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Effect of the load eccentricity on fracture behaviour of cementitious materials subjected to the modified compact tension test
Seitl, Stanislav; Ríos, J. D.; Cifuentes, H.; Veselý, V.
2017 - anglický
Fracture properties of quasi-brittle cementitious composites are typically determined from the load–displacement response recorded during a fracture test by using the work-of-fracture method or possibly other relevant fracture models. Our contribution is focused on a set of experimental tests which are used to study the fracture behaviour on notched dog-bone-shaped specimens made of cementitious materials. These specimens are subjected to modified compact tension (ModCT) test under a specific range of eccentricity of the tensile load. This type of test generates a stress state in the specimen ligament which combines a direct tension with a defined level of bending due to eccentricity of the tensile load. Several values of relative notch length are also considered. While the crack propagates, a variety of stress states, resulting in variations in the crack-tip stress and deformation constraint, appears in the ligament zone because of the changes in the eccentricity of the applied load, which influences the fracture behaviour of the investigated specimens. The K-calibration, T-stress, CMOD and COD curves for ModCT specimens are introduced and variations of these curves with varying load eccentricity are discussed.
Klíčová slova:
constraint; fracture; load accentricity
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Effect of the load eccentricity on fracture behaviour of cementitious materials subjected to the modified compact tension test
Fracture properties of quasi-brittle cementitious composites are typically determined from the load–displacement response recorded during a fracture test by using the work-of-fracture method or ...
Crack initiation in austenitic stainless steel sanicro 25 subjected to thermomechanical fatigue
Petráš, Roman; Škorík, Viktor; Polák, Jaroslav
2017 - anglický
Thermomechanical fatigue experiments were performed with austenitic stainless Sanicro 25 steel. Several amplitudes of mechanical strain in a wide temperature interval (250-700 °C) were applied to the specimens. Mechanical response was recorded and fatigue lives were obtained. Scanning electron microscopy combined with FIB technique was used to study the mechanism of crack initiation in in-phase and in out-of-phase thermomechanical cycling. Different mechanisms of the crack initiation were found in these two types of loading. During in-phase loading fatigue cracks start in grain boundaries by cracking of the oxide. Cracks grew preferentially along grain boundaries which resulted in rapid crack initiation and low fatigue life. In out-of-phase loading multiple cracks perpendicular to the stress axis developed only after sufficiently thick oxide layer was formed and cracked in low temperature loading half-cycle. The cracks in oxide allowed localized repeated oxidation and finally also cracking. The cracks grow transgranularly and result in longer fatigue life.
Klíčová slova:
Damage mechanism; FIB cutting; Localized oxidation-cracking; Sanicro 25 steel; Thermomechanical fatigue
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Crack initiation in austenitic stainless steel sanicro 25 subjected to thermomechanical fatigue
Thermomechanical fatigue experiments were performed with austenitic stainless Sanicro 25 steel. Several amplitudes of mechanical strain in a wide temperature interval (250-700 °C) were applied to the ...
Lifetime Assessment of Particulate Ceramic Composite with Residual Stresses
Náhlík, Luboš; Majer, Zdeněk; Štegnerová, Kateřina; Hutař, Pavel
2017 - anglický
A micro-crack propagation in particulate ceramic based composite was studied using finite element method (FEM). Subcritical crack growth (SCG) was numerically simulated under complex load conditions (mechanical loading and loading by internal residual stresses). The effect of residual stresses on the crack propagation was studied. Two-dimensional computational model of particulate ceramic composite with material properties corresponding to low temperature co-fired ceramics (LTCC) was developed. The results indicate that the presence of residual stresses significantly reduces values of stress intensity factor in the vicinity of composite surface and the direction of residual stresses around the particles contributes to the micro-crack deflection from the particles. The time to failure of the composite under mechanical loading was determined. Results obtained contribute to a better understanding of the role of residual stresses during micro-crack propagation in ceramic particulate composites.
