Annealing impact on mechanical performance and failure analysis assisted with acoustic inspection of carbon fiber reinforced poly‐ether‐ketone‐ketone composites under flexural and compressive loads

This study investigates the effect of the annealing treatment for carbon fiber reinforced Polyether-ketone-ketone (CF/PEKK) composite structures under flexural and compressive loadings through reference, pre-damaged, and annealed sample sets. Significant recovery of pre-existing damage is observed after the annealing process, following both flexural and compressive loading. Acoustic emission (AE) inspection is employed to monitor the failure behavior and assess the impact of pre-damage and annealing on CF/PEKK composite. Initially, AE inspection reveals that the reference CF/PEKK material exhibits a notable fiber-related failure with 85% of cumulative AE counts under flexural load, whereas matrix-related failures are more pronounced with 92% cumulative AE counts under compressive load. Pre-damages in the matrix alter the cumulative count percentages and initiation time that are related to matrix, interface, and fiber-related failures, under flexural and compressive loadings. After annealing, each cumulative AE count percentages are comparable to reference sample values, due to changes in microstructure and relieving of residual stresses. The annealing effect is further validated through dynamic scanning calorimetry (DSC) analysis results with increased glass transition temperature (Tg) and degree of crystallization (Xc). Overall, these findings indicate that annealing treatment effectively restores structural integrity and improves the mechanical performance of CF/PEKK composites.