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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, original scientific article

Abstract: 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.
Keywords: smart materials, shape memory polymer, 3D printing, 4D printing, thermo-mechanical experiments
Published in DKUM: 29.05.2024; Views: 141; Downloads: 6
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Numerical analysis of a transtibial prosthesis socket using 3D-Printed Bio-Based PLA
Vasja Plesec, Jani Humar, Polona Dobnik-Dubrovski, Gregor Harih, 2023, original scientific article

Abstract: Lower-limb prosthesis design and manufacturing still rely mostly on the workshop process of trial-and-error using expensive unrecyclable composite materials, resulting in time-consuming, material-wasting, and, ultimately, expensive prostheses. Therefore, we investigated the possibility of utilizing Fused Deposition Modeling 3D-printing technology with inexpensive bio-based and bio-degradable Polylactic Acid (PLA) material for prosthesis socket development and manufacturing. The safety and stability of the proposed 3D-printed PLA socket were analyzed using a recently developed generic transtibial numeric model, with boundary conditions of donning and newly developed realistic gait cycle phases of a heel strike and forefoot loading according to ISO 10328. The material properties of the 3D-printed PLA were determined using uniaxial tensile and compression tests on transverse and longitudinal samples. Numerical simulations with all boundary conditions were performed for the 3D-printed PLA and traditional polystyrene check and definitive composite socket. The results showed that the 3D-printed PLA socket withstands the occurring von-Mises stresses of 5.4 MPa and 10.8 MPa under heel strike and push-off gait conditions, respectively. Furthermore, the maximum deformations observed in the 3D-printed PLA socket of 0.74 mm and 2.66 mm were similar to the check socket deformations of 0.67 mm and 2.52 mm during heel strike and push-off, respectively, hence providing the same stability for the amputees. We have shown that an inexpensive, bio-based, and bio-degradable PLA material can be considered for manufacturing the lower-limb prosthesis, resulting in an environmentally friendly and inexpensive solution.
Keywords: 3D printing, bio-based, polylactic acid, PLA, prosthesis, prosthesis socket, numerical model, finite element method
Published in DKUM: 14.03.2024; Views: 147; Downloads: 24
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Computer modelling of the residual limb for the development of prosthetic sockets and liners with the cellular structure : doctoral disertation
Vasja Plesec, 2023, doctoral dissertation

Abstract: The production of lower limb prostheses continues to rely primarily on manual methods, which are outdated and characterized by labour-intensive processes, lengthy time requirements, high costs, and a heavy reliance on the expertise of prosthetists. Achieving a satisfactory fit between the residual limb and socket remains a challenge, often leading to discomfort, pain, and potential wearer tissue damage. However, advancements in computer technology and numerical simulation offer an opportunity to predict stresses and strains experienced by the residual limb during prosthesis usage. This, in turn, aids in the development process by enhancing the design of the prosthetic socket and liner through virtual environments. In this dissertation we developed a generic numerical transtibial model to bridge the gap between clinical practice and numerical simulations. Biomechanically validated, this model generates outcomes applicable to a broader amputee population, facilitating comparative analysis of socket and liner designs and materials under different loading conditions. Furthermore, the dissertation explores the utilization of a 3D-printed socket manufactured through the cost-effective fused filament fabrication process, using polylactic acid filament, aiming to reduce the costs and establish a streamlined production process. The 3D-printed socket was evaluated within the virtual environment using the developed transtibial model. The numerical findings indicate that the 3D-printed socket can effectively withstand the loads encountered during the stages of prosthesis donning, single-leg stance, heel strike, and push-off, thereby presenting a viable alternative to the prevalent composite socket. Additionally, a cellular structure composed of a flexible thermoplastic elastomeric material is proposed as a prosthetic liner to enhance comfort by reducing contact pressure while maintaining the required stability. Numerical results indicate that by manipulating cellular parameters such as unit cell type and relative density of the structure, a customized response can be achieved. This customized response effectively reduces contact pressure for a given scenario without increasing displacement, thereby improving comfort while maintaining stability.
Keywords: lower-limb prosthesis, generic numerical transtibial model, 3D-printed socket, cellular structure liner, finite element method
Published in DKUM: 14.11.2023; Views: 607; Downloads: 38
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Avtomatizacija delovnega procesa v konstrukterstvu s pomočjo tabelarične metode modeliranja in makrov v programskem okolju solidworks : diplomsko delo
Klemen Plut, 2023, undergraduate thesis

