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...[ Read more ]

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.