Number of found documents: 1018
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Influence of severe plastic deformation and subsequent annealing on creep behaviour of martensitic 9% Cr steel
Král, Petr; Dvořák, Jiří; Sklenička, Václav; Horita, Z.; Tokizawa, Y.; Tang, Y.; Kunčická, Lenka; Kuchařová, Květa; Kvapilová, Marie; Svobodová, M.
2021 - English
The objective of the study is to evaluate the effects of severe plastic deformation (SPD) and annealing on creep behaviour of advanced tungsten modified creep-resistant 9 % Cr martensitic P92 steel. The as-received P92 steel was deformed by high-pressure torsion (HTP), high-pressure sliding (HPS) and rotary swaging (RS) at room temperature prior creep testing. These SPD methods imposed significantly different equivalent plastic strain in the range from 1 up to 20. Constant load creep tests in tension were performed in an argon atmosphere at 873 K and applied stress ranging from 50 to 200 MPa. The microstructure and phase composition of P92 steel were studied using a scanning electron microscope Tescan Lyra 3 and a transmission electron microscope Jeol 2100F. The results show that under the same creep loading conditions the HPT and HPS-processed P92 steel exhibited significantly faster minimum creep rates, creep fracture strain and the decrease in the value of the stress exponent of the creep rate in comparison with as-received P92 steel. However, it was revealed that the RS-processed specimens exhibited one order of magnitude lower minimum creep rate and lower ductility compared to commercial P92 steel. The creep curves for the HPT and HPS-processed states exhibited a pronounced minimum of strain rate. The pronounced minimum of strain rate disappeared when these states were annealed at 923K/500h before application of creep loading. The microstructure changes occurring during creep and different creep behaviour between as-received and deformed states are discussed. Keywords: Creep-resistant 9 %Cr steels; severe plastic deformation; creep; microstructure Available at various institutes of the ASCR
Influence of severe plastic deformation and subsequent annealing on creep behaviour of martensitic 9% Cr steel

The objective of the study is to evaluate the effects of severe plastic deformation (SPD) and annealing on creep behaviour of advanced tungsten modified creep-resistant 9 % Cr martensitic P92 steel. ...

Král, Petr; Dvořák, Jiří; Sklenička, Václav; Horita, Z.; Tokizawa, Y.; Tang, Y.; Kunčická, Lenka; Kuchařová, Květa; Kvapilová, Marie; Svobodová, M.
Ústav fyziky materiálů, 2021

AB INITIO STUDY OF SILVER NANOPARTICLES, GRAIN BOUNDARIES AND THEIR \nQUADRUPLE JUNCTIONS
Polsterová, Svatava; Všianská, Monika; Friák, Martin; Pizúrová, Naděžda; Sokovnin, S.; Šob, Mojmír
2021 - English
Motivated by our experimental research related to silver nanoparticles with various morphologies, we have employed quantum-mechanical calculations to provide our experiments with theoretical insight. We have computed properties of a 181-atom decahedral silver nanoparticle and two types of internal extended defects, -5(210) grain boundaries (GBs) and quadruple junctions (QJs) of these GBs. We have employed a supercell approach with periodic boundary conditions. Regarding the thermodynamic stability of the decahedral nanoparticle, its energy is higher than that of a defect-free face-centered cubic (fcc) Ag by 0.34 eV/atom. As far as the -5(210) GB is concerned, its energy amounts to 0.7 J/m2 and we predict that the studied GBs would locally expand the volume of the lattice. Importantly, the system with GBs is found rather close to the limit of mechanical stability. In particular, the computed value of the shear-related elastic constant C66 is as low as 9.4 GPa with the zero/negative value representing a mechanically unstable system. We thus predict that the -5(210) GBs may be prone to failure due to specific shearing deformation modes. The studied GBs have also the value of Poisson’s ratio for some loading directions close to zero. Next, we compare our results related solely to -5(210) GBs with those of a system where multiple intersecting -5(210) GBs form a network of quadruple junctions. The value of the critical elastic constant C66 is higher in this case, 13 GPa, and the mechanical stability is, therefore, better in the system with QJs. Keywords: Elasticity; Grain boundaries; Junctions; Nanoparticles Available at various institutes of the ASCR
AB INITIO STUDY OF SILVER NANOPARTICLES, GRAIN BOUNDARIES AND THEIR \nQUADRUPLE JUNCTIONS

Motivated by our experimental research related to silver nanoparticles with various morphologies, we have employed quantum-mechanical calculations to provide our experiments with theoretical insight. ...

