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    Wyświetlanie 1-13 z 13
    Tytuł:
    Acoustic Emission Study of Plastic Instabilities in AlSi1MgMn
    Autorzy:
    Molnárová, O.
    Dobroň, P.
    Chmelík, F.
    Powiązania:
    https://bibliotekanauki.pl/articles/1402161.pdf
    Data publikacji:
    2015-10
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    43.40.Le
    81.40.Lm
    62.20.F-
    46.32.+x
    Opis:
    The influence of the strain rate and heat treatment on the occurrence of plastic instabilities in a cast AlSi1MgMn alloy was studied. The samples were uniaxially loaded in compression at various strain rates and at room temperature. The tests were done with concurrent acoustic emission monitoring and the acoustic emission parameters are correlated to the microstructure and to the stress-strain curves in order to better understand the patterns of plastic deformation. All samples exhibited the Portevin-Le Chatelier effect of different types, dependently on the heat treatment and the applied strain rate. The occurrence of the Portevin-Le Chatelier effect is manifested by acoustic emission signals with high amplitudes. Statistical analysis of the acoustic emission signals shows the power-law probability distribution.
    Źródło:
    Acta Physica Polonica A; 2015, 128, 4; 801-804
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Differences in the intensity of physical activity during school days and weekends in Polish and Czech boys and girls
    Autorzy:
    Fromel, K.
    Kudlacek, M.
    Groffik, D.
    Chmelik, F.
    Jakubec, L.
    Powiązania:
    https://bibliotekanauki.pl/articles/52063.pdf
    Data publikacji:
    2016
    Wydawca:
    Instytut Medycyny Wsi
    Źródło:
    Annals of Agricultural and Environmental Medicine; 2016, 23, 2
    1232-1966
    Pojawia się w:
    Annals of Agricultural and Environmental Medicine
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    The Influence of Rolling Conditions on Deformation Behavior of Magnesium Alloy Sheets
    Autorzy:
    Drozdenko, D.
    Bohlen, J.
    Chmelík, F.
    Letzig, D.
    Dobroň, P.
    Powiązania:
    https://bibliotekanauki.pl/articles/1402160.pdf
    Data publikacji:
    2015-10
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    81.70.Bt
    81.20.Wk
    61.72.Mm
    61.72.Hh
    43.40.Le
    Opis:
    The influence of texture on deformation behavior was investigated for conventionally rolled magnesium alloy slabs and rolled twin roll cast magnesium alloy strips in the form of sheets. The Mg-Zn based sheets were deformed at room temperature with the tensile axis oriented in the rolling and transversal directions. The texture with respect to different rolling conditions was characterized by X-ray diffraction. In the case of Mg-Zn-rare earth alloy sheets, the basal pole intensity, aligned with the sheet normal direction, is lower for conventionally rolled sheet in comparison to the rolled twin roll cast strip. Difference in angular distribution of basal planes influences on the mechanical behavior of the sheets. The yield strength is higher for the tension along rolling direction than along transversal direction for the conventionally rolled sheets, whereas the opposite deformation behavior is observed for the rolled twin roll cast strips. Furthermore, the planar anisotropy of the yield strength is less pronounced for the rolled twin roll cast strips. The deformation behavior of the sheets was also investigated by the acoustic emission technique. The acoustic emission signal analysis correlates the microstructure and the stress-time curves with active deformation mechanisms. It highlights the activity of a basal slip and tensile twinning, particularly during the transverse direction tension.
    Źródło:
    Acta Physica Polonica A; 2015, 128, 4; 795-800
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Acoustic Emission Study of the Deformation Behavior of Mg-Mn Alloys Containing Rare Earth Elements
    Autorzy:
    Illkova, K.
    Dobroň, P.
    Chmelík, F.
    Letzig, D.
    Bohlen, J.
    Powiązania:
    https://bibliotekanauki.pl/articles/1419114.pdf
    Data publikacji:
    2012-09
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    81.05.Bx
    81.20.Hy
    83.50.Uv
    81.40.Ef
    83.50.-v
    43.40.Le
    Opis:
    Magnesium-manganese (Mg-Mn) based alloys with various chemical composition were processed by indirect extrusion at two different speeds. Alloying with Mn and rare earth elements has significant influence on the microstructure and on the texture of the alloys under investigation. This paper deals with the acoustic emission analysis of the deformation behavior of the extruded Mg-Mn alloys. The acoustic emission measurements were performed during the uniaxial tension and compression tests, and the obtained results are discussed with respect to the influence of rare-earth elements on the deformation behavior, particularly in terms of the activation of dislocation glide and twinning.
