20.500.12556/RUL-142170 Stabilnost superelastičnih tankostenskih lupin iz materiala z oblikovnim spominom za uporabo v elastokalorični tehnologiji Stability of superelastic thin-walled shape memory alloy shells for apllications in elastocaloric technology V zadnjih letih se je elastokalorična tehnologija hlajenja (ETH), ki temelji na elastokaloričnem učinku materialov z oblikovnim spominom (MOS), uveljavila kot ena najbolj obetavnih alternativ parno-kompresijske tehnologije hlajenja. Glavna omejitev ETH je kratka življenjska doba, ki se lahko bistveno podaljša, če MOS namesto nateznemu izpostavimo tlačnemu obremenjevanju. Enega največjih izzivov pri razvoju tlačno obremenjenih elastokaloričnih naprav predstavlja iskanje kompromisa med sposobnostjo hitrega prenosa toplote, ki zahteva tankostenske elemente in strukturno (ne)stabilnostjo, na katero so takšni elementi občutljivi. Najboljši kompromis zaenkrat izkazujejo tankostenske cevi z okroglim prerezom, zato so bile osrednji predmet obravnave tega dela. Eksperimentalno smo določili stabilne dolžine cevi različnih prečnih prerezov ter izdelali dva fazna diagrama uklonskih oblik. Ugotovili smo, da temperaturne spremembe zaradi elastokaloričnega učinka zmanjšajo stabilnost. Z uporabo vmesnih podpor smo izboljšali stabilnost daljših cevi. Kot prvi smo razvili 3D lupinski končni element, ki temelji na teoriji velikih deformacij in vključuje konstitutivne enačbe za MOS. Izdelali smo numerični model za napovedovanje nestabilnosti cevi iz MOS, ki je bil verificiran s pomočjo eksperimentalnih rezultatov. Uporaba razvitega lupinskega elementa omogoča določitev odziva poljubne tankostenske strukture iz MOS, zato je njegova aplikativnost široka in se lahko uporabi tudi za načrtovanje elementov na področju medicine, avtomobilske ali letalske industrije itd. In recent years, elastocaloric cooling technology (ECT), based on the elastocaloric effect of shape memory materials (SMA), has emerged as one of the most promising alternatives to vapor compression cooling technology. The main limitation of ECT is its short fatigue life, which can be significantly improved if compressive loading is applied instead of tensile. One of the major challenges in the development of compression-loaded elastocaloric devices is to find a compromise between the capability of rapid heat transfer, which requires thin-walled structures, and the structural (in)stability to which such structures are prone. Thin-walled tubes with round cross-sections have shown the best compromise so far and have therefore been the main focus of this work. We have experimentally determined stable tube lengths of different cross-sections and defined two phase diagrams of buckling mode shapes. We found that temperature changes reduce the stability due to the elastocaloric effect. It has been shown that the use of intermediate supports increases the stability of long tubes. For the first time, a 3D shell finite element based on large deformation theory with incorporated SMA constitutive equations has been developed. A numerical model for predicting of instabilities of SMA tubes was developed and verified by the experimental results. The developed shell element can be used to model the response of arbitrary thin-walled SMA structures. Its applicability is therefore broader and can be used to design SMA components also in various branches of industry, such as medical, automotive, aerospace, etc. strukturna stabilnost uklon materiali z oblikovnim spominom lupine superelastičnost elastokalorični učinek structural stability buckling shape memory materials shells superelasticity elastocaloric effect true false false [L. Porenta] Slovenski jezik Angleški jezik Doktorsko delo/naloga 2022-10-22 08:30:23 2022-10-22 08:30:30 2023-10-20 09:43:20 0000-00-00 00:00:00 2022 0 Ljubljana 0 XXXIV, 156 str. 0000-00-00 NiDoloceno NiDoloceno NiDoloceno 0000-00-00 0000-00-00 0000-00-00 621.56/.59+624.074.43(043.3) 246704 131257347 21307.pdf 21307.pdf 1 D5D9427E836F8106DC62637877D04C6B d756114c6b59fd850642b5309e001bccf64ff5baf65714c493f21dfaf21b5e0a f90175ff-51d2-11ed-9c94-00155dcfd717 https://repozitorij.uni-lj.si/Dokument.php?lang=slv&id=163452 Fakulteta za strojništvo 0 0 0