Abstract:The characteristics of silica aerogel skeleton reinforced modifications are described in detail.Research progress and future development trend of reinforced skeleton of silica aerogel by co-precursor,chemical additive,aging,surface modification and heat treatment technique are described.The aim of this paper is to provide theoretical bases and methods for designing and optimizing the microstructure and properties of silica aerogel.

Abstract:Out of autoclave process (OoA) technology is an effective way to achieve low cost manufacturing of structural composites and one of the hotspots in the field of composite materials research.The research frontiers and applications of OoA composites in aerospace field at domestic and overseas are introduced and the defect control methods in OoA forming process are summarized from two aspects of material system and forming process.In the process of OoA preprepreg forming,the void fraction of composites can be effectively reduced by minimizing the volatile content in the resin, fine controlling the reaction and rheological properties of the resin,controlling the infiltration degree of fibers and resins in the prepreg and optimizing the forming process.

Abstract:Under high temperature heating condition,calculation result of the temperature profile of the the polytetrafluoroethylene was effect by the dynamic ablation pyrolysis greatly.To improve the computing precision of the temprature profile,the method for computing the ablation temperature field for polytetrafluoroethylene has been set up,which has been tested by the thermal response charactericstic of the polytetrafluoroethylene under arc heater high temperature environment.By comparing the theoretical and the experimental results under arc heater high temperature environment,the results show that the temperature increases with the time passes during 230 ℃ to 323 ℃ temperature rising zone. The theoretical result changes in the same tendency with the experimental result.During 323 ℃ to 680 ℃ temperature rising zone,the temperature of experiment increases with the time passes.When the theoretical temperature is fixed,the theoretical result deviates from the experimental result.During 680 ℃ to 390 ℃ temperature reducing zone,the temperature of experiment decreases with the time passes.The theoretical temperature is higher than that of the experimental result. It is associated with the computing deviation of the ablative data.By using ablation temperature computing method, it can simulate the thermal response characteristics of the polytetrafluoroethylene under the arc heater high temperature environment effectively.It can provide reference for the design of products.

Abstract:Based on genetic optimization algorithm,the diffusion bonding process of T2 copper was studied. Used orthogonal test method and combined with back propagation（BP） neural network and multi-objective genetic algorithm,the temperature,pressure and holding time of the diffusion bonding are taken as input variables and the bonding rate and deformation of the sample were taken as output variables after diffusion bonding.The process parameters of diffusion bonding were optimized,and the corresponding diffusion bonding verification test was carried out.The results show that the appropriate diffusion bonding process parameters of T2 copper are:the temperature is 780 ℃,the pressure is 7.5 MPa and the holding time is 120 min. Under this condition,the bonding rate can reach 95.26% and the deformation is 0.166 mm.The above-mentioned process parameters are used to manufacture the parts of the microchannel heat exchanger,and the deformation in the thickness direction is 0.162 mm.After ultrasonic C-scanning,the bonding condition is good, and the sealing and design requirements are satisfied after the pressure-proof and leak-proof detection.

Abstract:In order to explore the microscopic cutting mechanism of carbon fiber reinforcement plastics (CFRP),the zero thickness cohesive element was used to simulate the interface phase by finite element method.The carbon fibers were cylindrical and randomly distributed in the matrix to reflect the microstructure of CFRP.Different constitutive rules,material failure and evolution criteria were set up for each constituent phase.Four typical orientation (0°,45°,90° and 135°) were simulated to investigate the microscopic cutting mechanism of unidirectional carbon fiber reinforced plastics (UD-CFRP) under different fiber orientation.The results show that the microcosmic damage of CFRP is different at different fiber orientation.Interfacial cracking and fiber breakage are the main failure modes in cutting 0°CFRP,tool invasion is the main failure mode in cutting 45°and 90°CFRP,fiber breakage and cracks along fiber direction occur in cutting 135° CFRP,fiber breakage point is below the edge of the tool. Finally,the accuracy of the microscopic model is verified by experiments.

