No (1010)
Yes (3)
Number of found documents:
1013
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Basic features of aggregate-matrix-interface fracture of concrete: pilot modelling
Vyhlídal, M.; Šimonová, H.; Veselý, V.; Keršner, Z.; Klusák, Jan; Malíková, Lucie
2017 - English
In this paper, the attention is paid to investigation of the importance of the Interfacial Transition Zone (ITZ) in concrete for the global fracture behaviour. A simplified cracked geometry (consisting matrix, ITZ and aggregate) is modelled by means of the finite element method with a crack terminating at the matrix-ITZ interface. Numerical studies assuming two various ITZ thicknesses and several various ITZ elastic moduli are performed. Based on the values of the opening stress ahead of the crack tip (its average value and stress range) a few conclusions are discussed. The pilot analyses dealing with the effect of ITZ on the stress distribution should contribute to better description of toughening mechanisms in silicate-based composites.
Keywords:
Fracture behaviour; Interfacial transition zone; Matrix interfaces; Toughening mechanisms; Concrete; Fracture mechanics
Available at various institutes of the ASCR
Basic features of aggregate-matrix-interface fracture of concrete: pilot modelling
In this paper, the attention is paid to investigation of the importance of the Interfacial Transition Zone (ITZ) in concrete for the global fracture behaviour. A simplified cracked geometry ...
Development of the bulge test equipment for measuring mechanical properties of thin films
Holzer, Jakub; Pikálek, Tomáš; Buchta, Zdeněk; Lazar, Josef; Tinoco, H.A.; Chlupová, Alice; Kruml, Tomáš
2017 - English
The bulge test apparatus designed for the measurement of mechanical material properties of thin films was constructed and tested. The principle of the test is to apply pressure on a free-standing membrane, to measure the membrane shape and to analyse the results. Commercially available silicon nitride (Si3N4) thin films were used for the testing. It is shown that interferometric set-up designed and assembled for the apparatus enables precise determination of 3D shape of the whole membrane, which allows more precise determination of materials parameters compared to measurement of the height of the center of the membrane only. Fit of an analytical formula gives values of Young modulus and residual stress with very good agreement with the literature data. Moreover, FEM model of the bulged membrane was developed. The main aim of the effort is to enable measurement of plastic properties of a thin film of interest, that will be deposited on the Si3N4 membrane with known properties and bulge test will be performed on the bilayer specimen. Subsequently, the material properties of the thin film will be obtained using FEM analysis.
Keywords:
thin films; bulge test; mechanical properties
Available at various institutes of the ASCR
Development of the bulge test equipment for measuring mechanical properties of thin films
The bulge test apparatus designed for the measurement of mechanical material properties of thin films was constructed and tested. The principle of the test is to apply pressure on a free-standing ...
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:
advantages; coatings; 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 ...
Multi-parameter based stress distribution in vicinity of sharp material inclusion tip
Krepl, Ondřej; Klusák, Jan
2017 - English
General Singular Stress Concentrators (GSSCs) which exhibit singular stress concentration are often responsible for crack initiation and thus failure of the component. The GSSC of the type of bonded bi-material junction occurs in a variety of technical applications including but not limited to sharp material inclusions, silicate based composites and electronic components. The GSSC cannot be assessed by means of standard fracture mechanics. Approaches of generalized fracture mechanics require precise description of stress distribution near the stress concentration points. In order to determine the stress field accurately, the paper incorporates the multi-parameter based description.
Keywords:
Bi-material junction; General singular stress concentrator; Generalized fracture mechanics; Muskhelishvili plane elasticity; Sharp material inclusion
Available at various institutes of the ASCR
Multi-parameter based stress distribution in vicinity of sharp material inclusion tip
General Singular Stress Concentrators (GSSCs) which exhibit singular stress concentration are often responsible for crack initiation and thus failure of the component. The GSSC of the type of bonded ...
Determination of Mechanical Properties of Metallic Materials from Very Small Volumes by Means of Small Punch Test
Dymáček, Petr; Dobeš, Ferdinand; Kloc, Luboš
2017 - English
The paper summarizes capabilities of the small punch tests on miniature disc specimens\nfrom metallic materials. Results obtained by small punch tests can be correlated with mechanical\nproperties determined by conventional or other miniature tests. Three basic types of small punch test\nsetup: i) static/fracture, ii) creep and iii) stress relaxation are described and the basic quantities that\ncan be obtained are shown. Relations for an assessment of conventional mechanical properties from\nquantities obtained by small punch test are presented.
Keywords:
small punch test; uniaxial test; creep; stress relaxation
Available at various institutes of the ASCR
Determination of Mechanical Properties of Metallic Materials from Very Small Volumes by Means of Small Punch Test
The paper summarizes capabilities of the small punch tests on miniature disc specimens\nfrom metallic materials. Results obtained by small punch tests can be correlated with mechanical\nproperties ...
Influence of Extension of Load Spectrum on Estimation of Residual\nFatigue Lifetime of Railway Axle
Pokorný, Pavel; Hutař, Pavel; Náhlík, Luboš
2017 - English
Railway axles are subjected to cyclic amplitude loading which can lead to fatigue failure.\nFor safe operation of railway axles a damage tolerance approach taking into account a possible\ndefect in railway axle is often required. Because of different operation regimes of trains (fast/slow\nride, ride on straight track, on curved track, over switches etc.) the load amplitude of axle is not\nconstant. The variability of load is defined by a load spectrum, which is determined experimentally\nby measuring of load in service conditions. Even though the load spectrum is measured on several\nhundreds or thousands of operation kilometres, the railway axles are in operation much longer time\n(often tens of years). Therefore, some load amplitudes higher than ones measured in the test can\noccur during a long-term axle service. The contribution presented deals with the effect of extension\nof load spectrum by rare high load amplitudes, which can occur during long-term operation, on\nresidual fatigue lifetime of railway axles.
