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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Fig. 7. (a) Side view of crack growth around the fiber TOWs (optical images, magnifications x6.7) and (b) SEM micrograph of crack opening path around the filling cross-section.

4. Conclusions The shear and toughness properties of the p-aramid stitch fibers and multiwall carbon nanotube introduce composite structures were studied. It was found that nanostitch yarn addition on the thickness of aramid composites marginally enhanced their in-plane shear strength. However, addition of MWCNTs in the base aramid structure produced infinitesimal augmentation to its shear strength. It was also identified that both carbon nanotubes and stitching roughly affected the composite shear modulus. Conversely, nanostitch significantly improved the toughness of the aramid composite structures. In-plane shear failure modes of the nanostitch composites were the local interlayer and the intralayer delaminations. Nonetheless, Intra-fiber crack opening and the interlaminar delamination were confined because of the through-the-thickness filament assemblage where discrete nanotubes were placed at the out-of-plane of composite via fiber bundles. The mechanism for increasing the mode-II fracture toughness of the nanostitch structure was the interlayer matrix failure, in that the hackle marks in the blunt region was sporadically found. Cracks growth in the inter- and intra-filament bundle fronts were grown, in that the matrix was failed interlaced region of each yarn cross-section. Furthermore, the nanostitching probably supported to the overthrow of the crack initiation and propagation near to the failed matrix, and nanostitching confined delamination in the stitch zone meanwhile the multidirectional crack propagations. MWCNTs in the matrix and fiber TOWs near to the blunt crack tip perhaps mitigated stress clustering by means of via debonding, pull-out, friction and stick-slip. Therefore, nanostitch and stitch composite structures were recognized a ―damage tolerant material‖. Acknowledgements This work was supported by Roketsan Industries Grant No. RS/ERCİYES DSM -76301-14-01N/R. References Adams, D.F., Carlsson, L.A., Pipes, R.B., 2003. Experimental characterization of advanced composite materials. 3th ed. New York: CRC Press, pp. 185-190. ASTM Standard D792 – 91: 1991. Standard test method for density and specific gravity (relative density) of plastics by displacement. ASTM Standard D3171 – 99: 1999. Standard test methods for constituent content of composite materials. ASTM Standard D3518M-13: 2013. Standard test method for in-plane shear response of polymer matrix composite materials by tensile test of a ±45° laminate. ASTM Standard D7905‒14: 2014. Standard test method for determination of the mode II interlaminar fracture toughness of unidir ectional fiber reinforced polymer matrix composites ASTM, West Conshohocken, PA, USA. Bilisik, K., 2010. Dimensional stability of multiaxis 3D woven carbon preform. Journal of Textile Institute 101, 380 – 388. Bilisik, K., 2011. Bending behavior of multilayered and multidirectional stitched aramid woven fabric structures. Textile Research Journal 81, 1748 – 1761. Bilisik, K., Sahbaz, N., 2012. Structure-unit cell base approach on three dimensional representative braided preforms from 4-step braiding: Experimental determination of effect of structure-process parameters on predetermined yarn path. Textil e Research Journal 82, 220‒241. Bilisik, K., Erdogan, G., Sapanci, E., 2018. Flexural behavior of 3D para-aramid/phenolic/nano (MWCNT) composites. RSC Advances 8, 7213‒7224.