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Application of the Williams expansion near a bi-material interface
Malíková, Lucie; Seitl, Stanislav
2017 - anglický
A simplified model of a crack approaching a bi-material interface is modelled by means of the finite element method in order to investigate the significance of the higher-order terms of the Williams expansion for the proper approximation of the opening crack-tip stress near the bi-material interface. The discussion on results is presented and the importance of the higher-order terms proved.
Klíčová slova:
Bi - material interface; Crack - tip stress distribution; Finite elements; Over - deterministic methods; Williams expansion
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Application of the Williams expansion near a bi-material interface
A simplified model of a crack approaching a bi-material interface is modelled by means of the finite element method in order to investigate the significance of the higher-order terms of the Williams ...
Creep damage tolerance factor lambda of selected creep-resistant steels
Sklenička, Václav; Kuchařová, Květa; Dvořák, Jiří; Kvapilová, Marie; Král, Petr
2017 - anglický
The creep damage tolerance factor lambda as an important outcome of the continuum damage mechanics approach has been used to asses the creep fracture mode and the susceptibility of material to localized cracking at strain concentrations. In this work, using sets of our earlier published creep data of three advanced ferritic creep-resistant steels (T23 low alloy steel, P91 and P92 chromium steels) are analysed in terms of the creep damage tolerance factor lambda. It was found that the value of the creep damage factor lambda is not constant and depends on the creep loading conditions. The data analysis is followed by fractographic investigations, which is used to identify the creep fracture mode(s) experimentally.
Klíčová slova:
creep; creep damage tolerance factor lambda; fracture mode; creep fracture plasticity
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Creep damage tolerance factor lambda of selected creep-resistant steels
The creep damage tolerance factor lambda as an important outcome of the continuum damage mechanics approach has been used to asses the creep fracture mode and the susceptibility of material to ...
Characterization of Ta-B-C nanostructured hard coatings
Buršík, Jiří; Buršíková, V.; Souček, P.; Zábranský, L.; Vašina, P.
2017 - anglický
Microstructure and mechanical properties of Ta-B-C nanocrystalline layers prepared by magnetron sputtering were studied. DC magnetron sputtering was used to prepare thin layers on rotated substrates. Various deposition parameters were tested. Microstructure of layers was studied by means of scanning and transmission electron microscopy on thin lamellar cross sections prepared using a focussed ion beam. Both undisturbed layers and the volume under relatively large indentation prints (load of 1 N) were observed. The microstructure observations were correlated with mechanical properties characterized by means of nanoindentation experiments in both the static and the dynamic loading regime. Elastic modulus, indentation hardness and fracture resistance of prepared nanostructured coatings were evaluated and discussed.
Klíčová slova:
coating; nanostructure; analytical electron microscopy
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Characterization of Ta-B-C nanostructured hard coatings
Microstructure and mechanical properties of Ta-B-C nanocrystalline layers prepared by magnetron sputtering were studied. DC magnetron sputtering was used to prepare thin layers on rotated substrates. ...
Subsized Specimens for Fracture Resistance Characterisation Including Transferability Issues
Dlouhý, Ivo; Stratil, Luděk; Šiška, Filip
2017 - anglický
The contribution is focused on characterization of methods enabling to apply small/subsized specimens for fracture resistance characterization. The applied methods are divided into transition region and upper shelf region. The approaches used in the upper shelf region represent at the same time methods applicable for ductile materials without transition. Relating to subsized samples two basic approaches are applicable: (i) miniaturized samples based on common standard ones and (ii) specific specimens/methods, e.g. small punch test etc. The results described in the paper belong to the first group. For interpretation of data generated under low constraint conditions toughness scaling models and master curve approached are commented. In ductile region, either the sample used generate valid toughness characteristics, or, if not, there is no way how to correct measured data except damage quantification through micromechanical models.
Klíčová slova:
Fracture toughness; Crack resistance curve; Transferability; Crack tip constraint; Subsized specimen
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Subsized Specimens for Fracture Resistance Characterisation Including Transferability Issues
The contribution is focused on characterization of methods enabling to apply small/subsized specimens for fracture resistance characterization. The applied methods are divided into transition region ...
Fracture-mechanics behaviour of ceramic foam with macroscopic stress concentrator upon the tensile test
Ševeček, O.; Majer, Z.; Bertolla, Luca; Chlup, Zdeněk; Kotoul, M.
