For the degree of Doctor of Engineering Sciences and Technology

The recent development of Elium, a range of thermoplastic monomer formulas compatible with liquid composite moulding processes, has initiated the transition from thermosetting to thermoplastic polymer matrices for the manufacturing of structural composite parts. However, Elium remains a whole new resin system and, as such, must continue to prove its worth to the composite industry. This thesis lies at the heart of the ongoing research effort directed towards manufacturing fibre-reinforced Elium composites, understanding the mechanisms occurring during processing and how these impact the structural behaviour of the parts under mechanical loading. From an industrial perspective, mitigating void formation in thick (> 1 cm) Elium laminates manufactured by vacuum infusion followed by in-situ polymerisation was the first motivation for this work. The second, more fundamental objective was to contribute to the understanding of Elium composite properties at the microscale.

Through the development of a thermokinetic model, the main mechanism leading to void formation in Elium composites, i.e. monomer boiling during polymerisation, could be accurately captured. For any set of preform thickness, resin formula and fibre volume fraction, the model allows predicting whether the monomer will boil or not depending on the selected heating parameters. A miniature in-situ infusion experiment followed by dynamic X-ray computed tomography was also designed for monitoring void formation events in thick Elium laminates during processing. The results confirmed the particular sensitivity of the polymerisation step to void formation.

The deformation and failure mechanisms occurring at the constituent level in Elium composites were explored via a newly-developed nanoscale digital image correlation (DIC) method. Strain localisation events were exclusively observed in a thin (a few 100 nm) crown of matrix surrounding the fibres. This region was found to be the interphase region of the composite, beyond which the mechanical response of the polymer remains broadly similar to that of an unreinforced Elium resin.

Jury members :

• Prof. Thomas Pardoen (UCLouvain, Belgium), supervisor
• Prof. Christian Bailly (UCLouvain, Belgium), supervisor
• Prof. Hervé Jeanmart (UCLouvain, Belgium), chairperson
• Prof. Bernard Nysten (UCLouvain, Belgium)
• Dr. Pierre Gérard (Arkema, France)
• Prof. Yentl Swolfs (KU Leuven)
• Prof. Véronique Michaud (EPFL, Suisse)
• Dr. Julie Diani (Ecole Polytechnique Paris, France)

Visio conférence link : https://teams.microsoft.com/l/meetup-join/19%3ameeting_NTQ3MzBjZDktM2E5OC00YTIyLWE4Y2UtNzBjZTcwMTlkZGM2%40thread.v2/0?context=%7b%22Tid%22%3a%227ab090d4-fa2e-4ecf-bc7c-4127b4d582ec%22%2c%22Oid%22%3a%223b538b2d-1afb-47fe-8739-f4a7614af4c1%22%7d