The lightweight of vehicles is one of the important means to solve the energy crisis and environmental problems, which has been paid great attention by scholars at home and abroad.Carbon fiber-reinforced polymer (CFRP) composites and light alloys such as aluminum and magnesium alloys have a series of excellent mechanical properties and processing performance, representing lightweight materials with great application prospects. It has become a hot research topic to realize the effective joining between the CFRP and aluminum/magnesium alloys which are the promising lightweight materials. However, due to the significant differences in physical and chemical properties between these dissimilar materials, the mixed application of a variety of lightweight materials in the production process is still facing great challenges.The research progress, advantages and disadvantages, and development trend of bonding, mechanical fastening, friction stir welding and its variants were summarized and analyzed. The micro morphology of joints obtained under different bonding methods was investigated. Three mechanisms of friction stir joining between CFRP and aluminum/magnesium light alloys were preliminarily summarized through investigating the micro morphology of joints, including macro anchoring, micro mechanical chimerism and chemical bonding. Finally, based on the above joining mechanism, it is pointed out that the key to further improving the performance of hybrid joints is to increase the surface roughness of the base metal, increase the area of the molten polymer and adopt the hybrid joining techniques.

Thermoplastic polyether ether ketone (PEEK) composites are widely used in aerospace field due to their excellent fracture toughness, impact resistance and material versatility. Sizing agent as the core auxiliary product of carbon fiber has an important impact on the interface of composites. Limited by the decomposition temperature, the traditional thermosetting sizing agents are difficult to meet the use of PEEK composites, which restricts the development and application of high-performance PEEK composites. Therefore, it is of great significance to develop a matching carbon fiber sizing agent for PEEK composites. In this paper, the interfacial properties of composites and the action mechanism of sizing agent were analyzed and introduced; the research progress and results of modified PEEK, polyimide precursor and polyetherimide sizing agents were focused, and different systems of sizing agents were analyzed and summarized.Finally, the relevant suggestions on carbon fiber sizing agents for PEEK composites were put forward while the environmental and multi-function developments for sizing agents were prospected.

The hygrothermal aging of T800 carbon fiber/epoxy resin composites in seawater environment were studied. The prepared specimens were immersed in artificial seawater 70 ℃, 3.5% NaCl solution for 30, 60 and 90 days for corrosion. The mechanical properties of the materials were analyzed by mass change, surface morphology before and after aging, infrared spectroscopy, dynamic mechanical properties, compression test and interlayer shear test. The results show that the moisture absorption rate of T800 carbon fiber/epoxy resin matrix composites in 3.5% NaCl solution is 0.39%, 0.47%, 0.53%. Good adhesion between unaging sample fiber and matrix, and the damage of the interface between the fiber and the matrix become more serious with the increase of time after aging in 3.5% NaCl solution. The glass transition temperature(T_g) is decreased from 189.16 ℃ to 177.54, 171.88 ℃ and 168.06 ℃ after 30, 60 and 90 days aging. After aging with 3.5%NaCl solution, the maximum compressive failure load of specimens for 30, 60 and 90 days is decreased by 3.2%, 8.4% and 15.3%, respectively, and the compressive strength is decreased by 3.0%, 8.2% and 15.9%, respectively. The maximum interlaminar shear failure load is reduced by 3.0%, 9.2% and 14.9%, and the shear strength is reduced by 3.0%, 9.7% and 16.4%, respectively.

As one kind of advanced high temperature structural and functional materials, it is necessary for fiber reinforced silicon carbide matrix composites (SiC CMCs) in the field of thermal management (TM) to combine the efficient heat transfer and high temperature heat resistance. Common fibers reinforced SiC CMCs, such as carbon fibers reinforced SiC CMCs (C_f/SiC or C_f/C-SiC), silicon carbide based fiber reinforced SiC CMCs (SiC_f/SiC), etc., have a low degree of graphitization of the reinforcing fiber and are difficult to form an effective heat transport network. The latest research progress on the preparation and properties of fiber reinforced SiC CMCs with highly thermal conductivity was reviewed in this paper. The heat transport ability of fiber reinforced SiC CMCs can be improved by introducing highly thermal conductive phase, optimizing interfacial structure, making silicon carbide crystal coarse-grained, and designing preform structure. Moreover, the development of the fiber reinforced SiC CMCs with highly thermal conductivities was prospected, that is, comprehensively considering the factors that affect the performance of SiC CMCs, flexibly using the structure-activity relationship between the microstructure and properties of the composites, in order to prepare fiber reinforced SiC CMCs with stable size, excellent properties.

