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Title:Malociklično utrujanje avksetičnih celičnih struktur : doctoral disertation
Authors:ID Nečemer, Branko (Author)
ID Glodež, Srečko (Mentor) More about this mentor... New window
ID Kramberger, Janez (Mentor) More about this mentor... New window
Files:.pdf DOK_Necemer_Branko_2021.pdf (20,01 MB)
MD5: 67DBB5760D15D01C4604E75F30B31587
PID: 20.500.12556/dkum/589e1e70-157d-4ecd-9f9b-07b15bc14b50
 
Language:Slovenian
Work type:Doctoral dissertation
Typology:2.08 - Doctoral Dissertation
Organization:FS - Faculty of Mechanical Engineering
Abstract:V doktorski disertaciji sta predstavljena razvoj in potrditev računskega modela za napovedovanje življenjske dobe 2D-avksetičnih celičnih struktur, katerih karakteristična lastnost je negativno Poissonovo razmerje. Predstavljeni računski model temelji na energijskem pristopu in sestoji iz določitve števila ciklov za iniciacijo in širjenje poškodbe do končne odpovedi.Raziskovalno delo je obsegalo mehansko karakterizacijo aluminijeve zlitine 5083-H111, razvoj in potrditev računskega modela ter analiziranje avksetičnih celičnih struktur z numeričnim in eksperimentalnim pristopom. Eksperimentalno testiranje aluminijeve zlitine je zajemalo kvazi-statično in dinamično preizkušanje v režimu malocikličnega utrujanja. Dinamični testi so bili izvedeni s kontrolo deformacije pri razmerju deformacije R=-1 in R=0 na različnih nivojih amplitudne deformacije. V nadaljevanju so bili iz eksperimentalnih rezultatov določeni materialne konstante energijskega pristopa (c1, c2, c3 in c4) in materialni parametri konstitutivnega materialnega modela, uporabljenega v računskem modelu, ki je bil zgrajen v programskem paketu Simulia Abaqus. V računskem modelu za napovedovanje življenjske dobe je bil za pospešitev numerične simulacije in izračuna življenjske dobe analiziranih vzorcev uporabljen algoritem neposredne ciklične analize (ang. Direct cyclic analysis), ki je vgrajen v omenjenem programskem paketu. V računskem modelu sta bili najprej analizirani geometriji ploščatega in CT-vzorca, ki sta bili uporabljeni v eksperimentalnih testih mehanske karakterizacije osnovnega materiala. Računski model za napovedovanje življenjske dobe je bil uspešno validiran na podlagi primerjave numeričnih in eksperimentalnih rezultatov ploščatega in CT-vzorca. Validirani računski model je bil v nadaljevanju uporabljen kot osnova za določitev življenjske dobe kiralne in vbočene šestkotne avksetične strukture. V numeričnih analizah je bila življenjska doba avksetične strukture določena z odpovedjo ene izmed celičnih povezav, medtem ko je bila celotna življenjska doba sestavljena iz števila ciklov, potrebnih za iniciacijo in širjenje poškodbe do končne odpovedi. Numerične analize utrujanja avksetičnih vzorcev so bile izvedene s kontrolo deformacije pri R=-1 na različnih nivojih amplitudne deformacije. Izvedeni so bili tudi eksperimentalni testi kiralne in vbočene šestkotne avksetične strukture v režimu malocikličnega utrujanja. Zaradi različne togosti vzorcev so bili eksperimentalni rezultati LCF-testov predstavljeni v treh različnih oblikah vzdržljivostnih krivulj. Iz slednjih je bilo ugotovljeno, da obe avksetični strukturi kljub različni togosti vzorca pri enaki povprečni deformacijski energiji na cikel dosežeta podobno število obremenitvenih ciklov do odpovedi prve celične povezave. Na koncu je bila izvedena primerjava numeričnih in eksperimentalnih rezultatov življenjske dobe kiralne in vbočene šestkotne avksetične strukture. Na podlagi te primerjave lahko zaključimo, da je bil razvit računski model napovedovanja življenjske dobe kiralne in vbočene šestkotne avksetične strukture uspešno verificiran.
Keywords:malociklično utrujanje, numerična analiza, avksetične celične strukture, energijska metoda
Place of publishing:Maribor
Place of performance:Maribor
Publisher:[B. Nečemer]
Year of publishing:2021
Number of pages:X, 120 str.
PID:20.500.12556/DKUM-78918 New window
UDC:519.6:[620.178.3:669.715](043.3)
COBISS.SI-ID:80029187 New window
Publication date in DKUM:11.10.2021
Views:1409
Downloads:252
Metadata:XML DC-XML DC-RDF
Categories:KTFMB - FS
:
NEČEMER, Branko, 2021, Malociklično utrujanje avksetičnih celičnih struktur : doctoral disertation [online]. Doctoral dissertation. Maribor : B. Nečemer. [Accessed 14 March 2025]. Retrieved from: https://dk.um.si/IzpisGradiva.php?lang=eng&id=78918
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Licences

