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Item type:Publication, Access status: with files , Experimental and numerical investigation of bio-inspired CFRP structures with layer thickness gradients(Elsevier, 2026-03-15); ; ; ; Throughout evolutionary history, mineralised tissues have developed remarkable skeletal microstructures that combine exceptional damage tolerance with adaptation to challenging environmental conditions. These tissues typically feature composite architectures with spatially varying fibre orientations and layer thicknesses. This study utilises the microstructure of deep-sea sponge spicules and the cuticle of the lobster Homarus americanus as bioinspiration. Sponge spicules, found at depths between 1100 m and 2100 m, consist of radially arranged layers of hydrated silicon dioxide. Their curvature adapts to ocean currents, and analyses reveal graded layer thickness from 0.6 µm to 10 µm. Thinner layers in tensile regions enhance tensile strength due to scaling relationship with layer thickness h<sup>−1/2</sup>, while thicker layers in compressive zones improve stability and reduce buckling. Unlike this microstructure, the cuticle of Homarus americanus comprises epicuticle, exocuticle, and endocuticle, with the latter two forming helicoidal fibre architecture. In the claws, exocuticular layers are thinner, facilitating energy absorption under impact, whereas thicker endocuticular layers provide structural stabilisation through increased stiffness. Inspired by these biological systems, thin-ply carbon fibre reinforced polymer laminates were designed for out-of-plane loading conditions. A quasi-isotropic layup 45°,90°,-45°,0° was chosen to reflect amorphous nature of hydrated silica. To mimic natural gradients, layers of varying thin-ply thickness were employed within thermally balanced laminate sequence. Layer configurations were initially optimised using finite element three-point bending simulations and subsequently validated experimentally. The graded design approach resulted in improved flexural performance and reduced damage propagation under impact loading, demonstrating potential of bio-inspired layer thickness gradation for development of advanced composite structures.Publicationtype: Journal Article90 35 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Coelacanth-scale inspired thin-ply composites for load-bearing applications(Elsevier, 2025-10-18); ; ; ; Thin-ply composites are known for their superior in-situ strength and manufacturing quality, offering higher unnotched tensile and compressive strengths compared to conventional laminates. However, their damage suppression capability leads to increased notch sensitivity, where the delamination and matrix cracking mechanisms are suppressed. As a result, thin-ply laminates are limited in their use in critical load-bearing applications. To address this, bio-inspired Bouligand structures, defined by their helical fibre arrangements, have shown promise in reducing notch sensitivity through helicoidal matrix cracking and stress redistribution. This study explores the mechanical performance of partial Bouligand layups derived from biological fibre architectures observed on coelacanth fish scales, where fibrils reorient under load. An analytical stiffness-based optimization was performed to match the mechanical properties of the conventional [0◦, ±45◦, 90◦] (50%, 40%, 10% load introduction layup used in bolted and riveted aircraft structures, while integrating the partial Bouligand structure. The weights of the two-layer fibres (30 gsm and 60 gsm) were investigated, resulting in different pitch and stack angles. Tensile and bearing tests were conducted to evaluate the influence of the partial Bouligand structure on bearing sensitivity. The results indicate that bio-inspired fibre orientation can improve load redistribution and damage tolerance in thin-ply laminates, making them compatible for off-axis and notched applications.Publicationtype: Journal Article49 17 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Coelacanth-scale inspired thin-ply composites for load-bearing applications(2025); ; Thin-ply composites are known for their superior in-situ strength and manufacturing quality, offering higher unnotched tensile and compressive strengths compared to conventional laminates. However, their damage suppression capability leads to increased notch sensitivity, where delamination and matrix cracking mechanisms are suppressed. As a result, thin-ply laminates are limited in their use in critical load-bearing applications.To address this, bioinspired Bouligand structures, defined by their helical fiber arrangements, have shown promise in reducing notch sensitivity through helicoidal matrix cracking and stress redistribution. This study explores the mechanical performance of partial Bouligand layups derived from biological fiber architectures observed in coelacanth fish scales, where fibrils reorient under load [1]. An analytical stiffness based optimization was performed to match the mechanical properties of the conventional [0 °, ±45 °, 90 °] (50 %, 40 %, 10 %) load introduction layup used in bolted and riveted aircraft structures [2, 3], while integrating the partial Bouligand structure.Two layer fiber areal weights (30 gsm and 60 gsm) were investigated, resulting in different pitch and stack angles. Tensile and bearing tests were conducted to evaluate the influence of the partial Bouligand structure on notch sensitivity. The results indicate that nature inspired fiber orientation can improve load redistribution and damage tolerance in thin ply laminates, making them compatible for off-axis and notched applications.Publicationtype: Book Part77 21 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Using thermokinetic methods to enhance properties of epoxy resins with amino acids as biobased curing agents by achieving full crosslinking(Macmillan Publishers Limited, part of Springer Nature, 2024-02-22); ; Fibre-reinforced polymers (FRPs) are used in numerous industrial sectors and contribute to reducing CO2 emissions due to their outstanding properties in lightweight design. However, sustainable alternatives must be developed since the matrix polymers utilised contain substances hazardous to health and the environment. In widely used epoxy resins, the curing agents are mainly critical. Using biomolecules instead of synthetic curing agents can significantly reduce composites' toxicity and petrol-based carbon content. This study considerably exceeds the thermo-mechanical properties of epoxies cured with amino acids described in the literature until now. It demonstrates competitive or even better properties than state-of-the-art epoxies cured with petrol-based amine curing agents. For instance, the tensile strength of arginine-cured epoxy is more than twice as high as reported before and 13.5% higher compared to the petrol-based reference. At the same time, a high elongation at break of over 6% was accomplished, making these polymers suitable as matrix materials in FRPs. Furthermore, the glass transition onset of up to 130 °C is sufficiently high for many applications. The key to success is the development of individual curing profiles based on thermokinetic analysis. The work provides the development and analysis of several biomolecule-cured epoxies with promising property spectra.Publicationtype: Journal Article43 34