PSI - Issue 52

Miray Yasar et al. / Procedia Structural Integrity 52 (2024) 165–175 Miray Yasar et. al. / Structural Integrity Procedia 00 (2019) 000 – 000

167

3

(MWCNTs) were supplied by Graphene Supermarket. N-N Dimethylformamide (DMF) and acetone were procured from Merck Ltd. A Polyphenylene sulfide (PPS) veil with an areal density of 5g/m 2 was procured from Technical Fibre Products, UK. 2.2. Methodology 2.2.1. Preparation of PVDF Impregnated PPS Veils A 50/50 (w/w) solution of DMF and acetone was used to dissolve 20 wt.% PVDF, which was then stirred using a mechanical mixer at 50 o C for 2 hours. 0.2 wt.% MWCNTs was added to the solution and mixed for an additional 2 hours. Ultrasonication was carried out for 1 hour to obtain uniform distribution of MWCNTs in the mixture. The PVDF-MWCNTs solution was poured onto a 5 g/m 2 PPS veil and left to evaporate the solvent at room temperature for 48 hours. The resulting PVDF-impregnated PPS veil was compressed in a hot press operated at 180 o C under 500 kN pressure for 15 minutes, causing the PVDF to melt. Then it is cooled down to room temperature while maintaining the same pressure to obtain high β phase content of PVDF. To enhance the infusion of the Elium resin between carbon fibres during the composite manufacturing process, the consolidated PVDF-MWCNTs-PPS film, which will be referred to as the “ PVDF layer ” for the rest of the paper, was subsequently perforated. The perforation consisted of 4 holes/cm 2 arranged in a straight line, with each hole having a diameter of 0.8 mm and spaced 5 mm apart. 2.2.2. Preparation of Carbon Fibre Reinforced Composites Carbon fibre reinforced Elium composites (CFRC) and composites that include a perforated PVDF layer (P-PVDF CFRC) were fabricated using the vacuum assisted resin infusion method. To investigate the significance of PVDF layer perforation, the mechanical performance of non-perforated (NP-PVDF CRFC) and perforated composites were compared to analyse the effect of perforation on the wetting behaviour of the fibre surface. Elium 150 was kept at 25 o C for 1 hour prior to the process to reduce the viscosity for effective infusion. Unidirectional carbon fibres and P-PVDF or NP-PVDF layers were subsequently infused with the Elium resin which was mixed with BPO curing agent at a ratio of 3 wt.% for 5 minutes at room temperature. The schematic representation of the production of the carbon fibre reinforced thermoplastic piezoelectric composites is given in Figure 1.

Fig. 1. Schematic Representation of Carbon Fibre, PVDF-MWCNTs Impregnated PPS Veil (PVDF Layer) and Carbon Fibre Composite Production

The composite was then cured at 40 o C for 24 hours. The stacking sequence for both interlaminar shear strength and 3-point bending tests consisted of 4 layers of carbon fibre, a PVDF layer, and 4 layers of carbon fibre. For mode I fracture toughness tests, the stacking sequence consisted of 7 layers of carbon fibre, a PVDF layer and 7 layers of carbon fibre. Test specimens were cut from the fabricated layups to the dimensions recommended by the respective ISO standards. The volume fraction of the composites was maintained at 67%. Samples were poled by using the contact poling unit which consisted of an in-house designed poling unit, a high voltage power supply (Branderburg, Alpha III, 30 kV-1.5mA), a silicone oil bath and a hot plate. Prior to poling, the