Polsterová, Svatava; Všianská, Monika; Friák, Martin; Pizúrová, Naděžda; Sokovnin, S.; Šob, Mojmír
Ústav fyziky materiálů, 2021

Snímání akustických emisí při zkoušce tečením (creepem) v ochranné atmosféře
Dvořák, Jiří; Svobodová, M.; Sklenička, Václav
2020 - Czech
Cílem vypracované metodiky snímání akustických emisí 'in-situ' v průběhu creepové zkoušky v ochranné atmosféře byla minimalizace či odstranění šumů na záznamech akustické emise způsobených synergicky působícími oxidačními procesy, které mohou kriticky ovlivňovat identifikaci a intenzitu působících vlastních creepových degradačních procesů a relevantní vyhodnocení naměřených dat. The objective of the developed methodology for sensing 'in-situ' acoustic emissions during a creep test in a modified atmosphere was to minimise or eliminate noise on acoustic emission records caused by synergistic acting oxidation processes that may critically influence the identification and intensity of the acting own creep degradation processes and the relevant evaluation of the measured data. Keywords: acoustic emission; creep mechanical properties testing; protective atmosphere testing Available at various institutes of the ASCR
Snímání akustických emisí při zkoušce tečením (creepem) v ochranné atmosféře

Cílem vypracované metodiky snímání akustických emisí 'in-situ' v průběhu creepové zkoušky v ochranné atmosféře byla minimalizace či odstranění šumů na záznamech akustické emise způsobených synergicky ...

Dvořák, Jiří; Svobodová, M.; Sklenička, Václav
Ústav fyziky materiálů, 2020

MULTI-PARAMETER MTS AND SED CRITERION APPLIED ON A CRACK IN AN ALKALI-ACTIVATED CONCRETE SPECIMEN UNDER MIXED-MODE LOADING
Malíková, Lucie; Miarka, Petr; Simonová, H.
2020 - English
The paper is devoted to an analysis of a crack propagation in a semi-circular concrete specimen under three-point bending. I+II mixed-mode loading is ensured via an inclined crack. Crack deflection angle is investigated by means of the generalized/multi-parameter form of the Maximum Tangential Stress (MTS) criterion and Strain Energy Density (SED) criterion as well as experimentally. The multi-parameter fracture mechanics concept applied in this work is based on the approximation of the crack-tip stress field by means of the Williams series expansion (WE). It has been proved that this approach can help to describe crack behavior in some kinds of materials better than the classical (one-parameter: stress intensity factor) fracture mechanics. This conclusion is discussed also in this paper. Keywords: t-stress; fracture; field; Multi-parameter fracture mechanics; Alkali-activated concrete; Mixed-mode loading; mts; sed Available at various institutes of the ASCR
MULTI-PARAMETER MTS AND SED CRITERION APPLIED ON A CRACK IN AN ALKALI-ACTIVATED CONCRETE SPECIMEN UNDER MIXED-MODE LOADING

The paper is devoted to an analysis of a crack propagation in a semi-circular concrete specimen under three-point bending. I+II mixed-mode loading is ensured via an inclined crack. Crack deflection ...

Malíková, Lucie; Miarka, Petr; Simonová, H.
Ústav fyziky materiálů, 2020

MATERIAL MODEL PARAMETER IDENTIFICATION OF STAINLESS STEEL (AISI 304L)
Jindra, D.; Kala, Z.; Seitl, Stanislav; Kala, J.
2020 - English
Identification of Ramberg and Osgood nonlinear material model parameters for hot rolled stainless steel material grade 1.4307 (AISI 304L) was conducted. Reference data (stress-strain relation) were obtained from experimental program performed on normalized specimens. Parametrical numerical finite element model was created using commercially available software ANSYS classic APDL, and the subsequent optimization process was conducted in the environment of OptiSLang software. Keywords: Stainless steel; Finite element numerical model; Parameter identification; Ramberg and Osgood model Available at various institutes of the ASCR
MATERIAL MODEL PARAMETER IDENTIFICATION OF STAINLESS STEEL (AISI 304L)

Identification of Ramberg and Osgood nonlinear material model parameters for hot rolled stainless steel material grade 1.4307 (AISI 304L) was conducted. Reference data (stress-strain relation) were ...

