Investigation of sub-melt temperature bonding of carbon-fibre/PEEK in an automated laser tape placement process

Automated placement of thermoplastic-based composite tape is a highly non-isothermal process with temperature gradients often exceeding 1000 °C/s. Models for the process often assume that bonding ceases below the melting point, however the extreme cooling rates combined with high placement velocities can result in a highly amorphous polymer during consolidation. Bonding below the melting point is generally limited due to the presence of crystallites which impede reptation of the polymer molecules, however in the case of an amorphous state, autohesion should proceed. This paper investigates bonding of carbon-fibre(CF)/PEEK with experimental trials performed where sub-melting point temperatures occur at the nip point. The thermal history was recorded with thermocouples embedded in the substrate. Bond predictions are compared with experimental strengths determined by lap shear measurements. Bonding below the melting point was shown to occur, indicating the processing window could be wider than previously estimated by bonding models, particularly for higher placement rates.