Polymer dynamics applied to PEEK matrix composite welding

Continuous composite processes such as thermoplastic automated tow placement are based on fusion bonding or healing of thermoplastic matrix. A good understanding of interdiffusion and crystallization, the main phenomena at the interface, is important. In order to investigate self-bonding in PEEK (Poly-ether-ether-ketone) and then in the same matrix reinforced by carbon fibers, a new experimental device has been developed allowing to prepare short-time welded samples which were then mechanically characterized using a wedge double cantilever beam test. The corresponding data on mode I critical strain energy release rate as function of processing conditions clearly show that both interdiffusion across the interface and crystallization are key parameters for the strengthening of the interface. Thermal modeling has also been developed and explains the importance of the interface cooling curve for healing.