2017 - anglický
The work investigates an influence of the macroscopic stress concentrator inside the ceramic open cell foam structure on the fracture-mechanics response of the foam upon the tensile test. As the concentrator, the central crack/rectangular notch was taken into account. The influence of the crack/notch length and width on the stress concentration ahead the concentrator tip was assessed using the simplified FE beam element based model with irregular cells simulating the real ceramic foam structure. Average principal stresses calculated on set of struts ahead the crack/notch tip were compared with average stresses in the intact structure. It was found that the ratio of these stresses increases linearly with the crack length. The stress concentration ratio is slightly lower in case of thick rectangular notch than in case of a thin crack. Furthermore, the failure load leading to complete fracture of the studied specimens, subjected to the tensile loading, were calculated using the same model. It is shown that the difference factor between the critical fracture force in case of structure without concentrator and with concentrator is very close to the concentration factor calculated from the average stresses on particular struts in the region in front of the concentrator tip.\n
Klíčová slova:
Fracture-mechanics; ceramic foam; tensile test
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Fracture-mechanics behaviour of ceramic foam with macroscopic stress concentrator upon the tensile test
The work investigates an influence of the macroscopic stress concentrator inside the ceramic open cell foam structure on the fracture-mechanics response of the foam upon the tensile test. As the ...
Prediction of the Traction Separation Law of Ceramics Using Iterative Finite Element Modelling
Kozák, Vladislav; Chlup, Zdeněk; Padělek, P.; Dlouhý, Ivo
2017 - anglický
Specific silicon nitride ceramics, the influence of the grain size and orientation on the bridging mechanisms was found. In ceramic matrix composites, crack-bridging mechanisms can provide substantial toughness enhancement coupled with the same and/or increased strength. The prediction of the crack propagation through interface elements based on the fracture mechanics approach and cohesive zone model is investigated. From a number of damage concepts the cohesive models seem to be especially attractive for the practical applications. Within the standard finite element package Abaqus a new finite element has been developed; it is written via the UEL (user’s element) procedure. Its shape can be modified according to the experimental data for the set of ceramics and composites. The element seems to be very stable from the numerical point a view. The shape of the traction separation law for four experimental materials is estimated via the iterative procedure based on the FEM modeling and experimentally determined displacement in indentation experiments, J-R curve is predicted and stability of the bridging law is tested.
Klíčová slova:
cohesive zone model; Si3N4 composite; finite element user’s procedure
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Prediction of the Traction Separation Law of Ceramics Using Iterative Finite Element Modelling
Specific silicon nitride ceramics, the influence of the grain size and orientation on the bridging mechanisms was found. In ceramic matrix composites, crack-bridging mechanisms can provide substantial ...
LCF behaviour of 301LN steel: coarse-grained vs. UFG-bimodal structure
Man, Jiří; Chlupová, Alice; Kuběna, Ivo; Kruml, Tomáš; Man, O.; Järvenpää, A.; Karjalainen, L. P.; Polák, Jaroslav
2017 - anglický
Low-cycle fatigue (LCF) behaviour of metastable austenitic 301LN steel with different grain sizes – coarse-grained (14 µm) and UFG (1.4 µm) with a grain bimodality – produced by reversion annealing (RA) was investigated. Symmetrical push-pull LCF tests were conducted on flat sheet specimens at room temperature with constant strain rate of 2×10–3 s–1 and constant total strain amplitude ranging from 0.4% to 0.8%. After completion of fatigue tests a ferritescope was adopted for quantitative assessment of volume fraction of deformation induced martensite (DIM). Microstructural changes, distribution and morphology of DIM in the volume of material were characterized at different scales by colour etching, TEM and EBSD techniques. Experimental data on microstructural changes are confronted with the stress-strain response and with the chemical heterogeneity present in the material.
Klíčová slova:
low cycle fatigue; 301LN austenitic stainless steel; UFG microstructure; reversion annealing; deformation induced martensite
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
LCF behaviour of 301LN steel: coarse-grained vs. UFG-bimodal structure
Low-cycle fatigue (LCF) behaviour of metastable austenitic 301LN steel with different grain sizes – coarse-grained (14 µm) and UFG (1.4 µm) with a grain bimodality – produced by reversion annealing ...
