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Optical fibre based resin detection and cure monitoring for infusion Disclosure Number: IPCOM000242825D
Publication Date: 2015-Aug-21
Document File: 2 page(s) / 19K

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Subject: Accurately tracking resin infusion front through a fibrous lay-up.

Summary: Lay one or more loops of standard optic fibre “up and back” through the fibrous lay-up, with a Rayleigh backscatter detector associated with the fibre.  A reference “fingerprint” of the fibre may be made in a bagged, vacuumed, pre-infusion state of the lay-up and then stored in a normalised numeric form. In this partial vacuum state, the optic fibre is slightly strained due to the compressive effect of the vacuum bag.  As resin is then infused through the layers, it envelops the optic fibre(s) thereby slightly de-stressing it as it progresses.  The relaxation of the fibre can be “read” from its backscatter pattern, when compared with the reference “fingerprint” values. A sequence of backscatter readings taken during the infusion process will show the transition from tense fibre shape to a relaxed fibre shape, progressing along the fibre.  Also a local temperature change of the fibre resulting from resin exposure can be detected in a changed backscatter pattern.  The degree of infusion may also be detected by isolating a thermal effect on the fibre backscatter pattern from a relaxation effect.  This may be achieved by running a parallel optic fibre in a silica sleeve which will decouple the inside fibre from strain effects of the resin front.  By subtracting one characteristic from the other, the temperature effect can be isolated and compensated for as necessary.  As the resin hardens (cures), it puts more strain on the fibre.  Knowing the backscatter effect due solely to hardening, the “degree of cure” can be isolated.

Main text: The technique utilises the ability of a Rayleigh backscatter measurement system to measure the flow of resin during the infusion and cure of the resin during the cure of a composite part. A Rayleigh backscatter system can measure the distributed temperature and strain effects on an optical fibre which allows for these parameters to be measured online and during the manufacturing process. Typically the system can attain mm spatial resolution along the length of measurement fibre with ±1°C temperature resolution and excellent; strain resolution. It is because of this high resolution capability the ability to measure resin flow is possible. The optical fibre to be measured is embedded within the composite structure that requires resin flow detection. The optical fibre can be embedded within the composite structure because of its small size (typically less than 250microns in overall diameter) and its similar mechanical properties to the structure itself (standard optical fibre is made from silica glass). The fibre may be laid in a path in the product where it is known there may be resin infusion problems. The measurement process involves; (1) taking a Rayleigh backscatter image of the fibre along its length while the fibre is laid in the composite or during the layup, (2) taking a subsequent image of the f...