Abstract:A two-dimensional cutting simulation model of high speed high temperature alloy GH4169 was established by using ABAQUS finite element analysis software,and the cutting process was simulated.The stress change and distribution in the cutting process,the effects of cutting speed and cutting depth on stress distribution,residual deformation and cutting force at cutting end were obtained.The results show that the maximum equivalent stress of the first deformation zone varies little in different cutting stages of the cutting process.The cutting speed has little influence on the stress distribution at the cutting end of the workpiece.The larger stress distribution area increases obviously with the increase of cutting depth.Plastic extension deformation will be formed at the cutting end of the workpiece after the cutter cut out of the workpiece.When the cutting speed is low,the plastic extension length is large,while when the cutting speed is high,it is small.The plastic extension length increases with the increase of cutting depth.The cutting force F_x increases with the increase of cutting speed and depth.The cutting force F_y increases with the increase of cutting depth,but cutting speed has little effect on F_y.The effect of cutting depth on F_x is greater than cutting speed.

Abstract:The insulating tile reinforcement was fabricated using mullite fiber,basalt fiber as main components and silica sol as binder.And insulating tiles/SiO₂ aerogels composite was prepared by infiltrating the silica sols into the insulating tiles via vacuum infiltration,followed by gelation,aging and supercirtical drying.The microstructure, thermal stability,and insulating properties of the composite were characterized and measured.The results show that with the increasing of the content of basalt fiber of the insulating tiles,the room-temperature thermal conductivitie decreased from 63 mW/(m•K) to 47 mW/(m•K),and the cold-face temperature dropped from 200 ℃ to 117 ℃ in the back-temperature tests heated at 600 ℃ for 15 min,due to the thinner diameter and infrared radiation containing materials of basalt fiber.However the linear shrinkage increased thus the thermal stability of the composition weakened,due to the remarkably low thermal stability of basalt fiber.

Abstract:In order to acquire the ablation properties of carbon/quartz composites,the ablation experiment was carried out under the condition of different stagnation pressures,different heat flux and different total enthalpy using the arcing heater and carbon/quartz flat head stagnation model in this paper.Based on the experimental data, the mathematical model between mass ablation rate and the three major factors,namely heat flux,stagnation pressure and total enthalpy is established by using multiple regression analysis method,and the rationality of the model was tested. The results show that the established three-parameter mathematical model has a good fitting degree to the experimental data,and the heat flux is the most relative parameter.Compared with the single-parameter and two-parameter mathematical models,the three-parameter mathematical model has a better fitting effect on the experimental data and can better reflect the ablation properties of the carbon/quartz heat-resistant composites.

Abstract:Basis on the surface morphology of carbon fiber and viscosity characteristicstwo epoxy resin,the appropriate curing pressures have been defined.The expansion pressure design and curing process parameters was compared between the two epoxy resin with different viscosity.The results demonstrate that the epoxy resin with high viscosity has an obviously optimized manufacturability and shorten the curing cycle by 13.6%.The gel pressure design temperature（135±5） ℃ can guarantee the internal quality of the product，the curing temperature（170±5） ℃ reduces the risk of product deformation.The defect proportion of composites supporting beams can be controlled below 0.5%,implemented the quality requirement for aerospace structure composites.

Abstract:Conventional chopped fiber reinforced insulations have poor lateral properties,low interlaminar shear strength,and insufficient impact resistance.We prepared several fabric reinforced ethylene-propylene-diene monomer（EPDM） insulations.The effects of methods of fiber surface modification on the adhesion properties between EPDM and fabrics including polyimide (PI),aramid (F-12) and carbon fiber (CF) was investigated.We choose preferred fiber treatment methods to modify the fabrics and fabricate several fabric reinforced EPDM insulations.The mechanical properties and ablation resistance of the insulations were characterized by tensile strength,elongation at break and linear ablation.The results show that the tensile strength of the insulations are all above 30 MPa,and the ablation resistance is excellent. Under the three fabric-specific woven structures,PI/EPDM has lower ablation rate,the most complete carbon layer retention,so PI/EPDM is expected to be used in high-performance solid rocket motors.