License:CC BY-NC-ND 4.0, Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International
Link:http://creativecommons.org/licenses/by-nc-nd/4.0/
Description:The most restrictive Creative Commons license. This only allows people to download and share the work for no commercial gain and for no other purposes.
Licensing start date:30.03.2021

Secondary language

Language:English
Title:Low cycle fatigue of auxetic cellular structures
Abstract:The doctoral thesis presents the development and validation of the computational model for predicting the fatigue life of 2D auxetic cellular structures, characterised with a negative Poisson’s ratio. The presented computational model is based on the energy approach and consists of damage initiation and damage evolution period up to final failure. In this study, research was focused on the mechanical characterisation of aluminium alloy 5083-H111, the development and validation of the appropriate computational model and, finally, the numerical and experimental analysis of the given auxetic cellular structures. Experimental testing of the analysed aluminium alloy included the quasi-static and dynamic testing in the low-cycle fatigue regime. Dynamic tests were performed in a strain control at the strain ratios R=-1 and R=0 at different amplitude strain levels. The experimental results were served as a basis for determining the material constants of the energy approach (c1, c2, c3 and c4) and the material parameters of the constitutive material model, which was then used in the subsequent computational analysis using the Simulia Abaqus software. In the computational model for fatigue life prediction, the algorithm of direct cyclic analysis integrated into the Simulia Abaqus software was used to accelerate the numerical simulation and determination of the fatigue life of the analysed samples. In the proposed computational model, the flat and CT specimens' geometries were analysed first. Both geometries were used also in the previous experimental testing to obtain the mechanical characterisation of the base material. The computational model for fatigue life prediction was successfully validated, based on the comparison of numerical and experimental results for flat and CT specimens. Furthermore, the validated computational model was used as a basis for determining the fatigue life of the chiral and re-entrant auxetic structure. The auxetic structure's fatigue life was defined by the failure of one cell strut, while the total fatigue life consists of the number of cycles required for damage initiation and for damage evolution up to final failure. Computational analyses of auxetic specimens were performed in a strain control at the strain ratio R=-1 at different amplitude strain levels. Furthermore, the LCF experimental tests of the chiral and re-entrant auxetic structure were also performed. Due to different stiffness of the specimens, the experimental results of the LCF tests were presented in three various forms of endurance curves, on the basis of which it was found that both auxetic structures, despite different sample stiffness at the same average deformation energy per cycle, achieve a similar number of cycles up to failure of first cell strut. Finally, a comparison between computationally and experimentally obtained fatigue lives of the chiral and re-entrant auxetic structure was performed. Based on this comparison it was concluded that the developed computational model is suitable for fatigue life prediction of chiral and re-entrant auxetic structures.
Keywords:low cycle fatigue, numerical analysis, auxetic cellular structures, energy method


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