C_f/SiC composites are considered as one of the most important candidates for aerospace thermal protection systems because of their low density, high specific strength, good thermal shock, oxidation and ablation resistance, and excellent high temperature strength retention. However, C_f/SiC composites are prone to oxidize at a temperature above 500 ℃ due to inevitable fabrication defects. So it is necessary to carry out effective oxidation protection for the composites. Oxidation resistant coating is an efficient technology to realize long-term oxidation protection. Based on harsh requirement of thermal protection systems, the research progress of anti-oxidation coatings for C_f/SiC composites was summarized, mainly focusing on the coating material systems and their preparation technologies. Improving the service temperature (≥1800 ℃) and bonding strength of the coatings is an important issue to be solved at present.The preparation of multi-functional coating with longer service time and higher service temperature, as well as oxidation resistance, water vapor corrosion resistance and even good heat insulation performance is an important direction for future development.

The performance change and mechanism of polyimide composites with carbon fiber sizing and desizing states during thermal aging at 330 ℃ were compared and analyzed from the aspects of thermal oxidation mass loss, surface morphology and micro morphology, mechanical properties and glass transition temperature. The results show that carbon fiber desizing can reduce the mass loss rate of thermal oxidation of polyimide composites. The interface layer of the composites with sizing carbon fiber contains epoxy sizing agent, which has low temperature resistance. Therefore, the interface is easy to be damaged in the process of thermal aging, resulting in more cracks and rapid separation of edge fibers. Although the composites with sizing carbon fiber has high interlaminar shear strength before aging, it decreases rapidly in the early stage of thermal aging. On the contrary, the interlaminar shear strength of the composites with desizing carbon fiber is higher after aging for 200 h. The bending strength of the two composites before aging is basically the same, but the bending strength of the composites with sizing carbon fiber decreases rapidly in the early stage of aging; however, desizing has little effect on bending modulus. The glass transition temperature of the composites with desizing carbon fiber increases by about 15 ℃. After thermal aging, the glass transition temperature of the composites with sizing carbon fiber increases slightly, while the composites with desizing carbon fiber remain unchanged. Therefore, the high temperature desizing treatment of carbon fiber is conducive to improving the stability of polyimide composites for long-term use at high temperature.

The N-doped carbon nanofiber coated graphene nanosheets (NFGNs) were designed and constructed using EGNs as the skeleton and PPy as the carbon source. The samples were characterized by SEM, XRD, Raman, FTIR, XPS and BET. The results show that the interconnected N-doped carbon nanofibers are uniformly coated on the surface of EGNs. The NFGNs-800 presents high-level nitrogen atom doping of 11.53% and large specific surface area of 477.65 m²·g^-1. The capacitance performance test results show that the NFGNs-800 electrode material exhibits high specific capacitance of 323.3 F·g^-1 (1.0 A·g^-1) and good rate characteristic. NFGNs-800 supercapacitor shows high energy density of 87.1 Wh·kg^-1 at power density of 10500 W·kg^-1. The specific capacitance of the supercapacitor is 95.9% of the initial specific capacitance and the columbic efficiency still remains above 99% after 10000 constant current charge discharge cycles.

To improve the mechanical properties of carbon fiber reinforced polymer (CFRP) bonding interface, the surface treatment of CFRP was performed using low-temperature oxygen plasma treatment equipment. The surface physico-chemical properties including surface wettability, surface energy, surface morphology and surface chemical components of CFRP were characterized by contact angle measurement, scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) test equipment, as well as the mechanical properties of CFRP bonding interface was tested by double cantilever beam (DCB) test. The results show that the water contact angle of surface decreases from 97° to 29° with the increase of oxygen plasma treatment time from 0 s to 30 s, as well as the surface wettability of CFRP is the best and the percentage of polar components increases significantly. As the increase of treatment time, the surface roughness and the maximum height difference of CFRP decrease significantly, and more nanoscale grooves with valley distribution are formed and thus the surface area of substrate increases. Meanwhile, the content of oxygen-containing polar functional groups including C—O and C＝O on the surface are increased obviously, the content of C—C/C—H and Si—C functional groups are decreased, and the surface contaminants are effectively removed or transformed. In comparison with the untreated specimens, the maximum peeling load and mode Ⅰ fracture toughness of CFRP adhesive interface are improved by 1.01 times (62.73 N) and 1.92 times (649.21 J/m²) after oxygen plasma treatment for 20 s, respectively. The study reveals that oxygen plasma treatment can significantly improve the physico-chemical properties of CFRP surface, which is conducive to better bonding between CFRP and adhesive, and improve the peel strength and toughness of the adhesive interface.

