Graupner, Nina
Lade...
30 Ergebnisse
Gerade angezeigt 1 - 10 von 30
- Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Making positive use of the fibrillation of lyocell fibres in composite materialsThe present study investigates the influence of surface fibrillation of lyocell fibres on the adhesion and resulting properties of short fibre-reinforced polypropylene (PP) and polylactide (PLA) composites. Fibrillation was shown to reduce the tensile strength and elongation at break of the fibres, while not affecting Young's modulus. It was demonstrated that fibrillation improved adhesion significantly compared to non-fibrillated (untreated) fibres, and the critical fibre length determined by microbond tests was reduced. Despite the reduced tensile strength of the fibrillated lyocell fibres, the tensile strength of the composites was increased by a factor of 1.15 for PP and 1.62 for PLA compared to composites produced with untreated fibres. The Young's modulus of the composites was increased using fibrillated fibres by a factor of 1.41 for PP and 1.20 for PLA. The impact strength was also improved by using fibrillated fibres by a factor of 1.38 for PP-based and 1.23 for PLA-based composites. Surface fibrillation of lyocell offers interesting application possibilities, particularly for short fibre-reinforced materials, as the higher specific fibre surface reduces the critical fibre length of lyocell, leading to improved stress transfer from the matrix to the fibre. These fibres seem particularly promising to enhance the mechanical properties of short-fibre reinforced composites for 3D printing applications.Wissenschaftlicher ArtikelHeft:1194 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Influence of sample thickness, curvature and notches on the Charpy impact strength - An approach to standardise the impact strength of curved test specimens and biological structuresThe specimen geometry has a significant influence on the Charpy impact strength. This is often a problem when it comes to the analysis of materials that can only be prepared with a curved shape, or which, like some biological structures, are naturally given in curved form like nutshells. The question repeatedly arises to what extent the curvature influences the impact strength. Hence, the present study deals with the dependence of the specimen geometry like specimen thickness, curvature and notches on the impact properties of concrete, gypsum, polyurethane (PUR) and epoxy-based (EP) samples. Increasing sample thickness from 2 to 10 mm resulted in increased toughness for brittle materials, whereas more ductile materials did not show any significant change in toughness. Increasing span length showed an increase of the unnotched impact strength for brittle gypsum, while toughness increased for a more ductile PUR sample. For the curved specimens both, the unnotched and the notched Charpy impact strength could be shown to increase with a reduction of the specimen radius (higher curvature) while the notch-sensitivity was not significantly affected. Material-specific linear relationships between the impact strength and the curvature of the samples were found. These relationships were used to create a model to calculate the influence of the curvature on the impact strength. For all materials, the characteristic values of a normalised flat standard sample could be well predicted from measured values of curved specimens. This calculation approach was used to predict the impact strength of an isotropic biological sample (sweet potato) concerning a flat sample and different curved specimens. The results show a good trend with the measured values.Wissenschaftlicher ArtikelBand:93117 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, The role of the membrane in the hen's egg as a model for increasing the toughness of engineered brittle materialsEggshell and the attached membrane are the focus of many fields of research, but their mechanical properties as a biomineralised composite are seldom explored. This investigation aimed to asses the influence of the membrane on energy dissipation during macroscopic structure failure, and if this effect could be reproduced with artificial membranes for later use in biomimetic materials. Compression tests followed by fracture pattern analysis were conducted for five types of manipulated egg halves: samples with and without the natural membrane, and three samples where the membrane was replaced with artificial membranes made from epoxy resin, polyurethane resin, or wood glue. To preserve the shell's shape, the natural membrane was removed with NaClO. Significant differences regarding the fracture forces between samples with the natural membrane and no membrane (20 % decrease of average), and the natural and artificial membranes (30 % increase of average) were measured. Fracture pattern analysis and investigation of the total work performed during compression testing revealed the highest improvements in toughness for the artificial polyurethane-resin membrane. Without any membrane, very small amounts of work were required to completely shatter the egg, and no fragment cohesion was observed. The presence of the membrane significantly enhanced the effective toughness of the eggshell, and the biomimetic abstraction of this concept is considered feasible for further investigation involving engineered brittle materials.Wissenschaftlicher ArtikelBand:17011 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, 74 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Mechanical characterisation and interfacial analysis of continuous flax fibre reinforced unidirectional green composites using filament windingPlant fibre-reinforced biobased thermoplastics (also known as “green composites”) are interesting materials from the point of view of eco-sustainability but still have problems of lower mechanical properties and difficult processability