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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 - anglický
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.
Klíčová slova:
Multi-parameter fracture mechanics; Alkali-activated concrete; Mixed-mode loading; MTS; SED
Dokument je dostupný na externích webových stránkách.
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 ...
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 - český
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.
Klíčová slova:
Acoustic emission; creep; coper
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
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 ...
WE43 BIOCOMPATIBLE ALLOY AFTER SEVERE PLASTIC DEFORMATION: STRUCTURE CHARACTERIZATION
Kunčická, Lenka; Král, Petr; Dvořák, Jiří; Kocich, R.
2019 - anglický
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.
Klíčová slova:
Magnesium alloys; texture; scanning electron microscopy; X-ray diffraction
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
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 ...
HYDROGEN SORPTION IN ORDERED Mg-In ALLOYS
Čermák, Jiří; Král, Lubomír; Roupcová, Pavla
2019 - anglický
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.
Klíčová slova:
Hydrogen storage; Mg alloys; hydride stability; ordering
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
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 ...
Effect of casting conditions and heat treatment on high temperature low cycle fatigue performance of nickel superalloy Inconel 713LC
Šulák, Ivo; Obrtlík, Karel; Hrbáček, Karel
2019 - anglický
The present work is focused on the study of high temperature low cycle fatigue behaviour of Inconel 713LC produced by a vibratory investment casting (VIC) in as-cast conditions and in the condition after heat treatment (HT) consisting of hot isostatic pressing (HIP) followed by precipitation hardening. Low cycle fatigue tests were carried out on cylindrical specimens in symmetrical push-pull cycle under strain control with constant total strain amplitude and strain rate at 800 °C in air. Hardening/softening curves and fatigue life curves of both materials were assessed and compared with data of Inconel 713LC produced by a conventional investment casting (CIC). Cyclic hardening can be observed in the high amplitude domain while saturated stress response is apparent for low amplitude cycling for all material batches. Data presented in Basquin representation show an increase in fatigue life of both VIC batches compared to the CIC batch, however, no effect of HT on fatigue life of Inconel 713LC produced by VIC was observed. In contrast, the heat treated Inconel 713LC demonstrates slightly higher fatigue life in Coffin-Manson representation. The microstructure of both superalloys was studied by means of scanning electron microscopy (SEM). The microstructure of superalloy is characterized by dendritic grains with casting defects. It comprises the γ matrix, cubic γ´ precipitates, eutectics and carbides. The effect of the VIC and HT on fatigue performance and microstructure of Inconel 713LC is discussed.
Klíčová slova:
Inconel 713LC; vibratory investment casting; hot isostatic pressing; high temperature low cycle fatigue; stress-strain response
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Effect of casting conditions and heat treatment on high temperature low cycle fatigue performance of nickel superalloy Inconel 713LC
The present work is focused on the study of high temperature low cycle fatigue behaviour of Inconel 713LC produced by a vibratory investment casting (VIC) in as-cast conditions and in the condition ...
PHASE COMPOSITION OF CHOSEN Mg-BASED MATERIALS DURING HYDROGEN SORPTION
Čermák, Jiří; Král, Lubomír; Roupcová, Pavla
2019 - anglický
Phase transformation during hydrogen sorption was investigated in ten chosen magnesium-based hydrogen storage (HS) materials. Chemical composition of the materials consisted of Mg, as a principal hydrogen-binding element, additive X and amorphous carbon (CB), as an anti-sticking component. In order to assess the effect of X itself upon the structure, values of concentration of both X and CB were fixed to about 12 wt. %. The influence of X = Mg2Si, Mg2Ge, Mg17Al12, Mg5Ga2, NaCl, LiCl, NaF, LiF and two combinations Ni+Mg17Al12 and Ni+Mg2Si upon the changes in phase composition was tested. Phase content in HS materials was observed (i) after the intensive ball milling (BM), (ii) after the BM followed by hydrogen charging at 623 K and (iii) after the BM and one hydrogen charging/discharging cycle (C/D) at temperature 623 K. The study was carried out by SEM and XRD. It was found that, the C/D is approximately structurally reversible for X = Mg2Ge, Mg17Al12, NaF and LiF. However, additives X = Mg17Al12 and NaF decompose already during the BM. In alloys with combination of Ni with Mg17Al12, new phases NimAln are formed. Phase composition changed during C/D for X = Mg2Si Mg5Ga2 and Ni+Mg2Si due to equilibration of phases composition. Observed structure changes of HS materials with chloride ionic additives NaCl and LiCl are, most likely caused by the relatively strong affinity between Mg and Cl. Hydrogen storage capacity of all studied alloys was 6.0 +/- 0.3 wt. % H-2.
Klíčová slova:
Hydrogen storage; Mg alloys; carbon black
Dokument je dostupný na externích webových stránkách.
PHASE COMPOSITION OF CHOSEN Mg-BASED MATERIALS DURING HYDROGEN SORPTION
Phase transformation during hydrogen sorption was investigated in ten chosen magnesium-based hydrogen storage (HS) materials. Chemical composition of the materials consisted of Mg, as a principal ...
PILOT ANALYSIS OF CHEVRON NOTCH LIGAMENT AREA FOR APPLICATION\nON QUASI-BRITTLE MATERIALS
Seitl, Stanislav; Růžička, P.; Miarka, P.; Sobek, J.
