Effect Of Multi-walled Carbon Nanotubes On The Mechanical Properties Of Titanium/Carbon Fiber/PMR Polyimide Laminates

Fiber metal laminates(FMLs)act as one kind of hybrid materials which combine the impact resistance of metal sheets with unique fatigue properties of fiber composites.The FMLs are alternating layers of metal materials and fiber composite materials which possess a complex multi-interface system including the interfaces of fiber-resin and resin-metal sheet,in which the metal-resin interface was relatively fragile.The performance of the interface directly affected the bonding and stress transfer between layers,leading to the comprehensive performance and failure behavior of the FMLs.Thus,it is significant to modify the interfacial properties of FMLs.Firstly,multi-walled carbon nanotubes(MWCNTs)with different weight fractions(0wt%,2.5wt%,5wt% and 7.5wt%)were uniformly dispersed in polymerized monomer reactant(PMR)polyimide adhesives by ultrasonic dispersion.Single lap shear tests and interlaminar fracture toughness tests were experimentally conducted to characterize the interface bonding strengths between the titanium and polyimide,and the failure morphology was observed by scanning electron microscopy(SEM).The results revealed the shear strength and mode I interlaminar fracture toughness of the polyimide adhesive were further enhanced by incorporating MWCNTs with concentration up to 5wt%.According to Ti/PMR polyimide interface model,MWCNT dispersed the load of polyimide matrix as well as consumed the fracture energy when MWCNT was in the interface area.In addition,MWCNT prevented the crack expanding in the Ti/PMR polyimide interface,thereby enhanced the interface bonding strength.Secondly,MWCNTs at 5wt% were added into the primer or both primer and prepreg of FMLs.Meanwhile,the effect of MWCNTs on the static mechanical properties(interlaminar shear,bending,tensile properties)were investigated as well as on impact properties of the FMLs.The results indicated that the static mechanical properties and impact property were significantly improved after the incorporation of MWCNTs.It was worth noting that the FMLs possessed the best mechanical properties when MWCNT was added to both the primer and prepreg.Finally,the enhancement mechanism of MWCNTs on the mechanical properties of FMLs was discussed.The static mechanical properties were mainly improved because :(1)MWCNTs transferred cracks and prevented the cracks growth in the interface,which enhanced the Ti/PMR polyimide interface;(2)MWCNTs were uniformly dispersed in the primer layer and prepreg resin,could transfer the load from interface layer to the fiber layer,and absorb energy by fracture and pulling-out.Meanwhile,the impact property were enhanced because :(1)MWCNTs enhanced the interface of Ti/PMR polyimide.The delamination failure of the laminates was one of the ways of the impact energy consumption when the impact load was subjected.Hence excellent interface consumed more energy when stratification occurred;(2)The impact energy was consumed by breaking and debonding of carbon fiber and pulling-out,breaking and debonding of MWCNTs.In addition,the impact resistance of the laminates was enhanced after incorporating MWCNT in the PMR polyimide resin.