1 Extensive characterisation of the intrusiveness of Fibre Bragg Grating Sensors embedded in a carbon fibre reinforced polymer Authors: J.G. Carrión, M. Frövel, J.M. Pintado, F. Cabrerizo 1 ABSTRACT As a part of the contribution to the European project AHMOS-II, an extensive characterisation of embedded optical fibres inside carbon reinforced epoxy composite laminates has been undertaken, covering a set of properties relevant for certification purposes (Young modulus and strength parallel and perpendicular to main axis in laminates, shear modulus and stress, interlaminar shear stress). Optical fibres were located parallel or perpendicular to main carbon fibre axis, specimens submitted to dry or moisture saturation conditions, and then tested at several temperatures, aiming to assess their influence on their ‘host’ material if used for strain monitoring purposes. Only compression strength seems to be influenced by the optical fibres, and only if perpendicularly located, thus confirming precedent investigations. INTRODUCTION The state of maturity reached by the technology based on optical fibre sensors (Bragg gratings, more specifically) is taking to consideration the need of qualifying sensing systems to be embarked. This kind of sensors is appreciated as they can be embedded inside composite structures during current manufacturing operations, so allowing being located where they are more useful to witness the development of mechanical issues that could be detrimental for the composite behaviour. However, to be used for structural health monitoring, it is a must to check what effects could have the sensing system on the host composite own mechanical properties [1, 2]. The design of reinforced polymer structures manages composite properties under foreseen load spectra and environmental conditions to dimension aircraft parts with the required level of safety. However, a glass fibre for sensing purposes has a thickness close or higher than a single carbon fibre structural composite ply, so causing a distortion that is higher as its location deviates from main axis of composite laminate [3]. Such an effect should be taken to account in aircraft structural design. J.G. Carrión, M. Frövel, J.M. Pintado, F. Cabrerizo. INTA (Instituto Nacional de Técnica Aeroespacial - Spanish Institution for Aerospace Technology, Ministry of Defence), Composite Materials Area, Materials and Structures Department, Crta. Ajalvir P.K. 4, 28850 Torrejón de Ardoz – Madrid (Spain). E-mail: carrionmj@inta.es. 4th European Workshop on Structural Health Monitoring, Krakow, 2008