    Źródło:
    Acta Physica Polonica A; 2012, 122, 3; 634-638
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Evolution of Corrosion Resistance in the LAE442 Magnesium Alloy Processed by ECAP
    Autorzy:
    Minárik, P.
    Král, R.
    Janeček, M.
    Chmelík, F.
    Hadzima, B.
    Powiązania:
    https://bibliotekanauki.pl/articles/1402153.pdf
    Data publikacji:
    2015-10
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    81.05.-t
    82.45.Bb
    Opis:
    The influence of processing by equal channel angular pressing on the corrosion resistance was investigated in the extruded LAE442 magnesium alloy by the linear polarization method. Continuous increase of the corrosion resistance with the increasing number of passes was measured. The polarization resistance of the 12P sample was substantially higher as compared to the extruded state. The results were discussed in terms of the corrosion layers formed on the surface after seven days of immersion. It was concluded that the substantial increase of polarization resistance was caused by the combined effect of grain refinement and aluminum and lithium oxides formation within the corrosion layer.
    Źródło:
    Acta Physica Polonica A; 2015, 128, 4; 772-774
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    On the Effect of the Extrusion Speed on Microstructure and Plastic Deformation of ZE10 and ZEK100 Magnesium Alloys - an Acoustic Emission Study
    Autorzy:
    Dobroň, P.
    Chmelík, F.
    Parfenenko, K.
    Letzig, D.
    Bohlen, J.
    Powiązania:
    https://bibliotekanauki.pl/articles/1419005.pdf
    Data publikacji:
    2012-09
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    81.05.Bx
    81.20.Ev
    62.20.F-
    61.05.cp
    43.40.Le
    Opis:
    Mg-Zn-based alloys ZE10 and ZEK100 have been extruded at different speeds varying from 1 m/min to 20 m/min. Specimens taken in the extrusion direction were uniaxially loaded in tension and compression at room temperature. The results are discussed using concurrent acoustic emission monitoring during mechanical testing and the acoustic emission signal analysis that correlates the microstructure and the stress-strain curves to the possible deformation mechanisms. In all tests, the acoustic emission response exhibited a large acoustic emission peak at the beginning of plastic deformation. A small local maximum on the onset of the acoustic emission activity was frequently observed, i.e. at very low stresses. For the alloys with bimodal grain structure tested in compression, an additional acoustic emission peak appeared at larger strains. This peculiar behavior can be explained by interplay of (10-12)-twinning and dislocation slip in samples with various grain size distributions.
    Źródło:
    Acta Physica Polonica A; 2012, 122, 3; 593-596
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Positron Lifetime Spectroscopy of Nanocrystalline Copper
    Autorzy:
    C̆ížek, J.
    Procházka, I.
    Vostrý, P.
    Chmelík, F.
    Islamgaliev, R. K.
    Powiązania:
    https://bibliotekanauki.pl/articles/2007957.pdf
    Data publikacji:
    1999-04
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    78.70.Bj
    79.60.Jv
    Opis:
    Positron lifetime spectroscopy was applied to investigate the thermal stability of nanocrystalline copper prepared by severe plastic torsion deformation. Positrons annihilating in as prepared specimens exhibited free positron component τ$\text{}_{1}$ and two defect components τ$\text{}_{2}$=164 ps and τ$\text{}_{3}$=255 ps. Evolution of the lifetimes and relative intensities of all the three components with increasing annealing temperature during step-by-step isochronal annealing up to 630°C was studied. Behaviour of positrons in nanocrystalline copper could not be interpreted in the frame of conventional 3-state trapping model due to highly inhomogeneous defect distribution. Therefore a modified trapping model was developed and applied to explain the experimental results.
    Źródło:
    Acta Physica Polonica A; 1999, 95, 4; 487-495
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Acoustic Emission During Firing of the Illite-Based Ceramics with Fly Ash Addition
    Autorzy:
    Knapek, M.
    Húlan, T.
    Dobroň, P.
    Chmelík, F.
    Trník, A.
    Štubňa, I.
