Domun, Nadiim (2018) Improving ballistic impact performance of fibre reinforced polymer composite materials using nano-modified polymer matrix. (PhD thesis), Kingston University, .
Abstract
In this research, glass fibre reinforced polymer (GFRP) with novel epoxy nanocomposite matrices have been developed by tailoring the properties of the matrix system at a nanoscale level using one-dimensional (1D, two-dimensional (2D) nanomaterials and a combination of both (1D) and (2D) nanofillers, thereby developing a hybrid system. The performance of the GFRP with the newly developed nanocomposite epoxies have been studied under static loading, delamination tests and ballistic impact. The main core of this present work consists of three main areas which are described in the following sections. The initial part reports improvement in the mechanical and fracture properties of epoxy nanocomposites using plasma functionalised graphene nanoplatelets (f-GNP) and functionalised multi-walled carbon nanotubes (f-MWCNTs) at low filler content. Most importantly, a significant enhancement in fracture toughness was achieved. The fracture toughness of neat epoxy resin was increased by over 50% with the incorporation of 0.25 wt. % f-GGNP loading, obtaining a value of 245 Jm-2, whilst the neat epoxy indicated a value of 162 Jm-2. For the instance of the f-MWCNTs/epoxy at 0.1 wt. % filler content, an increase by 57% in the fracture toughness was observed in comparison to the neat epoxy. Importantly, no degradation in the tensile of thermal properties of both the f-GNP/epoxy and f-MWCNT/epoxy nanocomposites was observed. When 2D boron nitride nanosheets (BNNS) were added along with the 1D f-MWCNTs, the fracture toughness increased further to 71.6% higher than that of the neat epoxy. Interestingly, when functionalised graphene nanoplatelets (f-GNPs) and boron nitride nanotubes (BNNTs) were used as hybrid filler, the fracture toughness of neat epoxy was improved by 91.9%. In neither of these hybrid filler systems the tensile properties were degraded, but the thermal properties of the nanocomposites containing boron nitride materials deteriorated slightly. The second part constituted of the experimental studies on the delamination behaviour of the nano-modified GFRP. The matrix of the GFRP was modified by the addition of graphene nanosheets (GNPs), carbon nanotubes (CNTs) combined hybrid hexagonal boron nitride nanosheets (BNNS/CNTs), and combined boron nitride nanotubes (BNNTs/GNPs) nanoparticles. The mechanical properties of the GFRP laminates with various nano-modified epoxies were obtained from tensile, shear, mode I and mode II interlaminar delamination tests. The results showed that the best matrix for mode I and mode II interlaminar delamination resistance in the GFRP was the instance of the (EP+BNNS+CNT) by 60% and (EP+CNT) by 59% respectively, relative to the control system. The transfer of toughness from the matrix GICm, to the initiation composite interlaminar toughness GICc, was significantly less than 1:1. This arises from the constraint imposed on the matrix deformation at the crack tip by the presence of the fibres in the GFRP composite. On the other hand, the coefficient of toughness transfer (CTT) of GFRP with modified epoxy was between 60% - 80% higher than CTT of unmodified GFRP at 85 mm propagation region. In the final part of this thesis, the ballistic impact performance of the nano-modified epoxy based GFRP were conducted at two projectile velocities of 76± 1 ms-1 for full-field deformation measurement and 134± 1.7 ms-1 for perforation tests. The exit velocity of the projectiles was measured. The deformation and strain of the GFRP target plates during the ballistic impact was precisely measured using a high-speed 3D digital image correlation (DIC) system, and post-impact damage was assessed by flash-pulsed infrared thermography (PT) and an optical microscope. The highest reduction in exit velocity was achieved in the instance of the GFRP with (EP+BNNT+GNP) modified matrix. This matrix reduced the incident velocity by 89.1% an additional 22.1% reduction of exit velocity on top of the reduction in exit velocity with the neat epoxy GFRP.
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