Modification Design Of Mechanical Properties For Poly-Ether-Ether-Ketone And Its Nanocomposites

Compared with thermosetting composite materials,thermoplastic composite materials have been used to design primary and secondary load-bearing structures of aircraft in recent years because of their strong toughness,impact resistance,and secondary processing.As a typical special engineering plastic,poly-ether-ether-ketone（PEEK）has become the most promising thermoplastic material in the current aviation industry.The next-generation aircraft is facing the wide-frequency vibration and shock load environment of launch and operation.The mechanical properties of PEEK cannot fully meet the requirements of multiple mechanical performance indicators such as lightweight,load-bearing,and vibration reduction of the aircraft load-bearing structure.Carbon nanoparticles represented by carbon nanotubes（CNT）and graphene（GNP）have ultra-high rigidity and strength,have achieved large-scale production,and are expected to become critical materials for the next generation of aerospace.However,the modification mechanism of tensile mechanical behavior,damping performance,and impact resistance of these carbon nanoparticles on PEEK materials are still unclear,limiting the development and application of the multifunctional design of PEEK nanocomposites.In addition,the current research and development of PEEK composite materials are still based on experimental trial and error.It relies heavily on the experience accumulated by developers for a long time,which significantly restricts the research and development of PEEK its derivative nanocomposites.It is urgent to combine traditional experimental trial and error methods and digital material research and development methods based on material genetic engineering to shorten the modification design cycle of PEEK nanocomposites and reduce the design cost.In this paper,the molecular design and experimental verification of PEEK and its nanocomposites are performed for tensile mechanical properties,interface characteristics,damping performance,and impact energy dissipation.Firstly,the microscopic tensile mechanical behavior of PEEK is revealed based on a molecular dynamics（MD）method.Furthermore,based on the material gene concept,a series of PEEK derivatives modified by function groups are constructed for screening multiple PEEK derivatives with light,high stiffness,and high damping properties.Then,the micro-mechanism of multi-layer graphene dissipating impact energy is revealed,and the enhanced effect of graphene on impact energy dissipation is verified through experiments.Finally,The strategy of CNT modified by amino is proposed to enhance the tensile modulus and interfacial shear strength of CNT/PEEK nanocomposite,and the effectiveness of the modified design is verified experimentally.The main research content is as follows:（1）The MD simulation method is used to predict the tensile mechanical properties of PEEK polymer,and the accuracy of MD is verified based on the tensile experiments and glassed transition temperature.The free volume characterizes the gap change of the system,and the mean square radius of gyration describes the molecular chain deformation,revealing the dominant mechanism of the non-bonding interaction on the tensile mechanical properties of PEEK.During the tensile deformation process,the non-bonding energy accounts for more than70%of the increase in total energy.Furthermore,the modification method of amino-functionalized PEEK is used to improve the non-bonding interaction between molecular chains.The MD results indicate that the elastic modulus and yield strength of the amino-functionalized PEEK system are increased by 21%and 34%,respectively,compared with the PEEK system.In addition,the influences of strain rate and temperature on the mechanical properties of PEEK and PEEK-NH₂ are also discussed.（2）Based on the concept of material genetic engineering,a series of PEEK derivatives modified by functional groups were designed,and the MD method was employed to predict the dynamic mechanical properties of PEEK derivatives.The influences of the type,content,and distribution of functional groups on the dynamic mechanical properties of PEEK derivatives were discussed.The microscopic mechanism of functional groups enhancing the dynamic mechanical properties of PEEK derivatives was revealed.Strong non-bonding interactions such as hydrogen bonds andπ-H bonds enhance the storage modulus of PEEK.The destruction and regeneration mechanisms of hydrogen bonds dissipate a large amount of energy to improve the loss modulus of PEEK derivatives.The decrease of free volume leads to the decline of the slip distance of the molecular chain,which makes the damping factor gradually converge.In addition,material gene maps of the specific stiffness and specific damping of PEEK derivatives have been established,and multiple groups of candidate materials with excellent properties such as lightweight,high stiffness,and high damping have been screened out.（3）Experiment and MD simulation methods were combined to study the static and dynamic mechanical properties of GNP/PEEK nanocomposites.The multilayer aggregation characteristics of graphene were observed by scanning electron microscopy and atomic force microscopy,enhancing the stiffness and energy dissipation performance of PEEK nanocomposites.Further,the MD simulation method for shockwave propagation in the GNP/PEEK nanocomposites was established,and the correlation between the micro-stacking characteristics of multilayer graphene and energy dissipation performance of the nanocomposite was systematically studied.The energy dissipation mechanism was revealed.The shockwave is reflected at the interface between multilayer graphene and PEEK due to their impedance mismatch.（4）The tensile MD simulation of the CNT/PEEK nanocomposite found that as the CNT content increases,the tensile modulus of the nanocomposite gradually converges.Furthermore,the interface is designed using the amino-functionalized CNT strategy,and the MD simulation of CNT pull-out is adopted to predict the interfacial shear strength between CNT and PEEK.The results indicate that the interface strength and tensile modulus of nanocomposites are increased by 45%and 27%at the highest.Furthermore,two experiments verified the effectiveness of the amino-functionalized modification strategy.The experimental tensile modulus of 1wt%CNT-NH₂/PEEK nanocomposite is 6.3%higher than that of CNT/PEEK nanocomposite,consistent with the 5.5%increase of MD simulations.The GNP/CNT/PEEK ternary nanocomposite was designed and prepared.Compared with 5wt%GNP/PEEK,the tensile strength and elongation at break of 4wt%CNT-NH₂/1wt%GNP/PEEK nanocomposite were increased by 26.8%and 14.7%,respectively.