Research On Interfacial Design And Mechanical Properties Of Twodimensional Fabric CF/PEEK Composites

Composites are rapidly developing in aerospace and automobile due to their lightweight and high strength.Carbon fiber reinforced thermoplastic（CFRTP）composites have become the preferred material in the lightweight process.Carbon fiber（CF）has the characteristics of high specific stiffness,specific strength,and high-temperature resistance.Polyether ether ketone（PEEK）,one thermoplastic engineering plastic,has excellent mechanical properties,high melting point,and acid and alkali corrosion resistance,which has attracted much attention in its application in CFRTP.However,the CF surfaces and PEEK are both inert structures,resulting in poor interface bonding.It weakens the overall performance of CF/PEEK composites and increases the uncertainty of safe service.The sizing method is a common interfacial modification method.The sizing agent coated on the CF surface acts as a bridge,which enhances the interface interaction and ensures compatibility with the matrix.Hence,it is crucial to select a sizing agent suitable for CF/PEEK interface.In addition,lightweight structural components have the risk of being impacted by low-velocity and low-energy objects,which can easily cause invisible or micro-scale damage and reduce structural stability.The quality of interface adhesion is one of the critical factors affecting the impact damage of CF/PEEK composites.Therefore,research on the interface issues and mechanical properties are essential to the safe service of CF/PEEK composites in multiple fields.This paper establishes a representative volume element（RVE）containing CF,PEEK,and the interface.The effect of interface strength on the equivalent properties of CF/PEEK composites is studied under different loadings.Based on the equivalent performance predicted by the RVE simulations,a macro-scale[090]₈ laminate of CF/PEEK composite is built and subjected to 2 J and 10 J impact.The simulation results show that increasing the interface strength improves the equivalent strength of CF/PEEK composites,and reduces the intra-laminar and inter-laminar damage of composites.The prediction results of damage morphology are consistent with the test results.To improve the CF/PEEK interfacial adhesion,molecular systems of sizing agents are designed based on molecular dynamics simulations.Results of compatibility and interactions energy show that hydroxylated PEEK（HPEEK）and phosphorylated PEEK（p-HPEEK）can effectively enhance the CF/PEEK interface.The elastic properties of sizing agents in the HPEEK class are gradually increased with the introduction of multi-walled carbon nanotube（MWCNT）and the formation of covalent bonds.Compared with pure HPEEK,Young’s modulus and shear modulus of HPEEK-g-MWCNT are increased by 78.33%and 42.95%,reaching 5.35 GPa and 2.13 GPa,respectively.In addition,HPEEK-g-MWCNT has an esterified covalent bond,which leads to stronger interaction,denser accumulation,and less mobility of HPEEK on the surface of MWCNT.As the sizing concentration of HPEEK20-g-MWCNT increases,more HPEEK20-g-MWCNT are coated on the CF surface,where has become rougher and more active.It improves the wettability of CF surface.In addition,the sizing process of HPEEK20-g-MWCNT protects the tensile performance of CF monofilament.The synergistic effect of these factors is contributed to the interfacial shear strength（IFSS）of HPEEK20-g-MWCNT modified CF/PEEK gradually increased.When the sizing concentration is 1.0%,the IFSS reaches 62.6 MPa,with an increment of 50.8%.The sizing agent of p-HPEEK30 has the best dispersion stability in water and can be uniformly dispersed for more than one month when the concentration of p-HPEEK30is 0.5%and the concentration of Triton X-100 is 1.5%.p-HPEEK30 sizing increases the roughness of CF surface,enhancing the dispersion component of surface energy and finally improving the wettability of the CF surface.The IFSS of p-HPEEK30 modified CF/PEEK with a concentration of 0.5%is increased by 27.2%to 52.8 MPa.Results of mechanical properties confirm that 0.7%is the optimal sizing concentration of HPEEK20-g-MWCNT.At this concentration,the interlaminar shear strength（ILSS）and flexural strength of CF/PEEK composites are increased by 73.0%and 163.2%,reaching 84.7 MPa and 906.2 MPa,respectively.For the sizing agent of p-HPEEK30,0.5%is the best sizing concentration.At this concentration,the ILSS and flexural strength of CF/PEEK composites are increased by 55.2%and 41.2%,respectively.The damage mode of modified CF/PEEK composites has changed from interface debonding and fiber pull-out to fiber and matrix fracture.