when compared to other more common composite materials, such as continuous glass or carbon fibre-reinforced thermosets. In this paper, unidirectional green composite laminae made of flax fibre-reinforced polylactide (PLA) were obtained through film stacking together with a filament winding process followed by a hot compaction phase. This technique permits to apply pretensioning on the flax rovings before hot compaction to limit possible misalignment. Interfacial properties measurement, analysis of fracture surfaces and a complete tensile mechanical characterisation were performed to evaluate the effectiveness of this procedure. The results showed that a structural composite in the longitudinal direction (∼170 MPa strength) can be obtained that has a low void content, an adequate fibre–matrix macro-impregnation and a limited dispersion in mechanical properties due to the limited fibre misalignment.Wissenschaftlicher ArtikelBand:19413 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, 3D-printed polylactide composites reinforced with short lyocell fibres – Enhanced mechanical properties based on bio-inspired fibre fibrillation and post-print annealingIn this study, 3D printable polylactide (PLA) composites reinforced with 10, 20 and 30 mass% of short lyocell fibres were produced by melt compounding PLA modified with maleic anhydride. Based on bio-inspired anchoring systems, fibrillated fibres were also employed in 30 mass% fibre composites. The resulting 3D printed samples displayed outstanding mechanical performance, particularly with high fibre content. Compared to neat PLA, unmodified formulations showed reduced tensile strength and strain at break with the addition of fibres, but they had a moderate improvement in Young's modulus. However, by combining fibre fibrillation, matrix modification, and post-printing annealing, we achieved an excellent balance of tensile strength (85 MPa), Young's modulus (7.2 GPa), and strain at break (3.2%) - the highest reported values for such composites. Incorporating fibres and increasing PLA crystallinity via heat treatment significantly enhanced the thermo-mechanical stability of the composites, raising the storage modulus up to 38 times at 60 °C and 200 times at 80 °C compared to neat PLA. This combined strategy paves the way for the 3D printing of high-performance structures using 100% bio-derived materials.Wissenschaftlicher ArtikelHeft:7790 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, 77 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Effectiveness of enzymatic treatment on a continuous flax fibre reinforced composite(European Society for Composite Materials, 2024-07); ; ; ; Wissenschaftlicher ArtikelHeft:249 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Structure, Properties and Degradation of Self-Assembled Fibrinogen Nanofiber Scaffolds(American chemical society, 2024-09-16); ; ; ; Self-assembled fibrinogen nanofibers are promising candidates for skin tissue engineering due to their biocompatibility and ability to mimic the native blood clot architecture. Here, we studied the structure-property relationship and degradation of rehydrated fibrinogen nanofibers prepared by salt-induced self-assembly, focusing on the effect of scaffold layering, cross-linking time and freeze-drying. Optimal fiber stability was achieved with cross-linking by formaldehyde (FA) vapor, while treatment with liquid aldehydes, genipin, EDC, and transglutaminase failed to preserve the nanofibrous architecture upon rehydration. Scaffold layering did not significantly influence the mechanical properties but changed the scaffold architecture, with bulk fiber scaffolds being more compact than layered scaffolds. Freeze-drying maintained the mechanical properties and interconnected pore network with average pore diameters around 20 μm, which will enhance the storage stability of self-assembled fibrinogen scaffolds. Varying cross-linking times altered the scaffold mechanics without affecting the swelling behavior, indicating that scaffold hydration can be controlled independently of the mechanical characteristics. Cross-linking times of 240 min increased scaffold stiffness and decreased elongation, while 30 min resulted in mechanical properties similar to native skin. Cross-linking for 120 min was found to reduce scaffold degradation by various enzymes in comparison to 60 min. Overall, after 35 days of incubation, plasmin and a combination of urokinase and plasminogen exhibited the strongest degradative effect, with nanofibers being more susceptible to enzymatic degradation than planar fibrinogen due to their higher specific surface area. Based on these results, self-assembled fibrinogen fiber scaffolds show great potential for future applications in soft tissue engineering that require controlled structure-function relationships and degradation characteristics.Wissenschaftlicher ArtikelBand:7Heft:987 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Innovative use of fluorescent grafting for damage and morphological monitoring during the extrusion process of PCL-flax fibre-reinforced composites(Elsevier, 2024-12); ; ; ; Limiting plant fibre damage during industrial processing is challenging for biobased composite development due to plant cell wall sensitivity to temperature and shear. This study developed an innovative fluorophore grafting method to indirectly monitor flax fibre morphological damage during twin-screw extrusion in a poly-(caprolactone) matrix. Results showed the fluorophore was strongly degraded after severe process conditions, with −87.1 % and −72.2 % changes in fluorescence intensity at 240 °C and 300 rotations per minute, respectively, compared to native fluorescence. The fluorescence intensity correlated well with the fibre aspect ratio and length, making it a reliable indicator of the fibre’s morphology degradation.Wissenschaftlicher ArtikelBand:222Heft:164