Abstract:Boronmullite ceramics in Al-B-O system such as Al ₅BO ₉and Al ₄B ₂O ₉ have superior properties,including low density,low thermal conductivity and wide band gap.They are promisingthe in applications including thermal protection,wave transparent and thermal sealing in hypersonic vehicles.In this paper, recent progress on structure,synthesis and properties of compounds in Al-B-O system were reviewed.Theoretically,first-principles calculation based on density functional theory(DFT) is introduced to predict the crystal structure,elastic and thermal properties of these materials.Experimentally,synthesis methods such as solid-phase reaction,high-temperature molten-salt method,sol-gel method and thermal decomposition method are summarized.The applications and perspective of these materials are also discussed.

Abstract:In order to study the temperature field of the mold for forming composite material components,this article takes the autoclave curing process of a certain type of aircraft wall as an example.Through model simplification,a numerical simulation model of the mold temperature field is established by using simulation software such as FLUENT,and the simulation data and experiments are used for comparison.The results show that the average relative error is 7.4%.In addition,a set of examples with the thickness of the support plate as a variable and two control groups with the thickness of the support plate in the U and V directions were simulated.By judgment the surface temperature variance of the mold plate,the effect law of the thickness of the support on the influence of mold temperature field distribution plate was studied.The results show that the uniformity of the mold temperature field gradually decreases with the increasing of the thickness of the support plate,and the change of the thickness of the support plate in U direction has a greater effect on the uniformity of the temperature field than that in the V direction.

Abstract:Carbon fiber reinforced polymers(CFRP) have the characteristics of low interlayer bonding strength and anisotropy and interlaminar damage,are easily generated during the cutting process.In order to study the interlaminar stress and interlaminar damage during the milling process of CFRP,a three-dimensional milling simulation model of composite materials was established.Equivalent homogeneous modeling was adopted in the structure.The three-dimensional Hashin initial failure criterion and damage evolution model were established by using VUMAT subroutine for the intralaminar element.The layers were connected by cohesive element to simulate the generation and expansion of interlaminar damage.The accuracy of the simulation model was verified by comparing the simulation and experimental cutting force values.The model was used to analyze the variation of cutting force,interlaminar stress and interlaminar damage with fiber orientation angle (0°,45°,90° and 135°).The results show that the machining damage during milling is mainly concentrated near the surface of the workpiece.Milling force,interlaminar stress and interlaminar damage are effected by fiber orientation angle.When the fiber orientation angle is 90°and 135°,the axial milling force is larger.The interlaminar stress and interlaminar damage increase with the increase of the fiber orientation angle.When the fiber orientation angle is 135°,the interlaminar stress is the largest,and the interlaminar damage is the most serious.

Abstract:In order to evaluate the effect of fiber direction deviation on the performance of composite propeller blades,a solid finite elements model was established based on the results of the draping simulation with Fibersim software.The FEM analysis results considering fiber direction deviation was compared with the results ignoring fiber direction deviation.The results show that the errors of natural frequencies and maximum deformation under uniformly distributed pressure are less than 5% while ignoring fiber direction deviation.But the maximum deformation under distributed temperature field of considering fiber direction deviation is about 2 times of that of ignoring it.Fiber direction deviations of the 0°,45°,and -45° plies exceed 25° in partial area of the blade.The FEM analysis of composite propeller blades should be based on the true fiber direction after draping.

Abstract:In order to solve the fracture of single point incremental forming parts due to uneven thining,the static pressure support was introduced into the forming process.Firstly,the mechanism of static pressure support-single point incremental forming was analyzed and the parts were divided into regions according to the degree of thining.Then,the law of thining rate change in different regions under different static pressure conditions was studied by simulation.Finally,the static pressure support-single point incremental forming experimental platform was built to verify the simulation results.The results show that the thining rate of region II increases along the node path and reaches the maximum at 37.5 mm away from the edge of the sheet metal.With the increase of the forming depth,the thining rate decreases slightly in the middle of region II and increases again near the bottom.The thining rate decreases with the increase of static pressure parameters,and the error between experimental results and simulation results is less than 5%.Compared with single point incremental forming,this technology can improve and control the uniformity of the thickness of parts effectively,delay or avoid the fracture of parts.

