Process monitoring of aluminum-foam sandwich structures based on thermoplastic fibre-metal laminates using fibre Bragg gratings

This paper reports the use of fibre Bragg gratings (FBGs) for monitoring the fabrication process in a novel sandwich structure based on thermoplastic fibre-metal laminate (FML) skins and an aluminum-foam core. The FBG sensors were embedded between two plies of glass fibre reinforced polypropylene within the FML and the shift in the Bragg wavelength was recorded during the fabrication cycle to monitor the melting and solidification processes in this system. The FBG response was then analysed by differentiating the wavelength shift with respect to temperature in order to highlight key transitions in the processing cycle, in particular the melt and recrystallisation temperatures of the polymeric matrix. The results were then compared to data obtained by differential scanning calorimetry (DSC). The study showed that FBGs offer the possibility of identifying key transition temperatures in the processing cycle and that they can be used to obtain an accurate estimation of the post-processing residual strain within the thermoplastic-based laminate.