Carbon fiber reinforced carbon/phenolic composites were prepared by using phenolic resin as matrix, plain carbon cloth and short carbon fiber as reinforcing agent. The ablation resistance of the composite was studied by oxygen/acetylene ablation test. The bending property of the composite was characterized by electronic tensile testing machine. The ablation surface of the composite was observed by scanning electron microscope. The ablation performance of the composite was verified by solid rocket motor. The results show that the mass ablation rate of oxyacetylene in carbon/phenolic composites prepared with these two structural forms of carbon fibers as reinforcements has a positive correlation with the size of carbon fiber tow. The smaller the carbon fiber tow, the lower the mass ablation rate of carbon fiber. When the carbon fiber reinforcer is in the single filament state, the oxyacetylene mass ablation rate of the composite is the lowest, which is 0.046 g/s, and the influence of carbon fiber type and specification on the mass ablation rate of oxyacetylene becomes smaller. The experimental results of solid rocket motor show that the ablation erosion resistance of carbon fiber/phenolic composites in monofilament state is obviously better than that of bundle carbon fiber/phenolic composites.

Different thermal-oxidative environments (70, 130 ℃ and 190 ℃) have important effects on the properties of carbon fiber composites. The mass loss characteristics of T800 carbon fiber/epoxy resin composites under different thermal-oxidative environments were analyzed, and the surface morphology, infrared spectra, dynamic mechanical properties and interlaminar shear properties of T800 carbon fiber/epoxy resin composites before and after aging were compared. The results show that in the initial stage of thermal-oxidative aging, the mass loss rate is increased rapidly, and the higher the aging temperature, the faster the mass loss. The extent of damage sample surface morphology is gradually increased with the increasing of thermal-oxidative temperature, after aging at 190 ℃, the resin on the fiber surface falls off seriously, the cracks and gaps appear between the fibers, and there is no resin filling, at this aging temperature, the sample has an irreversible chemical change. The glass transition temperature of the sample is increased with the increase of aging temperature, but the internal friction is decreased at first, then increased and then decreased. After thermal-oxidative aging at 70, 130 ℃ and 190 ℃, the shear strength of the samples is increased by 6.0%, 13.7% and 2.1%, respectively. The relevant test results and phenomena can provide data reference for the follow-up study of the new domestic T800 carbon fiber/epoxy composites.

Using carbon fiber cloth with different areal densities and tow sizes, two kinds of carbon fiber preforms with same carbon cloth laminated structure were produced through different z-direction stitching methods. Then, C/C-SiC composites were prepared by combining chemical vapor infiltration (CVI) with gas silicon infiltration (GSI). The influence of carbon fiber preform structure on the microstructure and mechanical properties of CVI-GSI C/C-SiC composites was studied. The results show that the density, phase composition, structure, and properties of the two composites prepared from preforms with the same fiber volume fraction and C/C preform density are significantly different. The smaller carbon fiber tow (1K) and carbon cloth surface density (92 g/m²), as well as the larger voids left by lock stitching, provide more sufficient channels for the infiltration of Si vapor in the GSI reaction process. Thus T1 composite finally prepared has low porosity, uniform structure, and higher performance, with bending strength, modulus, and fracture toughness of 300.97 MPa, 51.75 GPa, and 11.32 MPa·m^1/2, respectively. The comprehensive control of the initial preform structure and the C/C intermediate structure is the key to the preparation of high performance C/C-SiC composites by the CVI-GSI process.

The complex internal three-dimensional fiber distributions and the various microcrack propagation processes of the chopped carbon fiber sheet molding compound (SMC) composites aggravate the difficulty of failure analysis. In-situ micro X-ray computed tomography was proposed in this study to characterize the internal microstructure evolution under different tensile loading conditions. Combined with advanced image acquisition and image processing technologies, the three-dimensional microstructure of the SMC composites, including the complete microcrack propagation, under different loading conditions was reconstructed, where the microcrack geometric size was quantitatively measured. The failure mechanism of the SMC composites was explored via the Tsai-Wu failure criterion and the matrix stress field theory after interface cracking. The proposed method provides an important basis for studying the failure process of the SMC composites and the corresponding failure behavior.

