An Investigation of Optical Fiber Coating Performance in Embedded Sensing Applications

Abstract

The use of composite materials for aerospace applications has created an increased need for developing nondestructive methods for assessment of composite performance. Embedded optical fiber sensor technology provides the potential for monitoring parameters of interest during processing and testing of composite materials as well as the opportunity for tracking properties over the lifetime of composite parts in service. The successful development of this technology depends on designing optical fiber sensor systems suitable for embedding in composite structures.This paper focuses on the role played by optical fiber coatings in the design of embedded sensor systems. The performance of different optical fiber coatings under typical composite processing conditions will be discussed. Photomicrographs of test specimens containing embedded sensors will be presented which show delamination occurring at the coating/optical fiber interface in preference to the coating/epoxy resin interface. Coating performance criteria will be outlined for use in the selection of fiber optic sensors for composite applications.

Long-Term Durability Assessment of Optical Fiber Sensors

“…Static tensile testing has been conducted to compare the performance of polyimide coating to that of acrylate coating, and the failure mode (as well as location of delamination) of each was determined [4]. Their results reveal that delamination tends to occur at the coating/cladding interface rather than the coating/composite resin interface.…”

Demonstration of failure identification methodology incorporating sensor degradation

“…Haaksma et al demonstrated that debonding of the optical fiber from the coating occurred at lower stress levels than debonding of the adhesive for both acrylate and polymide coatings. 13 Therefore the role of this fiber/coating interface cannot be neglected in evaluations of sensor integrity.…”