Nelinearna analiza stabilnosti nosilcev iz materiala z oblikovnim spominom z uporabo metode končnih elementov

Brajnik, Luka (author), Brojan, Miha (mentor)

Za materiale z oblikovnim spominom (MOS) sta značilni lastnosti oblikovnega spomina in superelastičnosti. Obe spremlja fazna transformacija v materialu, pri kateri se porablja ali sprošča latentna toplota, kar imenujemo elastokalorični učinek. Zato se takšni materiali uporabljajo za izdelavo hladilnih/ogrevalnih sistemov, ki ta učinek izkoriščajo. V takšnih napravah najpogosteje uporabljajo tankostenske cevke, zaradi dobrih lastnosti prenosa toplote, vendar so pri tlačnem obremenjevanju občutljive na uklon. Pri uklonu imamo, poleg nelinearnih materialnih lastnosti MOS, opravka še z nelinearnimi geometrijskimi efekti zaradi uklona. Obravnavanje takšnih primerov je očitno mogoče z lupinskimi končnimi elementi (KE), vendar je zaradi potrebe bo velikem številu KE in visokem številu parametrov le teh, problem računsko zelo intenziven in časovno potraten. Cilj dela je razviti računski model za napoved uklona tankostenskih cevk s pomočjo linijskih korotacijskih KE nosilcev. Tak pristop omogoča znatno hitrejše prototipiranje in preliminarni razvoj sistemov, pri katerih se kaže problematika uklona. V magistrskem delu je prikazan razvoj takšnih KE in primerjava z eksperimentalnimi meritvami pridobljenimi iz literature in meritvami, ki smo jih opravili za potrebe te naloge v laboratoriju. Pokazano je, da je za mnoge primere praktične uporabe pristop z linijskimi KE ustrezen in učinkovit, kljub temu, da takšni elementi, za razliko od lupinskih, niso sposobni opisati lokaliziranih deformacij.

• Language: Slovenian
• Keywords: korotacijski končni elementi, material z oblikovnim spominom, nelinearna analiza, nadkritični uklon, elastokalorični učinek
• Work type: Master's thesis/paper
• Typology: 2.09 - Master's Thesis
• Organization: FS - Faculty of Mechanical Engineering
• Place of publishing: Ljubljana
• Publisher: [L. Brajnik]
• Year: 2023
• Number of pages: XXII, 71 str.
• PID: 20.500.12556/RUL-148759
• UDC: 620.174.22:536.65:519.61(043.2)
• COBISS.SI-ID: 171286787
• Publication date in RUL: 31.08.2023

BRAJNIK, Luka, 2023, Nelinearna analiza stabilnosti nosilcev iz materiala z oblikovnim spominom z uporabo metode končnih elementov [online]. Master’s thesis. Ljubljana : L. Brajnik. [Accessed 11 April 2025]. Retrieved from: https://repozitorij.uni-lj.si/IzpisGradiva.php?lang=eng&id=148759

Secondary language

• Language: English
• Title: Non-linear stability analysis of shape memory alloy beams with finite element method

Abstract

Alloys with shape memory (SMA) are characterized by the properties of shape memory and superelasticity. Both are accompanied by a phase transformation in the material, during which a latent heat is absorbed or released, known as the elastocaloric effect. Therefore, such materials are used for the production of cooling/heating systems that exploit this effect. In such devices, thin-walled tubes are most commonly used due to their good heat transfer properties. However, they are sensitive to buckling under compression. When considering buckling, we have to deal with geometric nonlinear effects in addition to material nonlinearities due to SMA. Addressing such cases is possible with shell finite elements (FE). However, due to the need for a large number of FE and their numerous parameters, the problem is computationaly very intensive and time-consuming. The aim of this work is to develop a computational model for predicting buckling of thin-walled tubes using corotational beam FE. This approach enables significantly faster prototyping and preliminary development of systems where buckling issues arise. In this master's thesis, the development of such FE is demonstrated, and a comparison is made with experimental measurements obtained from the literature and measurements conducted by ourselves. It is shown that for many practical cases, the approach with support FE is appropriate and efficient, despite these FE not being able to describe localized deformation, unlike shell FE.

• Keywords: corotational finite elements, shape memory alloys, nonlinear analysis, supercritical buckling, elastocaloric effect