THESIS
2020
xxii, 171 pages : illustrations ; 30 cm
Abstract
Fiber metal laminates (FMLs) are a sandwich combination of alternate layer of metal and
fiber-reinforced polymer (FRP) which has excellent specific strength, fatigue, stiffness and has
potential application in defence, aerospace, marine, and automotive due to its high impact
resistance. Sandwich combination of ultra-high molecular weight polyethylene (UHMWPE) fiber
and an infusible thermoplastic Elium
® matrix forms a complete thermoplastic FRP composite.
Combining UHMWPE/Elium
® composites with titanium metal alloy forms a hybrid UHMWPE-Ti
FML which can be a promising material system for impact damage problems. In achieving
optimal performance of this hybrid composite system, interfaces in the composite system play a
critical role, which includes a fiber-matrix interface, interla...[
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Fiber metal laminates (FMLs) are a sandwich combination of alternate layer of metal and
fiber-reinforced polymer (FRP) which has excellent specific strength, fatigue, stiffness and has
potential application in defence, aerospace, marine, and automotive due to its high impact
resistance. Sandwich combination of ultra-high molecular weight polyethylene (UHMWPE) fiber
and an infusible thermoplastic Elium
® matrix forms a complete thermoplastic FRP composite.
Combining UHMWPE/Elium
® composites with titanium metal alloy forms a hybrid UHMWPE-Ti
FML which can be a promising material system for impact damage problems. In achieving
optimal performance of this hybrid composite system, interfaces in the composite system play a
critical role, which includes a fiber-matrix interface, interlaminar interface, and metal
thermoplastic composite interface (MTCI). Therefore, proper tuning of these interfaces determines
the overall performance of the hybrid composite system. Two different strategies have been
adopted to improve the interfacial properties of the UHMWPE-Ti composites: i) modification of
the interfaces in UHMWPE fiber-reinforced system, and ii) tuning of the MTCI via the surface
treatment of titanium alloy.
Multiwalled carbon nanotubes (MWCNTs) are incorporated into dopamine coating
solution and applied onto UHMWPE fiber surface to enhance the interfacial bonding in UHMWPE
fiber-reinforced system. The results from the transverse tensile fiber bundle test (TFBT) shows the
interfacial strength of the prepared multi-scale phase reinforced composite (MPRC) can be
significantly increased in comparison with that of the common composite. It is observed that
densification of CNTs forest within the interphase between UHMWPE fiber and thermoplastic
matrix during the formation of the nano-composite coating can lead to a high-volume fraction of
CNTs within the interphase and augment effects of interface-interlocking, which makes the
coating-modification method a more efficient way than a traditional matrix-tuning method for
improving interfacial bonding. Results from double cantilever beam (DCB) test at 1 mm/min
shows improvement in Mode I interlaminar fracture toughness (G
IC) for PDA (polydopamine)
surface-treated sample and PDA with embedded MWCNT when compared with that of a common
composite (UHMWPE/Elium
®)
The surface of titanium alloy is treated by traditional anodization with post-processing of
etching and annealing, which is multiple processing steps to improve the MTCI. The generated
oxide layer on the metal alloy has the potential to react with recyclable thermoplastic Elium
® resin
matrix by the organo-metallic complex, facilitating the wettability of resin on the Ti metal surface.
The double cantilever beam test was utilised to evaluate the G
IC (Mode I interlaminar fracture
toughness at MTCI) for the FML sample with surface treated fiber (PDA and PDA+CNT) and
metal. The result shows, after the fiber and metal surface treatment, the average G
1C can be
increased and improving the delamination resistance at MTCI. Thus, surface treatment of fiber and
metal can enhance the fiber-matrix interface, interlaminar interface and MTCI. After showing
improved performance in the quasi-static test of FML composites, low-velocity dynamic impact
test was performed at different impact energy for the fabricated FML. The results show less
absorbed energy and low structural damage after the fiber and metal surface treatment. The
delamination resistance offered at the composite interface due to surface treatment plays a pivotal
role in enhancing the structural performance of UHMWPE-Ti FML composite.
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