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Title:Vpliv zaostalih napetosti na rast utrujenostne razpoke v upognjenem delu podnice tlačne posode
Authors:ID Jagarinec, Darko (Author)
ID Gubeljak, Nenad (Mentor) More about this mentor... New window
ID Predan, Jožef (Comentor)
Files:.pdf DOK_Jagarinec_Darko_2017.pdf (10,69 MB)
MD5: EA5763046AE0C1487E0DC5D521B06952
PID: 20.500.12556/dkum/2b5d3580-3186-4295-b295-382c6debca91
 
Language:Slovenian
Work type:Dissertation
Typology:2.08 - Doctoral Dissertation
Organization:FS - Faculty of Mechanical Engineering
Abstract:Postopek izdelave podnice ustvarja kompleksno deformacijsko-napetostno stanje, ki ga ni možno enostavno prenesti v laboratorijske pogoje testiranja. V nalogi smo pokazali, da s predhodnim upogibanjem in nato nateznim obremenjevanjem ustvarimo sestavljeno napetostno stanje, ki ga je možno analizirati le v eni kritični točki na notranji strani upognjenca. Z numeričnim modeliranjem napetostnega stanja smo se približali eksperimentalno določenim razmeram med utrujanjem s kombiniranim obremenjevanjem pred-deformiranih vzorcev. Na osnovi opravljenih numeričnih analiz, ki so bile podprte z eksperimentalnim testiranjem, kako v procesu upogibanja s tremi različnimi stopnjami pred deformacije tako tudi v procesu cikličnega natezno-upogibnega obremenjevanja z različnimi amplitudami sil in ob upoštevanju spremembe amplitude in napetostnega razmerja, smo dobili vrednosti dinamične trdnosti skladne s S-N Wohlerjevim diagramom. S tem smo potrdili, da je v doktorski disertaciji predstavljen postopek in model pravilen za določitev dejanskih napetostnih razmer v pred-deformiranih upognjenih vzorcih. V doktorski nalogi je pokazano, da zaostale napetosti v metastabilnem avstenitu AISI 316L, ki so posledice deformacije in fazne transformacije v martenzitno mikrostrukturo, vplivajo na iniciacijo in širjenje utrujenostnih razpok, pri čemer se napetostno razmerje v materialu razlikuje od razmerja sil R utrujanja zaradi teh zaostalih napetosti Rs. To smo pokazali na osnovi določitve napetostnega stanja z numeričnim modeliranjem in z eksperimentalno dobljenimi vrednostmi na S-N Wöhlerjevi krivulji, ki se ujemajo z rezultati upogibnega utrujanja ploščatih preizkušancev s polkrožnim utorom.
Keywords:metastabilni avstenit, podnica, S-N krivulja, utrujanje, zaostale napetosti, upogibanje, lomna žilavost
Place of publishing:Maribor
Publisher:[D. Jagarinec]
Year of publishing:2017
PID:20.500.12556/DKUM-67709 New window
UDC:539.55:621.22.011(043.3)
COBISS.SI-ID:293149440 New window
NUK URN:URN:SI:UM:DK:XX0MLH2O
Publication date in DKUM:29.11.2017
Views:1959
Downloads:255
Metadata:XML DC-XML DC-RDF
Categories:KTFMB - FS
:
JAGARINEC, Darko, 2017, Vpliv zaostalih napetosti na rast utrujenostne razpoke v upognjenem delu podnice tlačne posode [online]. Doctoral dissertation. Maribor : D. Jagarinec. [Accessed 26 March 2025]. Retrieved from: https://dk.um.si/IzpisGradiva.php?lang=eng&id=67709
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Secondary language

Language:English
Title:The influence of residual stresses on fatigue crack growth in the curved part domed end of a pressure vessel
Abstract:The domed end manufacturing process creates a complex deformation-stress state, which is not easily replicated in laboratory testing conditions. In this work we show that with prior bending and then tensile loading we create a composite stress state, which can only be analysed in a single critical point on the inner surface of the bent specimen. With numerical modelling of the stress state we approached the experimentally determined conditions during fatigue under constant loading of the pre-deformed specimens. On the basis of the numerical analyses, supported by experimental testing, we obtain values of the dynamic hardness/toughness in agreement with Wohler’s S-N diagram, both for bending with three different levels of pre-deformation as well as for cyclic tensile-bending loading with different force amplitudes, taking into account changes in the amplitude and the stress relation. This confirms that in the doctoral dissertation presented procedure and model for determining the stress state of pre-deformed bent specimens is correct. In the doctoral dissertation, it is shown that the residual stresses in metastable austenite AISI 316L, a consequence of deformation and phase transformation into a martensitic microstructure, influence initiation and growth of fatigue cracks, and the resulting stress state in the material is different from the force state of fatigue due to the residual stresses. This was shown on the basis of determining the stress state by numerical modelling and experimentally obtained values on Wohler’s S-N curve, which match the results of bending fatigue of flat specimens with a semi-circular notch.
Keywords:metastable austenite, domed end, S-N curve, fatigue, residual stresses, bending, fracture toughness


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