Tailored Interphases in Fibre Reinforced Polymers

Abstract

AbstractThe use of fibre coatings to enhance adhesion between fibres and polymers normally means that, in the fibre composite, some residue of the coating is present at the fibre-matrix interface. This constitutes the interphase. The mechanical properties of this material may be measured using simple fibre pull out tests. These tests have the advantage of revealing the interphase failure mode (i.e. brittle or ductile) as well as providing such data as work of fracture, yield stress, interfacial pressure and the coefficient of friction for post-debonding slip. Results obtained so far indicate some ductility and yielding with thermoplastic interphases, although final failure is brittle. Thermoset interphases appear to be universally brittle, with small works of fracture (10-200 Jm−2 ). The change in Young's modulus across the interphase may be a factor influencing brittle fracture, the biggest change giving the most brittle interphase.The ideal interphase should probably have a modulus intermediate between that of the fibre and the polymer, together with moderate yield stress, to give the composites adequate shear strength and good impact resistance through promotion of fibre pull outs.