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Wyszukujesz frazę "Dvorak, P." wg kryterium: Wszystkie pola


Wyświetlanie 1-4 z 4
Tytuł:
Influence of Long-term Annealing and Hot Bending on Creep of P92 Pipe
Autorzy:
Kral, P.
Dvorak, J.
Kvapilova, M.
Kucharova, K.
Sklenicka, V.
Svobodova, M.
Cmakal, J.
Powiązania:
https://bibliotekanauki.pl/articles/1402074.pdf
Data publikacji:
2015-10
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
81.05.-t
81.40.-z
62.20.Hg
68.37.Hk
Opis:
This work is focused on the creep behaviour of the thick-walled hot bended P92 pipe, with an outer diameter of 350 mm and wall thickness of 39 mm, in its different parts, namely in straight parts and bends. Selected creep specimens machined from axial section of pipe were thermally aged at 650°C to simulate microstructure degradation typical for long-term service conditions. Subsequent tensile creep tests at constant load were performed at 600°C under 140 MPa and creep behaviour of various structure states was compared. Microstructure was investigated by scanning electron microscopy equipped with electron backscatter diffraction. It was found that ageing at 650°C for 10⁴ h caused the significant reduction of creep resistance down to about 10% of initial state and an additional slight reduction of creep resistance after longer ageing for 2×10⁴ h. Further, creep behaviour was significantly influenced by specimen position in the extrados and intrados parts of bends. Microstructure investigation revealed that long-term annealing has negligible effect on high-angle grain boundary spacing and misorientation. By contrast, creep deformation of long-term annealed specimens led to significant decreasing in high-angle grain boundary spacing and caused a change in the misorientation distribution of boundaries.
Źródło:
Acta Physica Polonica A; 2015, 128, 4; 543-547
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Microstructure Mechanisms Governing the Creep Life of Ultrafine-Grained Cu-0.2 wt%Zr Alloy
Autorzy:
Kral, P.
Svoboda, M.
Dvorak, J.
Kvapilova, M.
Sklenicka, V.
Powiązania:
https://bibliotekanauki.pl/articles/1418438.pdf
Data publikacji:
2012-09
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
81.05.-t
61.66.Dk
62.20.Hg
68.37.Lp
Opis:
Equal-channel angular pressing was conducted at room temperature and extrusion was performed up to 12 passes using route where the billets were rotated by 90° in the same sense between consecutive passes. Tensile creep tests were performed at 473, 573 and 673 K at different constant applied stresses. It was observed that the original coarse grain size of unprocessed alloy was reduced to 0.3 μm after 8 equal-channel angular pressing passes and the grain growth during creep was restricted by precipitates with the mean diameter ≈ 4.0 nm. No significant effect on creep resistance was found after one equal-channel angular pressing pass at 473 and 573 K. However, the longest time to fracture was exhibited by alloy after 2 equal-channel angular pressing passes at 573 and 673 K but with further increasing number of equal-channel angular pressing passes a decrease in the time to fracture was observed. Nevertheless, the beneficial effect of equal-channel angular pressing on creep resistance was still documented after 8 passes for temperatures of 473 and 573 K. By contrast, creep tests performed at 673 K showed that the time to fracture of ultrafine-grained material is shorter as compared with that for as-received state. The 3D laser measurement of surface showed that the creep fracture process is accelerated by formation of vertical surface step relief and cavitation at the intersection of the shear bands during creep.
Źródło:
Acta Physica Polonica A; 2012, 122, 3; 457-460
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Creep Behavior of a Zirconium Alloy Processed by Equal-Channel Angular Pressing
Autorzy:
Sklenicka, V.
Dvorak, J.
Kral, P.
Svoboda, M.
Kvapilova, M.
Kopylov, V.
Nikulin, S.
Dobatkin, S.
Powiązania:
https://bibliotekanauki.pl/articles/1418491.pdf
Data publikacji:
2012-09
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
81.40.Lm
62.20.Hg
81.05.-t
81.07.Bc
81.70.Bt
Opis:
A Zr-2.5 wt%Nb alloy was processed by equal-channel angular pressing and then tested under creep conditions at 623 K using a tensile stress within the range from 120 to 300 MPa. The results show conventional power-law creep with a stress exponent of n > 3 which is consistent with an intragranular dislocation process involving the glide and climb of dislocations. It is demonstrated that diffusion creep is not important in these tests. For comparison purposes, the experiments were conducted using both the unprocessed alloy and after processing by equal-channel angular pressing. It was found that under same testing conditions the measured minimum creep rates in the pressed alloy with ultrafine grain sizes were faster than in the same alloy in a coarse-grained unprocessed condition.
Źródło:
Acta Physica Polonica A; 2012, 122, 3; 485-489
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Struktura czasu pracy harwesterów podczas pozyskania przygodnego
Structure of the operating time of the harvesters during casual logging
Autorzy:
Dvorak, J.
Walczyk, J.
Hoskova, P.
Powiązania:
https://bibliotekanauki.pl/articles/989858.pdf
Data publikacji:
2015
Wydawca:
Polskie Towarzystwo Leśne
Tematy:
lesnictwo
usuwanie szkod
pozyskiwanie drewna
harwestery
struktura czasu pracy
wydajnosc pracy
kleski zywiolowe
harvester
operational time
random logging
productivity
Opis:
Natural disasters often cause that large share of acquisitions are performed under contingent conditions. High concentration of raw wood material and urgent need for its rapid removal from the forest demand use of harvesters. Material acquisition in such conditions is much harder and causes loss of performance for working machines. The objective of this paper was to determine the decrease in harvester performance during acquisition of fallen trees, wood scrap and suspended trees compared to acquisition of undamaged trees. Performance analysis was conducted on 10 harvesters from different power class working in the Czech Republic in years 2007−2012. The time structure was determined for the timber acquisition under contingent conditions in 22 forest stands. Later on it was compared with acquisition under normal conditions, i.e. scheduled acquisition on areas with good load carrying capacity and without obstacles and with an inclination up to 33%. There was significant difference in the mean operating time requirements between harvesters from the analysed power classes. Machines form 1st class differed significantly form devices from 2nd and 3rd classed. Results indicate that in spruce stands with wood scrap time consumption increases by 7% when average and high performance harvesters are used. The increase is by 33% during acquisition of fallen trees, while time consumption increases by as much as 79% during acquisition of suspended trees. During acquisition of subversion and wood scrap, performance of average and high performance harvesters ranged between 1.71 up to 17.37 m³/h depending on thickness and type of the damage to obtained trees. Important achievement of presented research is correction factors allowing to change harvester performance standards, while acquisition of fallen trees, wood scrap and suspended trees. Average value of correction factor is 1.19.
Źródło:
Sylwan; 2015, 159, 04; 300-306
0039-7660
Pojawia się w:
Sylwan
Dostawca treści:
Biblioteka Nauki
Artykuł
    Wyświetlanie 1-4 z 4

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