PSI - Issue 35

Kadir Bilisik et al. / Procedia Structural Integrity 35 (2022) 210–218 Author name / StructuralIntegrity Procedia 00 (2019) 000 – 000

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1. Introduction Textile composites are employed in aviation, for instance, airplane, spacecraft, unmanned aerial vehicle (UAV), and helicopters. Moreover, they are employed some critical defence related specific areas such as ballistic and robotics due to their extraordinary performances considering mechanical, thermal and damage tolerance properties, Kamiya et al. (2000) and Bilisik (2011). But, they suffer for the out-of-plane properties including mode-I and mode II. Thus, the through-the-thickness reinforcement was placed via using the cost effective textile technologies including layered (3D) weaving, Bilisik (2010), over braiding or 3D braiding, Bilisik and Sahbaz (2012), and stitching processes, Tong et al. (2002). Last two decades, nanotubes were particularly utilized in 3D preforms in that multiwall nanotubes in the epoxy resin were dissipated such as mixing technique (mechanical base rolling and magnetic) and sonication technique, Garcia et al. (2008). Nanofibers were interconnected in the biaxial substrate via electrospinning or nanosubstrate integrated woven fabric were grafted, Khan and Kim (2011). Mechanical loading were transferred from matrix to filaments TOWs at the interface in which interfacial behavior of fiber and matrix were critical importance, Kim et al. (1997). Interfacial adhesion between filament TOWs and matrix in aramid composites were weak due to the low surface energy causing low mechanical properties, Chen et al. (2012). Carbon nanotubes (MWCNTs or SWCNTs) were used for aramid structure to enhance the interfacial shear properties, Meguid and Sun (2004). It was explained that the interlaminar shear failure mechanism (mode-II type) was significantly controlled by the properties of epoxy resin, Kuwata and Hogg (2011). It was identified that the interfacial fracture of fiber based structure was affected by epoxy resin and the interface region of fiber/resin structure, Deng and Ye (1999). One of the researches exhibited that the fracture toughness was improved by introducing the stitching fiber in the thickness of fiber based structure because of linear density of fiber assemblage and stitching density, Jain et al. (1998). Recently, it was disclosed that the nanostitched PAN based carbon composite exhibited a 3.4 fold improvement considering the neat structure, Bilisik et al. (2019a). Fracture toughness (mode-II type) of carbon nanoprepreg composite was improved (three fold) when compared to the pristine due to using the carbon nanotubes which led to complicated reciprocal action around matrix/fiber and nanotubes via delamination, fiber strengthening causing bridging effect, pull-out movement depending on friction, and stick-slip phenomenon, Garcia et al. (2008). The aramid/epoxy composite addition with short nano para-aramid fiber enhanced its mechanical properties due to strong bonding between nanofiber and epoxy resin, Patterson et al. (2018). The main goal of this research was to define the in- plane shear and mode‒II fracture toughness of nanostitch para Nanostitched preform was formed by employing the para- aramid fabrics (Twaron®, Teijin, Japan). The aramid fiber is 3200 MPa in tensile strength, 115 GPa in tensile modulus and 2.9% in breaking elongation. Aramid preforms were consolidated by employing the phenolic resin (Araldite EPN 1138, DE). The preforms were formed via aramid fabric which was interlaced by using 168 tex fiber texture as a basket style (CT 736). The directional densities were 6.25 ends/cm for filling and 12.7 ends/cm for warp. In addition, its unit area density was 410 g/m 2 . The multiwall carbon nanotube was received from Nanothinx, GR due to its outstanding mechanical properties, Nanothinx (2018). Its specification was length 10 μm x wall thickness 1-2 nm x diameter 15-35 nm; its purity and apparent density were ≥97% and 1.74 g/cm 3 , respectively. The carbon nanotube modulus was 1 TPa, and its strength was 200 GPa, Lehman et al. (2011). Nanostitching filament TOWs was 3360 tex aramid which was received from Teijin, JP. Its properties were 115 GPa for tensile modulus, 3.2 GPa for tensile strength and 2.9% for breaking elongations. Table 1 presents the developed preforms. Figure 1 illustrates basic processing flow chart to fabricate the nanostitched preform and para-aramid nanocomposites. Four types of composite materials were manufactured and they were coded as TBU-unstitched; TB-TS-stitched; TBU-N-unstitched nano and TB-TS-N-stitched nano. Table 1 also presents the composite densities, fiber weight fractions and the stitching yarn weight fraction along with carbon nanotube percentages, Bilisik et al. (2019b). Aramid nanocomposite was produced via hand-layup, Bilisik et al. (2018). The actual and schematic fabrication steps are illustrated in Figure 1. It included nanotubes dispersion and homogenization in the matrix by sonication; aramid/phenolic composites. 2. Materials and Methods 2.1. 3D nanostitched aramid composites