Keywords:
railway axle; fatigue crack; load spectrum; overload
Available at various institutes of the ASCR
Influence of Extension of Load Spectrum on Estimation of Residual\nFatigue Lifetime of Railway Axle
Railway axles are subjected to cyclic amplitude loading which can lead to fatigue failure.\nFor safe operation of railway axles a damage tolerance approach taking into account a possible\ndefect in ...
3D Model of Crack Propagation in Particulate Ceramic Composite Containing Residual Stresses
Štegnerová, Kateřina; Majer, Zdeněk; Hutař, Pavel; Náhlík, Luboš
2017 - English
A crack propagation and fracture behaviour of particulate ceramic composite were investigated. Influence of 3D shape of particles on the crack propagation was studied together with influence of the presence of residual stresses, which are developed inside the composite during manufacturing process. Finite element (FE) method was used for numerical simulation of propagating crack in the composite. Basic numerical models of low-temperature co-fired ceramics (LTCC) with alumina particles homogenously dispersed in the glass matrix were developed. Volume fraction of alumina phase was 20vol.%, which is typical amount for LTCC. The results show that existence of residual stresses retards the crack propagating under conditions of sub-critical crack growth (SCG). Presented results contribute to a better understanding of the role of residual stresses in particulate ceramic composites.
Keywords:
ceramic particulate composite; sub-critical crack growth; residual stresses
Available at various institutes of the ASCR
3D Model of Crack Propagation in Particulate Ceramic Composite Containing Residual Stresses
A crack propagation and fracture behaviour of particulate ceramic composite were investigated. Influence of 3D shape of particles on the crack propagation was studied together with influence of the ...
Short-term stable crack propagation through polyolefin singleand bilayered structures - Influence of welding, composition and direction of crack propagation
Lach, R.; Krolopp, T.; Hutař, Pavel; Nezbedová, E.; Grellmann, W.
2017 - English
The overall stable crack initiation and propagation behaviour of specimens cut from plastic pipes that were composed of different polyolefin materials were investigated using concepts of elastic–plastic fracture mechanics including the crack propagation kinetics. The effect of specimen shape, orientation, welding, lading rate, composition/microstructure and direction of crack propagation on the crack resistance (R) behaviour of these materials has been thereby assessed.
Keywords:
Plastic pipes; single- and bilayered structures; stable crack propagation; plastic constraint
Available at various institutes of the ASCR
Short-term stable crack propagation through polyolefin singleand bilayered structures - Influence of welding, composition and direction of crack propagation
The overall stable crack initiation and propagation behaviour of specimens cut from plastic pipes that were composed of different polyolefin materials were investigated using concepts of ...
Estimation of Anisotropy of Creep Properties in Al and Mg Alloys by Means of Small Punch Test
Dobeš, Ferdinand; Dymáček, Petr
2017 - English
Small punch test was used to determine the properties of light alloys and composites in various directions. Three different materials were studied:\n(i) magnesium alloy WE54 prepared by a powder metallurgical route with final hot extrusion,\n(ii) aluminium alloy reinforced with 20 vol. % of Saffil fibres with planar orientation, and\n(iii) Al-Al4C3 composite prepared by mechanical alloying and subjected to equal channel angularpressing as a final step.\nSmall punch tests were performed under constant force at elevated temperatures. The observed orientation dependence of creep properties is strongly material dependent. The results confirm the feasibility of the small punch test for determination of anisotropy of mechanical properties.
Keywords:
creep; small punch test; aluminium composite
Available at various institutes of the ASCR
Estimation of Anisotropy of Creep Properties in Al and Mg Alloys by Means of Small Punch Test
Small punch test was used to determine the properties of light alloys and composites in various directions. Three different materials were studied:\n(i) magnesium alloy WE54 prepared by a powder ...
High cycle fatigue life of Ti6Al4V alloy produced by direct metal laser sintering
Konečná, R.; Nicoletto, G.; Bača, A.; Kunz, Ludvík
2017 - English
High cycle fatigue life of Ti6Al4V alloy specimens manufactured by Direct Metal Laser Sintering (DMLS) was experimentally determined. The DMLS fabrication process was characterized by a 400 W laser power and 50 micrometer layer melted thickness. Post-fabrication heat treatment consisted in stress relieving for 3 h at 720 °C in vacuum with subsequent cooling in argon atmosphere. Fatigue testing of specimens oriented in three different directions with respect to the material build direction was performed with the aim to examine the influence of the layered microstructure on the fatigue behavior. Results of measurement of surface roughness, metallographic examinations of the layered material and fractographic investigation of the fatigue fracture surfaces were employed in the discussion of fatigue crack initiation in DMLS fabricated Ti6Al4V alloy.
Keywords:
Additive Manufacturing; Fatigue Life; Laser Powder Melting; Titanium Alloy
Available at various institutes of the ASCR
High cycle fatigue life of Ti6Al4V alloy produced by direct metal laser sintering
High cycle fatigue life of Ti6Al4V alloy specimens manufactured by Direct Metal Laser Sintering (DMLS) was experimentally determined. The DMLS fabrication process was characterized by a 400 W laser ...
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