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    Wyświetlanie 1-8 z 8
    Tytuł:
    A Constructive Characterization of Vertex Cover Roman Trees
    Autorzy:
    Martínez, Abel Cabrera
    Kuziak, Dorota
    Yero, Ismael G.
    Powiązania:
    https://bibliotekanauki.pl/articles/32083833.pdf
    Data publikacji:
    2021-02-01
    Wydawca:
    Uniwersytet Zielonogórski. Wydział Matematyki, Informatyki i Ekonometrii
    Tematy:
    Roman domination
    outer-independent Roman domination
    vertex cover
    vertex independence
    trees
    Opis:
    A Roman dominating function on a graph G = (V(G), E(G)) is a function f : V(G) → {0, 1, 2} satisfying the condition that every vertex u for which f(u) = 0 is adjacent to at least one vertex v for which f(v) = 2. The Roman dominating function f is an outer-independent Roman dominating function on G if the set of vertices labeled with zero under f is an independent set. The outer-independent Roman domination number γoiR(G) is the minimum weight w(f) = Σv∈V(G)f(v) of any outer-independent Roman dominating function f of G. A vertex cover of a graph G is a set of vertices that covers all the edges of G. The minimum cardinality of a vertex cover is denoted by α(G). A graph G is a vertex cover Roman graph if γoiR(G) = 2α(G). A constructive characterization of the vertex cover Roman trees is given in this article.
    Źródło:
    Discussiones Mathematicae Graph Theory; 2021, 41, 1; 267-283
    2083-5892
    Pojawia się w:
    Discussiones Mathematicae Graph Theory
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Accounting for the random character of nucleation in the modelling of phase transformations in steels
    Autorzy:
    Poloczek, Łukasz
    Kuziak, Roman
    Foryś, Jakub
    Szeliga, Danuta
    Pietrzyk, Maciej
    Powiązania:
    https://bibliotekanauki.pl/articles/29519774.pdf
    Data publikacji:
    2023
    Wydawca:
    Akademia Górniczo-Hutnicza im. Stanisława Staszica w Krakowie. Wydawnictwo AGH
    Tematy:
    stochastic model
    grain size
    phase transformations
    dislocation density
    cooling of rods
    heterogeneity of the microstructure
    Opis:
    In our earlier work, a stochastic model of multi-stage deformation at elevated temperatures was developed. The model was applied to calculate histograms of dislocation density and grain size at the onset of phase transformation. The histograms were used as input data for the simulation of phase transitions using the traditional deterministic model. Following this approach, microstructural inhomogeneity was predicted for different cooling conditions. The results obtained, showing the effect of dislocation density and inhomogeneity of austenite grain size on the microstructural inhomogeneity of the final product, can be considered reliable as they are based on material models determined in previous publications and validated experimentally. The aim of the present work was to extend the model by taking into account the stochastic nature of nucleation during phase transitions. The analysis of existing stochastic models of nucleation was performed, and a model for ferritic transformation in steels was proposed. Simulations for constant cooling rates as well as for industrial cooling processes of steel rods were performed. In the latter case, uncertainties in defining the boundary conditions and segregation of elements were also considered. The reduction of the computing costs is an important advantage of the model, which is much faster when compared to full field models with explicit microstructure representation.
    Źródło:
    Computer Methods in Materials Science; 2023, 23, 2; 17-28
    2720-4081
    2720-3948
    Pojawia się w:
    Computer Methods in Materials Science
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Fast model for phase transformations during cooling of pre-annealed multiphase steels
    Szybkie modele przemian fazowych podczas chłodzenia wstępnie wyżarzonych stali wielofazowych
    Autorzy:
    Szeliga, Danuta
    Kuziak, Roman
    Zalecki, Władysław
    Pidvysotskyy, Valeriy
    Chang, Yuling
    Bleck, Wolfgang
    Bachniak, Daniel
    Pietrzyk, Maciej
    Powiązania:
    https://bibliotekanauki.pl/articles/29520329.pdf
    Data publikacji:
    2019
    Wydawca:
    Akademia Górniczo-Hutnicza im. Stanisława Staszica w Krakowie. Wydawnictwo AGH
    Tematy:
    CP steel
    phase transformations
    mean field models
    stal CP
    przemiany fazowe
    średnie modele pola
    Opis:
    A thorough experimental and numerical analysis of phase transformations in a selected CP800 steel was the general objective of the paper. Dilatometric tests were performed for a wide range of cooling rates. Two models based on a mean field approach were considered. The first was an upgrade of the Johnson-Mehl-Avrami-Kolmogorov equation. The second model was based on the Leblond equation. Both models were identified using inverse analysis of the experimental data. Simulations of various cooling schedules were performed to validate the models. Phase compositions for these cooling schedules were determined. Following this the effect of elements' segregation during solidification of steel on the occurrence of marteniste/bainite bands was accounted for using the developed models.
    W artykule opisano doświadczalną i numeryczną analizę przemian fazowych w wybranej stali o podwyższonej wytrzymałości. Próby dylatometryczne wykonano w szerokim zakresie prędkości chłodzenia. Rozważono dwa modele wykorzystujące metodę średniego pola. Pierwszym modelem była zmodernizowana wersja modelu JMAK (Johnson-Mehl-Avrami-Kolmogorov). Drugim modelem było rozwinięcie równania Leblonda. Przeprowadzono identyfikację modeli wykorzystując rozwiązanie odwrotne dla prób dylatometrycznych. W celu walidacji modeli wykonano symulacje różnych schematów chłodzenia. Wyznaczono skład fazowy dla tych schematów. Następnie oszacowano wahania składu chemicznego w badanej stali i wykorzystano opracowane modele do określenie wpływu segregacji pierwiastków podczas krzepnięcia stali na powstawanie pasm martenzytu/bainitu.