CFRP composites are widely used in aerospace due to their excellent mechanical properties, however, due to the anisotropy of the individual plies, the electro magnetic interference(EMI) shielding efficiency(SE) for vertically polarized waves of the unidirectional fiber laminates is poor. In order to protect electronics within these equipments from increasingly severe electromagnetic interference, it is particularly important to enhance the electromagnetic shielding efficiency of the CFRP. In this paper, Al particles were introduced and a conductive network was constructed in the CFRP interlaminar region by condensing the Al particles on the prepreg surface. The effects of different Al particle contents on EMI SE and mechanical properties of composites were studied. With the increase of Al particle contents, the electrical conductivity and the EMI SE of CFRP composites increase. When the Al mass fraction in the resin is 33.3%, the in-plane conductivity of the composites increases by 3 orders of magnitude, the EMI SE of the Al particle sandwich CFRP composites is improved by more than 10 dB in the frequency range of 3-17 GHz. With the increase of Al particle contents, the interlaminar shear strength and bending strength of the composites increase first and then decrease. When the Al mass fraction in the resin is 33.3%, the interlaminar shear strength (ILSS) of the composites increases by 5.2% to 80.5 MPa, and when the Al mass fraction in the resin is 50%, the bending strength of the composites increases by 20% to 1441.0 MPa and the bending modulus increases by 10.2% to 101.83 GPa. It can be seen that the mechanical properties and electromagnetic shielding effectiveness of the Al particles sandwich CFRP composite can be improved simutaneously. It is a kind of structure electromagnetic shielding integrated composite with broad application prospects.

In order to effectively provide guidance for the selection of aircraft dissimilar metals from the perspective of corrosion protection, the corrosion behavior of typical aircraft lap structures was studied by finite element simulation and corrosion test for the specific service environment of aircraft. The aluminum alloy, composite material and lap joints were subjected to cyclic immersion corrosion test in the laboratory. Then the galvanic corrosion law between aluminum alloy and composite was revealed by polarization curve measurement test, macroscopic and microscopic morphology observation, fatigue test and XRD measurement. Taking the electrochemical parameters measured by polarization curve as boundary conditions, the corrosion simulation model of lap joint was established. After 0 cycle and 10 cycles of cyclic immersion corrosion test, the results show that the self-corrosion potential and self-corrosion current density of aluminum alloy are -802 mV and 2.357×10^-7 A/cm², -872 mV and 1.477×10^-6 A/cm². The self-corrosion potential and self-corrosion current density of composite material are -240 mV and 6.217×10^-7 A/cm², -98 mV and 2.286×10^-7 A/cm², respectively. With the extension of the corrosion cycle, 7B04 aluminum alloy shows a trend of increasing self-corrosion rate and negative shift of self-corrosion potential, while composite material shows a trend of positive shift of self-corrosion potential and slowly increasing self-corrosion rate. The corrosion products of lap joints gradually increase and the corrosion degree becomes more and more serious. With the extension of corrosion cycle, fatigue life decreases and the depth of corrosion pits increases. The corrosion products include Al(OH)₃, Al₂O₃, AlCl₃. The simulation results of lap joints are in good agreement with cyclic immersion corrosion test results. The corrosion prone parts of the typical lap structure of the aircraft were given, and the law of galvanic corrosion was revealed, which points out the direction for the corrosion protection of the aircraft structure.

The water-soluble thermoplastic polyimide sizing agent was synthesized from bisphe- nol A-type diether diether dianhydride (BPADA), m-phenylenediamine and 4, 4′-(1, 3-phenylenedioxy) dianiline (TPE-R). The surface of domestic high-strength and high-modulus carbon fiber (HMCF) was sized and prepared into composite material. The effects of molar ratios of different monomers on the characteristics of the sizing agent and the surface structure properties of the fibers after sizing treatment were studied, and the effects of thermoplastic sizing agents on the interfacial properties of domestic high-strength and high-modulus carbon fiber reinforced thermoplastic polyetherketone (PEKK) resin matrix composites were further analyzed. The results show that when the monomer molar ratio of BPADA to TPE-R is 1∶1, the synthesized thermoplastic sizing agent not only has a uniform molecular weight distribution, but also has excellent thermal stability, e.g. its thermal weight loss is only 5% with the temperature up to 554 ℃. After sizing, the surface O/C ratio is increased from 0.08 to 0.18 (increased by 125%). Besides, the fiber strength is slightly increased and the modulus is almost unchanged. More importantly, the interfacial performance of the composites is significantly improved after sizing treatment, and the interlaminar shear strength of the HMCF/PEKK composites can be improved from 38.5 MPa to a maximum of 59.4 MPa with an increase of up to 54.3%.