Klíčová slova:
ceramic particulate composite; sub-critical crack growth; residual stresses
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Lifetime Assessment of Particulate Ceramic Composite with Residual Stresses
A micro-crack propagation in particulate ceramic based composite was studied using finite element method (FEM). Subcritical crack growth (SCG) was numerically simulated under complex load conditions ...
Development of Creep Damage in Similar Weld Joints of P92 Steel Pipe
Král, Petr; Sklenička, Václav; Kuchařová, Květa; Svobodová, M.; Kvapilová, Marie; Dvořák, Jiří
2017 - anglický
The microstructure and creep behaviour of the welded joints of P92 steel pipe were\ninvestigated in order to determine the influence of orbital heat welding technology on the creep\nresistance. Creep specimens were machined from the welded joints. Tensile creep tests of welded\njoints were performed at 873 K using different stresses. The microstructure of tested specimens was\ninvestigated by scanning electron microscope Tescan equipped with an electron-back scatter\ndiffraction. The creep results showed that the creep fracture strain of the welded joints decreases\nwith decreasing value of applied stress. Microstructure investigation showed that fracture behaviour\nof welded joints is influenced by an enhanced cavity formation at grain boundaries in the heataffected\nzone causing lower fracture ductility.
Klíčová slova:
P92 steel; welding; creep damage; creep fracture; microstructure
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Development of Creep Damage in Similar Weld Joints of P92 Steel Pipe
The microstructure and creep behaviour of the welded joints of P92 steel pipe were\ninvestigated in order to determine the influence of orbital heat welding technology on the creep\nresistance. Creep ...
Influence of surface morphology on fatigue behavior of metastable austenitic stainless steel AISI 347 at ambient temperature and 300°C
Smaga, M.; Skorupski, R.; Mayer, P.; Kirsch, B.; Aurich, J. C.; Raid, I.; Seewig, J.; Man, Jiří; Eifler, D.; Beck, T.
2017 - anglický
The effect of surface modification by cryogenic turning on fatigue behavior of metastable austenitic stainless steel AISI 347 was investigated in stress-controlled fatigue tests at ambient temperature (AT) and 300 °C in air. Five different surface morphologies were manufactured by the variation of turning parameters. Surface and near surface morphology were comprehensively characterized by various experimental techniques. The experimental data on the cyclic deformation behavior, stress-strain response and fatigue life for all surface morphologies are reported.
Klíčová slova:
metastable austenitic stainless steel; cryogenic turning; fatigue; surface morphology; martensite
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Influence of surface morphology on fatigue behavior of metastable austenitic stainless steel AISI 347 at ambient temperature and 300°C
The effect of surface modification by cryogenic turning on fatigue behavior of metastable austenitic stainless steel AISI 347 was investigated in stress-controlled fatigue tests at ambient temperature ...
Detekce plasticity v tenkých hliníkových vrstvách pomocí bulge testu
Holzer, Jakub; Pikálek, Tomáš; Buchta, Zdeněk; Lazar, Josef; Tinoco, H.A.; Chlupová, Alice; Náhlík, Luboš; Sobota, Jaroslav; Fořt, Tomáš; Kruml, Tomáš
2017 - anglický
The Bulge test proved to be a useful tool for measuring elastic properties of thin films and\nfree standing membranes, particularly Young’s modulus and residual stress. The basic principle\nof bulge test is application of differential pressure on one side of the a membrane, measurement of\nthe shape of bulged surface as a function of pressure, in this case via laser interferometer, and\nevaluation of a pressure-deflection relationship. In this study, bilayer membrane consisting of a\nsilicon nitride supporting layer and an aluminium layer deposited by means of magnetron\nsputtering is subjected to the bulge test. The results clearly show signs of a non-linear behavior\nthat is caused by plastic deformation in the aluminium layer. Finite element analysis is being\ndeveloped to describe this behavior because analytical model using deflection of central point and\npressure relation falls apart in case of non-linearity.
