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Title:Računalniško modeliranje avksetičnih struktur
Authors:ID Novak, Nejc (Author)
ID Vesenjak, Matej (Mentor) More about this mentor... New window
Files:.pdf DOK_Novak_Nejc_2019.pdf (9,69 MB)
MD5: BF76629DBB110CB1CB45F8074F7C8152
PID: 20.500.12556/dkum/16c4450d-acb5-4647-8ca5-3536aea9e4c1
 
Language:Slovenian
Work type:Doctoral dissertation
Typology:2.08 - Doctoral Dissertation
Organization:FS - Faculty of Mechanical Engineering
Abstract:V doktorski disertaciji so predstavljeni rezultati geometrijske in mehanske karakterizacije avksetičnih celičnih struktur, katerih karakteristična in edinstvena lastnost je ta, da imajo negativno Poissonovo razmerje. Napredna karakterizacija je bila sestavljena iz treh delov: analize geometrije izdelanih avksetičnih celičnih struktur, eksperimentalnega testiranja in računalniških simulacij. Analiza geometrije je bila izvedena z mikroskopiranjem in mikroračunalniško tomografijo (µCT), kar je omogočilo natančno oceno pravilnosti in zanesljivosti izdelave preizkušancev z dodajalnimi tehnologijami. Temu je sledilo eksperimentalno tlačno testiranje pri različnih hitrostih obremenjevanja, kjer so bili ovrednoteni vplivi osnovnega materiala, poroznosti, geometrije in hitrosti obremenjevanja na mehanski odziv analiziranih avksetičnih celičnih struktur. V sklopu eksperimentalnega tlačnega testiranja so bile izdelane in preizkušene tudi avksetične celične strukture napolnjene s silikonom, z namenom dodatnega izboljšanja mehanskih lastnosti kompozitnih avksetičnih celičnih struktur. Rezultati eksperimentalnega testiranja so bili osnova za validacijo računalniških modelov in razvoj robustnega materialnega modela, ki omogoča opis deformacijskega obnašanja vseh, v tem delu analiziranih avksetičnih celičnih struktur. Za izvedbo eksplicitnih računalniških simulacij je bil uporabljen računalniški program LS-DYNA. Na podlagi verificiranih in validiranih računalniških modelov avksetičnih struktur so bili v nadaljevanju razviti tudi računalniški modeli sendvič struktur z avksetičnim jedrom, ki so bili uporabljeni za analizo eksplozijskega in balističnega obremenjevanja. Ugotovljeno je bilo, da uporaba avksetične celične strukture kot jedra sendvič struktur zviša sposobnost absorpcije energije v primerjavi s sendvič strukturo z neavksetičnim jedrom. Izvedeno je bilo tudi eksperimentalno testiranje gradiranih avksetičnih celičnih struktur pri kvazi-statičnih in dinamičnih hitrostih obremenjevanja. Pokazano je bilo, da lahko pri dovolj visokih (nadkritičnih) hitrostih s pomočjo usmerjenosti gradiranih avksetičnih celičnih struktur spremenimo njihov mehanski odziv pri tlačni obremenitvi. Deformacijsko obnašanje gradiranih avksetičnih struktur je bilo uspešno določeno tudi z računalniškimi simulacijami. Validirani računalniški modeli in optimizacijski algoritem pa so bili v nadalje uporabljeni kot osnova za določitev funkcionalno gradirane avksetične strukture, ki omogoča uporabniško določen mehanski odziv za predvideno obremenitveno stanje.
Keywords:avksetične celične strukture, mehanske lastnosti, udarne obremenitve, računalniške simulacije
Place of publishing:Maribor
Publisher:[N. Novak]
Year of publishing:2019
PID:20.500.12556/DKUM-73370 New window
UDC:004:942:539.2/.3(043.3)
COBISS.SI-ID:22642454 New window
NUK URN:URN:SI:UM:DK:F5WFSK4O
Publication date in DKUM:04.10.2019
Views:2115
Downloads:405
Metadata:XML DC-XML DC-RDF
Categories:KTFMB - FS
:
NOVAK, Nejc, 2019, Računalniško modeliranje avksetičnih struktur [online]. Doctoral dissertation. Maribor : N. Novak. [Accessed 14 March 2025]. Retrieved from: https://dk.um.si/IzpisGradiva.php?lang=eng&id=73370
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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:01.04.2019

Secondary language

Language:English
Title:Computer modelling of auxetic structures
Abstract:The doctoral dissertation presents the results of the advanced mechanical characterization of auxetic cellular structures, which are modern metamaterials with a negative Poisson’s ratio. The advanced mechanical characterization was composed of three parts: the analysis of the geometry of the fabricated auxetic cellular structures, experimental testing and computer simulations. The geometry analysis was observed by microscopy and microcomputed tomography scanning, which enable accurate estimation of the accuracy and reliability of the specimen’s fabrication with additive manufacturing technologies. This was followed by experimental compression testing at various strain rates, where the effects were evaluated of the base material, porosity, geometry and loading velocity on the mechanical response of the analysed auxetic cellular structures. As part of the experimental compression testing, auxetic cellular structures filled with silicon were also tested, which made it possible to improve the mechanical properties of composite auxetic cellular structures further. The results of the experimental testing were the basis for the validation of computational models and the development of a robust computational material model, which provides a description of the deformation behaviour of all analysed auxetic cellular structures. LS-DYNA software was used to perform the explicit computer simulations. On the basis of verified and validated computational models of auxetic structures, computational models of auxetic sandwich structures were developed further. They were used for analysis of explosion and ballistic loading of sandwich structures with an auxetic core. It has been shown that the use of the auxetic cellular core of the sandwich structures increases their capability to absorb energy compared to the sandwich structure with a non-auxetic core. Experimental testing of graded auxetic cellular structures was also performed under quasi-static and dynamic loading conditions. It has been shown that, at sufficiently high velocities, by means of the orientation of the graded auxetic cellular structures, their compressive mechanical response can be changed. The deformation behaviour of graded auxetic structures was also determined successfully by computer simulations. Furthermore, the validated computational models and the optimization algorithm were the basis for determining a functionally graded auxetic cellular structure that enables a user-defined mechanical response of a functionally graded auxetic structure under particular loading conditions.
Keywords:cellular materials, auxetic cellular structures, impact testing, computational simulations


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