A micro-computed tomography technique to study the quality of fibre optics embedded in composite materials.

Gabriele Chiesura,Wim Van Paepegem,Thomas Geernaert,Joris Degrieck,Manuel Dierick,Nicolas Lammens,Eli Voet,Geert Luyckx,Luc Van Hoorebeke,Pieter Vanderniepen,Sanne Sulejmani,Francis Berghmans,Camille Sonnenfeld

doi:10.3390/s150510852

Gabriele Chiesura, Wim Van Paepegem + Show 11 more

Open Access

https://doi.org/10.3390/s150510852

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Abstract

Quality of embedment of optical fibre sensors in carbon fibre-reinforced polymers plays an important role in the resultant properties of the composite, as well as for the correct monitoring of the structure. Therefore, availability of a tool able to check the optical fibre sensor-composite interaction becomes essential. High-resolution 3D X-ray Micro-Computed Tomography, or Micro-CT, is a relatively new non-destructive inspection technique which enables investigations of the internal structure of a sample without actually compromising its integrity. In this work the feasibility of inspecting the position, the orientation and, more generally, the quality of the embedment of an optical fibre sensor in a carbon fibre reinforced laminate at unit cell level have been proven.

Highlights

Amongst different sensing techniques, condition monitoring of composite structures using optical fibre sensors (OFS), and in particular fibre Bragg gratings (FBGs) appears to be the most suitable, because of their high accuracy (±1 με), their immunity to electromagnetic interference and their small intrusive character when embedded in composite materials [1,2,3]
As already stated, keeping track of the sensor position after embedding is of relevance to define the real stress acting on the embedded fibre sensor and, on the structure
Cross-section of the scanned sample is the result of about 1500 radiographs taken at different orientations over 360°. This allows one to define the position of the embedded fibre, but normally the scanning time and the reconstruction process are time-consuming operations

Summary

Introduction

Condition monitoring of composite structures using optical fibre sensors (OFS), and in particular fibre Bragg gratings (FBGs) appears to be the most suitable, because of their high accuracy (±1 με), their immunity to electromagnetic interference and their small intrusive character when embedded in composite materials [1,2,3]. OFS technology has already proven to be useful as a monitoring tool for composite manufacturing [4]. Despite their small intrusive character, uncertainty still exists on the quality of embedding, on the exact position after production, on the embedded sensor’s measuring accuracy [3] and on their interaction with the composite during the whole life cycle of the structure [5,6,7]. First is the embedding depth of the sensor, which is an essential design parameter when evaluating a composite beam in flexion. The basic beam theory expresses the flexural stress component [8] at a given depth, as: σ

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