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Application of simplified mechanical model for description of specimen size effect on resistance against stable tearing
Stratil, Luděk; Šiška, Filip; Hadraba, Hynek; Dlouhý, Ivo
2014 - English
This contribution deals with a size effect on J-R curve of three points bend specimens made from Eurofer97 steel and with possibilities to predict the specimen behaviour between various specimen sizes. To do it, a simplified mechanical model proposed by Schindler is applied to obtained tests results in order to predict observed size effect on J-R curve.
Keywords:
size effect; three point bend; scalinq laws; Eurofer97; J-R curve
Available at various institutes of the ASCR
Application of simplified mechanical model for description of specimen size effect on resistance against stable tearing
This contribution deals with a size effect on J-R curve of three points bend specimens made from Eurofer97 steel and with possibilities to predict the specimen behaviour between various specimen ...
Dynamic stability of Ni fcc crystal under isotropic tension
Řehák, Petr; Černý, M.
2014 - English
Lattice dynamics and stability of fcc crystal of Ni under isotropic (hydrostatic) tensile loading are studied from first principles using supercell method and a harmonic approximation. According to the results, strength of the crystal is determined by occurrence of an instability related to soft phonons with finite wave vector. On the other hand, the critical strains and stresses associated with such instabilities are only slightly lower than those related to the volumetric instability.
Keywords:
lattice dynamics; phonon instability; isotropic loading; ab initio calculations
Available at various institutes of the ASCR
Dynamic stability of Ni fcc crystal under isotropic tension
Lattice dynamics and stability of fcc crystal of Ni under isotropic (hydrostatic) tensile loading are studied from first principles using supercell method and a harmonic approximation. According to ...
Near threshold fatigue crack growth in ultrafine-grained copper
Arzaghi, M.; Fintová, S.; Sarrazin-Baudoux, C.; Kunz, Ludvík; Petit, J.
2014 - English
The near threshold fatigue crack growth in ultrafine-grained (UFG) copper at room temperature was studied in comparison to conventional coarse-grained (CG) copper. The fatigue crack growth rates da/dN in UFG copper were enhanced at Delta K <= 7 MPa root m compared to the CG material. The crack closure shielding, as evaluated using the compliance variation technique, was shown to explain these differences. The effective stress intensity factor amplitude Delta K-eff appears to be the same driving force in both materials. Tests performed in high vacuum on UFG copper demonstrate the existence of a huge effect of environment with growth rates higher of about two orders of magnitude in air compared to high vacuum. This environmental effect on the crack path and the related microstructure is discussed on the basis of fractography observations performed using scanning electron microscope and completed with field emission scanning electron microscope combined with the focused ion beam technique.
Keywords:
SEVERE PLASTIC-DEFORMATION; BEHAVIOR; ALLOYS; METALS
Available at various institutes of the ASCR
Near threshold fatigue crack growth in ultrafine-grained copper
The near threshold fatigue crack growth in ultrafine-grained (UFG) copper at room temperature was studied in comparison to conventional coarse-grained (CG) copper. The fatigue crack growth rates da/dN ...
MICROSTRUCTURAL INVESTIGATION AND MECHANICAL TESTING OF AN ULTRAFINE-GRAINED AUSTENITIC STAINLESS STEEL
Chlupová, Alice; Man, Jiří; Polák, Jaroslav; Karjalainen, L. P.
2014 - English
Special thermomechanical treatment based on high degree deformation followed by reversion annealing was applied to 301LN austenitic stainless steel to achieve ultrafine-grained (UFG) structure with considerably enhanced mechanical properties. Two different conditions of the thermomechanical treatment were adopted and resulting microstructures with different grain sizes were characterised by optical and high resolution scanning electron microscopy (FEG SEM). Hardness measurements and tensile tests were performed to characterize mechanical properties. To reveal structural changes induced during thermomechanical treatment and during tensile tests a magnetic induction method was additionally applied. Experimental study validated the ability of the treatment to produce an austenitic stainless steel with the grain size of about 1.4 mu m which exhibits tensile strength of around 1000 MPa while ductility remains close to 60 %. The results obtained for both thermomechanical conditions are compared and the relationship between microstructure refinement, phase content and mechanical properties is discussed.
Keywords:
behavior; austenitic steel; ultra-fine grained microstructure; thermomechanical heat treatment; mechanical properties; hardness
Available at various institutes of the ASCR
MICROSTRUCTURAL INVESTIGATION AND MECHANICAL TESTING OF AN ULTRAFINE-GRAINED AUSTENITIC STAINLESS STEEL
Special thermomechanical treatment based on high degree deformation followed by reversion annealing was applied to 301LN austenitic stainless steel to achieve ultrafine-grained (UFG) structure with ...
FRACTURE MECHANICS ASSESSMENT OF CRACKED WELDED POLYOLEFIN PIPES
Mikula, Jakub; Ševčík, Martin; Hutař, Pavel; Náhlík, Luboš
2014 - English
The aim of this paper is to present methodology for estimation of fracture mechanics parameters in polyolefin pipes with an axially oriented crack using three dimensional numerical analyses. Linear elastic fracture mechanics is used for description of fracture behavior. In the paper, three different variants of pipe weld with an internal axial semi-elliptical crack are studied. Numerical models correspond to a cracked pipe containing material nonhomogeneity in the welding area caused by welding process. A critical locations of the crack initiated along the pipe wall is found and the stress intensity factor for such cracks with real crack shape are numerically estimated in these critical locations. The methodology presented here can be used for estimation of residual lifetime of welded polymer pipes containing crack.
