Abstract:Benzoxazine resin as a new type of thermosetting resin has been widely used in electronic packaging materials， aerospace industry， rail transportation and other fields. In this paper， preparation routes and synthesis methods of benzoxazine monomer are summarized， and the ring-opening polymerization mechanism of benzoxazine monomer is summarized. The modification progress of benzoxazine resin in heat resistance， toughness and other aspects are emphatically described， and then the application progress of benzoxazine resin in the molding process of composite materials such as prepreg and RTM is introduced. Finally， the development trend of benzoxazine resin and its composites are prospected.

Abstract:Edge effect seriously restricts the processing accuracy and efficiency of CCOS， which is one of the technical difficulties needed to be solved urgently. An important approach to solve this problem is to establish a quantitative removal model of tool pad based on the Preston equation on the edge of the workpiece. The model includes some process parameters such as the workpiece size， the tool pad size， the processing pressure， velocity， time and position. The model calculates accurately the edge pressure distribution and the processing cumulative time. The processing pressure increases exponentially with the edge exposure area of the tool pad on the edge of the workpiece. The accumulated processing time of workpiece presents stage variation with the central point of tool pad in different workpiece sections. A single shaft machine with numerical control function has been developed. Combining with the established model， the machine is used to control edge effect effectively. The scale coefficient k of Preston equation is worked out in the experiment firstly. The model is in good agreement with the actual experiment results， and the accuracy can reach to 91.9%. The edge effect control method with the CNC single shaft machine and the relative model are well in guiding the actual grinding and polishing process.

Abstract:Aiming at the fact that the existing ground surface topography modeling method was only effective for a certain type of parts， a modeling method suitable for the processing of space curved parts was proposed. Based on the grinding process principle， the homogeneous transformation matrix between the grinding wheel and the surface part was established， and the three-dimensional equation of the abrasive particles was obtained. By proposing a surface area approximation solution algorithm， a prediction model was established. Taking gears and bearing inner sleeves as examples ， the maximum errors obtained are 11.338% and 18.91%，which has verified the validity and scientificity of the prediction model proposed.

Abstract:Flower-like NiCo₂O₄ wave absorbing material was prepared by the co-precipitation method. The composition and structure of NiCo₂O₄ was characterized by XRD， FTIR， BET， XPS and SEM. The samples were synthesized under various calcination temperature （300，400，500，600，700 ℃）， and the wave-absorbing properties of the samples were calculated depend on vector network analyzer （VNA） by coaxial method with different thickness. The results show the NiCo₂O₄ calcinated at 400 ℃ exhibits superior electromagnetic wave attenuation performance in reflection loss value， absorption bandwidth and thickness of sample. The effective absorption bandwidth of flower-like NiCo₂O₄ is 4.48 GHz （12.08~16.56 GHz） at the thickness of 1.5 mm. Moreover， The minimum reflection loss of flower-like NiCo₂O₄ reach to -43.71 dB at the 14.32 GHz. Hence， it is evident that NiCo-based spinel oxide material is anticipated to possess a potential implication in the field of electromagnetic wave absorption.

Abstract:A 2，2-bis［N-（4-propargyloxyphenyl）-3，4-dimidophenyl］ hexafluoropropane （6FDPE） was synthesized and blended with （4，4’-diphenylmethane） bismaleimide（BDM） and diallyl bisphenol A（DABPA） modified bismaleimide （BD/DABPA） resin to prepare BD/DABPA/6FDPE blend resins. The viscosity-temperature behavior and cure reactions of the blend resins of the cured blend resin， and the thermal stability and mechanical property of the cured blend resins were studied. The results show that the processing window of BDM/DABPA/6FDPE resins are broader than 70 ℃. The thermal stability of the cured blend resin increases with increase of 6FDPE content. The temperature of 5% weight loss （） and residual yield at 800 ℃ （Y_r800℃） of the cured blend resin can increase to 416°C and 41%， respectively. The impact strength can increase by 55%， to 23.9 kJ/m². However， the glass transition temperature （T_g） of the cured BDM/DABPA resin decreases with increase of 6FDPE content in the blend resin. Accordingly， the bending strength and tensile strength of the cured blend resin drop by 13%， to 132 MPa and 78 MPa， respectively.