HYDROGENATION PROPERTIES OF Mg-Al-Ti-Zr-C COMPOSITE
Král, Lubomír; Čermák, Jiří; Roupcová, Pavla
2017 - anglický
The improvement of hydrogen storage properties of ball-milled Mg-Al-Ti-Zr-C composite was studied in this\npaper. It has been previously shown, that the addition of Ti, Zr, Al and C improves storage properties of Mg.\nThis beneficial effect of additives upon hydrogen storage properties can be explained by catalysis by the\nnanoparticles rich in Ti, Zr or Al located on the surface of Mg grains. They provide effective pathways for the\nhydrogen diffusion into the MgH2. The morphological and microstructural characteristics were investigated by\nscanning electron microscope Tescan Lyra 3 and by X-ray diffraction. The hydrogen sorption was measured\nby Sieverts method using Setaram PCT-Pro device.\nStudied experimental composite absorbed 4.2 wt.% H 2 at 573 K and 3 wt.% H 2 at 523K within 10 min. The\nhydrogen storage capacity of the composite was about 4.6% wt.% H 2 and 4.2% wt.% H 2 at 573K and 523K,\nrespectively.
Klíčová slova:
Hydrides; hydrogen storage; catalysis; hydrogen; Mg-alloys
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
HYDROGENATION PROPERTIES OF Mg-Al-Ti-Zr-C COMPOSITE
The improvement of hydrogen storage properties of ball-milled Mg-Al-Ti-Zr-C composite was studied in this\npaper. It has been previously shown, that the addition of Ti, Zr, Al and C improves storage ...
Nanoscale phases on surface Fe-6Si magnetic sheets
Švábenská, Eva; Roupcová, Pavla; Král, Lubomír; Bulín, Tomáš; Vondráček, Martin; Foldyna, Josef; Čechal, J.; Schneeweiss, Oldřich
2017 - anglický
Analysis of the nanoscale phases which appear on the surface Fe-6Si samples were carried out after the various treatments – grinding and etching, annealing, and water jet abrasion. The basic information on structure, chemical and phase composition was obtained by X-Ray Powder Diffraction (XRD), Scanning Electron Microscopy with EDX, Glow Discharge Optical Emission Spectrometry (GDOES), Mössbauer Spectroscopy and X-ray Photoelectron Spectrometry (XPS). The results show high stability of the surface phase composition after the mechanical and heat treatments. Results obtained from the surface analysis in micrometer depth (XRD, EDX, GDOES) do not show any changes after the different treatments. Iron oxides were detected in XPS and conversion electron Mössbauer spectra (CEMS) which analyze the surface composition in a nanometer scale. In addition to, fine changes in atomic ordering on the surface can be observed after mechanical and heat treatments in the CEMS spectra.
Klíčová slova:
Fe-Si alloy; surface modification; nanostructure
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Nanoscale phases on surface Fe-6Si magnetic sheets
Analysis of the nanoscale phases which appear on the surface Fe-6Si samples were carried out after the various treatments – grinding and etching, annealing, and water jet abrasion. The basic ...
CHANGES IN ELECTRICAL STEEL SHEETS INDUCED BY HEAT TREATMENT
Bulín, Tomáš; Švábenská, Eva; Hapla, Miroslav; Ondrušek, C.; Schneeweiss, Oldřich
2017 - anglický
Surface coating of electrical steel sheets is very important due to minimizing eddy current losses in electrical machines. The quality of coating can differ according to the composition. The coating layer has limited heat stability and after crossing of the guaranteed temperature it can be significantly degraded and its insulation properties may change importantly. The aim of this study is to describe changes in parameters of magnetic behavior of the non-oriented Si electrical steel sheet due to degradation of the coating by annealing in air. The parameters were acquired from the measuring of magnetic hysteresis loops on two types of samples with different excitation. The basic information on structure was obtained by optical microscopy. Acquired data are compared between samples with the damaged coating layer by annealing and the original coating layer. The results are discussed from the point of view of the possibility of using sheets with damaged insulation in electrical machines.
Klíčová slova:
Surface coating; magnetic properties; annealing; degradation
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
CHANGES IN ELECTRICAL STEEL SHEETS INDUCED BY HEAT TREATMENT
Surface coating of electrical steel sheets is very important due to minimizing eddy current losses in electrical machines. The quality of coating can differ according to the composition. The coating ...
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