APPLICATION OF FBG SENSORS TO MONITOR STIFFNESS DEGRADATION AND DAMAGE PROGRESSION IN POLYMER MATRIX COMPOSITES

摘要

There is a great deal of interest in developing effective techniques for health monitoring of polymer matrix composites (PMCs). Fiber optic sensors (FOS) are particularly attractive for internal strain measurements as they are compatible with common resins, allow for multiplexing and are small in size (250 μm). In this study, fiber Bragg grating sensors were embedded into cross-ply and woven PMC test specimens in order to assess their ability to detect stiffness degradation and monitor damage evolution during fatigue. For these purposes, load levels were chosen as to cause sufficient damage to the test specimens. Non-linear strain distributions due to the presence of damage caused distortion of the FBG spectra. For this reason a section of this report addresses the problems associated with chirping (or peak splitting), and presents the data analysis method applied. Overall, it was possible to quantify the stiffness drop, despite the presence of chirping. Results also show that it was possible to qualitatively monitor and detect damage by periodically recording FBG loading spectra with an optical spectrum analyzer (OSA) and noting any changes. Noteworthy observations were made regarding the evolution of FBG spectra during fatigue corresponding to the two laminate types.