Abstract: V diplomskem delu smo na kratko predstavili uporabo SolidWorks CAD programskega paketa, kjer smo opisali in uporabili osnovne operacije za izdelavo 3D modela manipulatorja. Podrobno smo opisali načine spreminjanja komponent in različne postopke konfiguriranja sestavnih elementov, ki se vsakodnevno uporabljajo v industriji. V našem primeru smo konfigurirali podajalno enoto, kjer je bilo potrebno prilagajati dolžino standardnih elementov in obdelovancev. Preučili in izdelali smo več vrst konfiguracij ter podali smernice za uporabo posameznih konfiguracij, ki so najprijaznejše za uporabnika. Med drugim smo podali razliko med konfiguracijami in možnostmi njihove uporabe v industrijskem okolju. Na koncu smo vse omenjene možnosti konkretizirali na realnem primeru.
Keywords: avtomatizacija, modeliranje, konfiguracije, SolidWorks
Published in DKUM: 17.10.2023; Views: 422; Downloads: 42
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Razvoj in konstruiranje stroja za trenje orehov za domačo in nizko industrijsko uporabo : diplomsko delo
Rok Gačnik, 2023, undergraduate thesis

Abstract: Naloga dela je bila razvoj in konstruiranje stroja za trenje orehov. Začetek razvoja je bil pogled že obstoječih izdelkov. Nato sem se lotil izdelave zahtevnika, iz katerega nato izhajajo različne funkcije in metode iskanja rešitev, iz katerih sledi izbira najboljše rešitve. Nato je sledila izdelava virtualnega modela, ki sem ga izdelal na podlagi skic in raznih katalogov. Glede na virtualni model sem naredil preračun najpomembnejših komponent, ter primerjavo analitičnega preračuna in numerične analize. Na koncu sem naredil načrte in sestavne risbe za izdelavo stroja. Pri končnem produktu so bili vsi rezultati v dopustnih merah, kar pomeni da bi bilo projekt možno izvesti.
Keywords: trenje orehov, razvoj stroja, oreh, analiza modela
Published in DKUM: 09.10.2023; Views: 221; Downloads: 20
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Development, fabrication and mechanical characterisation of auxetic bicycle handlebar grip
Nejc Novak, Vasja Plesec, Gregor Harih, Andrej Cupar, Jasmin Kaljun, Matej Vesenjak, 2023, original scientific article

Abstract: The auxetic cellular structures are one of the most promising metamaterials for vibration damping and crash absorption applications. Therefore, their use in the bicycle handlebar grip was studied in this work. A preliminary computational design study was performed using various auxetic and non-auxetic geometries under four load cases, which can typically appear. The most representative geometries were then selected and fabricated using additive manufacturing. These geometries were then experimentally tested to validate the discrete and homogenised computational models. The homogenised computational model was then used to analyse the biomechanical behaviour of the handlebar grip. It was observed that handle grip made from auxetic cellular metamaterials reduce the high contact pressures, provide similar stability and hereby improve the handlebar ergonomics.
Keywords: auxetic cellular structures, computational simulations, experimental testing
Published in DKUM: 23.05.2023; Views: 335; Downloads: 40
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Konstruiranje novega manipulatorja za transport transportnih zabojnikov v podjetju container d.o.o. : diplomsko delo
Aleš Mohar, 2022, undergraduate thesis

