1. Reinforcing ethyl cellulose aerogels with poly(lactic acid) for enhanced bone regenerationGabrijela Horvat, Jan Rožanc, Uroš Maver, Matjaž Finšgar, Željko Knez, Zoran Novak, 2024, izvirni znanstveni članek Opis: Developing double porous biodegradable and biocompatible scafolds that can incorporate and release drugs in a controlled manner holds immense potential in regenerative medicine. This study presents a synthesis method for preparing a macro-mesoporous scafold, where poly(lactic acid) adds to the macroporous region and mechanical properties, and ethyl cellulose adds to the surface area (182 m2 /g). High surface area enables the incorporation of model drug indomethacin with an entrapment efciency of 17.0% and its later controlled release profle. The resulting scafold has desirable mechanical properties in the range of a natural trabecular bone with a compressive modulus of 22.4 MPa. The material is stable in the simulated body fuids for 120 days before the slow degradation starts. In vitro studies demonstrate the material’s ability to support bone cell adhesion, proliferation, and diferentiation, promoting osteogenic activity. Overall, the unique combination of poly(lactic acid) and ethyl cellulose produces advanced materials with tailored macro and mesopore properties, remarkable mechanical properties, optimal degradation rate, and drug delivery potential, making it a promising candidate for bone scafolds in regenerative medicine and tissue engineering
Ključne besede: bio composite, polymer-matrix composites (PMCs), polymers, porosity/voids, secondary ion mass spectrometry
Objavljeno v DKUM: 23.08.2024; Ogledov: 130; Prenosov: 6
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2. 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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3. A computational model for analysing the dry rolling/sliding wear behaviour of polymer gears made of POMAljaž Ignatijev, Matej Borovinšek, Srečko Glodež, 2024, izvirni znanstveni članek Opis: This study presents a computational model to determine the wear behaviour of polymer gears. Using PrePoMax finite element numerical calculation software, a proposed computational model was built to predict dry rolling/sliding wear behaviour based on Archard’s wear model. This allows the calculation of the wear depth in each loading cycle with constant mesh updating using the finite element method. The developed computational model has been evaluated on a spur gear pair, where the pinion made of POM was meshed with a support gear made of steel. The computational results obtained were compared with the analytical results according to the VDI 2736 guidelines. Based on this comparison, it was concluded that the proposed computational model could be used to simulate the wear behaviour of contacting mechanical elements like gears, bearings, etc. The main advantage of the model, if compared to the standardised procedure according to the VDI 2736 guidelines, is the geometry updating after a chosen number of loading cycles, which enables a more accurate prediction of wear behaviour under rolling/sliding loading conditions.
Ključne besede: polymer gears, rolling/sliding contact, wear, computational modelling
Objavljeno v DKUM: 12.04.2024; Ogledov: 189; Prenosov: 12
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5. Incorporating graphene nanoplatelets and carbon nanotubes in biobased Ppoly(ethylene 2,5-furandicarboxylate): Fillers’ effect on the matrix’s structure and lifetimeDimitra Kourtidou, Dimitrios Karfaridis, Thomas Kehagias, George Vourlias, Dimitrios Bikiaris, Konstantinos Chrissafis, 2023, izvirni znanstveni članek Ključne besede: polymer nanocomposites, poly(ethylene 2, 5-furandicarboxylate) (PEF), carbon nanofillers, structural analysis, lifetime predictions
Objavljeno v DKUM: 10.04.2024; Ogledov: 196; Prenosov: 8
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6. Computational model for analysing the tooth deflection of polymer gearsAljaž Ignatijev, Srečko Glodež, Janez Kramberger, 2024, izvirni znanstveni članek Opis: A computational model for analysing the tooth deflection of polymer gears is presented in this paper. Because polymer gears have less stiffness compared to metal gears, the proposed approach considers a comprehensive analysis to determine the most suitable numerical model, i.e., the number of teeth that should be modelled for a given gear’s geometry and material. The developed computational model has been evaluated using a spur gear pair, where the pinion made of POM was meshed with a support gear made of steel. Material properties were assigned with linear elastic characteristics for the gear, while the pinion was characterised by hyperelastic properties using POM material. Furthermore, a nonlubricated frictional contact between the gear and pinion was considered in the numerical computations. The computational results that were obtained were compared to the empirical results according to VDI 2736 guidelines. Here, the computational approach showed more accurate results due to the hyperelastic material characteristics of POM and the simulation of multiple teeth meshing. However, VDI 2736 calculation showed comparability with the computational results, with a slightly larger deviation at higher loads. In this respect, the proposed computational approach is more suitable for analysing the tooth deflection of polymer gears under higher loads.
