| Carbon fiber-reinforced resin matrix composites（CFRPs）are widely used in the aerospace field due to their high specific modulus and specific strength.When the CFRP structures on the surface of the aircraft are subjected to a low-velocity impact load during service,invisible delamination damage occurs inside due to insufficient toughness,which limits its further application in the aviation field.How to effectively suppress out-of-plane debonding and delamination without affecting the in-plane mechanical properties and low-cost toughening of CFRP is one of the key problems that urgently needs to be solved in the field of composites.Multicomponent hybrid nanofiber interleave is expected to achieve multiscale synergistic toughening between composite layers,which is a simple,low-cost method with almost no loss of in-plane properties.Therefore,the effects of the microstructure of a single component（polyacrylonitrile,PAN）,two components（silica/polyacrylonitrile,Si O2/PAN）,and multiple components（silica/polyacrylonitrile/polyvinyl alcohol,Si O2/PAN/PVA）nano structure interleave on the interlaminar fracture toughness of composites were studied in this paper,and the corresponding synergistic toughening mechanism was analysed and established.Finally,the optimized nanofibre interleave was used to toughen the triangular area of the composite T-joint.The tensile properties and failure mechanism of the modified composite T-joint were studied,and the feasibility of the application of the prepared interleave in the composite structure was verified.The main work and conclusions of this paper are as follows:（1）Single-component,two-component and multi-component nanofiber films were prepared by electrospinning,and their microstructure,material structure,thermal stability,and tensile mechanical properties were characterized.According to the tensile property test,the single-component PAN nano-interleave under the optimal spinning parameters was obtained.The mode II interlaminar fracture toughness of the composite modified by this interleave is 43.97%higher than that of the unmodified composite.Based on the spinning parameters,the optimal Si O2 loading,particle size,and spinning method in the preparation of two-component hybrid nano-interleaves are15 wt%,15 nm,and the solution blending method,respectively.The mode II interlaminar fracture toughness of the modified composite is 81.53%higher than that of the unmodified composite.Compared with the former two interleaves,the addition of PVA greatly improves the ductility of the multicomponent hybrid nano-interleaves.The mode II interlaminar fracture toughness of multicomponent hybrid nano-interleave-modified composites is 64.97%higher than that of unmodified composites.（2）Through microstructure characterization,the interlaminar toughening mechanism of single-component PAN nano-interleave-modified composites can be summarized as the bridging,debonding,plastic deformation,and crack deflection of nanofibers.The interlaminar synergistic toughening mechanism of two-component hybrid nano-interleave modified composites shows that Si O2 enhances the bridging and plastic deformation of hybrid fibers,deflects cracks in multiple directions,and enables hybrid fibers to fracture in advance.The multicomponent hybrid nano-interleave enhances the effect of plastic deformation of nanofibers in absorbing energy due to its better ductility.（3）Single-component,two-component and multi-component nano-interleaves are laid in the weak triangular interface and the interface extension area of the composite T joint.The tensile test results show that the multicomponent hybrid nano-interleave modified T joint has the highest tensile load.Based on the analysis of the macroscopic and microscopic failure morphology,it can be seen that nano-interleave improves the interface strength of the web/bottom plate and web/triangle area,which is the main reason for the increase in the tensile load of the T joint.Moreover,the nano-interleave changes the failure mode of the T joint as well.The initial position of delamination damage of the modified composite T-joint changes from the triangular zone of the unmodified T-joint to the edge of the web.The delamination damage of the modified composite T joint mainly expands along the inner interface of the web,rather than the web/bottom interface. |
