Compartemented fibres

The concept of multiple self-healing in advanced fibre composites

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Polymers reinforced with high performance fibres are successfully replacing metal alloys in lightweight aircraft structures. A critical factor in structural design is the resistance of a structure to progressive damage which develops during its service time. The brittle nature of matrix cracking is the main source of composite failure initiating ply delamination and fibre to matrix debonding. Bio-inspired autonomous healing systems, embedded in a polymer matrix, are being developed to improve the fracture resistance of structural composites [1, 2, 3]. An exemplary system can consist of fibres with individual compartments, i.e. compartmented fibres, which are filled with a healing liquid. The healing agent is distributed within the fibre in the form of long elongated compartments of ellipsoidal shape with high aspect ratio. The fibres are designed to release the liquid healing agent at multiple specific microcrack sites developed in the polymer matrix as a result of structural loading during its life-time. The advantage of such a fibre as a healing agent carrier is obvious - compartmented fibres enable multiple local healing events. Neither is the whole healing agent consumed in the first damage/healing event (as for hollow fibres) nor is the functionality of remaining compartments affected by the healing event (compared to vascular networks). Compartmented fibres were spun from an oil/water emulsion of a healing agent in an aqueous solution of sodium alginate. The retention of the liquid healing agent (orthodichlorobenzene) in a solid fibre was provided by the coagulation of the alginate polymer during fibre formation. Spun fibres were embedded in polymethylmethacrylate, pre-cracked in 3 point bending and allowed a certain period of time to self-heal before they were loaded again. Computed micro-tomography was used to visualise damage and healing sites. Test samples with the new fibres located at the likely damage sites were able to recover, (in part) their mechanical properties. The concept of multiple release of healing agent from a compartmented fibre into the surrounding polymer matrix was demonstrated successfully.