    Powiązania:
    https://bibliotekanauki.pl/articles/1402156.pdf
    Data publikacji:
    2015-10
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    64.70.ph
    61.43.Fs
    65.60.+a
    81.70.Pg
    43.40.Le
    Opis:
    In this work, illite-based ceramic body with power plant fly ash addition (60 wt.% of illite, 30 wt.% of fly ash and 10 wt.% of illite fired at 1100°C) was investigated by the thermal analysis techniques (differential thermal analysis, thermodilatometry and thermogravimetry) and the acoustic emission technique. The green body was heated up to 1100°C at three different rates 2.5, 5, 10 K/min. The most intense acoustic emission was recorded at the highest rate 10 K/min. Mutual correlations between thermal analyses and acoustic emission data were also examined. The first acoustic emission response appears at 430°C, corresponding to a small endotherm on the DTA curve, where the thermal decomposition of mineral portlandite takes place. In the temperature range from 600 to 900°C, high acoustic emission activity correlates with dehydroxylation and expansion of the sample. At temperatures higher than 800°C, the source of acoustic emission signals is the thermal decomposition of calcite. The amorphous phase created from illite at 920°C becomes pyroplastic, therefore it is not documented by the acoustic emission technique.
    Źródło:
    Acta Physica Polonica A; 2015, 128, 4; 783-786
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Influence of Pre-Compression on Tensile Behaviour in Wrought Mg-Zn-Ce Alloy Studied by the Acoustic Emission Technique
    Autorzy:
    Dobroň, P.
    Drozdenko, D.
    Bohlen, J.
    Yi, S.
    Letzig, D.
    Chmelík, F.
    Powiązania:
    https://bibliotekanauki.pl/articles/1402159.pdf
    Data publikacji:
    2015-10
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    81.05.Bx
    62.20.M-
    61.05.J-
    81.70.Bt
    43.40.Le
    Opis:
    Wrought Mg-Zn-Ce alloy (ZE10) has been pre-compressed and subsequently subjected to tensile loading. Due to a fibre texture of the samples, the level of pre-compression stress significantly influences the subsequent tensile behaviour. The acoustic emission technique was used for monitoring active deformation mechanisms during mechanical testing. The obtained acoustic emission results are correlated to the stress-time curves and the differences in the acoustic emission count rate were used to reveal changes in underlying deformation mechanisms. Firstly, a compression-tension cycle was monitored by the acoustic emission technique. Then, the samples were deformed to specific points on the stress-time curve, where acoustic emission exhibits strong changes in the activity. The following microstructure analysis of the samples, deformed to different strain-levels, by using electron back scattered diffraction method brought a detailed insight into active deformation mechanisms. Twinning during the pre-compression was followed by detwinning during the tensile loading. Two consecutive acoustic emission peaks, which appeared at larger strains, are explained by interplay of detwinning and dislocation slip and a nucleation of compression twins, respectively.
    Źródło:
    Acta Physica Polonica A; 2015, 128, 4; 790-794
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    The Effect of Reversed Loading Conditions on the Mechanical Behaviour of Extruded Magnesium Alloy AZ31
    Autorzy:
    Bohlen, J.
    Dobron, P.
    Nascimento, L.
    Parfenenko, K.
    Chmelik, F.
    Letzig, D.
    Powiązania:
    https://bibliotekanauki.pl/articles/1418429.pdf
    Data publikacji:
    2012-09
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    43.40.Le
    61.72.Mm
    81.05.Bx
    81.70.Bt
    Opis:
    An indirectly extruded round bar of magnesium alloy AZ31 has been subjected to a cyclic test consisting of preloading in compression to different values of maximum stress followed by a single tensile test segment. Concurrent acoustic emission measurements were used to determine the active deformation mechanisms during plastic flow and work hardening. Electron backscattering diffraction was applied to obtain local orientation images in order to reveal twins and twinned fractions of the microstructure. Twins form preferentially in larger grains during the compression test segment and only with increasing stress do smaller grains show twinning. Some grains are completely re-oriented as a result of twinning. During the tensile test segment, untwinning is the most significant deformation mechanism although in some re-oriented grains new twins also nucleate. The acoustic emission count rates confirm that this is only the case after compression to higher stress levels.
    Źródło:
    Acta Physica Polonica A; 2012, 122, 3; 444-449
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Psychological, social and environmental predictors of physical activity in Mexican adolescents
    Psychologiczne, społeczne i środowiskowe czynniki wpływające na aktywność fizyczną u nastolatków meksykańskich
    Autorzy:
    Cocca, A.
    Chmelik, F.
    Cocca, M.
    Verdugo, F.D.E.
    Cuenca, L.T.R.
