Fiber optic thermal detection of composite delaminations

Abstract

A recently developed technique is presented for thermographic detection of delaminations in composites by performing temperature measurements with fiber optic Bragg gratings. A single optical fiber with multiple Bragg gratings employed as surface temperature sensors was bonded to the surface of a composite with subsurface defects. The investigated structure was a 10-ply composite specimen with prefabricated delaminations of various sizes and depths. Both during and following the application of a thermal heat flux to the surface, the individual Bragg grating sensors measured the temporal and spatial temperature variations. The data obtained from grating sensors were analyzed with thermal modeling techniques of conventional thermography to reveal particular characteristics of the interested areas. Results were compared and found to be consistent with the calculations using numerical simulation techniques. Also discussed are methods including various heating sources and patterns, and their limitations for performing in-situ structural health monitoring.

Use of FBG Sensors for SHM in Aerospace Structures

“…Okabe et al (2000) [11] and Takeda et al (2002) [12] first utilized this feature to detect internal damage in the carbon fiber reinforced polymer (CFRP) laminates. Yashiro et al (2005) [20] also demonstrated that the reflection spectrum of an embedded FBG sensor was useful for identifying damage patterns within the gauge section for notched FRP laminates [23].…”