Abstract:C_f/C-ZrC-SiC composites were fabricated via reactive melt infiltration （RMI） with stitched carbon fiber preform and Si-Zr alloy as reactants. The microstructure of C_f/C-ZrC-SiC composites was analyzed by SEM-EDS and XRD. It can be concluded that SiC-ZrC ceramic matrix has uniform distribution in the C_f/C-ZrC-SiC composites. Benefiting from the above matrix microstructure， the bending strength and modulus of C_f/C-ZrC-SiC composites can reach up to 323.2 MPa and 46.6 GPa， respectively. The mass ablation rate and linear ablation rate of C_f/C-ZrC-SiC composites with high ZrC content are 1.263 mg/s and 2.367 μm/s， respectively； and 2.056 μm/s and 5.067 mg/s for C_f/C-SiC-ZrC composites with less ZrC content， respectively. C_f/C-ZrC-SiC composites show good ablation resistance.

Abstract:The prepare graphene oxide/polyhdral oligosilsesquioxanes （GO/POSS_C-I） composite was prepared by the in-situ method under acid and miscellaneous conditions. SEM， XRD and IR were performed to characterize morphologies and crystallizations of as-prepared material. The results show that considerable inorganic-organic hybrid POSS nano-material with shell-core structure is inserted into the surfaces of well dispersed lamllar GO. In the curing process of modified bismaleimide（BMI） resin， GO/POSS_C-I composite material is well dispersed in the matrix of resin to form homogeneous black cured compound resin. Results of DMA tests show that GO/POSS_C-I composite material has obvious restriction effect on the movement of organic carbon chains and improve the thermal stability of material.The optimum glass transition temperature is 27℃ higher than that of unmodified bismaleimide resin. Furthermore， the mechincal properties of composite are improved because of the crack passivation or pull-out effect of GO/POSS_C-I composite. The bending strength and modulus of modified BMI resin are incresed by 16.5% and 3.4% ，respectively.

Abstract:Liquid ceramic precursor was synthesized by boron trichloride and methyldichlorosilane as raw materials through the two-step reaction with hexamethyldisilazane and ammonia. The precursor was pyrolyzed and decarbonized in ammonia to produce SiBN ceramics. The ceramic yield and elemental composition of the precursor were easily regulated by changing the feeding ratio. The pyrolysis process of the precursor and the ceramic products obtained from different temperatures were characterized by NMR， FTIR， XRD， SEM and elemental analysis. The results show that the ceramization is completed at 900 ℃ under ammonia， and the boron content of the pyrolyzed product is more than 13 %（w）. The ceramic product， which is obtained at 1 400 ℃ nitrogen or air environment， remains amorphous and has high temperature and oxidation resistance.

Abstract:The high-density rib structure composite panel could be formed at one time by using the vacuum assisted resin infusion process （VARI）. However， there were issues in the molding process， such as the difficulty of preforming the fabrics at rib area and complex resin flow control. So it was difficult to guarantee the dimensional accuracy and internal defects of the part. Based on the structural characteristics of the multi-featured area of the high-density rib structure composite panel， the resin flow simulation and compaction test were implemented to optimize the preforming process parameters and the partitioned resin injection scheme. The results show that the compaction parameters of the agent concentration of 4%， temperature of 120 ℃， pressure of 0.1 MPa， and holding time of 60 min can effectively ensure the satisfied fiber volume fraction. Adopting a graded glue injection scheme that combines line injection， line riser， and rib point riser can effectively infiltrate the panel structure. The optimized process parameters and the partitioned resin injection scheme are successfully applied to the VARI forming of a high-density rib structure integral panel belonging to an aircraft. The effectiveness of the used analysis method is verified in this paper. The critical reference value for the use and development of low-cost integrated forming technology for rib structure composite panels in military and commercial aircraft is provided.

Abstract:In order to meet the requirements of light weight， high strength and near net forming of a complicated aerospace component， an isothermal superplastic forward and backward extrusion near net forming method based on thin-walled component of low-density Mg-Li alloy was proposed. The formability of as-cast and the mechanical properties of as-cast and as-rolled at different temperatures were studied. The results show that the elongation of as-cast is about 12%， and the tensile strength is about 145 MPa. The elongation of as-rolled has little change， but the tensile strength increases to more than 180 MPa. The elongation and tensile strength obtained by this method are significantly improved， reaching 21% and 216 MPa， respectively， which indicates that the grain refinement is realized in the process of high temperature and large deformation. While many reinforcement phases are dispersed in the grain， which plays the role of performance enhancement. The performance enhancement and precision forming of complicated structural parts are successful achieved.

