Abstract
In this study, the mechanical responses of polycarbonate (PC) and PC/multi-walled carbon nanotubes (MWCNTs) to dynamic loadings at low and high velocities impacts were investigated experimentally using an instrumented falling weight impact tester (IFWIT) and a split Hopkinson pressure bar (SHPB), respectively. The results from the IFWIT tests revealed that impact strength, impact failure energy and fracture toughness were dramatically enhanced by the incorporation of a very small amount of the MWCNTs into the PC matrix. The maximum load and the impact failure energy increased by ∼320% and ∼350%, respectively, when only 1wt% MWCNTs was incorporated. The results from the SHPB tests demonstrate that all the materials showed strain-rate sensitivity. The MWCNTs nanocomposites exhibited higher yield stress and energy absorption characteristics compared to the PC matrix material. However, the enhancement by MWCNTs was very limited for the PC containing higher percentage of the filler at higher strain rates. This could be resulted by a thermal-softening effect. In addition, the density of the pure PC and PC/MWCNTs nanocomposite specimens before or after SHPB testing was examined to gain insight into the microstructure changes. The results show that the density decreased significantly after the SPBH tests. With increasing strain rate the density decrease in PC nanocomposite is faster than that in the pure PC. It is believed that more cracks formed in the PC nanocomposite during the SHPB tests, which could result in high energy dissipation.
Highlights
As terrorist attacks have increased around the globe in recent years, the issue of combat survivability has become a primary concern for the public and governments [1,2,3,4,5]
The semi-crack fracture behavior was observed for the PC and its multi-walled carbon nanotubes (MWCNTs) nanocomposites
The results indicated that after the split Hopkinson pressure bar (SHPB) tests, the density of the pure PC and its nanocomposites decreased and the density drop with increasing strain rate in the nanocomposites was faster than that in the pure PC
Summary
As terrorist attacks have increased around the globe in recent years, the issue of combat survivability has become a primary concern for the public and governments [1,2,3,4,5]. Once soldiers are deployed from their protected vehicles, they require lightweight body protection that allows them to operate freely at high or low temperatures and altitudes whilst carrying a full battle load These considerations have led to an increase in interest. The development of nano-reinforced composites materials has garnered great interest in the material science community These materials, a synthesis of a base matrix polymer and particle, where at least one aspect of the particle is in the nanometre-scale, have been shown to improve a wide range of physical and engineering properties, e.g. stiffness, impact resistance, fracture toughness and the ability to absorb energy, of the matrix material [2,10,11,12]. With the future application of such types of nanocomposite materials in high strain rate environments in mind, high performance PC based nanocomposites were fabricated and the impact responses of these materials under dynamic loadings at low and high velocity impacts were characterised and are discussed here
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