Abstract:A new kind of epoxy resin used in prepreg was preprared by taking dicyandiamide as the curing agent,UR500 as the accelerator and M as the flame retardant.The room temperature storage of the resin was more than 30 days and the resin exhibited excellent mechanical properties.The tensile,flexural and impact strength are 66.5 MPa,133 MPa and 10.7 kJ/m².V-0 level is reached during the UL-94 vertical combustion and the limiting oxygen index(LOI) is 33.6%.The results reveal that the resin exhibits self-extinguish properties away from the fire due to the more dense carbon layer after burning by scanning electron microscope and thermogravimetric analysis.

Abstract:Resin transfer moulding(RTM) technology can be used to realize high surface quality and net size moulding of composite force-bearing components.Composite skirt of solid rocket motor case was prepared by RTM process using formula A that resin is as matrix and 3K satin carbon cloth as reinforcement material.The RTM process characteristics of A formula and the properties of resin castable were analyzed,the injection mould and equipment for composite skirt were introduced,the RTM process parameters and the properties of composite skirt materials were discussed.The results show that the fiber volume fraction of composite skirt reached 54.5%.Under combined load（axial compression +bending moment），the axial compression reaches 748 kN and the bending moment reaches 94N·m, pure axial compression load reaches 1 062 kN,pure bending moment load reaches 143.1 N·m.High strength of shell composite skirt meets the design and application repuirements.

Abstract:Silver nanowires（AgNWs）were prepared by atmospheric drip route and hermetic-solvothermal route respectively to enhance the aspect ratio of classic polyol method products. The effects of reaction time，reaction atmosphere and reactant feed ratio on the yield and aspect ratios of AgNWs were discussed in detail. The AgNWs growth process was more eco-friendly and less disturbances in hermetic-solvothermal route.The AgNWs products show that an average diameter of approach 55 nm and length of about 65 μm and a high aspect ratio of about 1 200. The transparent conductive film fabricated by hermetic-solvothermal AgNWs exhibit sheet resistance of 6 Ω at 78.6% transmission of 550 nm and a factor of merit（FOM） of 246,better than that of atmospheric drip route.

Abstract:In order to improve the damping properties of silicone rubber at high temperature,a silicon intermediate with high phenyl content is added to the silicone rubber and co-vulcanized with silicone rubber using 2,4-dichloroperoxybenzoyl(DCLBP) as vulcanizing agent.Silicone rubber were characterized by the rotorless vulcanizer,SEM,DMA and TG.The results show that with the increasmet of the amount of phenyl silicon intermediate, the degree of vulcanization of silicone rubber,the hardness and tensile strength decrease, while the elongation at break,tear strength and loss factor tanδ at high temperature are significantly improved.When the using amount is 15 parts,the tensile strength of the silicone rubber is 7.75 MPa, and tanδ_max increases from 0.2 to 0.3.

Abstract:The 2219 aluminum alloy with 4 mm thickness,which was used in the launch vehicle's booster tank widely,was taken as the research object.The floating bobbin tool was developed,and the internal plastic metal flow pattern had been analyzed.The matching welding heat input of the weld seam with high quality could be obtained.The process exploration and optimization test results verified the plastic metal flow pattern inside the weld and the process speculation directly.The results of macroscopic morphology analysis of the joints show that the onion ring characteristics can be observed in the macroscopic morphology of the weld cross section at different welding speeds, and the onion ring characteristics increase with the welding speed increasing.This phenomenon validats the design idea of the bobbin use for the thin-plate aluminum alloy effectively.The microhardness distribution of the cross-section of FSWed thin plate aluminum alloy is U-shaped,and the lowest point of the microhardness of the joint is located at the junction of the weld nugget zone and the RS thermo-mechanical affected zone.The mechanical properties test results show that the tensile strength of the joint increased gradually with the welding speed increasing,and the tensile strength of the joint reach the highest value when the welding speed reachs 350 mm/mim.The floating bobbin FSWed aluminum alloy joints has a high elongation,and the welding speed has little effect on it.The floating bobbin FSWed joints can achieve 180° without cracks in both front and back bending tests.Based on the vertical longitudinal seam friction stir welding system,the floating bobbin friction stir welding of 2 m long test piece is realized successfully.The cumulative weld length reachs 60 m and the floating bobbin tool is intact with no cracks,distortion or other damage.