In order to prepare low expansion, high strength and light weight composites, ZrW₂O₈-C_f/E51 composites were prepared by compression molding method, and the effects of ultrasonic time on its microstructure, thermal expansion behavior and ultimate tensile strength were studied. The results show that the agglomerated particles will be blocked by the fibers and gather on the surface of fiber bundles during the preparation. Within 20 minutes, the agglomeration of ZrW₂O₈ particles can be reduced by prolonging the ultrasonic time. With the decrease of particle agglomeration, the fracture surface of the composites will be changed from plane without fiber pull-out to uneven with fiber pull-out. During the thermal expansion process, the d_L/L₀of ZrW₂O₈-C_f/E51 composites show three stages: increase, decrease and slow increase under the combined action of carbon fiber and ZrW₂O₈ particles. When ultrasonic time increases from 5 min to 20 min, the average thermal expansion coefficient of ZrW₂O₈-C_f/E51 composites decreases by about 130%, and the ultimate tensile strength increases by about 8%.

A series of processable and high-temperature resistant polyimide resins terminated with 4-phenylethynyl phthalic anhydride were synthesized by PMR (for in situ polymerization of monomer reactants) using isopropyl alcohol as esterifying agent. The resin solution stored at room temperature for sixteen weeks has no solid precipitation, and the viscosity of the solution does not change significantly, which shows good storage stability at room temperature. The minimum melt viscosity of the imide oligomers is less than 300 Pa·s, which is suitable for compression moulding or autoclaved process. The cured polyimides exhibit extremely high glass transition temperatures (T_g) up to 462℃. The flexural strength and modulus of T300/PMR-PE-2 carbon fiber composite are 963 MPa and 53 GPa, respectively. The inter-laminar shear strength of the composite is 56 MPa. Moreover, the composite can maintain no lower than 66% of their room temperature mechanical properties at 300℃. After isothermal aging in air atmosphere for 500 h at 300℃, the mass loss of the composite is only 0.96%, meanwhile, the composite retention rate maintains 72% of its room temperature flexural strength and 98% of its room temperature inter-laminar shear strength, which demonstrates its excellent thermal-oxidative aging resistance.

Aimed at the problem of insufficient heat resistance and poor ablation resistance of phenolic resin (RF), and the compatibility of SiO₂ particles with phenolic resin, the nano-scale SiO₂/RF hybrid aerogel was prepared by the co-gel method. The interpenetrated gel network was constructed to increase the compatibility of two phases. The microstructure, chemical structure and thermophysical properties of the SiO₂/RF hybrid aerogel were explored. The silica-modified phenolic/carbon fiber composite material was prepared. The ablation properties of the composite material before and after modification were compared. The results show that the hybrid aerogel possesses a bi-continuous structure of skeleton and pores. The density of the hybrid aerogel fluctuates in the range of 0.145-0.160 g/cm³. As the silica content increases, the residual carbon ratio of the hybrid aerogel increases, and the Si—O bond absorption vibration peak is more obvious, but XRD has no diffraction peak. Considering the pore size distribution and thermal physical properties, the silica-modified phenolic/carbon fiber composite material was prepared with the best performance hybrid aerogel. The mass ablation rate of the modified composite material is 0.046 g/s, and the linear ablation rate is 0.074 mm/s. Compared with the unmodified composite material, the mass ablation rate is reduced by 20.7%, the linear ablation rate is reduced by 21.3%. The oxidation resistance and the residual carbon ratio of the modified material are significantly improved.

Carbon fiber reinforced silicone resin derived SiOC ceramic (C/SiOC) composite is a high-temperature structural material with good application prospect due to its performance/cost ratio. In order to further reduce the cost, carbon fiber needled felt with low price was selected as the reinforcement, and C/SiOC composites were prepared by precursor impregnation pyrolysis (PIP) process. The hot molding process was introduced in the first cycle of PIP route. By optimizing the concentration of precursor solution, molding temperature and pressure, the fiber volume fraction and matrix content in the first cycle were effectively improved without damaging the structure of needled felt. Accordingly, the bending strength at room temperature and fracture toughness of C/SiOC composites were increased to 331 MPa and 16.0 MPa·m^1/2, respectively. Then the microstructure evolution during the fabrication of C/SiOC composites was evaluated. The results show that SiOC matrix grows in the carbon fiber bundle firstly, then grows from inside to outside of carbon fiber bundle during fabrication. The pores are distributed around Z direction fibers. Porosity of the composites is decreased gradually and pores of the composites transformed from connected ones into isolated ones as the fabrication cycles is increased. When the fabrication cycles reach 8, the porosity of the composites is unchanged basically. At the same time, the densification of composites is completed.

