Influence of stacking sequence and compaction force during the AFP process on mechanical performance and damage mechanisms elucidated by acoustic emission insights

This study examines the effect of consolidation force during Automated Fiber Placement (AFP) on the mechanical and fracture behavior of carbon fiber-reinforced polymer composites with different stacking sequences. Unidirectional (UD), cross-ply (CP), and quasi-isotropic (QI) laminates are fabricated using consolidation forces of 300 N and 600 N. Tensile, mode-I, mode-II, and short beam shear (SBS) tests are conducted, complemented by in-situ acoustic emission (AE) analysis to monitor real-time damage progression. Higher consolidation forces enhance tensile strength, particularly in QI laminates, resulting in a 12% increase, while Young's modulus remains unaffected for UD and CP laminates. Mode-I interlaminar fracture toughness improves by 16% for UD and CP laminates under higher consolidation forces, while QI laminates exhibit minimal change. Mode-II tests reveal that QI laminates demonstrate superior delamination resistance, whereas UD composites show lower toughness due to rapid crack propagation. AE analysis indicates that QI laminates have higher cumulative acoustic counts and energy, reflecting increased damage accumulation and energy dissipation under both mode-I and mode-II loading conditions. Additionally, AE data highlight enhanced interfacial bonding, supported by peak-frequency rates and AE energy levels. This study emphasizes the critical roles of fiber orientation and consolidation force in determining the mechanical performance and damage behavior of AFP-manufactured composites. By integrating in-situ AE techniques, it provides insights into optimizing AFP processes for improved composite performance.