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

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1. Introduction Carbon fibre reinforced composites have excellent mechanical performance, a high strength to weight ratio and provide design flexibility. Since they are used in many areas such as automobiles, aircrafts, boats, etc., they are exposed to loads which can result in damage such as matrix cracking, fibre failure, debonding or delamination. It is crucial to maintain the high performance and structural integrity of the composite structure in service and detect damage initiation as quickly as possible to prevent catastrophic failures (Groo et al., 2021). Structural health monitoring is a process to determine the safety and durability of the structures and detect any damage or defect by using some in-situ monitoring methods such as acoustic emission testing, resistance-based monitoring, embedding the sensors into the structure, production of self-sensing materials and fibre optic sensors (Groo et al., 2021; Haghiashtiani and Greminger, 2015). A new Infusible and recyclable thermoplastic, called Elium resin, with low viscosity and room-temperature curability has recently entered the market, making it suitable for resin infusion (Nash et al., 2018). Bhudolia et al studied mode I fracture toughness and impact properties of Elium based carbon fibre reinforced composites (Bhudolia and Joshi, 2018), and Shanmugam et. al. investigated functionalized MWCNTs modified dopamine coating solution to enhance ultra-high-molecular weight polyethylene fibre, with Elium thermoplastic resin being used for composite production (Shanmugam et al., 2019). Polyvinylidene fluoride (PVDF) is a flexible piezoelectric polymer that includes five different phases in its structure. The p olar β phase is the most desirable phase in piezoelectric applications due to showing high piezo -, pyro and ferroelectric properties. Thus, increasing the β phase content of the material is important to obtain a piezoelectric response. However, phase is the most stable form in thermodynamics with non-polar crystalline phases, and thermal treatment or poling can transform phase into the polar β phase (Hu et al., 2021). Different additives such as multiwalled carbon nanotubes (MWCNTs) (Aqeel et al., 2015; Kim et al., 2009; Wu et al., 2013), graphene oxide (Bhavanasi et al., 2016), PAN (Aqeel et al., 2015), PZT (Renxin et al., 2006), ZnO (Jin et al., 2020), etc. were used to improve piezoelectric properties of PVDF. Zhu et. al. investigated the PVDF piezoelectric properties by increasing the rate of MWCNTs (Zhu et al., 2021). MWCNTs act as nucleating agent for growing the crystalline β phase of the PVDF structure (Abdolmaleki and Agarwala, 2020) which helps polarize the composite. Haghiastiani et. al. used 80 µm thick PVDF layers and prepared carbon fibre reinforced composite with Kevlar fabric in the mid layer. They investigated the piezoelectric and tensile properties of the composite structure (Haghiashtiani and Greminger, 2015). Loyola et. al. deposited MWCNTs-PVDF mixture in a glass fibre mat and prepared glass fibre reinforced composites and they investigated the damage sensitivity properties of the composite (Loyola et al., 2013). Likewise, Groo et. al. prepared dehydrofluorinated PVDF included CFRC for structural health monitoring. They prepared PVDF infused woven fibreglass and sandwiched PVDF between woven carbon fabric layers to form a piezoelectric sensor (Groo et al., 2021). In this study, a new carbon fibre reinforced composite was produced using a thermoplastic recyclable Elium resin. The composite, which included a MWCNT-incorporated PVDF layer, exhibited both piezoelectric self-sensitive functionality and enhanced mechanical properties. The electrical conductivity property of carbon fabric facilitates the use of these layers as electrodes. This approach ensured the uniform distribution of sensing capabilities throughout the composite, eliminating the need for multiple embedded sensors. The study investigated various properties, including mode I fracture toughness, interlaminar shear strength, bending properties, and piezoelectric properties. Additionally, the effect of perforation of PVDF-PPS layers on the wetting ability of the resin was also investigated. To the best of the authors ’ knowledge, there have been no previous studies on carbon fibre reinforced thermoplastic composites incorporating a PVDF-MWCNTs-PPS mid-layer. Investigating 3-point bending, Mode I fracture toughness, and interlaminar shear strength together with piezoelectric characteristics is another novelty of this study. 2. Experimental 2.1. Materials Thermoplastic resin, Elium 150 was purchased from Arkema Global, and benzoyl peroxide (BPO) catalyst was obtained from Sigma-Aldrich. Unidirectional carbon fibre is supplied by SAERTEX GmbH & Co. KG, Germany. Polyvinylidene fluoride (PVDF) (M w =64.03 g/mol) was purchased from abcr GmbH. Multiwalled carbon nanotubes