Abstract:The coating process of white inorganic coating on aluminum honeycomb sandwich plate in satellite structure was investigated.The effects of grinding process on strength of structural board and adhesion of coating were investigated.And the effects of curing at lower temperature on the appearance,thickness and thermal radiation properties of the coating were studied.The results show that the cross grinding of 80^# sandpaper for 2 to 3 times can satisfy the adhesion of inorganic coating on the surface of structural board,and there are no effects on the strength of 0.3 mm thick skin structural board.The strength index still meet the strength requirement of thin-walled honeycomb sandwich.There are no obvious changes in the strength of structural board before and after grinding.The curing process of 85 ℃/12 h can meet the requirements of appearance,thickness and thermal radiation properties of the coating.

Abstract:A innovative technique named acid zinc dipping method was developed and applied to the pre-treatment process for electroplating on titanium alloy.The surface was activated and the problem of poor bonding strength at the interface was solved.For optimal performance of the metal coating,the effect of P contcent on bonding strength of electroless nickel coating was further investigated.After improved pre-treatment method and optimal process,electroless nickel,silver,gold coatings with high bonding strength were prepared respectively on the surface of TC4 and TA1 titanium alloys.The bonding strength of coatings was characterized by thermal shock test and cross cut test.The microstructure of coating was characterized by scanning electron microscopy(SEM)，energy dispersive spectroscopy(EDS),3D microscopy and metallographic examination.Moreover,electrochemical property,conductivity and thermal radiation performance of coatings were also measured.Results show that through employing acid zinc dipping pretreatment method and adding medium phosphorus electroless nickel coating as bottom layer,the bonding strength,corrosion resistance,conductivity and thermal control performance of coating are significantly improved.The corrosion potential of electroless nickel coating increases by 60 mV compared to that of titanium alloy substrate,and increases by 600 mV in case of gold coating.

Abstract:In order to solve the problem of low precision of the reflector profile,the optimal splicing process was obtained by theoretical analysis of the honeycomb splicing process of the reflector,and the process was tested and verified.The results show that the number of hexagonal honeycomb core splicing is generally 3 or 6 times,which is beneficial to symmetrical honeycomb structure,lattice regularly and reduction of the uneven distribution of in-plane stiffness,and improvement of the surface accuracy of reflector.J-310A film can be used as the first choice for the honeycomb splicing adhesive of high-precision reflector because of its convenient construction,the thin thickness after curing,which can greatly reduces the effects of expansion mismatch and sudden change of stiffness of different materials and be beneficial to improve the accuracy of the reflector profile.The pre-pressurization of the fixed clamp and the co-curing with the reflector can be used as the current optimal splicing process.The method is simple and low-cost.The 1.8 m diameter reflector prepared by the improved honeycomb splicing process has a profile accuracy of RMS=53 μm,which is 25 μm higher than the traditional process and meets the design requirements.The experimental results show that the reasonable splicing method of honeycomb can effectively avoid the influence of foam rubber and honeycomb expansion mismatch,reduce the influence of the agglomerate adhesive and honeycomb stiffness abrupt change,improve the symmetry of honeycomb structure and the accuracy of reflector profile greatly.The use of this process to splicing honeycombs can also effectively reduce the amount of glue used and reduce the structural quality of the product.

Abstract:Impregnated poly-p-phenylenebenzobisthiazole（PBO） multifilament was manufactured by soaking resin preparation and sample design.Chemical properties of PBO fiber and soaking resin were characterized by X-ray photoelectron spectroscopy (XPS).Differential scanning calorimeter (DSC) was used to analyze curing reaction and kinetics of soaking resin.Dynamic mechanical analysis (DMA) was chosen to characterize resin thermostability. PBO surface and multifilament fracture were observed by scanning electron microscopy (SEM).In addition,casting analysis was used to characterize mechanical properties of soaking resin,and the reliability of multifilament was also indicated by tensile analysis.The results show that the soaking resin is a high matching recipe with uniform infiltration and long storage life for PBO multifilament,which has firm tip reinforcement and short preparation period. The tensile data of multifilament has low volatility,and strength dispersion is under 3%.This would not only improve the reliability and stability of mechanical test,but also increase the efficiency of sample preparation.

