Research project on fixing damages of thermoplastic composite structures

This year Linda Grafen finalized the two-year research project called Fixing damages of thermoplastic Composite Structures (FICS), performed within the Top Technology Twente – Connecting Industry program of the University of Twente. The objective of her work was to investigate thermoplastic composites repair strategies based on fusion bonding techniques, thereby exploiting the melt-processable nature of the thermoplastic matrix.

In collaboration with the TPRC industrial partners, Linda chose to focus on repairing impact damages, such as matrix transverse cracks and delaminations. She explored two different repair methods, namely reconsolidation and patch repair. She conducted a coupon-level study to understand the effect of these repair techniques on quality and mechanical performance of UD C/PAEK laminates.

The reconsolidation of impacted laminates was conducted using the vacuum-bag-only (VBO) method. Their mechanical performance was assessed via compression testing and compared to the compressive properties of impacted samples and an open-hole reference sample. It was found that the reconsolidation fully healed delaminations and matrix cracks, resulting in a recovery of the mechanical performance, as the samples outperformed the reference notched compressive strength.

The same VBO process was used to investigate the patch repair method. The mechanical performance of different patch configurations, such as scarf, step and scarf doubler, was evaluated via tensile testing and compared to the tensile properties of the reference material. Tensile properties comparable to the reference material were achieved, depending on the patch configuration.

Overall, this study demonstrates the potential of reconsolidation and patches as methods for repairing impact damages, ranging from barely visible to severe structural damages, and represents a way forward for developing melt-processable repair strategies for larger and complex thermoplastic composites structures.

Photo ©Gijs van Ouwerkerk