Nano-Melez Sistemlerin Karbon Fiber Takviyeli Polimer Matris Kompozitlerde (KFTP) Arayüz Toklaştırma Amacıyla Kullanımı

Abstract

Composite materials are widely used in aircraft industry as they have high specific strengths. To increase the delamination resistance of layered composites, tough particles, films or fibers at different length scales can be interleaved between composite layers. Until now, electrospun nanofibers from homopolymers such as polycaprolactone (PCL), polyacrylonitrile (PAN), polyvinylidene difloruide (PVDF), polysulfone (PS), nylon 6,6, have been used to investigate their effects on the interlaminar fracture toughness. Besides the use of homopolymers, physically mixed polymer systems have also been used. In such systems, alternatives like; spinning of alternating layers of two polymers, co-electrospinning of different polymers at the same time from different needles, or core-shell configurations have been tried. Another category which could be named as, ‘hybrids’ were formed between different polymers and carbon based materials such as multi wall carbon nanotube (MWCNT), graphene (G) or graphene-oxide (GO) flakes. Nanofibers from polymer blends mixed in molecular chain level could bring certain advantages in improving the interlaminar toughness of layered composites. In addition, these blends can be hybridized with externally sprayed-on G or GO to trigger multiple toughening mechanisms. In this study, nylon 6 (N6), PCL and their blends with different mass ratios (N6/PCL: 100/0, 80/20, 60/40, 40/60 and 0/100) were electrospun and interleaved between carbon fiber reinforced polymer composites (CFRP). In addition, GO flakes were sprayed between the nanofiber layers to investigate the effect of these hybrid interleaves on Mode I interlaminar fracture toughness of CFRPs. With Differential Scanning Calorimetry (DSC) analyses, it was identified that weight ratios of polymers affect the phase separation characteristic of polymer blends. In Scanning Electron Microscope (SEM) analyses which were carried out after Double Cantilever Beam (DCB) test, it was observed that the specific phase separation behaviors facilitates the activation of different toughening mechanisms. N6/PCL with 60/40 ratio showed the best result with respect to the unmodified reference sample with a 69% improvement on the Mode 1 G1c initiation and 59% on that of G1c propagation. At 60/40 ratio, a phase separation between PCL and N6 was observed and this lead to a cooperative synergistic increase in the resistance against crack progression by activating the debonding and fiber bridging mechanisms simultaneously. GO flakes that were synthesized in different sizes were electrosprayed between elektrospun nanofiber veils and hybrids with different sandwich structures were produced. Due to the problems in optimization of electropsraying process parameters and dispersion of GO flakes in the spray solvent, the improvements in GIC were insignificant. However, load-displacement behavior of the composites were significantly altered. The reasons of this change were discussed. The main reason behind the poor mechanical performance was the dissolution of the veil layers by the spray solvent. Losing the structural integrity of base layer formed an asymmetry in the sandwiches’ mechanical behavior, which in turn lead to a crack diversion from tough veil layers to the brittle epoxy layers. However, it can be anticipated that, upon rectification of process parameters in spraying the GO component, the already observed significant changes in the load-displacement behavior can be utilized in favor of building structures with even higher interlaminar toughness.