Fully integrated monitoring systems have shown promise in improving confidence in composite materials while reducing lifecycle costs. A distributed optical fibre sensor is embedded in a fibre reinforced composite laminate, to give three sensing regions at different levels through-the-thickness of the plate. This study follows the resin infusion process during fabrication of the composite, monitoring the development of strain in-situ and in real time, and to gain better understanding of the resin rheology during curing. Piezoelectric wafer active sensors and electrical strain gauges are bonded to the plate after fabrication. This is followed by progressive loading/unloading cycles of mechanical four point bending. The strain values obtained from the optical fibre are in good agreement with strain data collected by surface mounted strain gauges, while the sensing regions clearly indicate the development of compressive, neutral, and tensile strain. Acoustic emission event detection suggests the formation of matrix (resin) cracks, with measured damage event amplitudes in agreement with values reported in published literature on the subject. The Felicity ratio for each subsequent loading cycle is calculated to track the progression of damage in the material. The methodology developed here can be used to follow the full life cycle of a composite structure, from manufacture to end-of-life.

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The total distributed strain produced during a vacuum-assisted resin infusion moulding composite manufacture process is measured in real time by using optical fibre sensors embedded in three different layers of a thin 5-harness satin weave flat plate cured with low-viscosity epoxy resin/cycloaliphatic polyamine epoxy resin polymer matrix. We present and discuss the chemical reaction of the epoxy resin polymer matrix adhesive to show that under manufacturing conditions, well below the glass transition point, substrates gradually come into contact with and become covered with epoxy resin polymer matrix strongly bonded to their surfaces. The fluid dynamics of the reaction system under such conditions reduces to a Cauchy equilibrium found in stressed solids, which leads to a strength of materials argument to show that the embedded, distributed optical fibres can accurately measure the motion of the surrounding epoxy resin polymer matrix before the gel point. The same argument is applied to the embedded 5-harness satin carbon fibre weave and leads immediately to an extension of the composite laminate theory for the thermodynamic liquid phase before the glass transition temperature. The predictions of the modified composite laminate theory framework are found to be consistent with experiment.

After manufacturing a composite element, it is expected to have residual stresses which affect the quality and the mechanical properties of the composite. In the present work, a distributed optical fibre sensor (DOFS) was embedded in a carbon fibre panel, measuring the development of residual stresses by monitoring in real-time the manufacturing process, from the resin infusion to the curing cycle, and the changes experienced within. An optical sensor interrogator detects and measures changes in strain and temperature along the DOFS with high precision and accuracy, making it possible to obtain a full strain/temperature profile. Data acquired from the embedded sensor led to track and characterize the strain profile at every stage of the manufacture process.

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