http://hdl.handle.net/10563/1000004 Mon, 02 Nov 2026 19:27:55 GMT 2026-11-02T19:27:55Z http://hdl.handle.net/10563/1012866 Effect of accelerated aging on the mechanical properties of FFF-manufactured polymers Kohutiar, Marcel; Bednařík, Martin; Labaj, Ivan; Janík, Róbert; Hanzlík, Jan; Krbata, Michal; Zatloukal, Jakub This study examines the effect of accelerated weathering on the mechanical and viscoelastic properties of thermoplastics produced by fused filament fabrication (FFF). Three polymers, acrylonitrile styrene acrylate (ASA), polyethylene terephthalate glycol (PETG), and polylactic acid (PLA), were subjected to alternating UV radiation and condensation cycles in a QUV chamber simulating environmental exposure. Tensile testing and dynamic mechanical analysis (DMA) were used to evaluate the changes in strength, stiffness, and glass-transition behavior. The results revealed distinct responses depending on the polymer structure. ASA maintained its ductility and even showed improved strength, confirming high UV resistance. PETG exhibited a moderate decrease in strength with negligible change in elongation, indicating partial photo-oxidation but stable viscoelastic behavior. PLA demonstrated the most significant stiffening and a noticeable upward shift of the glass-transition temperature due to crystallization and physical aging. Overall, short-term QUV exposure acted as a conditioning process, enhancing the thermal and structural stability of the tested FFF-printed polymers. Thu, 01 Jan 2026 00:00:00 GMT http://hdl.handle.net/10563/1012866 2026-01-01T00:00:00Z http://hdl.handle.net/10563/1012873 Experimental and numerical analysis of laser-welded GFRP–PBT joints for aerospace components Untariu, Ana-Teodora; Monková, Katarína; Marșavina, Liviu; Sîrbu, Nicușor-Alin; Galațanu, Sergiu-Valentin This study investigates laser transmission welding of 30% glass fiber-reinforced polybutylene terephthalate (PBT-GF30). Injection-molded plates were used as base material, from which specimens were prepared, welded, and experimentally tested. The influence of key process parameters, including laser power, beam size, and scanning speed, on weld quality was systematically evaluated through an iterative optimization approach. An optimized parameter set (400 W laser power, reduced beam size, and increased scanning speed) enabled stable and repeatable weld formation with minimal thermal degradation. Experimental results were further supported by finite element analysis, showing good agreement between numerical and experimental data. The findings confirm the feasibility of laser welding for PBT-GF30 and its potential for aerospace applications requiring precision, weight reduction, and structural reliability. Thu, 01 Jan 2026 00:00:00 GMT http://hdl.handle.net/10563/1012873 2026-01-01T00:00:00Z http://hdl.handle.net/10563/1012847 Effect of cutting conditions on roughness and cutting force when machining a freeform surface with Barrel tools Řezníček, Martin; Hořava, Cyril; Zajíček, Jakub; Ovsík, Martin Barrel tools are relatively new tools that use atypical geometries to achieve shorter production times and improve surface quality. They have been increasingly used in the finishing operations industry, where they are gaining more and more popularity. For their optimal use, it is necessary to know how these tools behave during work in terms of how they load the machined product and what surface qualities they can achieve. For this reason, this study was conducted to compare two tools when machining a free surface. The obtained surface quality and the force load caused by the tool were evaluated. It was found that barrel tool machining results in a heterogeneous surface caused by different cutting speeds along the length of the tool and that the two obtained regions show differences in the obtained roughness. Even though the operation was classified as a finishing process, a difference of up to 30% was identified in the cutting forces acting on the tool and the workpiece. Thu, 01 Jan 2026 00:00:00 GMT http://hdl.handle.net/10563/1012847 2026-01-01T00:00:00Z http://hdl.handle.net/10563/1012839 Physicochemical, rheological, textural, tribological, and sensory insights into the role of citrus fiber in quark cheese spreads with varying fat content Vincová, Anna; Šantová, Kristýna; Jaššo, Miroslav; Lorencová, Eva; Salek, Richardos-Nicolaos The objective of this study was to evaluate the effect of citrus fiber (1% wt/wt) on the physicochemical, rheological, textural, tribological, and sensory properties of quark cheese spreads with different fat content (10%, 15%, and 20% wt/wt). Physicochemical properties, including pH, DM, and water activity, were not affected by citrus fiber addition. Furthermore, rheological and textural analyses showed that citrus fiber increased samples' hardness and viscoelastic moduli, probably by reinforcing the protein-polysaccharide matrix, especially in low-fat variants. Tribological measurements indicated that higher fat improved lubrication, whereas fiber-containing quark cheese spread samples exhibited slightly higher coefficients of friction due to increased structural rigidity. Additionally, color analysis revealed minor shifts toward darker and more yellow tones when citrus fiber was used. Moreover, sensory evaluation confirmed that citrus fiber addition did not affect most of the tested organoleptic attributes, with slight improvement in flavor. The findings indicate that incorporating citrus fiber into quark cheese spreads can improve their functional properties, facilitate fat reduction, and promote the sustainable utilization of byproducts in dairy products. Thu, 01 Jan 2026 00:00:00 GMT http://hdl.handle.net/10563/1012839 2026-01-01T00:00:00Z