1. Thermo-mechanical behavior and strain rate sensitivity of 3D-printed polylactic acid (PLA) below glass transition temperature (Tg)Vukašin Slavković, Blaž Hanželič, Vasja Plesec, Strahinja Milenković, Gregor Harih, 2024, izvirni znanstveni članek Opis: This study investigated the thermomechanical behavior of 4D-printed polylactic acid (PLA), focusing on its response to varying temperatures and strain rates in a wide range below the glass transition temperature (Tg). The material was characterized using tension, compression, and dynamic mechanical thermal analysis (DMTA), confirming PLA’s strong dependency on strain rate and temperature. The glass transition temperature of 4D-printed PLA was determined to be 65 °C using a thermal analysis (DMTA). The elastic modulus changed from 1045.7 MPa in the glassy phase to 1.2 MPa in the rubber phase, showing the great shape memory potential of 4D-printed PLA. The filament tension tests revealed that the material’s yield stress strongly depended on the strain rate at room temperature, with values ranging from 56 MPa to 43 MPA as the strain rate decreased. Using a commercial FDM Ultimaker printer, cylindrical compression samples were 3D-printed and then characterized under thermo-mechanical conditions. Thermo-mechanical compression tests were conducted at strain rates ranging from 0.0001 s−1 to 0.1 s−1 and at temperatures below the glass transition temperature (Tg) at 25, 37, and 50 °C. The conducted experimental tests showed that the material had distinct yield stress, strain softening, and strain hardening at very large deformations. Clear strain rate dependence was observed, particularly at quasi-static rates, with the temperature and strain rate significantly influencing PLA’s mechanical properties, including yield stress. Yield stress values varied from 110 MPa at room temperature with a strain rate of 0.1 s−1 to 42 MPa at 50 °C with a strain rate of 0.0001 s−1. This study also included thermo-mechanical adiabatic tests, which revealed that higher strain rates of 0.01 s−1 and 0.1 s−1 led to self-heating due to non-dissipated generated heat. This internal heating caused additional softening at higher strain rates and lower stress values. Thermal imaging revealed temperature increases of 15 °C and 18 °C for strain rates of 0.01 s−1 and 0.1 s−1, respectively.
Ključne besede: smart materials, shape memory polymer, 3D printing, 4D printing, thermo-mechanical experiments
Objavljeno v DKUM: 29.05.2024; Ogledov: 248; Prenosov: 14
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2. Fatigue behaviour of brazed joints for heat exchangersBlaž Hanželič, Jernej Kralj, Tonica Bončina, Branko Nečemer, Janez Kramberger, Roman Satošek, Srečko Glodež, 2024, izvirni znanstveni članek Opis: The plate heat exchanger (PHE) is a component that provides heat to be transferred from hot water to domestic cold water without mixing them with high efficiency. Over the lifetime of the PHE, cyclic pressures act on the brazing points and the plates, and this may lead to fatigue failure. The fatigue behaviour of the PHE, designed using copper-brazed 316L stainless steel, was investigated in this study. First, the fatigue tests under the load ratio R = 0.1 were performed on the Vibrophore 100 testing machine to obtain the S-N curve of the analysed brazed joint. Based on the obtained experimental results, an appropriate material model of the analysed brazed joint has been created, which was validated with numerical calculation in the framework of a program code Ansys. A validated material model was then used for the subsequent numerical analysis of PHE. In order to carry out a numerical calculation using the finite element method (FEM), a three-dimensional model of the heat exchanger was created based on the previous scanning of PHE-geometry. Thereafter, the geometry was parameterised, which allowed us to perform parametric simulations (monitoring different responses depending on the input geometry). Numerical simulations were carried out in the framework of the Ansys 2023-R1 software, whereby the obtained results were analysed, and the responses were appropriately characterised according to previously determined load cases.
Ključne besede: brazed joint, fatigue, experimental testing, computational analyses, heat exchanger
Objavljeno v DKUM: 31.01.2024; Ogledov: 316; Prenosov: 58
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3. Trdnostna analiza toplotnega izmenjevalca : magistrsko deloBlaž Hanželič, 2023, magistrsko delo Opis: V magistrskem delu je predstavljen postopek trdnostne analize ploščnega tipa toplotnega izmenjevalca. Da lahko izvedemo numerični preračun po metodi končnih elementov (MKE), je potrebno pridobiti 3D model toplotnega izmenjevalca. Model ploščnega tipa toplotnega izmenjevalca je bil pridobljen s pomočjo skeniranja oz. 3D računalniške tomografije. Na podlagi pridobljene geometrije s skeniranjem je bilo potrebno le-to ustrezno popraviti, da smo jo lahko nato uporabili za numerični preračun (numerični 3D model). Geometrija je bila parameterizirana, kar nam je omogočilo izvedbo parametričnih simulacij (spremljanje različnih odzivov glede na vhodno geometrijo). V numeričnem preračunu smo se ukvarjali z obremenitvenimi primeri prelotanih in neprelotanih mest v toplotnem izmenjevalcu ter posledično z različnimi napetostno deformacijskimi stanji in njihovim vplivom na pričakovano življenjsko dobo toplotnega izmenjevalca. Numerični preračuni (MKE) so bili izvedeni v programskem paketu Ansys Workbench, pri čemer smo pridobljene rezultate analizirali ter ustrezno karakterizirali odzive glede na predhodno določene obremenitvene primere.
Ključne besede: toplotni izmenjevalec, modeliranje, trdnostna analiza, numerična simulacija, MKE
Objavljeno v DKUM: 24.08.2023; Ogledov: 589; Prenosov: 0
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4. Tehnična zakonodaja pri razvoju dvižne parkirne ploščadi : diplomsko deloBlaž Hanželič, 2021, diplomsko delo Opis: V okviru razvojnega projekta v podjetju MOS Servis d. o. o. je bilo potrebno za novi izdelek (dvižno parkirno ploščad) narediti tehnično mapo izdelka. Tehnična mapa zajema ključne podatke za potrebe konstruiranja in dimenzioniranja elementov naprave v skladu z aktualnimi standardi in zakonodajo, s ciljem pridobiti CE-oznako.
V diplomski nalogi so uvodoma podrobneje splošno opisani posamezni koraki pri razvoju izdelkov z upoštevanjem aktualnih standardov in zakonodaje glede na področje obratovanja naprave (tehnična zakonodaja pri konstruiranju). V nadaljevanju se tematika navezuje na izdelavo tehnične mape za dvižno parkirno ploščad. V zaključku diplomskega dela bodo navedeni vsi viri in priloge, ki sovpadajo z delom.
Ključne besede: zakonodaja, standardi, zasnova, tehnična mapa, zahtevnik, dvižna parkirna ploščad
Objavljeno v DKUM: 13.10.2021; Ogledov: 950; Prenosov: 168
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