Two different sizes of graphene oxide (GO) produced by the Hummers method had been incorporated into epoxy resins and used to fabricate GO modified carbon fiber reinforced epoxy resin composites (GO/CF/EP) by compression molding method, and the composite material was processed under damp and heat conditions. The modification effects of dry and wet composite materials were investigated through interlayer shear performance, dynamic thermomechanical properties and microscopic morphology. The results indicate that GO has a good improvement on the interlaminar shear strength and glass transition temperature of composite materials. In the dry state at room temperature, two sizes of GO have basically the same improvement effect on the interlaminar shear strength of the composite. With the increase of GO content, the small size of GO makes the hygrothermal interlaminar shear strength of composites decrease faster. When the GO content is 0.1%(mass fraction, the same as below), the improvement of the interlaminar shear performance of the composite material is better, however, the glass transition temperature of the composite material is better when the GO content is 0.2%. With the increase of GO content, the exothermic peak of the GO-EP composite resin matrix shifts to low temperature, and the small size of GO shortens the gel time of the composite resin. The micro-morphology analysis shows the presence of GO is beneficial for increasing the crack propagation path during the failure of composite material, thereby more conducive to the dissipate the crack tip energy by the material.

The interlaminar repairing behavior and thermoforming capacity of new carbon fiber reinforced Vitrimer epoxy resin (V-CFRP) composite and corresponding mechanisms were studied. The results reveal that the glass transition temperature (T_g) of the new Vitrimer epoxy resin is 92.8 ℃, and it exhibits significant stress relaxation behavior at temperatures higher than T_g. The stress relaxation time exhibits a linear relationship with temperature; The hot-press repair behavior and thermoplastic molding ability of V-CFRP composites were studied using a three-point bending experiment. The hot-press repair study shows that hot pressing at 180-220 ℃ for 1.5-2.0 h and 5 MPa can achieve nearly 100% repair of interlaminar damage in the composite; The bending modulus and bending strength of V-CFRP composites is decreased by more than 80% after pre-heating at 180-220 ℃ for 5-30 min. The significant decrease of bending modulus means that V-CFRP composite is suitable for thermoforming process. Moreover, a V-CFRP part with three-dimensional structure is successfully prepared by thermoforming process under the conditions of 200 ℃, 5 MPa and 2 h, which confirms the thermoforming capacity of V-CFRP composites.

The carbon nanotube (CNT)-polyetherimide (PEI) was successfully grafted onto the surface of carbon fibers (CF) through chemical grafting method for constructing a CF-g-CNT reinforcing phase. Results show the construction of CF-g-CNT fiber can effectively improve the interface, impact resistance and bending properties of the composites. Considering the effect of strengthening phase on the mechanical properties of composites, the interfacial shear strength, impact strength, flexural modulus and flexural strength of CF-g-CNT/BMI composites respectively increase by 48.8%, 10.8%, 5.2% and 14.6%, companed with those of CF/BMI. In addition, the interfacial shear strength, impact strength, flexural modulus and flexural strength of CF-g-CNT/BMI-PEI-CNT composites are 56.9%, 27.1%, 12.5% and 16.1% higher than those of CF/BMI-PEI-CNT, respectively. The interfacial shear strength, impact strength, flexural modulus and flexural strength of CF-g-CNT/BMI-PEI-CNT composites increase by 57.7%, 33.7%, 20.0% and 23.7% compared with CF/BMI. The CNT-PEI in CF-g-CNT can effectively change the interface composition and change the expansion path of horizontal stress or vertical stress at the interface, which is beneficial to disperse the stress concentration as well as improve the mechanical properties of the composites.

As the source of intense electron beam, the cathodes have an important effect on the performance of high power microwave source. Graphite is a common material for explosive emission cathodes of high power microwave source, which have the advantages of stable operation and long life under high pressure and repetition frequency. The carbon fiber with high aspect ratio and low emission threshold was chosen to be composited with the graphite cathode, and the field emission and high power microwave test platforms were adopted to analyse field emission properties, intense electron emission performances and output microwave characteristics of pure graphite cathodes and carbon fiber composited graphite cathodes. Meanwhile the effect of carbon fiber on the electron emission properties of graphite cathodes was studied combined with the microstructure characterization of the cathodes. The results show that compared with the flake graphite cathodes, the field emission threshold of 40%(mass fraction) carbon fiber composited graphite cathodes decreases from 143 kV/cm to 119 kV/cm, a reduction of about 16.8%, and the output pulse width and peak of 480 kV increase by 13.5% and 5.7%, respectively. Considering the structural stability of carbon-fiber in the process of explosive electron emission, the carbon-fiber is also beneficial for improving the service life of the cathodes.