2018 - anglický
Specimens for the bending tests with the chevron notch are standardized for the\nevaluation of the fracture toughness of various materials. The main advantage of this test\nset-up is that no sharp pre-crack has to be introduced, because a sharp crack is formed\nduring loading at the beginning of the test. Furthermore, no crack length measurement is\nrequired, and a stable crack growth can be reached due to geometry of the notch. In this\ncontribution a difference of the ligament area of the specimens with the straight through\nnotch and the chevron notch was investigated
Klíčová slova:
Fracture mechanics; chevron notch; ligament area; work of fracture; straight notch; blunt
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
PILOT ANALYSIS OF CHEVRON NOTCH LIGAMENT AREA FOR APPLICATION\nON QUASI-BRITTLE MATERIALS
Specimens for the bending tests with the chevron notch are standardized for the\nevaluation of the fracture toughness of various materials. The main advantage of this test\nset-up is that no sharp ...
Study of mechanical properties of nanolayered Ti/Ni coatings
Zábranský, L.; Václavík, R.; Přibyl, R.; Ženíšek, J.; Souček, P.; Buršík, Jiří; Fořt, Tomáš; Buršíková, V.
2018 - anglický
The aim of the present work was to study the dependence of mechanical properties of Ti/Ni multilayer thin films on the thicknesses of constituent Ti and Ni layers. The multilayer thin films were synthesized by deposition of Ti and Ni layers alternately on single crystalline silicon substrates using direct current magnetron sputtering method. Thicknesses of Ti and Ni layers varied from 1.7 nm to 100 nm. The micro-structure of the multilayer films was studied using X-ray diffraction technique, scanning electron microscopy with focused ion beam technique and transmission electron microscopy. Mechanical properties obtained from nanoindentation experiments were discussed in relation to microstructural observations.
Klíčová slova:
Ti/Ni; multilayers; magnetron sputtering; nanoindentation; TEM
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Study of mechanical properties of nanolayered Ti/Ni coatings
The aim of the present work was to study the dependence of mechanical properties of Ti/Ni multilayer thin films on the thicknesses of constituent Ti and Ni layers. The multilayer thin films were ...
HIGH - TEMPERATURE CREEP BEHAVIOUR OF CAST COBALT-BASE SUPERALLOYS
Dvořák, Jiří; Král, Petr; Kvapilová, Marie; Hrbáček, Karel; Sklenička, Václav
2018 - anglický
Two cast and heat-treated NbC and TaC – strengthened cobalt superalloys have been developed for a precision casting of spinner discs for glass wool industry. In this work constant load creep tests in tension were carried out in argon atmosphere at three testing temperature 900, 950 and 1000 °C and at the initial applied stresses ranged from 40 to 200 MPa. All the tests were continued until the final fracture. The results of creep testing were combined with microstructural and fractographic examinations by means of light and scanning electron microscopy. A mutual comparison of creep characteristics of the investigated superalloys under comparable creep loading conditions showed that NbC-strengthened superalloy exhibited longer creep life than TaC-strengthened one. Further, it was found that carbide precipitation is the primary strengthening mechanism in both cobalt-base superalloys under investigation and the amount, morphology\nand type of carbides have the decisive effect on the creep properties including creep damage and fracture processes. By contrast, NbC-superalloy exhibited a more brittle character of creep fracture mode than TaCstrengthened superalloy. This study was initiated to investigate in more details creep deformation processes and the effect of the creep microstructure and damage evolution on both investigated superalloys. The different behaviour and properties of studied superalloys were explained based on the received results of this study.
Klíčová slova:
Co-based superalloys; creep tests; microstructure evolution; carbide precipitation; damage process
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
HIGH - TEMPERATURE CREEP BEHAVIOUR OF CAST COBALT-BASE SUPERALLOYS
Two cast and heat-treated NbC and TaC – strengthened cobalt superalloys have been developed for a precision casting of spinner discs for glass wool industry. In this work constant load creep tests in ...
INFLUENCE OF GRAPHITE UPON THE KINETICS OF HYDROGEN SORPTION IN Mg@Mg17Al12
Čermák, Jiří; Král, Lubomír; Roupcová, Pavla
2018 - anglický
Influence of graphite addition to the ball-milling charge composed of Mg splinters and Mg17Al12 particles upon the hydrogen sorption was investigated at sorption temperature 623 K. Measurements were carried out by Sieverts method. Graphite facilitates the ball-milling: It prevents re-agglomeration of crushed particles into large secondary particles. It also suppresses sticking the milled material to the balls and walls of the milling jar. It was found that an increase of carbon concentration up to a certain limit c(L) lying between 14 and 23 wt. % C, carbon increases both the absorption and the desorption rates and hydrogen storage capacity. Above c(L), carbon causes a considerable decrease in HS capacity, which spoils the application potential of Mg@Mg17Al12/C. Crystallite size of the material under study, obtained by XRD, is in the order of tens of nm.
Klíčová slova:
storage; Hydrogen storage; Mg alloys; graphite
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
INFLUENCE OF GRAPHITE UPON THE KINETICS OF HYDROGEN SORPTION IN Mg@Mg17Al12
Influence of graphite addition to the ball-milling charge composed of Mg splinters and Mg17Al12 particles upon the hydrogen sorption was investigated at sorption temperature 623 K. Measurements were ...
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