Fiber Bragg gratings as strain and damage sensors for aerospaceapplications

摘要

Real aerospace composite parts, like curved stiffened panels used as cowlings inAirbus aircrafts, stiffened panels and ribs, have been instrumented with standard strain gauges andFBG sensors, and submitted to mechanical tests up to failure. Besides to identify the difficulties ofusing fiber optics as strain sensors, artificial delaminations and flaws were introduced, in order toevaluate the ability of fiber Bragg gratings for damage detection.Strain measurements of embedded FBGs can be compromised by spurious phenomena likebirrefringence promoted by residual stresses, with the subsequent spectral peak splitting, or spectralchirping caused by local non uniform strain fields. Surface bonded sensors are preferred for fabriclaminates to avoid a highly distorted reflected peak. Both surface bonded or embedded sensors in caseof tape laminates, showed a very good comparison or measurements from electrical and optical straingauges.Under static tests, fiber optic strain sensors were insensitive to damage, even in cases when sensorwas located at the surface on top of the delaminated region. Practical issues, as the use of optical fiberribbons for embedding a large array of sensors, and the ingress/egress of the optical fiber from thelaminate, will be discussed.