Carbon fiber reinforced polymer composites (CFRP) are widely used in the aerospace field. The efficient bonding technology has an important effect on the manufacturing cost and safety of CFRP components. In this paper, carbon fiber reinforced polyetherimide resin matrix composites (CF/PEI) were welded by ultrasonic welding technology. The effects of ultrasonic welding pressure and welding time on the strength of ultrasonic welded joints were studied by single lap shear strength (LSS) test, and the micro morphology of section was characterized by scanning electron microscope. The experimental data were analyzed by linear fitting, and the time pressure parameters were optimized and the joint strength was predicted by combining BP neural network and genetic algorithm. Finally, the influence mechanism of holding time on joint strength was studied. The results show that when the welding time is 2.5 s and the welding pressure is 0.45 MPa, the maximum LSS is 25.6 MPa, and it is found that the higher welding strength is due to the formation of dense and stable structure on the joint surface. The experimental data are refined by BP neural network. The LSS value simulated by genetic algorithm is 24.8 MPa, and the error between the simulation and the experimental results is only 3%.With the increase of the holding time, the strength of ultrasonic welding joint increases rapidly first and then tends to be stable. When the holding time is 5 s, the molten resin at the welding interface is basically cured completely, and the PEI resin and carbon fiber form a dense structure, and the strength of ultrasonic welding joint is stable.

Ultrasonic plastic welding is an efficient and green welding method, which has been widely used in the joining of carbon fiber reinforced thermoplastic composites (CFRTP) in recent years. An important step in the ultrasonic welding of CFRTP is the design of the welding joint, which largely determines the weld quality. An ultrasonic CFRTP welding method based on structured surfaces was proposed, that is, the surface of the workpiece is structured by ultrasonic embossing before welding, and energy director are processed. Taking carbon fiber reinforced nylon 66 (CF/PA66) as the research object, the effect of structured surface and welding energy on the weld formation was studied. Microstructure, tensile-shear performance and fracture characteristics of welded joint were analyzed. The results show that compared with the unstructured surface, the structured surface acting as energy director that can effectively concentrate welding energy and greatly reduce the randomness and dispersion of weld distribution, thereby improve the weld quality. Moreover, fewer defects in the weld joint can be obtained by pre-structuring two contacting surfaces.

The integrated castings fabricated by SiC_f/SiC composite and K403 Ni-based superalloy melt exhibited spontaneous fracture when cooled to room temperature. The integrated forming of SiC_f/SiC and K403 Ni-based superalloy and their firmly bonded interface were successfully realized by pretreatment of SiC_f/SiC surface using Ti powder embedded coating infiltration process at 1100 ℃ and ceramic mold precision casting with K403 superalloy melt under appropriate process. The results show that the Ti pretreatment layer has an average thickness of about 17 μm and microscopic structure including TiC, Ti₃SiC₂, Ti₅Si₃C_x and SiC phases owing to Ti permeation, diffusion and reaction to SiC_f/SiC. After composite casting of the pretreated SiC_f/SiC and high temperature nickel base metallic liquid, the pretreatment layer is evolved into the interface reaction layer with a thickness of about 120 μm and the typical microstructure composed of Ni₂Si, C, Al₄C₃ and MC (M containing mainly Ti and a small amount of Cr, Mo, W).The existence of pretreatment layer alleviates the harmful graphitization reaction between Ni and SiC, and the thermal shock of the high temperature melt on SiC_f/SiC during casting; the formed interface reaction layer reduces the interface thermal stress caused by the mismatch of thermal expansion coefficients. Consequently, the room temperature shear strength of the interface in the integrated casting of SiC_f/SiC and K403 reaches 63.5 MPa.

The inert surface of high-modulus carbon fiber leads to the weak interface between it and the resin matrix， which limits the performance of high-modulus carbon fiber composite in many application scenarios. Anodic oxidation is the only surface treatment technology that can be combined with carbon fiber production lines until now，but the commonly used alkaline electrolytes represented by ammonium bicarbonate exhibit limited effect on the oxidation of high-modulus carbon fiber. The acidic electrolyte system has stronger oxidation ability， lacks systematic researches on anodizing mechanism. In this paper， dilute sulfuric acid was used for the anodic oxidation for carbon fiber with a modulus of 371 GPa. The effects of key factors such as current density， electrolyte concentration on the polar structure of the surface of high-modulus carbon fiber were systematically studied， and then the effects of surface treatment on the interfacial shear strength of carbon fiber/epoxy resin composites were investigated. The correlation between surface treatment factors and interfacial properties of composites was established. The results show that after the treatment， the surface morphology and graphitized structure of the carbon fiber are maintained， and oxidation reactions occur in the amorphous carbon and aromatic ring structure regions of the carbon fiber. After the reaction， the graphitization degree of the fiber decreases apparently， the surface energy increases， and the content of surface oxygen-containing functional groups increases. When sulfuric acid concentration is 1.0%（mass fraction） and current density is 0.26 mA/cm²， the surface energy of carbon fiber is the highest （57.7 mN/m）， which is 62.08% higher than that of untreated carbon fiber. The interfacial shear strength between carbon fiber and epoxy resin reaches 80.9 MPa， which is 2.7 times higher than that of untreated one corresponding to 21.8 MPa.Furthermore， the single fiber tensile strength of the treated carbon fiber exhibits undamaged.

