Mechanical properties of high performance recyclable thermoplastic based composites for windmill applications

Fibre-reinforced polymers (FRP) have become a material of choice for many applications relying on stiff, strong, and light structures. The growing use of FRPs is perfectly illustrated by the aerospace industry, whose latest produced aircraft are composed of over 50% by weight of such composites. The FRP's matrix is typically made of a thermosetting polymer, whose convenient chemical and physical properties lead to cheap, industrial processes of manufacturing. However, one of the main drawback of the thermosetting-based FRPs is the lack of easy processes to recycle and repair them, leading to disposal and environmental concerns. The specialty chemicals and advanced materials French company Arkema developed a thermoplastic resin called Elium to address this problem. This resin enables easy recycling and post-thermoformability of the FRP, while allowing its manufacture with the already in place industrial processes. This master's thesis is dedicated to the mechanical characterisation of the Elium grades 188 and 190, both as bulk resins and as matrices of a glass fibre-reinforced polymer. First, the bulk behaviour of both grades is investigated through a campaign of uniaxial compression tests over 4 decades of strain rate and at 3 different temperatures. The compression tests were conducted at constant true strain rate on cylindrical specimens made of pure resin. Results showed that both grades exhibit the typical behaviour of glassy polymers. It was shown that Elium 190 has an overall better mechanical behaviour than Elium 188, with a higher Young's modulus, peak yield stress and stress at failure, among other properties. At higher strain rates, both grades experience a ductile-to-brittle transition as well as a pronounced adiabatic heating effect. A temperature and strain-rate dependent full-model from Nasraoui et al. was applied to Elium 190 and predicted satisfactorily its behaviour, except at higher strain rates. Second, the behaviour of both grades as matrices of a glass fibre-reinforced polymer (GFRP) was studied through a finite element analysis of a transverse compression conducted on Representative Volume Elements (RVEs) of a unidirectional GFRP. A linear Drucker-Prager law was used to model the behaviour of the resin, which is calibrated using the results of the uniaxial compression tests mentioned above. Results showed that Elium 190 forms a better matrix of GFRP than Elium, under the conditions tested in this work. The RVE composed of Elium 190 exhibited remarkably higher peak yield stress and stress at failure. In order to validate experimentally the results of the simulation, a precise lead was proposed in the form of a digital image correlation on similar GFRP specimens.