Residual strain measurement in bonded composite repairs for aging aircraft by embedded fiber Bragg grating sensors

Abstract

Embedded Fiber-Bragg-Grating sensors are used for tracking the initiation of structural bonding and measuring the residual strains, during the curing process, of bonded composite patches used for aging aircraft structural repairs. FBG reading are shown to have direct correlation with the residual strains that are important in assessing the long-term durability of the repaired structure under fatigue load spectrum.

Combined application of Bragg gratings and dielectric sensors for the cure monitoring of bonded composite repairs

“…However, very complicated stress/strain fields occur during and after curing of the patch, due to the mismatch of the thermal expansion coefficients between the composite patch and the metallic substrate. Consequently the detailed knowledge of residual stresses developed after curing is of great importance for the design of such repairs [4][5] . The purpose of this study is to correlate measurements acquired from the various sensors to improve understanding of the interactions between the various processes occurring during repair bonding.…”

Multi-parameter fiber optic sensors for structural health monitoring

“…Another important area where more progress needs to be done is temperature and strain discrimination. The most straight forward approach is to use a thermocouple or strain relieve package for one of the gratings in the grating array and use it to temperature compensate the rest of the FBGs, Kang et al 2002, Wu et al 2004and Ben-Simon et al 2007. However this often leads to bulky and costly systems which are difficult to interrogate.…”