<title>Health monitoring techniques for composite materials employing thermal parameters and fiber optic sensors</title>

Abstract

In this paper we investigate the performance of a SCS-6/Ti-15-3 composite system, a carbon/SiC woven composite system, and an AS4/3501-6 composite system, subjected to long term mechanical fatigue, with an extrinsic Fabry-Perot interferometric (EFPI) fiber optic strain sensor. Both stiffness reduction and the degradation of thermal expansion coefficient (TEC) are monitored. The obtained results show that the EFPI sensor provides reliable data during long term fatigue loading up to 1 million cycles. The results suggest that the EFPI sensor is a viable means to monitor current and proposed characteristic damage metrics for various composite systems. We also monitor the TEC degradation during the thermal fatigue of celion G30-500/PMR-15 woven cross-ply composite system, and present a simple micromechanical model, that employs a shear lag approach, utilized to predict the effect of matrix cracking on the TEC of the composite. Results show that good agreement between experimental data and theoretical results is obtained, and that this parameter changed by as much as 80% over the fatigue life of the composite.