No (1010)
Yes (3)
Number of found documents:
1013
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Prediction of the Traction Separation Law of Ceramics Using Iterative Finite Element Modelling
Kozák, Vladislav; Chlup, Zdeněk; Padělek, P.; Dlouhý, Ivo
2017 - English
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.
Keywords:
cohesive zone model; Si3N4 composite; finite element user’s procedure
Available at various institutes of the ASCR
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 - English
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.
Keywords:
low cycle fatigue; 301LN austenitic stainless steel; UFG microstructure; reversion annealing; deformation induced martensite
Available at various institutes of the ASCR
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 - English
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.
Keywords:
Hydrides; hydrogen storage; catalysis; hydrogen; Mg-alloys
Available at various institutes of the ASCR
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 - English
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.
Keywords:
Fe-Si alloy; surface modification; nanostructure
Available at various institutes of the ASCR
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 - English
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.
Keywords:
Surface coating; magnetic properties; annealing; degradation
Available at various institutes of the ASCR
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 ...
ON THE ENERGY RELEASE RATE OF THE CRACK EMANATING FROM THE INCLUSION INTERPHASE
Profant, T.; Hrstka, M.; Klusák, Jan; Kersner, Z.
2017 - English
The problem of the crack emanating from the interphase region of the circular inclusion is investigated. The problem combines an application of dislocation distribution technique for a crack modelling and the method of boundary integral equations to approximate the loading along the boundary of the domain containing an inclusion. The topological derivative method provides the combination of both approaches and results to the evaluation of the energy release rate of the arbitrary oriented microcrack emanating from the inclusion and matrix interphase. The fundamental solution intended to the boundary integral method such as the continuously distributed dislocation technique is based on the application of Muschelishvili complex potentials in the form of the Laurent series. The coefficients of the series are evaluated from the compatibility conditions along the interfaces of inclusion, interface and matrix.
Keywords:
Microcrack; Inclusion; Interphase; Singular integral equation; Dislocation distribution technique; Complex potentials
Available at various institutes of the ASCR
ON THE ENERGY RELEASE RATE OF THE CRACK EMANATING FROM THE INCLUSION INTERPHASE
The problem of the crack emanating from the interphase region of the circular inclusion is investigated. The problem combines an application of dislocation distribution technique for a crack modelling ...
LOW CYCLE FATIGUE BEHAVIOR AND FATIGUE CRACK INITIATION IN MAR-M247 AT 700 °C
Šulák, Ivo; Obrtlík, Karel; Hrbáček, K.
2017 - English
The second generation nickel-based superalloy MAR-M247 offers a satisfying combination of fatigue and creep properties and oxidation and corrosion resistance that are required for application at elevated temperatures in hostile environments. The microstructure consists mainly of the face centred cubic γ matrix and ordered γ´ strengthening precipitates (L12 crystal structure). The present work focuses on low cycle fatigue (LCF) behaviour of polycrystalline nickel-based superalloy MAR-M247 at high temperature. LCF tests were conducted on cylindrical specimens in a symmetrical push-pull cycle under strain control with constant total strain amplitude and strain rate at 700 °C in ambient air. Cyclic stress-strain curves and fatigue life curves in the representation of plastic strain amplitude vs. stress amplitude and stress amplitude vs. the number of cycles to failure, respectively, were plotted and compared with data obtained on Inconel 713LC. Special attention was paid to the investigation of crack initiation in MAR-M247 during low cycle fatigue. Crack initiation sites were studied by means of scanning electron microscopy (SEM) in dual beam microscope TESCAN LYRA 3 XMU FESEM equipped with focus ion beam (FIB). Specimens’ surface observations revealed the formation of pronounced surface relief indicating localisation of plastic deformation. Observations in transmission electron microscope (TEM) confirmed localisation of cyclic plastic deformation in persistent slip bands along {111} slip planes. Fractographic analysis revealed fatigue crack initiation sites. Fatigue crack propagation in stage I was typical of smooth facets up to 500 μm long.
