Fracture Toughness Enhancement of Fuzzy CNT-Glass Fiber Reinforced Composites with a Combined Reinforcing Strategy

Abstract

Low interlaminar mechanical properties is the foremost drawback of glass fiber reinforced composites (GFRPs). Hierarchical nanoparticles on fibers (e.g. carbon nanotubes (CNTs)) can improve interlaminar properties of composites with negligible weight increase because of excellent mechanical properties, and low density. Interlaminar properties of composites can be enhanced with the well-dispersed CNTs in polymer matrices as it facilitates load transfer from matrix to fibers. Particularly, structural improvements with no significant weight increase are highly desirable in the aerospace industry and therefore CNTs offer a wide and interesting research area. This paper investigates the mechanical properties of CNT-reinforced GFRPs. Two reinforcing strategies were studied as dispersion of CNTs in epoxy matrix and direct growth of CNTs onto glass fibers (GFs), simultaneously. The former is referred to as nanotube-reinforced composites (NRCs) while the latter is known as fuzzy architectures. Furthermore, the combination of NRCs and fuzzy glass fibers (F-GFs), also known as fuzzy nano-reinforced composites (F-NRCs), is used to fabricate composites and identify the reinforcing capabilities through both methods. In this study, the focus is given to F-GFs and F-NRCs, and the potential of these reinforcing strategies are evaluated through experimental studies. The morphology of the fabricated composite specimens is characterized using scanning electron microscopy (SEM) to observe the hierarchical CNT structures on the fibers. Additionally, Raman Spectroscopy and thermogravimetric analyses (TGA) are conducted to evaluate the quality and the thermal stability of the samples. Mechanical properties are investigated by Mode-I fracture toughness and unidirectional (UD) composite tensile tests. Even though F-NRCs yield 150% improvement in the fracture toughness compared to baseline samples, the tensile strength of F-NRCs is found to be decreasing by 25% due to heat treatment during the CNT synthesis.

Keywords

• carbon nanotubes
• fuzzy fiber
• glass/epoxy composites
• fracture toughness

KNT-Cam Fiber Takviyeli Kompozitlerin Kırılma Tokluğunun Birleşik Bir Güçlendirme Stratejisi ile İyileştirilmesi

Öz

Düzlem-dışı yükleme durumlarında karşılaşılan düşük katmanlararası mekanik özellikler, cam fiber takviyeli kompozitlerin (GFRP) sahip olduğu en büyük kusurlardan biris olarak bilinmektedir. Fiber üzerinde hiyerarşik yapıdaki nano boyutta güçlendiriciler (örneğin: karbon nanotüpler (KNT’ler)), sahip oldukları sıradışı mekanik özellikler ve düşük yoğunlukları sayesinde kompozitlerin katmanlararası özelliklerini geliştirmek için kullanılmaktadır. Bahsedilen bu iyileştirmeler, yapıda herhangi bir ciddi ağırlık artışına sebep olmadan gerçekleştirilebilmektedir. Özellikle, yapısal iyileştirmelerin ağırlık artışından bağımsız olarak yapılması havacılık ve uzay yapıları uygulamalarının bir isteri olup, KNT’lere bu alanda geniş bir araştırma alanı oluşturmaktadır. Yapılan bu çalışmada, KNT-takviyeli GFRP’lerin mekanik özellikleri incelenmiştir. KNT’lerin epoksi matris içerisinde dağıtılması ve cam fiber üzerinde direkt olarak büyütülmesi olmak üzere iki farklı güçlendirme stratejisi ele alınmıştır. Bunlardan ilki cam fiber üzerinde karışık mimaride KNT büyütülmesi (F-GFs) olarak bilinirken, diğeri ise nano-tüp takviyeli kompozitler (NRC) olarak literatürde yer edinmiştir. Bu iki farklı güçlendirme stratejisinin kullanılmasıyla elde edilen kompozitler ise bu çalışmada karışık nano-takviyeli kompozitler (F-NRC) olarak ele alınmıştır. Bu çalışmanın odak noktası olarak F-GF ve F-NRC’ler seçilmiştir ve güçlendirme stratejilerinin potansiyeli laboratuvar ölçütlerinde deneysel olarak incelenmiştir. Üretilen kompozitlerin fiberleri üzerindeki hiyerarşik KNT yapılanması taramalı elektron mikroskopisi (SEM) ile gözlenmiştir. Ayrıca, Raman spektroskopisi ve termogravimetrik analiz (TGA) ile KNT’lerin kalitesi ve ısıl kararlılığı araştırılmıştır. Kompozitlerin mekanik özellikleri ise Mod-I kırılma tokluğu testi ve tek yönlü kompozit çekme testi ile karakterize edilmiştir. Her ne kadar F-NRC’lerin kırılma tokluğunda %150’lik iyileştirmeler gözlenmiş olsa da çekme dayanımında, cam fiberlerin KNT üretimi sırasında maruz kalınan ısıl işlemin sonucu olarak %25’lik azalma elde tespit edilmiştir. Mekanik testler sonucunda elde edilen bulgular, yukarıda belirtilen karakterizasyon çalışmalarından çıkarılan sonuçlar ile desteklenmektedir.

Anahtar Kelimeler

• karbon nanotüp
• karışık fiber
• cam/epoksi kompozit
• kırılma tokluğu

Kaynakça

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