Two-Step Strategy for Use in Improving the Multiscale Mechanical Performances of Fiber Metal Laminates: Applying Multi-Walled Carbon Nanotubes and Metal Surface Treatment

Abstract

The interlayer performances of fiber metal laminates (FMLs) significantly affect their applications. This study aims to design the interlayer properties of carbon fiber/ ultra-thin stainless-steel FMLs (CUSFMLs) based on the fiber bridging and mechanical interlocking mechanism via a two-step modification strategy involving multi-walled carbon nanotube (MWCNT)-modified epoxy resin and metal surface treatment. This study combines short beam shear test and three-point bending tests, and uses digital image correlation to capture the strain field to explore the modification effects of the two methods in detail. Finite element analysis is conducted using ABAQUS/implicit modules to analyze the evolution of the delamination damage. The MWCNTs adhesive layer enhances the interlaminar shear strength of CUSFML by 16.4% via the fiber bridging effect, enabling metals with high stiffnesses and excellent corrosion resistances to be more effective. In addition, the potassium dichromate (PD) method of metal surface treatment displays superior results compared to those observed using the silane coupling agent method. The bending strength of the CUSFML is increased by 8.33% and the contact angle between the epoxy resin and metal is decreased by 7.7%. This improvement is because the metal treated using the PD method exhibits a larger surface roughness, which enables the epoxy resin to enter the grooves on the metal surface during curing, thus establishing a stronger mechanical interlocking effect.

Keywords: fiber metal laminates, multi-walled carbon nanotubes, interlaminar shear strength, fiber bridging, mechanical interlocking, delamination failure