Keywords:
Nickel-based superalloy; cyclic stress-strain curve; Fatigue life; fatigue crack initiation; focus ion beam
Available at various institutes of the ASCR
LOW CYCLE FATIGUE BEHAVIOR AND FATIGUE CRACK INITIATION IN MAR-M247 AT 700 °C
The second generation nickel-based superalloy MAR-M247 offers a satisfying combination of fatigue and creep properties and oxidation and corrosion resistance that are required for application at ...
Effect of rivet holes on calibration curves for edge cracks under various loading types in steel bridge structure
Seitl, Stanislav; Miarka, Petr; Kala, Z.; Klusák, Jan
2017 - English
Attention has been paid to fatigue cracks in steel structures and bridges for a long time. In spite of efforts to eliminate the creation and propagation of fatigue cracks throughout the designed service life, cracks are still revealed during inspections. There is some limitation of crack sizes which are detectable on structure (from 2 up to 10 mm). Note that depending on the location of the initial crack, the crack may dominantly propagate from the edge or from the surface. The theoretical model of fatigue crack progress is based on linear elastic fracture mechanics. Steel specimens are subjected to various load types (tension, three- and four-point bending, pure bending etc.). The calibration functions for short edge cracks that are near the hole for a rivet or bolt are compared for various loads and the discrepancies are discussed.
Keywords:
edge cracks; rivet holes; fracture mechanics; calibration curves
Available at various institutes of the ASCR
Effect of rivet holes on calibration curves for edge cracks under various loading types in steel bridge structure
Attention has been paid to fatigue cracks in steel structures and bridges for a long time. In spite of efforts to eliminate the creation and propagation of fatigue cracks throughout the designed ...
Interaction of Creep and High Cycle Fatigue of IN 713LC Superalloy
Horník, V.; Šmíd, Miroslav; Hutař, Pavel; Kunz, Ludvík; Hrbáček, K.
2017 - English
The study deals with the interaction of creep and high cycle fatigue of cast polycrystalline nickel-based superalloy IN 713LC at high temperatures. Previous works indicated that creep lifetime of superalloy structures was un-affected or even slightly increased in the cases with superimposed vibrations. The reason for this behaviour was not well described up to now. Therefore, set of fatigue tests was conducted at high mean stresses level to observe this phenomenon. The mean stress was kept constant while the stress amplitudes were selected in order to measure wide range of conditions from pure creep to pure fatigue. Fractographic analysis by scanning electron microscopy (SEM) was done with the aim to identify governing damage mechanisms for particular test conditions as a preliminary evaluation of conducted tests.
Keywords:
Creep-fatigue interaction; Fractography; High temperature; IN 713LC; Superalloy
Available at various institutes of the ASCR
Interaction of Creep and High Cycle Fatigue of IN 713LC Superalloy
The study deals with the interaction of creep and high cycle fatigue of cast polycrystalline nickel-based superalloy IN 713LC at high temperatures. Previous works indicated that creep lifetime of ...
Fracture Toughness of Massively Transformed and Subsequently Heat Treated TiAl Intermetallic Compound
Sakurai, K.; Hasegawa, M.; Dlouhý, Ivo
2017 - English
The effects of massive transformation and subsequent heat treatments on the microstructure of Ti-46Al-7Nb-0.7Cr-0.2Ni-0.1Si (mol%) intermetallic compounds are studied. Massive transformation occurs at the center region of the specimen by cooling from alpha single phase state. At the surface side of the specimen, alpha phase has remained. Fine convoluted microstructure with alpha 2, gamma phases and lamellar structure has formed by heating at (alpha + gamma) two phase state after massive transformation. Colony size or grain size is about 25 micrometer. Fine fully lamellar structure is obtained after heat treatment of convoluted microstructure at alpha phase for 60 s. Fracture toughness seems to be increasing with the increase in lamellar colony size. However, some massively transformed specimens show lower toughness due to the formation of microdamage present in samples before the test.
Keywords:
TiAl intermetallic compound; Massive transformation; Fracture toughness
Available at various institutes of the ASCR
Fracture Toughness of Massively Transformed and Subsequently Heat Treated TiAl Intermetallic Compound
The effects of massive transformation and subsequent heat treatments on the microstructure of Ti-46Al-7Nb-0.7Cr-0.2Ni-0.1Si (mol%) intermetallic compounds are studied. Massive transformation occurs at ...
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