An investigation of Polyether Imide (PEI) toughening of carbon fibre-reinforced Polyether Ether Ketone (PEEK) laminates

Current thermoset composite material systems have relatively low interlaminar fracture toughness, leaving them vulnerable to impact damage. While thermoplastic based systems are considered to be tougher, toughness levels can be dependent on processing parameters. In this study, Polyether imide (PEI) film layers were added to carbon fibre-reinforced Polyether ether ketone (CF/PEEK) laminate layups prior to consolidation to enhance the interlaminar toughness at key ply interfaces. It was found that the addition of the PEI film improves the Mode I and Mode II interlaminar toughness of the laminate. Low-velocity impact tests were performed on the PEI toughened CF/PEEK laminates, as well as a baseline CF/PEEK laminate and a CF/PEEK laminate with PEEK film inserts, for direct laminate thickness comparison. For low energy impacts (10 J), associated with tool drop events, it was found that the PEI toughened panel performed best. However, the performance difference decreased as the impact energy increased. Ultrasonic scans indicated that PEI toughened CF/PEEK laminates exhibited a smaller damage footprint. Compression after impact (CAI) and Combined Loading Compression (CLC) tests revealed that although the PEI inserts reduce the laminate undamaged compressive strength, they exhibited higher relative residual strengths compared to the other laminates tested.