Quantifying the carbon nanotubes enhanced interfacial mechanics in adhesively bonded fiber metal laminates using cohesive zone parameters

The mismatch in the average properties of metal and composite layers often causes delamination and loss of structural integrity in FMLs. CNTs have been widely used to improve the strength and toughness of composites. However, their role in the interfacial mechanics of adhesively bonded FMLs remains insufficiently explored and quantified. In this work, CNT-based interface modification strategies, namely CNT modified epoxy and BP interlayer, are investigated to enhance the interfacial strength and toughness. The effect of these modifications on flexural, indentation, and mode-I fracture response is experimentally investigated and quantified using TSL parameters with cohesive zone modelling. Experiments show that CNT-modified epoxy significantly improves the flexural modulus, indentation delamination strength and toughness, and mode-I delamination resistance. In contrast, BP interlayers improve the flexural response but deteriorate the interfacial strength under indentation and opening-mode loading. The calibrated TSL parameters reveal strong loading mode‑dependent interfacial behavior and quantify the superior interfacial properties of CNT-modified epoxy compared to BP-modified interfaces. Based on these insights, a hybrid BP-CNT modified laminate is prepared, exhibiting enhanced mode-I fracture toughness and in-situ damage sensing through electrical resistance monitoring. This study demonstrates an effective approach for designing multifunctional FMLs with improved toughness and structural health monitoring capability.