Research paper - Proceedings Volume 10567, International Conference on Space Optics — ICSO 2006; 105672F (2017)
Feasibility study on measuring axial and transverse stress/strain components in composite materials using Bragg sensors
G. Luyckx, J. Degrieck, W. De Waele, W. Van Paepegem, J. Van Roosbroeck, K. Chah, J. Vlekken, I. McKenzie, A. Obst
Short description
During the last decades, there has been an increased use of fibre-reinforced composite materials for aerospace and space applications, thanks to their high stiffness for low weight and their excellent corrosion resistance. ‘Damage tolerant’ design of such structures necessitates permanent monitoring of the stresses or strains and the temperature in the composite material. Such monitoring systems should ensure the safety of the in-service aircraft, reduce ‘time consuming’ conventional nondestructive inspections and maximize the safety in case of life extension programs [1].
It has been widely demonstrated in the international literature that optical fibres can be easily embedded into composite materials and that reliable and stable monitoring systems can be designed based on fibre Bragg grating (FBG) sensors [2]. The main advantages of the optical fibre technology are that the fibres are tiny (comparable to a human hair), explosion safe, immune against electromagnetic radiation, and fairly corrosion resistant. In spite of some disadvantages of using embedded optical fibres (brittleness, composite material distortion, fragile connectorization), the authors believe that this technology is one of the most promising for online monitoring of the mechanical behaviour of composite structures. Most of the reported applications are based on single axial deformation measurements. It is, however, only feasible to monitor the occurrence and growth of damage when the entire 3D stress or strain state is known. The following paragraphs report on the development of a sensor configuration based on FBG sensors, written in polarization maintaining fibres, for measuring multi-axial stresses (or strains) and temperature in thermo hardened composite elements. The expected accuracies are estimated, based on considerations of the condition number determined by the wavelength sensitivity values. Preliminary results of experiments on these multi-axial FBGs (bare as well as embedded in composite) will be presented and show the feasibility of the proposed sensor configuration.