Effect of ply orientation on bond strength in fiber-placed composites

The Laser-Assisted Fiber Placement (LAFP) process is an additive manufacturing technique with the potential for out-of-autoclave manufacturing. A thermoplastic composite pre-impregnated tape is heated with a laser above melting temperature and subsequently pressure is applied via a roller to bond the tape to previously laid down plies. LAFP offers the opportunity to combine the stacking and the consolidation, thereby reducing cost and process time compared to conventional processes, such as autoclave and press-consolidation. However, the consolidation quality achieved with LAFP is not yet at the same level as the conventional processes. One of the measures of consolidation quality is the interlaminar bond strength. The mandrel peel test is used as a method to quantify the effects of process parameters on the interlaminar bond strength. The aim is to optimize the interlaminar bond strength achieved and to increase the understanding of governing bonding mechanisms. A LAFP robot was used to place carbon/PEEK tapes onto pre-consolidated substrates with various laser power settings and two different top ply fiber orientations. The fracture toughness of the bond was measured using the mandrel peel test. The results showed that the fracture toughness strongly depends on laser power. Underheating and overheating resulted in a decline in fracture toughness and the highest fracture toughness of about 1.30 kJ/m² was obtained for a nippoint temperature of around 500^◦C. A similar maximum fracture toughness at equal laser power settings was measured for both 0^◦ and 90^◦ top ply orientations. However, the process window of the 90^◦ top ply orientation seems to be smaller.