    Powiązania:
    https://bibliotekanauki.pl/articles/2052689.pdf
    Data publikacji:
    2017
    Wydawca:
    Akademia Bialska Nauk Stosowanych im. Jana Pawła II w Białej Podlaskiej
    Tematy:
    health
    exercise
    youth
    environment
    behavior
    zdrowie
    ćwiczenia
    młodzież
    środowisko
    zachowanie
    Opis:
    Background. Sedentarism and Physical Activity (PA) are considered main components of people’s lifestyle and key indicators of health. Although they can be seen as opposite life conducts that reduce each other’s effects on health, no study has yet clarified the nature of their relation. However, both behaviors can be influenced by similar psychological, social, and environmental constructs. Material and methods. We selected 480 students (272 boys, 208 girls) from middle schools in the metropolitan area of Monterrey (Mexico), who filled in questionnaires on PA behaviors and social-environmental correlates through an online system. Results. Our outcomes highlighted overall low PA levels. Further, girls are more affected by their social environment, whereas physical environment barriers represent a fitting predictor of boys’ PA. Regardless of gender, PA engagement seems to be significantly determined by the level of enjoyment of sedentary behaviors. Conclusions. These results can help professionals in PA and health create gender-specific interventions targeting to raise youth’s PA levels by means of enhancing psychosocial and contextual features. Due to the lack of studies on psychological factors related to sedentary behaviors, our results could arouse attention on this issue and promote further research to better understand the processes beneath it.
    Wprowadzenie. Siedzący tryb życia i aktywność fizyczna (AF) są postrzegane jako główne elementy życia ludzi i kluczowe wskaźniki zdrowia. Chociaż można je uznać za przeciwstawne i wzajemnie wykluczające się w kontekście zdrowia, literatura nie wyjaśniła jeszcze charakteru ich relacji. Oba te style życia mogą jednakże być ukształtowane przez podobne czynniki psychologiczne, społeczne i środowiskowe. Materiał i metody. W badaniu wzięło udział 480 uczniów (272 chłopców, 208 dziewcząt) z gimnazjów w Monterrey (Meksyk), którzy wypełniali kwestionariusze w systemie online dotyczące ich aktywności fizycznej i relacji społeczno-środowiskowych. Wyniki. Uzyskane wyniki wykazują ogólnie niski poziom aktywności fizycznej. Ponadto, okazuje się, iż otoczenie społeczne ma większy wpływ na zachowanie dziewcząt w zakresie kultury fizycznej, podczas gdy głównym czynnikiem oddziałującym na chłopców są ich ograniczenie fizyczne. Niezależnie od płci, zaangażowanie w uprawianie aktywności fizycznej jest znacząco ograniczane poziomem zadowolenia z siedzącego trybu życia. Wnioski. Niniejsze wyniki mogą pomóc profesjonalistom z dziedziny zdrowia publicznego i aktywności fizycznej w stworzeniu programów interwencyjnych skierowanych do poszczególnych płci, które mogłyby okazać się pomocne w podniesieniu poziomu aktywności fizycznej wśród młodzieży poprzez poprawę funkcji psychospołecznych i środowiskowych. Ze względu na brak badań nad czynnikami psychologicznymi związanymi z siedzącym trybem życia, nasze wyniki mogłyby zachęcić badaczy do podjęcia dalszych prac, mających na celu lepsze zrozumienie procesów wpływających na aktywność młodzieży.
    Źródło:
    Health Problems of Civilization; 2017, 11, 3; 125-134
    2353-6942
    2354-0265
    Pojawia się w:
    Health Problems of Civilization
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Acoustic-Emission Study of Intermittency of Plastic Flow during Twinning and Dislocation Glide
    Autorzy:
    Shashkov, I.
    Lebedkina, T.
    Lebyodkin, M.
    Dobron, P.
    Chmelik, F.
    Kral, R.
    Parfenenko, K.
    Mathis, K.
    Powiązania:
    https://bibliotekanauki.pl/articles/1418404.pdf
    Data publikacji:
    2012-09
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    62.20.F-
    62.65.+k
    05.65.+b
    64.60.av
    Opis:
    Recent studies of plastic deformation with the aid of acoustic emission techniques proved an intermittent, scale-invariant character of plastic processes, as reflected in power-law statistical distributions. In some cases, the power-law exponents display close values leading to hypothesis of universality of scaling laws for various mechanisms of plasticity. Nevertheless, the accurate determination of the power law may be impeded by some sources of errors inevitable in real conditions, in particular, by superposition of individual acoustic emission events. In the present work, the sensitivity of the apparent statistics to the variation of the parameters of individualization of acoustic emission events is examined using Mg and Al based alloys. Both these alloys exhibit a highly cooperative character of plastic deformation, leading to strong acoustic activity which is governed by distinct microscopic mechanisms - mechanical twinning and the Portevin-Le Chatelier effect, respectively.
    Źródło:
    Acta Physica Polonica A; 2012, 122, 3; 430-434
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-13 z 13

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