Consolidation and interlaminar fracture properties of unidirectional commingled CF/PEEK composites

The main objective of this study was to investigate the relationship between consolidation quality and interlaminar fracture of CF/PEEK composites manufactured from commingled prepreg. A compression molding system using a hot press was applied to simulate the effect of processing conditions, such as holding time (10, 30 and 60 min) and processing temperature (400 degrees C and 415 degrees C). Consolidation quality was studied through void content and density measurement, while transverse flexural (TF) properties of consolidated CF/PEEK composites were measured and correlated with the processing conditions. Mode-I and mode-II interlaminar fracture behavior was studied using double cantilever beam (DCB) and end notch flexure (ENF) specimens. The results indicated that the consolidation quality of the composites is highly dependent on processing conditions, and it was clearly improved at 400 degrees C when the holding time was increased from 10 to 60 min. Material degradation was observed for the composite produced at 415 degrees C, especially when a long holding time was applied. Mode-I interlaminar fracture growth resistance had little correlation with consolidation quality, while apparent mode-II interlaminar fracture toughness decreased as the void content was reduced. Fracture mechanisms associated with material microstructure are discussed. The results indicate that consolidation quality is not the only aspect that controls interlaminar fracture properties.