Ključne besede: polymer gears, tooth deflection, computational modelling
Objavljeno v DKUM: 19.03.2024; Ogledov: 266; Prenosov: 16
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7. Nonlinear semi-numeric and finite element analysis of three-point bending tests of notched polymer fiber-reinforced concrete prismsŽiga Unuk, Milan Kuhta, 2024, izvirni znanstveni članek Opis: A nonlinear semi-numeric and finite element analysis of three-point bending tests of notched polymer fiber-reinforced concrete prisms was performed. The computational and experimental results were compared in terms of the load-displacement behavior. The vertical midspan displacement and the crack mouth opening displacement results were considered. The nonlinear semi-numeric computational procedure involved the moment-curvature relation, calculated by considering the constitutive material law from the fib Model Code for Concrete Structures 2010, and considered a plastic hinge mechanism to simulate the cracked region behavior. Two sets of tensile mechanical properties were considered for the constitutive material law: back-calculated (by an inverse analysis) tensile strength properties from the experimental results, and tensile strength properties calculated by simplified expressions from the fib Model Code for Concrete Structures 2010. Other mechanical properties were determined by additional compressive tests and standard relations for the dependency of various mechanical properties on the concrete compressive strength. The nonlinear finite element analysis incorporated the Menetrey-Willam material model to simulate the fiber-reinforced concrete behavior. The nonlinear semi-numeric analysis load-displacement results based on the back-calculated tensile strength properties relatively accurately matched with the experimental results, whereas the nonlinear semi-numeric analysis load-displacement results based on tensile strength properties calculated by simplified expressions from the fib Model Code for Concrete Structures 2010 and the nonlinear finite element analysis load-displacement results showed certain shortcomings.
Ključne besede: polymer fiber-reinforced concrete, moment-curvature relation, nonlinear plastic hinge, load-displacement relation, crack width, nonlinear analysis, finite element analysis, Menetrey-Willam material model, three-point bending test, compressive test
Objavljeno v DKUM: 19.02.2024; Ogledov: 350; Prenosov: 15
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8. Cotton woven fabrics as protective polymer materials against solar radiation in the range of 210–1200 nmPolona Dobnik-Dubrovski, Darinka Fakin, Alenka Ojstršek, 2023, izvirni znanstveni članek Opis: The proposed paper describes the influence of woven fabric constructional parameters (type of weave, relative fabric density) and colouration (obtained by eco-friendly dyeing) on the solar transmittance of cotton woven fabrics in the range of 210-1200 nm. The cotton woven fabrics in their raw state were prepared according to Kienbaum's setting theory, at three levels of relative fabric density and three levels of the weave factor, and then exposed to the dyeing process with natural dyestuffs (beetroot, walnut leaves). After ultraviolet/visible/near-infrared (UV/VIS/IRA) solar transmittance and reflection in the range of 210-1200 nm were recorded, the influence of the fabric construction and colouration were analysed. The guidelines for fabric constructor were proposed. The results show that the walnut-coloured satin samples at the third level of relative fabric density provide the best solar protection in the whole solar spectrum. All the tested eco-friendly dyed fabrics offer good solar protection, while only raw satin fabric at the third level of relative fabric density can be classified as solar protective material with even better protection in IRA region than some coloured samples.
Ključne besede: fabric engineering, solar protection, woven fabric structure, natural dyeing of polymer material, testing
Objavljeno v DKUM: 15.02.2024; Ogledov: 296; Prenosov: 5
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9. Long-term creep compliance of wood polymer composites: using untreated wood fibers as a filler in recycled and neat polypropylene matrixMarko Bek, Alexandra Aulova, Klementina Pušnik Črešnar, Sebastjan Matkovič, Mitjan Kalin, Lidija Slemenik Perše, 2022, izvirni znanstveni članek Opis: Neat (NPP) and recycled (RPP) polypropylene matrix materials were used to prepare wood–polymer composites with untreated wood fibers up to 40 wt.%. Long-term creep properties obtained through the time-temperature superposition showed superior creep resistance of composites with NPP matrix. In part, this is attributed to their higher crystallinity and better interfacial adhesion caused by the formation of a transcrystalline layer. This difference resulted in up to 25% creep compliance reduction of composites with NPP matrix compared to composites with recycled (RPP) polypropylene matrix, which does not form a transcrystalline layer between the fibers and polymer matrix. Despite the overall inferior creep performance of composites with RPP matrix, from the 20 wt.% on, the creep compliance is comparable and even surpasses the creep performance of unfilled NPP matrix and can be a promising way to promote sustainability.
Ključne besede: lesno-polimerni kompoziti, lezenje, vzdržljivost, les, recikliranje, wood–polymer composites, creep, durability, wood, recycling
Objavljeno v DKUM: 16.08.2023; Ogledov: 381; Prenosov: 25
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10. Wear Behaviour of Multilayer Al-PVD-Coated Polymer GearsTonica Bončina, Brigita Polanec, Franc Zupanič, Srečko Glodež, 2022, izvirni znanstveni članek Opis: A comprehensive experimental investigation of the wear behaviour of coated spur polymer gears made of POM is performed in this study. Three different thicknesses of aluminium (Al) coatings were investigated and deposited by the Physical Vapour Deposition (PVD) process. The Al coating was deposited in three steps: By plasma activation, metallisation of the aluminium by the magnetron sputtering process, and plasma polymerisation. The wear of the gears was tested on an in-house developed testing rig for different torques (16, 20, and 24 Nm) and a rotational speed of 1000 rpm. The duration of the experiments was set to 13 h, when the tooth thickness and, consequently, the wear of the tooth flank were recorded. The experimental results showed that the influence of metallisation with aluminium surface coatings on the wear behaviour of the analysed polymer gear is not significantly important. The results also showed that the gears with a thicker aluminium coating showed greater wear than gears with a thinner coating or even without a coating. This is probably due to the fact that the aluminium particles that started to deviate during gear operation represented the abrasive material, which led to the faster wear of the contacting surfaces of the meshing gear flanks.
Ključne besede: polymer gears, aluminium PVD coating, Physical Vapour Deposition process, multilayer coating, wear
Objavljeno v DKUM: 15.11.2022; Ogledov: 580; Prenosov: 58
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