable surface damage and crack propagation observation using optical light microscope, SEM. It was found that high density of extrusions and intrusions are formed on the specimen surface due to cyclic loading. TEM observations revealed that dislocation arrangement in well-known ladder-like structure is responsible for the localization of cyclic plastic deformation and for the origin of surface roughness in which the fatigue crack nucleate. The path of fatigue cracks leading to failure was observed, too. The crack path\nwas found to be dependent upon the applied shear strain amplitude.
Klíčová slova:
316L austenitic steel; fatigue crack initiation; Crack growth; Torsional loading; Crack path
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Fatigue crack initiation and growth in 316L steel in torsional cyclic loading
Fatigue crack initiation and growth study in 316L austenitic stainless steel was made in cyclic\ntorsion. The experiments on hollow cylindrical specimens were performed at room temperature using fully ...
NUMERICAL SUPPORT FOR STUDY OF STRESS RATIO EFFECT ON FATIGUE CRACK BEHAVIOUR IN THREE POINT BEND SPECIMEN MADE FROM VIBRATED CONCRETE
Seitl, Stanislav; Thienpont, T.
2016 - anglický
The fatigue behaviour of concrete has become more important for the design of structures due to more slender/slim structures, which are more sensitive to fatigue loading, or due to wind turbines, which are typically exposed to high-fatigue loading. The fatigue behaviour of concrete was investigated with respect to the influence of various stress ratios. Pilot analysis of fatigue crack propagation rate in three-point bend specimens made from ordinary vibrated concrete was done.
Klíčová slova:
Stress intensity factor; fatigue crack; Paris-Erdogan law; concrete; FEM; stress ratio
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
NUMERICAL SUPPORT FOR STUDY OF STRESS RATIO EFFECT ON FATIGUE CRACK BEHAVIOUR IN THREE POINT BEND SPECIMEN MADE FROM VIBRATED CONCRETE
The fatigue behaviour of concrete has become more important for the design of structures due to more slender/slim structures, which are more sensitive to fatigue loading, or due to wind turbines, ...
Changes in structure and phase composition in the surface of tram rail
Švábenská, Eva; Roupcová, Pavla; Schneeweiss, Oldřich
2016 - anglický
We have investigated structure and phase composition of surface layer of tram rails after long time running and the results were compared with those obtained on the original part of material. Changes due to effects of severe plastic deformation together with thermal shocks by friction process were expected. The information about structure and phase composition was obtained by optical and scanning electron microscopy, X-Ray Powder Diffraction, Mössbauer Spectroscopy and Glow Discharge Emission Spectroscopy (GDOES) and this was completed by microhardness measurements. The results show that the surface layer in comparison with the original material exhibits important changes in grain structure, an increase in microhardness and high content of iron oxide and hydrooxides. According to the depth profile of the chemical composition measured by GDOES there is an increase in carbon content in the surface layer which can be effect of up-hill diffusion.
Klíčová slova:
tram rail; microstructure analysis; surface
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Changes in structure and phase composition in the surface of tram rail
We have investigated structure and phase composition of surface layer of tram rails after long time running and the results were compared with those obtained on the original part of material. Changes ...
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