Sophie Vanpée
PhD student
Ir. at UCLouvain in 2021

Main project: Micromechanics of crystallization of thermoplastic matrices in the interfiber regions of high-toughness composites
Funding: UCLouvain
Supervisor(s): Thomas Pardoen

A major effort is being made all over the world by industrial and research actors to lead the technological mutation of the field of advanced continuous fibers polymer composites from the current use of thermosetting matrices to thermoplastic ones which gather economic (increased production rates), environmental (recyclable) and performance advantages (tougher matrices). However, until recently, this transformation was strongly hindered by processing difficulties. Today, a precise prediction of the behavior of these materials based on the processing conditions becomes essential for many actors, such as the company Solvay, the industrial partner of the present thesis.

It is in this context that the thesis will be carried out. The objective of the STOUGH project is to unravel the influence of the composite microstructure on the kinetics and morphology of crystallization within the matrix, particularly in the neighborhood of fibers, in order to evaluate their influence on mechanical properties of the matrix and, hence, of the composite. The project is thus intrinsically multi-scale, which necessitates a combination of analyses at the different levels of the composite system, from its constituents themselves to the unidirectional (UD) ply level and eventually to the macroscopic composite.

The main questions are around the positive or negative impact of the conditions and the type of crystallization on the fracture toughness via local damage or decohesion of the fibers, as well as on the transfer of these effects to the macroscopic scale and the properties of use. To do so, it is necessary to understand what makes the behavior of the semi-crystalline polymer confined between fibers and the non-reinforced version of the same polymer different, and how factors related to transcrystallization condition the local mechanical behavior. Does the crystal morphology induce a local softening of the strength or the opposite? Are macroscopic constitutive models adaptable to this scale? Do the local internal stresses affect the first order strength of the interfaces? These are some of the major scientific questions that motivate the fundamental side of this project and justify the framework of a PhD thesis in collaboration with Solvay.

The thesis will be based on an innovative methodology relying on the use of the appropriate experimental methods for each level of investigation. For instance, it will combine atomic probing and nanoindentation for the nano- and microscopic characterization of the matrix, fiber-matrix interface properties measurements, image correlation analyses at the scale of the representative volume of the UD ply as well as macroscopic tests at the coupon level. Additionally, the project will also include the specimens processing and manufacturing steps, as well as numerical aspects to incorporate the acquired knowledge in existing models.

IMMC main research direction(s):
Processing and characterisation of materials

multi-scale modeling

Research group(s): IMAP
Collaborations: Bernard Nysten