Klíčová slova:
Bulge test; thin films; mechanical test
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Detekce plasticity v tenkých hliníkových vrstvách pomocí bulge testu
The Bulge test proved to be a useful tool for measuring elastic properties of thin films and\nfree standing membranes, particularly Young’s modulus and residual stress. The basic principle\nof bulge ...
ON THE ENERGY RELEASE RATE OF THE CRACK EMANATING FROM THE INCLUSION INTERPHASE
Profant, T.; Hrstka, M.; Klusák, Jan; Kersner, Z.
2017 - anglický
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.
Klíčová slova:
Microcrack; Inclusion; Interphase; Singular integral equation; Dislocation distribution technique; Complex potentials
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
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 ...
Characterization of Mo-B-C nanostructured coating microstructure by means of AEM and GDOES
Buršík, Jiří; Svoboda, Milan; Švábenská, Eva; Buršíková, V.; Souček, P.; Zábranský, L.; Vašina, P.
2017 - anglický
A Mo-B-C nanostructured coating was prepared on WC-Co hard-metal substrate by magnetron sputtering. The details of microstructure of deposited thin layer as well as elements redistribution caused by subsequent annealing at 1000°C were studied by several experimental techniquec.
Klíčová slova:
coating; nanostructure; analytical electron microscopy
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Characterization of Mo-B-C nanostructured coating microstructure by means of AEM and GDOES
A Mo-B-C nanostructured coating was prepared on WC-Co hard-metal substrate by magnetron sputtering. The details of microstructure of deposited thin layer as well as elements redistribution caused by ...
Low cycle fatigue behaviour and fatigue crack initiation in MAR-M247 at 700 °c
Šulák, Ivo; Obrtlík, Karel; Hrbáček, K.
2017 - anglický
The second generation nickel-based superalloy MAR-M247 offersa satisfying combination of fatigue and creep properties and oxidation and corrosion resistance that arerequired for application at elevated temperatures in hostile environments. The microstructure consists mainly oftheface centred cubic γ matrix and ordered γ ́ strengthening precipitates (L12crystal 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 symmetrical push-pull cycle under strain control with constant total strain amplitude and strain rate at 700 °C in ambientair. Cyclic stress-strain curvesand fatigue life curves in the representation ofplastic strain amplitude vs. stress amplitude andstress amplitude vs. the number of cycles to failure, respectively,were plotted and compared with data obtained on Inconel 713LC. Special attention waspaid 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.
Klíčová slova:
Cyclic stress-strain curve; Fatigue crack initiation; Fatigue life
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Low cycle fatigue behaviour and fatigue crack initiation in MAR-M247 at 700 °c
The second generation nickel-based superalloy MAR-M247 offersa satisfying combination of fatigue and creep properties and oxidation and corrosion resistance that arerequired for application ...
Magnetic properties of 42CrMo4 steel
Bulín, T.; Švábenská, Eva; Hapla, Miroslav; Roupcová, Pavla; Ondrušek, C.; Schneeweiss, Oldřich
2017 - anglický
Low alloyed high-grade chrome-molybdenum ferritic steel was investigated from the point of views of magnetic properties in dependence on heat and mechanical treatment. This steel can be used as components of magnetic circuits or some parts in electrical equipment. The basic information on structure and phase composition was obtained by optical and scanning electron microscopy, X-ray Powder Diffraction and Mössbauer Spectroscopy. The temperature stability of the material was proved by measurements of temperature dependences of magnetic moment. The magnetic parameters were obtained by measuring of magnetic hysteresis loops in dependence on saturation field and their frequencies. The results are discussed from the point of view of possible applications as a magnetic material in the very extremely environment, where high mechanical stresses and elevated temperatures can occur.
Klíčová slova:
Magnetic materials; magnetic properties; steel
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Magnetic properties of 42CrMo4 steel
Low alloyed high-grade chrome-molybdenum ferritic steel was investigated from the point of views of magnetic properties in dependence on heat and mechanical treatment. This steel can be used as ...
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