    Źródło:
    Computer Methods in Materials Science; 2019, 19, 4; 150-161
    2720-4081
    2720-3948
    Pojawia się w:
    Computer Methods in Materials Science
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Mean field and full field modelling of microstructure evolution and phase transformations during hot forming and cooling of low carbon steels
    Autorzy:
    Szeliga, Danuta
    Bzowski, Krzysztof
    Rauch, Łukasz
    Kuziak, Roman
    Pietrzyk, Maciej
    Powiązania:
    https://bibliotekanauki.pl/articles/29520270.pdf
    Data publikacji:
    2020
    Wydawca:
    Akademia Górniczo-Hutnicza im. Stanisława Staszica w Krakowie. Wydawnictwo AGH
    Tematy:
    mean field models
    full field models
    finite element method
    level set method
    Opis:
    The paper describes a critical comparison of mean field and full field approaches to modelling hot deformation/controlled cooling sequences for steels. Classification of the models, based on the balance between predictive capabilities and computing costs, is presented. Mean field models, which describe microstructure evolution and phase transformations were connected with thermomechanical finite element program and applied to simulation of the hot strip rolling process and cooling of tubes after hot rolling. Full field model described in the paper is a connection of the finite element (FE) and level set (LSM) methods. These methods were used to simulate heating/cooling sequence in the continuous annealing line. A suggestion to use a stochastic model as a bridge between mean field and full field approaches is made.
    Źródło:
    Computer Methods in Materials Science; 2020, 20, 3; 121-132
    2720-4081
    2720-3948
    Pojawia się w:
    Computer Methods in Materials Science
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Physical and numerical simulation of the production chain of fasteners manufactured of 32CrB4 steel control-cooled in the stelmor process to develop the multiphase microstructure
    Autorzy:
    Piwowarczyk, Michał
    Wolańska, Natalia
    Wilkus, Marek
    Pietrzyk, Maciej
    Rauch, Łukasz
    Kuziak, Roman
    Pidvysots’kyy, Valeriy
    Radwański, Krzysztof
    Powiązania:
    https://bibliotekanauki.pl/articles/29519769.pdf
    Data publikacji:
    2023
    Wydawca:
    Akademia Górniczo-Hutnicza im. Stanisława Staszica w Krakowie. Wydawnictwo AGH
    Tematy:
    wire rod
    Stelmor process
    multiphase steels
    cold heading
    numerical modelling
    Opis:
    The development of the concept of Thermomechanical Controlled Processing (TMCP) in the wire rod rolling mill of CMC Poland has opened up new opportunities for the production of fasteners without the application of heat treatment. The crucial effect of TMCP in the case of wire rod rolling is its capability of shaping fine austenite grain size following the last pass, typically below 20–25 µm in the wire rod cross-section. This is a prerequisite for obtaining the required cold workability level for the cold forming of fasteners, even if hard constituents (bainite, martensite) are present in the wire rod structure. In this paper, the physical simulation and numerical modelling capabilities were described for the design of cooling conditions in the Stelmor process and cold heading operation. The investigated material was conventional 32CrB4 grade used for the fasteners production with the application of heat treatment.
    Źródło:
    Computer Methods in Materials Science; 2023, 23, 2; 5-16
    2720-4081
    2720-3948
    Pojawia się w:
    Computer Methods in Materials Science
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Thermal-mechanical finite element simulation of flat bar rolling coupled with a stochastic model of microstructure evolution
    Autorzy:
    Szeliga, Danuta
    Czyżewska, Natalia
    Kusiak, Jan
    Kuziak, Roman
    Morkisz, Paweł
    Oprocha, Piotr
    Pietrzyk, Maciej
    Piwowarczyk, Michał
    Poloczek, Łukasz
    Przybyłowicz, Paweł
    Rauch, Łukasz
    Wolańska, Natalia
    Powiązania:
    https://bibliotekanauki.pl/articles/29520070.pdf
    Data publikacji:
    2022
    Wydawca:
    Akademia Górniczo-Hutnicza im. Stanisława Staszica w Krakowie. Wydawnictwo AGH
    Tematy:
    flat bars
    hot rolling
    thermal-mechanical finite element model
    microstructure evolution
    stochastic model
    Opis:
    It is generally recognized that the kinetics of phase transformations during the cooling of steel products depends to a large extent on the state of the austenite after rolling. Austenite deformation (when recrystallization is not complete) and grain size have a strong influence on the nucleation and growth of low-temperature phases. Thus, the general objective of the present work was the formulation of a numerical model which simulates thermal, mechanical and microstructural phenomena during multipass hot rolling of flat bars. The simulation of flat bar rolling accounting for the evolution of a heterogeneous microstructure was the objective of the work. A conventional finite-element program was used to calculate the distribution of strains, stresses, and temperatures in the flat bar during rolling and during interpass times. The FE program was coupled with the stochastic model describing austenite microstructure evolution. In this model, the random character of the recrystallization was accounted for. Simulations supplied information about the distributions of the dislocation density and the grain size at various locations through the thickness of the bars.
    Źródło:
    Computer Methods in Materials Science; 2022, 22, 3; 137-148
    2720-4081
    2720-3948
    Pojawia się w:
    Computer Methods in Materials Science
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-8 z 8

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