Hochschule für Technik und Umwelt FHNW
Dauerhafte URI für den Bereichhttps://irf.fhnw.ch/handle/11654/35
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Bereich: Suchergebnisse
Publikation Multiscale characterisation of staple carbon fibre-reinforced polymers(MDPI, 06.11.2023) Zweifel, Lucian; Kupski, Julian; Dransfeld, Clemens; Caglar, Baris; Baz, Stephan; Cessario, Damian; Gresser, Götz T.; Brauner, ChristianThe aim of this study was to characterise the microstructural organisation of staple carbon fibre-reinforced polymer composites and to investigate their mechanical properties. Conventionally, fibre-reinforced materials are manufactured using continuous fibres. However, discontinuous fibres are crucial for developing sustainable structural second-life applications. Specifically, aligning staple fibres into yarn or tape-like structures enables similar usage to continuous fibre-based products. Understanding the effects of fibre orientation, fibre length, and compaction on mechanical performance can facilitate the fibres’ use as standard engineering materials. This study employed methods ranging from microscale to macroscale, such as image analysis, X-ray computed tomography, and mechanical testing, to quantify the microstructural organisations resulting from different alignment processing methods. These results were compared with the results of mechanical tests to validate and comprehend the relationship between fibre alignment and strength. The results show a significant influence of alignment on fibre orientation distribution, fibre volume fraction, tortuosity, and mechanical properties. Furthermore, different characteristics of the staple fibre tapes were identified and attributed to kinematic effects during movement of the sliver alignment unit, resulting in varying tape thicknesses and fuzzy surfaces.01A - Beitrag in wissenschaftlicher ZeitschriftPublikation Tailored flexibility in inherently brittle epoxy-based composites through gradient interphase formation with bio-based thermoplastic elastomer grades(Elsevier, 05.07.2023) Zweifel, Lucian; Kupski, Julian; Brauner, ChristianThis study focuses on tailoring elastic behaviour in an inherently brittle epoxy-based fibre-reinforced composite material formed through a gradient interphase with a bio-based thermoplastic elastomer. The fast-curing epoxy Araldite LY3585/Aradur 3475 was tested with two bio-based Pebax block copolymer grades. First, the interphase was characterised via optical hot-stage microscopy and Raman spectroscopy. The analysis unveiled pronounced diffusion followed by a reaction-induced phase separation, which led to the formation of an interphase with a thickness exceeding 200 μm at the temperatures associated with the curing process. Second, composite laminates were fabricated through a combined process of fused filament fabrication and vacuum infusion, incorporating a flexible domain with variable stiffness properties. The material architecture exhibited brittle-to-ductile behaviour at the micrometre scale, with tailored flexible response under bending and stiff behaviour in tension. Consequently, the study anticipates using multi-scale toughened material structures for more efficient generative design concepts.01A - Beitrag in wissenschaftlicher ZeitschriftPublikation Fused filament fabrication of bio-based polyether-block-amide polymers (PEBAX) and their related properties(MDPI, 23.11.2022) Schär, Matthias; Zweifel, Lucian; Arslan, Delal; Grieder, Stefan; Maurer, Christoph; Brauner, ChristianThis paper describes the application of poly(ether-block-amide) polymers, so-called Pebax, in fused filament fabrication (FFF). Pebax® is a thermoplastic elastomer (TPE), a copolymer based on rigid polyamide and soft polyether blocks. By variation of the blocks, unique properties such as soft or rigid behaviour are tailored without additional additives and plasticisers. Pebax®Rnew® polyamide blocks are bio-based and made from castor beans that allow the design of sustainable applications. In this study, two types of Pebax were selected, processing parameters were characterised, filaments were extruded and applied to FFF printing, and the final mechanical characteristics were determined. Both types were suitable for FFF processing with improved process stability due to less shear thinning and good mechanical performance. The connection strength between the grades was also described in the design context for complex parts with tailored soft or hard regions. Combining the two materials in one design is a promising concept, and the adhesion strength is close to the strength in the Z-direction of the flexible Pebax®Rnew®35R53 grade.01A - Beitrag in wissenschaftlicher ZeitschriftPublikation The mechanical characterization of welded hybrid joints based on a fast-curing epoxy composite with an integrated phenoxy coupling layer(MDPI, 08.02.2022) Zweifel, Lucian; Ritter, Klaus; Brauner, ChristianThe joining of composites mostly relies on traditional joining technologies, such as film or paste adhesives, or mechanical fasteners. This study focuses on the appealing approach of using standard thermoplastic welding processes to join thermosets. To achieve this, a thermoplastic coupling layer is created by curing with a thermoset composite part. This leads to a functional surface that can be utilized with thermoplastic welding methods. The thermoplastic coupling layer is integrated as a thin film, compatible with the thermoset resin in the sense that it can partially diffuse in a controlled way into the thermoset resin during the curing cycle. Recent studies showed the high affinity for the interphase formation of poly hydroxy ether (phenoxy) film as coupling layer, in combination with a fast-curing epoxy system that cures within 1 min at 140 °C. In this study, an investigation based on resistance and ultrasonic welding techniques with different testing conditions of single-lap shear samples (at room temperature, 60 °C, and 80 °C) was performed. The results showed strong mechanical strengths of 28.9 MPa (±0.7%) for resistance welding and 24.5 MPa (±0.1%) for ultrasonic welding, with only a minor reduction in mechanical properties up to the glass transition temperature of phenoxy (90 °C). The combination of a fast-curing composite material with an ultra-fast ultrasonic joining technology clearly demonstrates the high potential of this joining technique for industrial applications, such as automotive, sporting goods, or wind energy. The innovation allowing structural joining performance presents key advantages versus traditional methods: the thermoplastic film positioning in the mold can be automated and localized, joint formation requires only a fraction of a second, and the joining operation does not require surface preparation/cleaning or structure deterioration (drilling).01A - Beitrag in wissenschaftlicher ZeitschriftPublikation In situ characterization of the reaction-diffusion behavior during the gradient interphase formation of polyetherimide with a high-temperature epoxy system(MDPI, 21.01.2022) Zweifel, Lucian; Brauner, Christian; Teuwen, Julie; Dransfeld, ClemensThis study presents two novel methods for in situ characterization of the reaction-diffusion process during the co-curing of a polyetherimide thermoplastic interlayer with an epoxy-amine thermoset. The first method was based on hot stage experiments using a computer vision point tracker algorithm to detect and trace diffusion fronts, and the second method used space- and time-resolved Raman spectroscopy. Both approaches provided essential information, e.g., type of transport phenomena and diffusion rate. They can also be combined and serve to elucidate phenomena occurring during diffusion up to phase separation of the gradient interphase between the epoxy system and the thermoplastic. Accordingly, it was possible to distinguish reaction-diffusion mechanisms, describe the diffusivity of the present system and evaluate the usability of the above-mentioned methods.01A - Beitrag in wissenschaftlicher Zeitschrift