Keywords:
Polyolefin pipes; butt weld; stress intensity factor; numerical loading
Available at various institutes of the ASCR
FRACTURE MECHANICS ASSESSMENT OF CRACKED WELDED POLYOLEFIN PIPES
The aim of this paper is to present methodology for estimation of fracture mechanics parameters in polyolefin pipes with an axially oriented crack using three dimensional numerical analyses. Linear ...
GRAIN REFINEMENT EFFECT ON FATIGUE PROPERTIES OF AUSTENITIC STAINLESS STEEL WITH DEFORMATION INDUCED MARTENSITE FORMATION
Chlupová, Alice; Man, Jiří; Polák, Jaroslav; Škorík, Viktor; Karjalainen, J.
2014 - English
Fatigue properties of metastable austenitic 301LN steel with coarse and ultrafine-grained microstructures were investigated at ambient temperature and the effect of grain refinement was evaluated. Two different microstructural states of material were introduced by different annealing conditions during special thermo-mechanical treatment. Fatigue life curves were obtained and compared for both coarse-grained and ultra-fine-grained states of austenitic stainless steel. Magnetic measurements before, during and after cyclic loading were performed to reveal structural changes, i.e. formation of deformation-induced martensite. Relationship between microstructure refinement, phase composition and fatigue properties was discussed.
Keywords:
Fatigue; 301LN austenitic stainless steel; grain refinement
Available at various institutes of the ASCR
GRAIN REFINEMENT EFFECT ON FATIGUE PROPERTIES OF AUSTENITIC STAINLESS STEEL WITH DEFORMATION INDUCED MARTENSITE FORMATION
Fatigue properties of metastable austenitic 301LN steel with coarse and ultrafine-grained microstructures were investigated at ambient temperature and the effect of grain refinement was evaluated. Two ...
Thermodynamics of Dislocation Pattern Formation at the Mesoscale
Gröger, Roman
2014 - English
We introduce a mesoscopic framework that is capable of simulating the evolution of dislocation networks and, at the same time, spatial variations of the stress, strain and displacement fields throughout the body. Within this model, dislocations are viewed as sources of incompatibility of strains. The free energy of a deformed solid is represented by the elastic strain energy that can be augmented by gradient terms to reproduce dispersive nature of acoustic phonons and thus set the length scale of the problem. The elastic strain field that is due to a known dislocation network is obtained by minimizing the strain energy subject to the corresponding field of incompatibility constraints. These stresses impose Peach-Koehler forces on all dislocations and thus drive the evolution of the dislocation network.
Keywords:
dislocation; pattern; incompatibility; thermodynamics; Nye tensor; mesoscale
Available at various institutes of the ASCR
Thermodynamics of Dislocation Pattern Formation at the Mesoscale
We introduce a mesoscopic framework that is capable of simulating the evolution of dislocation networks and, at the same time, spatial variations of the stress, strain and displacement fields ...
Applicability of small punch test to determine the material mechanical properties at room and high temperatures
Dymáček, Petr; Ječmínka, M.
2014 - English
The paper is focused on testing of mechanical properties by small punch test (SPT) and comparison of these properties with mechanical properties obtained by conventional tensile tests of steels P92 and AISI 316L. The yield stress and ultimate tensile stress obtained by SPT at constant deflection rate (SPT-CDR) were evaluated. Values of initial stress and residual stress were evaluated from relaxation small punch test (SPT-R). Mechanical properties obtained by SPT-CDR and SPT-R are compared with mechanical properties obtained by conventional tensile test and relaxation tensile test, respectively. Modified empirical relationships for an assessment of tensile test properties from quantities determined by small punch test are proposed. Good agreement of results of SPT-R and relaxation tensile test is shown by their comparison.
Keywords:
small punch test; stress relaxation
Available at various institutes of the ASCR
Applicability of small punch test to determine the material mechanical properties at room and high temperatures
The paper is focused on testing of mechanical properties by small punch test (SPT) and comparison of these properties with mechanical properties obtained by conventional tensile tests of steels P92 ...
The Gurson-Tvergaard-Needleman model calibration from sub-size test specimens by size corresponding to the half of Charpy specimen
Stratil, Luděk; Šiška, Filip; Hadraba, Hynek; Dlouhý, Ivo
2014 - English
The paper deals with a utilization of miniaturized tensile specimens for purposes of local approach application from limited amount of test material. The motivation for application of those miniaturized specimens is the utilization of volume of test material corresponding to the half of Charpy specimen. The tensile testing of miniaturized specimens was conducted at room temperature in ductile regime of the Eurofer97 steel followed by detailed fractography and quantitative analysis of micromechanism of damage. The parameters of Gurson-Tvergaard-Needleman micromechanical model of ductile fracture were calibrated. Except for the slight differences in strength and deformation characteristics no other differences between two sizes of tensile specimens were found. The calibrated sets of parameters of GTN model using the same element size were very similar. The application of different calibrated sets of GTN model parameters for simulation of damage in cracked specimen (R-curve) is sensitive to the element size and needs its calibration.
Keywords:
GTN model; miniaturized specimens; fractography analysis; ductile damage
Available at various institutes of the ASCR
The Gurson-Tvergaard-Needleman model calibration from sub-size test specimens by size corresponding to the half of Charpy specimen
The paper deals with a utilization of miniaturized tensile specimens for purposes of local approach application from limited amount of test material. The motivation for application of those ...
Z-phase in Cr-Nb-N system studied by analytical electron microscopy
Buršík, Jiří; Kroupa, Aleš
2014 - English
In this work we study the Z-phase in model Cr-Nb-N alloys by means of analytical electron microscopy (SEM and TEM).
Keywords:
Cr-Nb-N system; SEM and TEM; EDX
Available at various institutes of the ASCR
Z-phase in Cr-Nb-N system studied by analytical electron microscopy
In this work we study the Z-phase in model Cr-Nb-N alloys by means of analytical electron microscopy (SEM and TEM).
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