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Popis zdržljivostnih krivulj lezenja z uporabo časovno-temperaturnega parametra
Bertoncelj, Luka (Author), Nagode, Marko (Mentor) More about this mentor... This link opens in a new window, Šeruga, Domen (Co-mentor)

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Abstract
Magistrsko delo predstavlja izpeljavo in oblikovanje splošnega matematičnega modela za popis deformacijskega mehanizma lezenja ter njegovo naknadno pretvorbo v uporabno numerično obliko. V praksi se zaradi enostavnosti in hitrosti računalniškega procesiranja, za popis lezenja, uporablja aproksimacijski polinom 2. stopnje. Z njim z zadovoljivo kakovostjo popišemo set eksperimentalnih točk v področju visokih in srednjih temperaturnih in napetostnih nivojev, v področju nizkih temperatur in napetosti pa z njim ne moremo celovito zajeti fizikalnega dogajanja. V ta namen smo, z uporabo metode najmanjših kvadratov, zapisali splošni numerični model ter na primeru eksperimentalnih točk dveh vrst jekel (1.25Cr0.5Mo in 5Cr0.5Mo) izoblikovali zdržljivostne krivulje z uporabo aproksimacijskih polinomov 2., 3., 4. in 5. reda ter jih medsebojno primerjali. Ugotovili smo, da s polinomi višjih redov bolj natančno popišemo ekstrapolirano območje nizkih napetosti in temperatur, vendar njihova korektna fizikalna vpeljava zajema tudi veliko izzivov. V splošnem se izkaže, da je metoda zelo občutljiva na raztros podatkov, poleg tega pa se, še posebej v primeru polinomov višjih redov (>2.), zaradi večje prostosti lahko pojavi fizikalno neutemeljena usmeritev zdržljivostnih krivulj. To nam daje vedeti, da je za večjo stabilnost numeričnega modela potrebno definirati dodatne pogoje, s katerimi bi njihovo gibanje omejili.

Language:Slovenian
Keywords:zdržljivostne krivulje, lezenje, aproksimacijski polinom, ekstrapolacija, optimizacija, mehanizmi lezenja, enačbe tečenja, diagram mehanizmov lezenja
Work type:Master's thesis/paper (mb22)
Organization:FS - Faculty of Mechanical Engineering
Year:2017
Views:617
Downloads:247
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Secondary language

Language:English
Title:Description of creep master curves with a time-temperature parameter
Abstract:
The master thesis presents the evolution of a mathematical and later on, numerical model that defines the creep deformation mechanism. Due to limitations of computational speed, in reality, a 2nd-degree approximation polynomial is used, which enables a quality presentation of the high and middle temperature and stress zones; however, in the low temperature and stress zone, it does not consider the physical phenomena that are related to creep. For that reason, the \emph{Least Square Method} was used to define a general numerical model that was later on tested on two materials (1.25Cr0.5Mo and 5Cr0.5Mo). By using it, we formed 2nd, 3rd, 4th and 5th-grade master curves and compared them to each other. We determined that higher grade polynomials enable physically better definition of the extrapolated low temperature and stress zone; however, their usage also creates several problems related to data scatter. This is especially proven with higher grade polynomials (> 2nd) due to more degrees of freedom, which can result in a physically incorrect behavior of the master curves. This clearly indicates that in order to establish a stable and robust numerical model, additional conditions need to be applied.

Keywords:master curves, creep, approximation polynomial, extrapolation, optimization, creep mechanisms, rate equation, deformation map

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