Toughening strategies for co-cured composite joints by Charline VAN INNIS

Carbon fibre reinforced polymer composites are broadly used in complex structures. Manufacturing of these structures requires joining composite parts with each other or with other materials. Adhesive bonding offers many advantages compared to mechanical fastening such as lightweight and homogeneous stress transfer. However, adhesive joints suffer from low fracture toughness and time- and labour-intensive processes preventing intensive use by the industry.

The first objective pursued by this thesis is to investigate composite co-curing through a thermoplastic interlayer to tackle the process intensity issue. PEI, PES, PSU, PA, PC and PMMA are the thermoplastic materials investigated for this purpose. Interdiffusion is key to achieve a good toughness but under certain conditions a weak interface can develop along the morphological gradient, resulting in a brittle joint or interphase.

Secondly, toughening strategies are investigated. First, polyethylene filaments are inserted to trigger significant bridging. As an alternative, a TP film is manufactured through 3D printing to introduce channels that can be filled or left empty during the co-curing process. This controlled filling allows fine tuning the properties of joints in terms of toughness and shear resistance. The last investigated strategy is the addition of a dissipative layer which proves to be efficient if this layer is soft and stacked between two thin brittle layers.

Strategies to improve the joint toughness also affect other properties such as the shear strength and stiffness of the joint. To compare toughened joints with their classical counterpart, a selection methodology is developed to determine under which loading conditions the toughened solutions performs the best.

Jury members :

• Prof. Thomas Pardoen (UCLouvain, Belgium), supervisor
• Prof. Sandra Soares-Frazao (UCLouvain, Belgium), chairperson
• Prof. Michal K. Budzik (Aarhus University, Denmark)
• Prof. Thierry Massart (ULB, Belgium)
• Prof. Aude Simar (UCLouvain, Belgium)
• Prof. Norman Fleck (Cambridge university, England)
• Prof. Julie Teuwen (TUDelft, Netherlands)

Visio conference link : https://teams.microsoft.com/l/meetup-join/19%3ameeting_YThlYTdlMTctN2QwOS00M2ZjLThkZjYtMGI1NjM0MGUzYzc1%40thread.v2/0?context=%7b%22Tid%22%3a%227ab090d4-fa2e-4ecf-bc7c-4127b4d582ec%22%2c%22Oid%22%3a%2240c84eb0-81d4-4433-be79-c9af220924ef%22%7d