1. Načrtovanje 3d tiskane podkolenske proteze za izboljšan prenos obremenitev na ležišče : diplomsko deloMatic Kramberger, 2024, diplomsko delo Opis: Diplomska naloga se je osredotočala na načrtovanje 3D tiskane podkolenske proteze za izboljšan prenos obremenitev na ležišče. Raziskane in razvite so bile različne konstrukcijske rešitve za distalni del protetičnega ležišča, ki bi izboljšale trdnost 3D tiskanih protez. Cilj je bil porazdeliti obremenitve na več slojev 3D tiska z uporabo cenovno dostopnih tehnologij, kot je tehnologija ciljnega nalaganja slojev (ang. Fused Filament Fabrication, krajše FFF) in materiala poliaktične kisline (ang. polylactic acid, krajše PLA). Naloga je vključevala teoretične osnove protetike spodnjih okončin, 3D tiska v protetiki in numeričnih metod. Razvitih je bilo več konceptnih in variantnih rešitev, ki so nato bile predelane v konstrukcijske modele. Pet modelov je bilo nato analiziranih z numeričnimi metodami. Analize so pokazale, da je bil model z vstavljenimi karbonskimi palicami najbolj učinkovit pri zmanjševanju napetosti na kritičnih mestih ležišča. Rezultati so pokazali, da je mogoče z uporabo tehnologije FFF doseči pomembne izboljšave pri izdelavi podkolenskih protez, vendar so potrebne nadaljnje raziskave in eksperimentalni testi za optimizacijo in praktično uporabo teh rešitev.
Ključne besede: podkolenska proteza, 3D tiskano ležišče, metoda končnih elementov, prenos obremenitev
Objavljeno v DKUM: 01.10.2024; Ogledov: 0; Prenosov: 21
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2. Bioinspired design of 3D-printed cellular metamaterial prosthetic liners for enhanced comfort and stabilityVasja Plesec, Gregor Harih, 2024, izvirni znanstveni članek Opis: Traditional prosthetic liners are often limited in customization due to constraints in manufacturing processes and materials. Typically made from non-compressible elastomers, these liners
can cause discomfort through uneven contact pressures and inadequate adaptation to the complex
shape of the residual limb. This study explores the development of bioinspired cellular metamaterial
prosthetic liners, designed using additive manufacturing techniques to improve comfort by reducing
contact pressure and redistributing deformation at the limb–prosthesis interface. The gyroid unit
cell was selected due to its favorable isotropic properties, ease of manufacturing, and ability to
distribute loads efficiently. Following the initial unit cell identification analysis, the results from the
uniaxial compression test on the metamaterial cellular samples were used to develop a multilinear
material model, approximating the response of the metamaterial structure. Finite Element Analysis
(FEA) using a previously developed generic limb–liner–socket model was employed to simulate
and compare the biomechanical behavior of these novel liners against conventional silicone liners,
focusing on key parameters such as peak contact pressure and liner deformation during donning,
heel strike, and the push-off phase of the gait cycle. The results showed that while silicone liners
provide good overall contact pressure reduction, cellular liners offer superior customization and
performance optimization. The soft cellular liner significantly reduced peak contact pressure during
donning compared to silicone liners but exhibited higher deformation, making it more suitable for
sedentary individuals. In contrast, medium and hard cellular liners outperformed silicone liners for
active individuals by reducing both contact pressure and deformation during dynamic gait phases,
thereby enhancing stability. Specifically, a medium-density liner (10% infill) balanced contact pressure
reduction with low deformation, offering a balance of comfort and stability. The hard cellular liner,
ideal for high-impact activities, provided superior shape retention and support with lower liner
deformation and comparable contact pressures to silicone liners. The results show that customizable
stiffness in cellular metamaterial liners enables personalized design to address individual needs,
whether focusing on comfort, stability, or both. These findings suggest that 3D-printed metamaterial
liners could be a promising alternative to traditional prosthetic materials, warranting further research
and clinical validation
Ključne besede: bioinspired design, metamaterial model, cellular structure, additive manufacturing, lower-limb prosthetic, 3D printing, finite element method
Objavljeno v DKUM: 19.09.2024; Ogledov: 0; Prenosov: 2
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3. 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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5. Numerical analysis of a transtibial prosthesis socket using 3D-Printed Bio-Based PLAVasja Plesec, Jani Humar, Polona Dobnik-Dubrovski, Gregor Harih, 2023, izvirni znanstveni članek Opis: 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.
Ključne besede: 3D printing, bio-based, polylactic acid, PLA, prosthesis, prosthesis socket, numerical model, finite element method
Objavljeno v DKUM: 14.03.2024; Ogledov: 208; Prenosov: 32
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6. Computer modelling of the residual limb for the development of prosthetic sockets and liners with the cellular structure : doctoral disertationVasja Plesec, 2023, doktorska disertacija Opis: 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.
Ključne besede: lower-limb prosthesis, generic numerical transtibial model, 3D-printed socket, cellular structure liner, finite element method
Objavljeno v DKUM: 14.11.2023; Ogledov: 696; Prenosov: 49
Celotno besedilo (3,64 MB) |
7. Development, fabrication and mechanical characterisation of auxetic bicycle handlebar gripNejc Novak, Vasja Plesec, Gregor Harih, Andrej Cupar, Jasmin Kaljun, Matej Vesenjak, 2023, izvirni znanstveni članek Opis: 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.
Ključne besede: auxetic cellular structures, computational simulations, experimental testing
Objavljeno v DKUM: 23.05.2023; Ogledov: 413; Prenosov: 54
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8. Numerična simulacija trka pri pristanku letala z možnostjo navpičnega vzletanja in pristajanja : magistrsko deloVasja Plesec, 2019, magistrsko delo Opis: V magistrski nalogi so predstavljena priporočila za snovanje varnega letala odpornega na vertikalni trk. Sestavo letala smo razdelili na tri glavne komponente namenjene absorpciji energije v primeru vertikalnega trka: sedež, struktura trupa in podvozje. Za vsak del posebej je bila izvedena eksplicitna časovno odvisna numerična simulacija v programskem paketu Abaqus/Explicit. Iz dobljenih rezultatov smo med seboj primerjali pospeške, ki delujejo na telo potnika ter sile in pomike strukturnih delov, iz katerih se vidi količina absorbirane energije. Na koncu smo izvedli še računalniško simulacijo sestave generičnega letala, ki je vsebovalo vse zgoraj naštete komponente.
Ključne besede: vertikalni trk letala, eksplicitne numerične simulacije, absorpcija energije, metoda končnih elementov, deformacijska struktura
Objavljeno v DKUM: 06.05.2019; Ogledov: 1451; Prenosov: 160
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