Study Of Interlaminar Toughness Of CF/EP Composites Reinforced By Micro And Nano Particles In Concert With PA66 Electrospun Nanofibers

Carbon fiber/epoxy resin（CF/EP）composite materials are widely used in aircraft due to their low density,high specific strength,high specific modulus,fatigue resistance,corrosion resistance,ablation resistance,and strong designability,as well as in fields of electronics,automotive,sporting goods,building materials,pressure vessels and ships,and other industrial and defense fields.Compared with other materials,although carbon fiber reinforced epoxy resin composites show many advantages,due to the inherent brittleness of the resin matrix,it is easy to cause delamination failure between layers,resulting in serious safety hazards and endangering life and property safety.This becomes one of the main bottlenecks limiting the further breakthrough development of high-performance CF/EP composites.Therefore,how to further improve the interlaminar fracture toughness of CF/EP composites has become the research focus.To effectively solve this key problem,based on the intercalation and toughening technology of electrospun membrane,first,three kinds of PA66 electrospun fiber films with different areal densities were prepared by electrospinning technology,and then the most effective areal density for improving interlaminar fracture toughness was selected.on this basis,two different inorganic rigid particles（BN and Si O₂）were introduced by spraying and combined with PA66 electrospun fibers in the middle layer to synergistically strengthen the layers of the CF/EP composite laminate.To further improve the toughening efficiency of the particles and strengthen the synergistic toughening effect,two different inorganic rigid particles（BN and Si O₂）were mixed with electrospinning solution precursors by blending to prepare BN@PA66 and Si O₂@PA66 hybrid fiber film.the interlaminar fracture toughness of the composite is significantly improved by the hybrid fiber film as an intercalation material.The functional groups and crystal forms of the hybrid fiber film after particle blending were analyzed by Fourier transform infrared spectroscopy（FTIR）and X-ray diffraction（XRD）.The mechanical properties of the blended fiber membrane and laminate were tested by a universal material testing machine.Scanning electron microscopy（SEM）was used to study the micro-morphology of CF after spraying particles,the micro-morphology of the electrospun fiber film and the fracture surface of the composite laminate.The main conclusions are as follows:（1）Study on the interlaminar fracture toughness of PA66 electrospun film enhanced CF/EP composites:PA66 electrospun nanofibers prepared by electrospinning showed disordered arrangement,with smooth fiber surface,uniform thickness,and good porosity that is conducive to resin infiltration.After addition of of the PA66 film in the interlaminar region,the sliding friction coefficient of the resin matrix can be effectively improved,which provides the possibility for interlaminar toughening.The results show that under the mode I test,when the added PA66 areal density is 10 g/m²,the mold I interlaminar fracture toughness of the laminate exhibits the best toughening effect.Compared with the control group,its initial fracture toughness(G_{IC init})and crack propagation fracture toughness(G_{IC prop})reached 1.03 and 1 k J/m²,an increase of 110%and 96%,respectively.Under the mode II test,when the added PA66 has an areal density of 20 g/m²,the mold II interlaminar fracture toughness of the laminate shows the best toughening effect.Compared with the control group,its G_IICreached 3.56 k J/m²,a relative increase of 99%.These enhancements are mainly attributed to bridging,pulling out,debonding,necking,and breaking of PA66fibers.（2）Study on the interlaminar toughness of CF/EP composites enhanced by PA66electrospun film with different particles synergy:By adding the particles into the CF/EP interlayer by spraying,the problem that the particles are difficult to uniformly disperse in the resin matrix is effectively avoided.The addition of BN and Si O₂can not only hinder the crack propagation but also pin the PA66 fiber,thereby strengthening the toughening behavior of PA66.The results show that,compared with the control samples,the laminates reinforced by 1 g/m²1μm Si O₂cooperating PA66 showed the best toughening effect.Among them,the mold I and mold II interlaminar fracture toughness of the laminates with only PA66 were increased by 96%and 53%,respectively.The G_ICand G_IICof the sprayed1 g/m²1μm Si O₂&PA66-CF/EP laminates were increased by 145%and 82%,respectively.Among the BN-sprayed laminates,the laminates reinforced with 0.5 g/m²1μm BN and PA66（BN&PA66-CF/EP）showed the best toughening effect.For the sprayed 0.5 g/m²1μm BN&PA66-CF/EP laminate,the G_ICand G_IICwere increased by 120%and 73%,respectively.It can be seen that the addition of BN and Si O₂can synergize with PA66nanofibers to play a positive role in improving the anti-delamination performance.（3）Study on the synergistic enhancement of interlaminar fracture toughness of CF/EP composites by PA66 electrospun films blended with different particles:By blending with PA66,the toughening effect of particles can be fully exerted,and the synergistic effect between the particles and PA66 fibers can be enhanced.The results show that in the blended system,no matter what kind of particles are added,the optimal addition amount is5wt%,and the added particle morphology also has a great influence on the interlaminar fracture toughness.On the whole,the spherical Si O₂particles are superior to the lamellar BN particles.Compared with the control laminate,the G_ICof the samples with Si O₂@PA66hybrid nanofiber film was increased by up to 176%,and the G_IICwas increased by up to109%.While for the samples with BN@PA66 hybrid nanofiber film,the mode I and mode II interlaminar fracture toughness were increased by up to 147%and 90%,respectively.It can be seen that combination of the particles and PA66 by blending is better than by spraying directly onto CF.These enhancements are mainly because the addition of particles can effectively improve the mechanical properties of the hybrid fiber itself,which greatly improves the bonding strength between the fiber and the matrix,and also greatly hinders the expansion of cracks.Thus the interlaminar fracture toughness of the laminate is greatly improved.