Abstract: Cilj naloge je bil izdelati novo transportno napravo za transport kontejnerjev oznake ISO, JUMBO in ostalih nestandardnih kontejnerjev. Lotili smo se razvoja in konstruiranja nove transportne naprave prav iz vidika omejitve prostora in delovnega procesa v lakirnici. Raziskali smo tržišče s transportnimi napravami, preverili njihove zmogljivosti dvigovanja, zmožnost umestitve transportne naprave v prostor lakirnice in delovni proces. Eden glavnih razlogov proti nakupu nove transportne naprave na trgu je omejitev prostora in nezmožnost dvigovanja različnih širin kontejnerjev. Obstoječa transportna naprava ne omogoča varnega dvigovanja kontejnerjev različnih širin, zaradi česar prihaja v delovnem procesu do neprimernih tehnik ravnanja z njo. Pri iskanju rešitev smo si pomagali s pregledom trga in ponudb transportnih naprav. Poleg pregleda trga smo za snovanje transportne naprave uporabili metoda dialoga in metodo 635. V procesu razvoja in konstruiranja smo izdelali 3D model, izvedli trdnostno analizo in izdelana potrebna tehniška dokumentacija. Cilj diplomske naloge je bil uspešno dosežen.
Keywords: Transportna naprava (manipulator), konstruiranje, numerična analiza, MKE, PTC Creo, Container d.o.o, ISO, JUMBO, kontejner.
Published in DKUM: 19.09.2022; Views: 611; Downloads: 77
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Konstruiranje nosilca za avtonomno testiranje krmilja vgradnih pečic v podjetju gorenje d.o.o. : diplomsko delo
Jan Gril, 2022, undergraduate thesis

Abstract: Zaradi potrebe po avtonomnem testiranju krmilja vgradnih pečic v podjetju Gorenje d. o. o. smo se lotili konstruiranja prosto stoječe naprave za testiranje, ki bo zmožna univerzalnega prileganja, ne glede na tip naprave in tip čelne plošče. Naprava mora biti zmožna proženja tipk čelne plošče preko linearnih aktuatorjev, prav tako mora biti zmožna proženja gumbov preko radialnih stepper motorjev. Potrebno je določiti rešitev za proženje tipk na zaslonu, občutljivem na dotik. Modeliranja naprave smo se lotili v programu NX. Ob koncu modeliranja smo dobili ustrezen model ter vse potrebne načrte za sestavo naprave, ki bo zmožna prileganja na vse vrste čelnih plošč na vgradnih pečicah.
Keywords: Gorenje, vgradne pečice, kuhalni aparati, naprava, avtonomno testiranje, Hisense, nosilec, aktuator, Siemens NX, konstruiranje, stroškovna analiza, laboratorij za meritve, kontrolni panel.
Published in DKUM: 12.09.2022; Views: 550; Downloads: 0

Oblikovanje modularnega uličnega pohištva : magistrsko delo
Jernej Kortnik, 2021, master's thesis

Abstract: Ulično pohištvo nas obdaja na vsakem koraku, kljub temu, da se morda tega niti ne zavedamo. Koše, klopi, mize, ulične svetilke, stojala za kolesa, pitnike in mnoge druge elemente uličnega pohištva vsakodnevno srečujemo, ko pohajkujemo po mestu. Cilj naloge je oblikovati družino izdelkov uličnega pohištva, ki bo upoštevalo ergonomske in estetske smernice. Izdelek mora biti zasnovan tako, da bo njegova izdelava okolju čimbolj prijazna in bo dolgotrajno njegov okoljski odtis čim manjši. V sklopu projekta bom izdelal idejne zasnove klopi, koša za smeti, stojala za kolesa, ter pitnika.
Keywords: Ulično pohištvo, klop, koš za smeti, stojalo za kolo, pitnik, oblikovanje izdelka, 3D modeliranje
Published in DKUM: 10.06.2021; Views: 870; Downloads: 59
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