In situ process monitoring for automated fibre placement using fibre Bragg grating sensors

The potential for increased productivity offered by automated fibre placement method has opened up a wider range of applications as well as new markets for composite materials. However, like many other manufacturing methods, different flaws such as voids or delamination may still occur during or after lay-up. Therefore, the use of automated fibre placement as an open-mould process where fibre/tape material is fed brings with it a need and an opportunity to establish a reliable inspection and monitoring method to ensure structural integrity not only after fabrication but also one step earlier, during the manufacturing process. Since optical fibre-based photonic sensing technologies are increasingly common for structural health monitoring of composite structures, selection of optical fibre Bragg grating sensors for manufacturing process monitoring has been successfully implemented here. Experiments are carried out on glass fibre/high-density polyethylene laminates with embedded fibre Bragg grating in the automated fibre placement method. The lay-up process conditions are monitored by the fibre Bragg grating sensors via measuring the reflected wavelengths which are related to pressure and temperature. The results presented in this article indicate that fibre Bragg grating sensing technique can be reliably employed for online monitoring of lay-up process to ensure the quality of final product.