PSI - Issue 10

G.V. Seretis et al. / Procedia Structural Integrity 10 (2018) 249–256

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G.V. Seretis et al. / Structural Integrity Procedia 00 (2018) 000 – 000

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ratio, have promoted them to one of the mostly applied materials which see service in a great variety of applications (Colangelo et al. (2017)). However, an always increasing need for further improvement of these materials has been risen due to the extension of their use to more demanding applications. To meet the requirements and the specifications of such applications, the use of nanoparticle reinforced composite matrices was unavoidable. Graphene nanoparticles are of the newest and most commonly used nanofillers (Seretis et al. (2017a)), due to their extraordinary properties as well as the matrix properties improvement can be achieved by using them (Potts et al. (2011); Kostagiannakopoulou et al. (2017); Seretis et al. (2017a); Seretis et al. (2017b); Wang and Tsai (2016)). Graphene is a 2-D layer of sp2-bonded carbon atoms arranged in a honeycomb-like form (Geim and Novoselov (2007); Park and Ruoff (2009); Wang et al. (2012)). Graphene nanoplatelets (GNPs) are of the newest graphene based nanoparticles. Each GNP is comprised from several layers of graphene nanocrystals which are stack together due to the Van der Waal’s forces through the (002) plane (Hu et al. (2012); Moriche et al. (2015); Seretis et al. (2017a)). It was found that the addition of graphene nanoparticles in a polymer matrix impressively improves the mechanical performance (Kostagiannakopoulou et al. (2017); Miller et al. (2010); Seretis et al. (2017a); Yang et al. (2011)), and also the thermal (Chu et al. (2012); Kim et al. (2010); Shahil and Balandin (2012); Yang et al. (2011)) and electrical (Kuilla et al. (2010); Singh et al. (2011); Shahil and Balandin (2012)) properties of the reinforced matrix material. However, the morphology of the nanoparticles affects significantly all the nanoparticle properties and, therefore, all the properties of the produced nanocomposite (Moriche et al. (2015); Prolongo et al. (2014)). This is because of the effect of the nanoparticle morphology on the nanoparticle/matrix interface interaction and interface strength (Li et al. (2013); Starr et al. (2002); Wan et al. (2014)). The morphology of graphene nanoparticles is closely correlated with the disper sion method applied (Li et al. (2013); Moriche et al. (2015); Starr et al. (2002); Wan et al. (2014); Zegeye et al. (2014)). Due to the “young” age of the specific nanoparticles, graphene nanoplatelets (GNPs) reinforced nanocomposites have been hardly investigated as per the dispersion techniques and methods, which are still being developed, and their mechanical and physical properties. Tensile properties are of the most important mechanical properties for all compos ite/nanocomposite materials as well as for all engineering materials (Dai et al. (2017); Gusel and Deveci (2017); Naous et al. (2006); Sereis et al. (2017a); Song et al. (2017); Wu et al. (2002)). This study focuses on the effect of the GNPs content on the tensile performance of GNPs/glass fabric/epoxy nanocomposites. Five different GNPs contents were tested, i.e. 1%, 2%, 3%, 4% and 5% w.t., for two different specimens’ series. For the specimens of the first series a Twill 2×2 E -glass fabric and for the specimens of the second series a Uni-Directional E-glass fabric was employed. The specimens were investigated using a scanning electron microscope as well as an atomic force microscope.

2. Experimental procedure 2.1. Materials

The medium viscosity epoxy system ES35A/B (ES35A monomer and ES35B hardener) was used as matrix material for the composite laminae investigated in the present study. Two E-glass fabric types were used for matrix reinforce ment, a Twill 2×2 (T2×2) and a Uni -Directional (UD), the properties of which can be found in Table 1. Pre-dried graphene nanoplatelets (GNPs), by Alfa Aesar, of surface area (S.A.) 500 m 2 /g were also used as additives, to produce

a particulate nanocomposite matrix material. 2.2. Preparation of GNPs/epoxy nanocomposites

To ensure homogeneity of the suspension (GNPs) in the matrix material, weighed amounts of pre-dried graphene nanoplatelets were stirred gently into epoxy resin (monomer) at the constant speed of 200 rpm for a process time of 25 min using a laboratory mixer. Subsequently, the hardener was added in the mixture at a 2:1 by volume ratio, which was the manufacturer recommended monomer/hardener proportion, followed by a 5 min mechanical stirring at 200 rpm before using the matrix mixture (Seretis et al. (2017a; 2018a,b)). The GNPs contents used for both fabric rein forcements were 1%, 2%, 3%, 4% and 5%. To produce the nanocomposite laminae, the prepared matrix mixture was coated under constant stirring and hand-rolled on E-glass fabrics using a hand lay-up procedure. One layer of E-glass fabric was employed for each specimen in [45°] stacking sequence , see positioning angle in Fig.1. The total thickness of the produced composite laminae was 0.4 mm in the case of UD fabrics and 0.27 mm in the case of T2×2 fabrics. The final dimensions of