Coelacanth-scale inspired thin-ply composites for load-bearing applications

Abstract

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.