The bonding performance of CFRP-steel joints between carbon fiber reinforced polymer （CFRP） plate and steel is seriously affected by marine environment. In order to evaluate the bonding strength of CFRP-steel joints exposed to marine environment， a double-lap shear joint on five specinmens with different bonding lengths were corroded for 7 to 21 days in the NaCl solution. The technique of digital image correlation （DIC） was applied to measure the normal strain distribution on the surface of CFRP. Scanning electron microscope （SEM） and energy dispersive spectrometer （EDS） were used to observe microscopic information and monitor element content changes of CFRP surface. The results show that the contents of Na⁺ and Cl^- on the CFRP surface are increased with the increase of corrosion period， which induces charge compensation. Electrolyte penetration into the interface leads to free volume expansion， resulting in a decrease in the interfacial binding strength. The adhesion failure at the interface of adhesive and CFRP is observed in the experiment. The corrosion is aggravated with the increase of time， leading to the decrease of the ultimate load and the ductility. The interface ductility decreases after corroding for 7 to 14 days and the strain softening disappears and exhibits characteristics of the brittle failure after corroding for 21 days. The finite element model was established based on the Fickian theory and bonding-slip constitutive parameters.The diffusion characteristics of seawater between bonding interfaces and the interface typeⅡ delamination process were simulated，and the numenical results are in good agreement with the expermental results.

The carbon fiber triaxial woven fabric has good application prospects in the field of space deployment devices because of its advantages of stable structure， light density and quasi-isotropic. In order to study the deformation properties of carbon fiber triaxial woven fabric/thermoplastic polyurethanes （TPU） flexible composite， TPU and carbon fibertriaxial woven fabric were composited by hot pressing. The unit cell model of triaxial woven fabric was established by metallographic microscope and SEM.The moment of inertia of different sections was calculated by the model， the moment of inertia of the weft section is greater than that of the warp， and the triaxial woven fabric is more difficult to deform in the weft direction. Drape experiments were performed on carbon fiber plain fabric and triaxial woven fabric.The results show that the deformation ability of the triaxial woven fabric is stronger than plain fabric， and the warp direction deformation of triaxial woven fabric is greater than the weft when it is draped， which is consistent with the calculation result of the moment of inertia of the model section； triaxial woven fabric is subjected to tensile tests in the 0°，15°and 30°directions， the load curve changes and ultimate loads of the three angles are analyzed at different strain stages.

Carbon fiber-reinforced Al-Mg-Ti laminated composites were prepared by vacuum hot-press diffusion technique and "foil-fiber-foil" method using 1060 pure aluminum， TC4 titanium alloy， AZ31 magnesium alloy and nickel-plated carbon fiber woven fabric as raw materials. The effect of Al-Mg diffusion layer thickness on the material tissue properties was analyzed by controlling the Al-Mg holding time， and the strengthening mechanism of carbon fiber was discussed. The phase composition， element distribution and crack extension morphology of the composites were analyzed by X-ray diffraction （XRD）， energy spectrum （EDS） analyzer and scanning electron microscopy （SEM）， and the flexural strength and impact toughness of the composites were tested. The results show that the thickness of diffusion layer of carbon fiber-reinforced Al-Mg-Ti laminated composites increases with the increase of holding time， and the mechanical properties show a trend of increasing and then decreasing， and the carbon fiber absorbs a large amount of fracture energy through fiber debonding， fiber pull-out and fiber splitting， which plays a significant toughening effect. The mechanical properties of the composites are optimal at the hot pressing temperature of 640 ℃ for 2 h for Al-Ti and 440 ℃ for 8 h for Al-Mg， with flexural strength of 380 MPa and impact toughness of 26.2 J/cm²， which are increased by 10.8% and 30.3% respectively， relative to the matrix flexural strength and impact toughness.