Abstract:In order to solve the problems of high brittleness and poor adhesion of the existing thermal-protection coating for the inner wall of launch canister， silicone modified epoxy resin as the matrix， a variety of high-temperature resistant fillers and polyamide as the curing agent were used to prepare the thermal-protection coating. Its flame resistance， heat resistance， "three-proofings" and thermal aging performance had been fully characterized and analyzed. The results show that the coating can withstand a long-term high temperature of 200~300 ℃， ablation at 900 ℃ within 10 s， and its adhesion and "three-proofings" are superior.

Abstract:The high-temperature alloy Inconel 718 was a typical difficult-to-machine material. In this paper， DEFORM-3D software was used to carry out the simulation test of drilling high-temperature alloy Inconel 718 with uncoated， TiC single-coated and TiC/Al2O3 composite coated carbide tools. The cutting performances of composite coating tools under different drilling conditions were researched and were verified by drilling experiments. The results show that the TiC/Al₂O₃ composite coating tool can effectively reduce the drilling axial force and the drilling temperature， the maximum reduction of the axial force is 20%， and the maximum reduction of the drilling temperature is 35%. The accuracy of the simulation model is verified by drilling experiments， and a certain reference for the selection of coating types and drilling parameters in the actual drilling of high-temperature nickel-based alloy Inconel 718 is provided.

Abstract:Utilizing different material properties of thermal cured epoxy matrix before and after the glass transition temperature （T_g）， Kevlar29 aramid fabric/E51 epoxy resin based composites and three inflatable unfolded support booms were prepared. The fabrication process was illustrated， electrical resistant wire was used to control temperature of thermal cured matrix， and an enclosed Kapton membrane was used for inflatable pressurization to control the final shape of booms. The folding and unfolding characteristics of the support were investigated. The boom was curled and folded when T>T_g and then cooled and shaped for storage， and the unfolding process was controlled by secondary heating T>T_g and inflatable pressurization method， and the final support tube shape recovery rate was 100%. Modal analysis was used to discuss the effect of parameters such as temperature， resin content， fabric layup thickness and internal pressure of inflation on the natural frequencies of the support boom under cantilever condition. The results show that the natural frequencies of the support tube of the aramid fabric reinforced epoxy resin increase as the inflation pressure increases， the resin content increases， the fabric layup thickness increases， and the substrate temperature decreases. A curve fitting method is used to obtain the variation law of the natural frequencies with the inflation pressure and temperature， and the results can provide reference for the design of the inflatable unfolded support boom.

Abstract:In order to solve the problems of unknown bandsaw blade wear state and the deterioration of sawing quality in sawing process， the sawing behavior change of FTCUT bimetallic bandsaw blade during sawing of 42CrMoA alloy structure steel was studied and the relationship between acoustic emission signal and the single-blade sawing process， saw teeth wear and sawing surface quality change was discussed. The results indicate that with the change of sawing depth， the number of saw teeth increases first and then decreases and the constraints of the bandsaw change constantly， which affects the acoustic emission signal amplitude and sawing surface quality. Based on the time domain analysis， the saw teeth wear process can be divided into three stages： run-in wear， fast wear and stable wear. Based on the FFT frequency domain analysis， it is found that when there are multiple dominant frequencies in the spectrum diagram and the amplitude of the first dominant frequency decreases， the acoustic emission signal sources are scattered， and the bandsaw blade failure can be determined. Based on the analysis of wavelet packet frequency domain， it is found that the 7^th frequency band signal has the highest proportion and can reflect the change of workpiece surface quality.A certain relationship can be established between the fluctuation and micro grain and ripple of the sawing surface. Therefore， the saw teeth wear and sawing surface deterioration can be analyzed and judged based on acoustic emission signal in time domain and frequency domain.A certain idea for online monitoring of saw teeth wear and sawing surface quality is provided.

Abstract:In order to explore the influence of different outlet pressure difference and feeding speed on the expansion effect of carbon fiber bundles in the air spreading process， an air spreading platform was established according to Venturi principle. The process of carbon fiber broadening was recorded， and the ratio and uniformity of carbon fiber broadening at different stages were calculated under different technological parameters. The results show that the carbon fiber bundles with a broadening rate of more than 400% and a broadening uniformity of more than 90% can be obtained by the air flow spreading test platform.The expansion rate of the carbon fiber bundle is positively correlated with the outlet pressure difference and negatively correlated with the feeding speed. The evenness of the expansion of the carbon fiber bundle is negatively correlated with the outlet pressure difference and positively correlated with the wire feeding speed.