Lightweight, electromagnetic interference (EMI) immune, fiber-optic, sensorbased structural health monitoring (SHM) will play an increasing role in aerospace structures ranging from aircraft wings to jet engine vanes. Fiber Bragg Grating (FBG) sensors for SHM include advanced signal processing, system and damage identification, and location and quantification algorithms. Potentially, the solution could be developed into an autonomous onboard system to inspect and perform non-destructive evaluation and SHM.
A novel method has been developed
to massively multiplex FBG sensors,
supported by a parallel processing
interrogator, which enables high sampling
rates combined with highly distributed
sensing (up to 96 sensors per
system). The interrogation system comprises
several subsystems. A broadband
optical source subsystem (BOSS) and
routing and interface module (RIM)
send light from the interrogation system
to a composite embedded FBG sensor
matrix, which returns measurand-dependent
wavelengths back to the
interrogation system for measurement
with subpicometer resolution. In particular,
the returned wavelengths are
channeled by the RIM to a photonic
signal processing subsystem based on
powerful optical chips, then passed
through an optoelectronic interface to
an analog post-detection electronics
subsystem, digital post-detection electronics
subsystem, and finally via a data
interface to a computer.
A range of composite structures has been fabricated with FBGs embedded. Stress tensile, bending, and dynamic strain tests were performed. The experimental work proved that the FBG sensors have a good level of accuracy in measuring the static response of the tested composite coupons (down to sub-microstrain levels), the capability to detect and monitor dynamic loads, and the ability to detect defects in composites by a variety of methods including monitoring the decay time under different dynamic loading conditions.
In addition to quasi-static and dynamic load monitoring, the system can capture acoustic emission events that can be a prelude to structural failure, as well as piezoactuator-induced ultrasonic Lambwaves- based techniques as a basis for damage detection.
This work was done by Behzad Moslehi and Richard J. Black of Intelligent Fiber Optic Systems Corp. and Yasser Gowayed of Auburn University for Dryden Flight Research Center. DRC-011-004