Jindra, D.; Kala, Z.; Seitl, Stanislav; Kala, J.
Ústav fyziky materiálů, 2020

NUMERICAL STUDY OF UNIVERSAL BEAM (I SECTION) UNDER BENDING LOAD WITH CRACK
Morán, Alvarez J.; Seitl, Stanislav; Miarka, Petr
2020 - English
The structural components often contain cracks as a results of applied load. Therefore, these cracks must be studied how they affect the structural behavior and the total service life-time of the component. Bearing beams of the bridges have usually cross-section in the shape of an I-profile. In this contribution, a numerical parametric model was made in order to study the influence of the crack length, Poisson's ratio and web thickness on the stress distribution in the structural element, for which a three-point bending specimen was applied. The model is based on the linear elastic fracture mechanics (LEFM), with focus set on the determination of the stress intensity factor, as it is one of the main parameters used in the description of the stress fields in vicinity of the crack tip. Keywords: Stress Intensity Factor; Linear Elastic Fracture Mechanics; Finite Element Method; I-Profile; Poisson's ratio Available at various institutes of the ASCR
NUMERICAL STUDY OF UNIVERSAL BEAM (I SECTION) UNDER BENDING LOAD WITH CRACK

The structural components often contain cracks as a results of applied load. Therefore, these cracks must be studied how they affect the structural behavior and the total service life-time of the ...

Morán, Alvarez J.; Seitl, Stanislav; Miarka, Petr
Ústav fyziky materiálů, 2020

Multi-parameter MTS and SED criterion applied on a crack in an alkali-activated concrete specimen under mixed-mode loading
Malíková, Lucie; Miarka, Petr; Šimonová, H.
2020 - English
The paper is devoted to an analysis of a crack propagation in a semi-circular concrete specimen under three-point bending. I+II mixed-mode loading is ensured via an inclined crack. Crack deflection angle is investigated by means of the generalized/multi-parameter form of the Maximum Tangential Stress (MTS) criterion and Strain Energy Density (SED) criterion as well as experimentally. The multi-parameter fracture mechanics concept applied in this work is based on the approximation of the crack-tip stress field by means of the Williams series expansion (WE). It has been proved that this approach can help to describe crack behavior in some kinds of materials better than the classical (one-parameter: stress intensity factor) fracture mechanics. This conclusion is discussed also in this paper. Keywords: Multi-parameter fracture mechanics; Alkali-activated concrete; Mixed-mode loading; MTS; SED Fulltext is available at external website.
Multi-parameter MTS and SED criterion applied on a crack in an alkali-activated concrete specimen under mixed-mode loading

The paper is devoted to an analysis of a crack propagation in a semi-circular concrete specimen under three-point bending. I+II mixed-mode loading is ensured via an inclined crack. Crack deflection ...

Malíková, Lucie; Miarka, Petr; Šimonová, H.
Ústav fyziky materiálů, 2020

DETEKCE PORUCH POMOCÍ AKUSTICKÉ EMISE (AE) V PODMÍNKÁCH VYSOKOTEPLOTNÍHO CREEPU
Dvořák, Jiří; Sklenička, Václav; Král, Petr; Kvapilová, Marie; Svobodová, M.; Šifner, J.; Koula, V.
2019 - Czech
Současné aplikace akustické emise (AE) jsou přednostně orientovány na průběžný monitoring provozu strojních komponent. AE je perspektivní nedestruktivní metodou pro včasnou predikci a identifikaci poruch materiálu dříve než dojde k havárii sledovaných zařízení. Příspěvek analyzuje naměřená data a rozbor signálů na úrovni jednotlivých emisních událostí v průběhu creepové zkoušky mědi na základě výsledků předchozí mikrostrukturní a fraktografické analýzy jejího creepového porušení a lomu. Cílem modelové studie je přispět k úspěšné aplikaci AE pro reálné provozní komponenty energetických zařízení a tím ke zvýšení jejich provozní bezpečnosti. Current acoustic emission (AE) applications are preferably oriented to continuous monitoring of machine component operation. AE is a perspective non-destructive method for early prediction and identification of material defects to avoid a disaster of running equipment. The paper analyzes the measured data and analysis of signals at the level of individual emission events during the creep test of a copper based on the results of previously performed microstructural and fractographic analyses of its creep damage evolution and fracture. The aim of the model study is to contribute to the successful application of AE for real operating components of power equipments and thus to increase their operational safety. Keywords: Acoustic emission; creep; coper Available at various institutes of the ASCR
DETEKCE PORUCH POMOCÍ AKUSTICKÉ EMISE (AE) V PODMÍNKÁCH VYSOKOTEPLOTNÍHO CREEPU

Současné aplikace akustické emise (AE) jsou přednostně orientovány na průběžný monitoring provozu strojních komponent. AE je perspektivní nedestruktivní metodou pro včasnou predikci a identifikaci ...

