UNDERSTANDING INTERLAMINAR BONDING AND FRACTURE TOUGHNESS IN IN-SITU CONSOLIDATED AUTOMATED FIBER PLACEMENT OF CARBON FIBER LMPAEK COMPOSITES

Fiber reinforced thermoplastic composites (TPC) are advantageous due to their out-of-autoclave processability, higher toughness, recyclability, weldability, and ease of repair. Yet, difficulty manufacturing at scale has limited their application in the aerospace industry. Developing high rate in situ consolidation automated fiber placement of TPCs (ICAT) is essential to realize TPC's potential. Recent studies by the authors have investigated how processing parameters affect interlaminar bonding, void development, and crystallinity in ICAT parts. This study aims to further our understanding of bond strength and fracture toughness in ICAT parts. A laser powered Automated Fiber Placement (AFP) machine, built in-house, is used to manufacture ICAT Short Beam Shear (SBS) and Mode II fracture toughness coupons from carbon fiber reinforced low-melt Polyarlyletherketone (LM-PAEK) quarter inch tapes. Processing parameters were varied to fabricate specimens at two different sets of bonding strengths and crystallinities: one specimen with both a high bonding strength (58 MPa) and high crystallinity (23%), the other with low bonding strength (41 MPa) and low crystallinity (9%). The two sample sets were evaluated based upon their interlaminar bonding strength, mode II fracture toughness, crystallinity, void content, and failure modes. Results from all testing provided insight on how differing bonding and crystallinity levels affect fracture toughness and failure mechanisms in ICAT samples. High quality ICAT parts (<1% void content) with mode II fracture toughness values on par with compression molded samples and relatively high SBS strength (60% of compression molded samples) are demonstrated.