Abstract:C/SiC composite material bolt was a kind of important fastener that applied in hypersonic vehicles widely.However,the mechanical properties of this material had a relatively large amount of scatter while the distribution pattern still remained in blurry, resulting in significant difficulty in material selection and structure design.In this paper,tensile strength testing experiments were conducted using three kinds of C/SiC composite material bolts (M8,M10,M12) on an electronic-controlled universal testing machine.The probability distribution pattern of tensile strength was obtained.The two-parameter Weibull distribution model was fitted based on the statistical data,and the Kolmogorov-Smirnove test was conducted.The results indicate that the tensile strength distribution of C/SiC composite material bolts accords with the Weibull distribution model,with a characteristic strength β 212 MPa and a shape parameter α 9.45.Moreover,the allowable strength design can be realized based on the present Weibull distribution.

Abstract:The cross section morphology and metallographic structure in the weld zone of the 2024-T351 aluminum alloy friction stir lap welded joint was observed by experiment.It indictated that there are asymmetric hook-shaped defects on both the advancing side and the retreating side of the friction stir lap welded joint.Friction stir lap welded joints were tested under constant-amplitude fatigue loading on MTS test frame to obtain the S-N curve of nominal stress amplitude.The elastic-plastic finite element model of lap joints was established according to the test.Using the SWT fatigue damage equation and cyclic stress strain data of stress concentration region from finite element analysis,the fatigue lives of lap joints were predicted,and further compared with the experimental results. The results show that the prediction results for the low-cycle fatigue lifetime of friction stir lap joints by the SWT fatigue damage formula are close to the experimental results,and the errors are all within 2 factors,while large error is in the prediction results for the high-cycle fatigue lifetime.At the same time,it shows that the stress concentration of lap joints has greater influence on the fatigue lifetime than the effective thickness.

Abstract:Using the penetrating voltage and the higher level of exposure could enhance the contrast of the image,thereby the sensitivity of radio graphic inspection was improved.But in order to achieve the high efficiency inspection of the variable cross-section objects,the method with the penetrating voltage and the lower level of exposure called latitude camera was normally used,which decreased the sensitivity of inspection.For demonstrating the changing of the sensitivity between those two methods,theoretical analysis of the interaction between trans-illumination voltage and current had been considered.In addition,a latitude camera sensitivity analysis model of aluminum product was designed.Then the data from the model was analyzed to describe the trend of inspection sensitivity in a latitude camera mode.So in theory,the latitude photography mode has considerable inspection sensitivity;and in practice,the changing law of model sensitivity is verified.When the penetrating voltage increases 40%,the inspection sensitivity still meets the relevant standards.As a result,the latitude camera has reliable inspection sensitivity.

Abstract:In order to study the formation cause of abnormal bright spots on the surface of 1420 Al-Li alloy bottom cover plate for aerospace applications,the abnormal traces were analyzed by means of microstructure analysis,fracture morphology observation,energy dispersion spectrum analysis,micro-hardness test and chemical composition analysis.The results show that the abnormal traces on the surface of the bottom cover plate are bright crystalline defects which penetrate through the whole plate.The microstructure and composition of the traces are abnormal.Considering the production process of the bottom cover plate,the bright crystalline defects are formed during the melting of 1420 aluminum-lithium alloy ingots,which are metallurgical defects.Due to the poor quality of the film layer in the defect section,the bright spots are formed during the process of phosphoric acid anodizing.

Abstract:In order to study the one-shot welding of multiple brazing seams in different parts of the injector,an experimental study on the vacuum brazing process of the injector by using BNi-2 solder was carried out.The effects of surface cleaness, brazing temperature and brazing gap on the sealing performance of the injector were analyzed.The results show that the gaps between brazing seams have an important influence on the sealing performance of the brazed joints of the injection body composed of high temperature alloy and stainless steel.A reasonable brazing seam assembly gap is 10 to 15 μm,and this gap makes the filling rate of the brazing seam more than 90%,and obtains a joint with excellent internal and external quality and sealing property is obtained.