Dvořák, Jiří; Sklenička, Václav; Král, Petr; Kvapilová, Marie; Svobodová, M.; Šifner, J.; Koula, V.
Ústav fyziky materiálů, 2019

WE43 BIOCOMPATIBLE ALLOY AFTER SEVERE PLASTIC DEFORMATION: STRUCTURE CHARACTERIZATION
Kunčická, Lenka; Král, Petr; Dvořák, Jiří; Kocich, R.
2019 - English
The report presents results of the analyses of biocompatible WE 43 Mg-based alloy processed by friction stir processing (FSP) at two different rotational speeds of 400 RPM, and 1200 RPM. The structures were observed by scanning electron microscopy (SEM), electron backscattered diffraction (EBSD). Observations were primarily focused on characterizations of grains and textures, supplementary testing of mechanical properties was performed via tensile tests. The results of low angle grain boundaries fractions and grain sizes showed that both the processing methods led to significant grain refinement and recrystallization, the average grain diameter within the 1200 RPM sample was less than 2 μm. Texture observations showed slight tendencies of the grains to align in the {0001}〈101̅0〉 and {0001}〈112̅0〉 preferential orientations, however, the maximum intensities were only about two times random. Supplementary tensile tests confirmed the positive effects of FSP on structures and properties of both the samples. Keywords: Magnesium alloys; texture; scanning electron microscopy; X-ray diffraction Available at various institutes of the ASCR
WE43 BIOCOMPATIBLE ALLOY AFTER SEVERE PLASTIC DEFORMATION: STRUCTURE CHARACTERIZATION

The report presents results of the analyses of biocompatible WE 43 Mg-based alloy processed by friction stir processing (FSP) at two different rotational speeds of 400 RPM, and 1200 RPM. The ...

Kunčická, Lenka; Král, Petr; Dvořák, Jiří; Kocich, R.
Ústav fyziky materiálů, 2019

HYDROGEN SORPTION IN ORDERED Mg-In ALLOYS
Čermák, Jiří; Král, Lubomír; Roupcová, Pavla
2019 - English
Hydrogen storage (HS) performance of three Mg- x In- y CB alloys (CB - amorphous carbon, x = 55, 64, 73 y =\n10 wt%) was studied. Indium concentration covered an area of ordered β structures. Alloys were prepared by\nball-milling in hydrogen atmosphere. Kinetic curves and PCT isotherms were measured in the temperature\ninterval from 200 °C to 325 °C. X-ray diffraction spectroscopy (XRD) was used for structure investigation. Alloy\nwith x = 73 wt% In ( β ’’ structure) showed reversible amorphization during temperature cycling between about\n100 °C and 350 °C. Hydrogen sorption experiments were done by the Sieverts method under the hydrogen\ngas pressure ranging from 0.1 MPa to 2.5 MPa. It was found that hydrogen sorption capacity varied between\n0.47 and 1.1 wt% H 2 . Hydride formation enthalpy ∆H calculated from desorption PCT experiments was\nsignificantly lower than ∆H , known for pure Mg. This invoked an idea that atomic order of Mg-based HS\nmaterials might decrease the high thermodynamic stability of hydride phase. Keywords: Hydrogen storage; Mg alloys; hydride stability; ordering Available at various institutes of the ASCR
HYDROGEN SORPTION IN ORDERED Mg-In ALLOYS

Hydrogen storage (HS) performance of three Mg- x In- y CB alloys (CB - amorphous carbon, x = 55, 64, 73 y =\n10 wt%) was studied. Indium concentration covered an area of ordered β structures. Alloys ...

Čermák, Jiří; Král, Lubomír; Roupcová, Pavla
Ústav fyziky materiálů, 2019

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