The application of optical fiber sensors in advanced fiber reinforced composites. Part 1: Introduction and issues

Abstract

1.1 INTRODUCTION Advanced fibre reinforced composites (AFRCs) are a class of materials which are made up of a reinforcing phase and a matrix phase. The reinforcing phase can be short fibres or continuous fibres. Typical examples of fibres which are used include carbon, glass, silicon carbide and polyaramid. The matrix phase can be a thermoplastic, thermoset, ceramic or metal. A summary of selected properties for engineering materials are presented in.Table 1. With reference to Table 1, it is readily apparent that the specific properties (property of interest divided by the density) of AFRCs are superior to that of other engineering materials. This makes AFRCs ideal materials for primary and secondary load-bearing applications where weight is at a premium. Hence there is extensive utilization for aerospace and other transport-based applications. The drive to reduce the overall weight of AFRCs has resulted in the development of hollow glass and carbon fibres. Other advantages of AFRCs include their ease of manufacture and flexibility of design to yield the desired mechanical and thermal properties. For example, unique mechanical properties can be obtained by hybridising (mixing) two different fibre types: the impact resistance of a carbon fibre composite can be enhanced by hybridising it with polyaramid fibres. The strength and stiffness of the hybrid composite will then be dictated by the relative volume fractions of the two fibres and their relative positions within the laminated composite. The function of the fibres is to carry the majority of the load which is imposed on the composite. The matrix on the other hand transfers the applied load to the fibres and also secures the position of the individual fibres within the composite. The efficiency of this load-transfer process from the matrix to the fibres is dictated by a number of factors including the nature and the strength of the interfacial bond. As will be seen later, this is an important issue with the use of embedded optical fibres sensors in AFRCs.