Multiplexed fibre optic sensors for monitoring resin infusion, flow, and cure in composite material processing

Abstract

The infusion, flow and cure of RTM6 resin in a carbon fibre reinforced composite preform have been monitored using a variety of multiplexed fibre optic sensors. Optical fibre Fresnel sensors and tilted fibre Bragg grating (TFBG) sensors were configured to monitor resin infusion/flow in-plane of the component. The results obtained from the different sensors were in good agreement with visual observations. The degree of cure was monitored by Fresnel sensors via a measurement of the refractive index of the resin which was converted to degree of cure using a calibration determined from Differential Scanning Calorimetry. Fibre Bragg grating sensors fabricated in highly linearly birefringent fibre were used to monitor the development of transverse strain during the cure process, revealing through-thickness material shrinkage of about 712  and residual strain of 223 . An alternative approach to infusion monitoring, based on an array of multiplexed tapered optical fibre sensors interrogated using optical frequency domain reflectometry, was also investigated in a separate carbon fibre preform that was infused with RTM6 resin.

Resin Directional Flow and Degree of Cure Sensing Using Chirped Optical Fiber Long Period Gratings

“…A range of optical techniques have been investigated for composite material processing, with demonstrations of the ability to detect the presence of resin using a single sensor [20,21], to measure resin flow during the infusion when the sensors are spatially multiplexed [14,22], and to monitor the cure of the resin [11,21,22]. Superimposed fibre grating sensors, offering strain-temperature discrimination, have also been demonstrated for cure monitoring [23].…”

“…Etched fibre sensors, where the cladding of the fibre has been partially or completely removed, or tapered optical fibres, where the diameter of the fibre is reduced by heating and stretching to allow the evanescent wave of the propagating mode to interact with the surrounding medium, have been used to allow the detection of the presence of resin at the sensor location [1,5,[14][15][16].…”

“…The interaction of the evanescent field of the cladding modes causes the coupling conditions, and thus the transmission spectrum of the device, to be sensitive to changes in the RI of the surrounding material. Both devices can indicate the arrival of the resin at the sensor location, and can be used to subsequently monitor the cure of the resin [11,14].…”

“…The determination of the direction of flow of the resin is particularly important in complex shaped preforms [18], as it enables the appropriate resin inlet gates to be regulated in order to control the amount of resin pumped into the preform. [24]; standard tilted fibre Bragg grating (TFBG) [14] Step change in attenuation of an LPG (TFBG) spectrum detected resin arrival. A serial array of LPGs (TFBGs) at different wavelengths detected resin flow.…”

Noise Cancellation of Helicopter Blade Deformations Measurement by Fiber Bragg Gratings

“…The existing approaches to helicopter blade deformation measurement can be divided into four main categories: the systems based on the detection of reflected light [2][3][4], the systems based on laser units [5], the systems based on electrical resistance strain gauges [6][7][8], and the fiber-optic strain measurement systems [9][10][11].…”