A bio-inspired embedded composite stiffener for improved damage tolerance via AFP

Composite stiffened panels are a mass effective solution to provide structural stiffness and stability. Traditional designs are vulnerable to unstable debonding failure of the stiffeners from the skin, contributing to conservative certification requirements being necessary which increases structural mass. In this work we propose a design, inspired by damage tolerant tree-branch attachments, to embed the stiffener to the skin to eliminate this premature failure mechanism. Automated fibre placement (AFP) is increasingly used in industry to manufacture composites, and in this work we develop a manufacturing route for composite stiffened panels, skin and stiffener, to be manufactured in a single AFP process. This is a desirable manufacturing route which additionally enables the realisation of damage tolerant designs such as that presented in this work. Three-point-bend testing reveals that whilst a traditional design suffers premature unstable stiffener debonding failure, the bio-inspired design prevents this failure mechanism. Our results show that this unlocks a 78% increase in peak load, and drastic improvements to failure stability and energy absorption capabilities. This work demonstrates that embedding of the stiffener into the skin can address the problematic failure of unstable stiffener debonding, and can be achieved with an industrially relevant manufacturing route.

This repository contains the raw data from the 3PB tests of this work.