2023-11-06, Zweifel, Lucian, Kupski, Julian, Dransfeld, Clemens, Caglar, Baris, Baz, Stephan, Cessario, Damian, Gresser, Götz T., Brauner, Christian

The 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.

2023-07-05, Zweifel, Lucian, Kupski, Julian, Brauner, Christian

This 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.