Multi-scale characterization of carbon-fibre reinforced PEEK composites manufactured by laser-assisted tape placement

The Laser-Assisted Tape Placement forming process of thermoplastic composites enables the rapid production of laminates. However, it requires the tuning of the processing parameters, which is currently limited by a misunderstanding of the consolidation phenomena occurring during process and the interlaminar properties related with strong welded interfaces. This study aims at establishing correlations between physical properties and mechanical strength of welded thermoplastic composites, by using several methods and characterizations at different scales. Carbon-fibre reinforced PEEK (CF/PEEK) composites produced by a LATP process were investigatedby varying the Laser Setpoint Temperature (LST) and Tool Temperature (TT). The results show that laminates manufactured at a LST of 350 °C have high void content, with the location of the voids depending on the TT: at a TT of 25 °C (unheated tool), interply and intraply voids are present while for a TT of 250 °C they are mainly intraply. Laminates produced at a LST of 450 °C also have mainly intraply voids, although their void content is significantly lower than that of laminates produced at an LST of 350 °C. For laminates having mainly intraply voids, ILSS testing demonstrates failure by an intralaminar failure mode. An increase in intralaminar shear strength is observed as the intraply void content decreases and the degree of crystallinity increases, related to the LST and the TT. The combination of experimental techniques thus allowed to provide understanding on the influence of local physical properties of the composites manufactured by LATP on specific interface-related mechanical properties, and demonstrate that, despite variations of mechanical performances with processing conditions, interfaces are no longer a weak point within the laminates when the processing conditions allow for sufficient intimate contact to occur during the consolidation phase.