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    Fracture toughness (Mode I) characterization of SiO2 nanoparticle filled basalt/epoxy filament wound composite ring with split-disk test method
    (Elsevier Sci Ltd, 2017) Demirci, Mehmet Turan; Tarakcioglu, Necmettin; Avci, Ahmet; Akdemir, Ahmet; Demirci, Ibrahim
    Matrix cracking which is the major initial form of damage in fiber reinforced polymer composites plays significant role in determining the fracture toughness. The fast crack propagation in polymer matrix causes to decrease the fracture toughness of fiber reinforced polymer (FRP) composite. In order to retard the fast crack propagation in polymer matrix and provide to increase of the fracture toughness of FRP composite, the polymer matrix of FRP composite is modified by filling the different kinds of nano particles. In such a way, the crack propagation leads to retard and dissipate the stress concentration affected to form the fiber cracks along of fibers in composite structure. In this study, basalt fiber was used as reinforcement material in +/-[55]6 filament wound ring composite for creating the alternative to carbon, kevlar and glass fibers, to contribute to the research studies and literature. SiO2 nanoparticles that provides to form the effects of fracture toughness mechanism based on the effect of retarding crack propagation were filled into epoxy matrix to increase the mechanical properties and fracture toughness of +/-[55]6 filament wound BFR/Epoxy ring composite. The split-disk tensile tests of single edge notched and un-notched +/- 155]6 filament wound BFR/Epoxy ring composite specimens were conducted to determine the mechanical properties and mode I fracture toughness. SiO2 nanoparticle addition into epoxy matrix of +/-[55]6 filament wound BFR/Epoxy ring composites has given the results of hoop tensile stress within the range of 27.7-30.3%. The fracture toughness of composite ring specimen was specified by ASTM E 399-12E3 by adapting to the directed mode I crack propagation and compared with each other. An effective increase in mode I fracture toughness of 43%-50% was obtained at 4 wt% addition level of SiO2 nanoparticles. The crack branching in epoxy matrix provided by SiO2 nanoparticle, matrix cracking, debonding, delamination and fiber breakage failures has been observed via microscope and SEM analysis. (C) 2017 Elsevier Ltd. All rights reserved.
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    Investigation of nano-hybridization effects on low velocity impact behaviors of basalt fiber reinforced composites
    (Sage Publications Ltd, 2021) Demirci, Ibrahim; Avci, Ahmet; Demirci, Mehmet Turan
    In general the nanoparticles increase the mechanical and impact behaviors of fiber reinforced polymer based composites. However, the effects of the hybridization of nanoparticles and their reasons over the nano scale fracture mechanisms have not been adequately studied for fiber reinforced composites. In this study, the low velocity impact responses and the mechanical behaviors were investigated for 4%wt. SiO(2)nanoparticles filled BFR/Epoxy nanocomposites, 0.5%wt. MWCNTs filled BFR/Epoxy nanocomposites, 4%wt. SiO(2)nanoparticles and 0.5%wt. MWCNTs nano-hybrid filled BFR/Epoxy nanocomposites and unfilled BFR/Epoxy composites. The tensile and low velocity impact tests at 10 J and 20 J of energy levels were applied to nanoparticles, nano-hybrid and unfilled BFR/Epoxy composites in order to define the effects of nanoparticles and nano-hybrid particles on the impact and mechanical features according to in accordance with ASTM D3039/D3039M-14 and ASTM D7136/7136M standards. It was observed that SiO(2)nanoparticles addition to BFR/Epoxy for both 10 J and 20 J showed the highest tensile strength, maximum force, rebound energy and the lowest displacements and absorbed energy. SiO2+MWCNTs nano-hybrid addition to BFR/Epoxy improved higher low velocity impact responses and tensile strength than MWCNTs addition. The specimens of unfilled BFR/Epoxy composites showed the lowest tensile strength and maximum force and the highest maximum force, displacements and absorbed energy. Microscope and SEM analyses demonstrated that minimum failures like fiber breakages, delamination and debonding were observed by filling SiO(2)nanoparticles provided the nano scale fracture mechanisms. In addition MWCNTs hybridization with SiO(2)nanoparticles minimizes negative effects of MWCNTs micro size length and improved the impact and mechanical behaviors.