Abstract:In the process of disc milling grooving in blisk,the milling force is large and the milling temperature is high,these factors will form a deep residual stress layer on the machined surface,which will seriously affect the fatigue life of the parts.In order to improve the fatigue life of parts,based on the titanium alloy block as the research object,the surface residual stress is measured by the residual stress test analysis system,and the subsurface residual stress is studied using the dial layer method.The linear regression technique is adopted to establish the prediction model of residual stress,and the range analysis method is used to analyze the influence law of process parameters on the residual stress.The test results show that the residual compressive stress are generated on the machined surface caused by extrusion effect,and the residual stress on hub surface is greater than that on the convex/concave surface. The significance level of the regression prediction model is 0.01,and the regression effect is good.The influence degree of each factor on σ_Ax 、σ_Ay （σ_Ax 、σ_Ay represent residual stress in x and y directions of hub surface respectively) is spindle speed＞feed speed＞depth of cut (DOC) respectively.The influence degree of each factor on σBx (σBx refers to residual stress in the x direction on the convex/concave surface) is in turn spindle speed＞DOC＞feed speed respectively.The longitudinal residual stress is compressive stress,the distribution depth on the hub surface is 230 to 270 μm,and the distribution depth on the convex/concave surface is 170 to 175 μm.

Abstract:The big exit burr would be formed after the common drilling (CD) process of titanium alloys (Ti6Al4V) using a traditional twist drill,which would lead to the difficulty in deburring operations and has a negative influence on assembly quality of fastener.In this paper,a novel tool of 8-facet drill was introduced and the ultrasonic vibration drilling (UVD) technology was employed so as to perform the basic theory and experiment study of exit burr formation in ultrasonic vibration drilling titanium alloys using 8-facet drill.The exit burr formation process of CD and UVD as well as the exit burr reduction mechanism of UVD were analyzed by theoretical method, meanwhile the exit burr reduction effects of UVD were verified by experimental method.The results indicate that compared with the CD of Ti6Al4V,in the UVD process,the cutting ability of drill bit tool is greatly enhanced.The thrust force,cutting temperature and exit burr height decrease by 16% to 20%,18% to 21% and 82% to 89% respectively,as well as the trouble and cost of deburring operations in assembly process will be effectively reduced.

Abstract:In order to detect the inner surface defects of the pressurized conveying pipeline of rocket and improve the quality of the pipeline,investigation on the application of endoscope technology in the inner surface of the rocket pipeline was carried out.In this paper,the technical characteristics of the endoscope equipment and the selection of the equipment probe and the technological methods of the size measurement and to calibrate the dimension of defects are introduced.The types of the detected inner surface defects were classified and summarized.Electron microscope and the metallographic techniques were used to analysis defects that are difficult to be identified.The results show that when video endoscope inspection technology was used to inspect the inner surface of the rocket pipeline,the probe with a larger diameter should be preferentially selected according to the inner diameter size of the pressurized pipeline.By using the defect comparison method of the measurement calibration,the results are more accurate with strong on-site detection applicability.The image of the defect by endoscope display technology is clear and stable,and the types of the defect in the inner surface can be correctly identified.Finally,the effect of the detection can meet the processing requirements.

Abstract:Temperature field is an important process index of multi-material cocuring of composite material case.Thermocouples were pre-implanted in order to acquire temperature data during the two different curing cycles,named 1 ^# curing cycle and 2 ^# curing cycle.The curing degrees and properties for F-3/EP-04 winding layers and ethylene-propylene-diene monomer(EPDM) insulation were investigated under the cocuring conditions.The results showed that the internal temperature existed obvious hysteresis phenomena,and the curves of temperature-curing time displayed parabola shape approximately.Under the 1 ^# curing cycle condition,the winding layers could be cured completely,but EPDM insulation could not.By contrast,the winding layers and the EPDM insulation could be cured completely with no mechanical decrease under the 2 ^# curing cycle condition because of the highest curing temperature increase and the holding time extension.Temperature gradient was very small for EPDM insulation,but big in the composite winding layers,which could be lowered through enhancing cocuring temperature and holding cocuring times.

Abstract:The friction stir welding test was performed on the 2219C10S aluminum alloy.It was found that there was abnormal aggregation of aggregates in the weld.The aggregated phase was shown as bright white aggregates on X-ray inspection.The main forms were divided into clumps,lines and fingers,and the mechanical properties of the welds in the aggregate phase were basically the same as those of the welds without the aggregate phase.The distribution position of each form of aggregated phase is different depending on the area affected by the welding of the mixing head.The agglomerate aggregate phase mainly existed at the center of the weld or the upper surface of the weld,and the linear and finger-like aggregates mainly existed in the weld center or the position of the weld root.The energy spectrum analysis of the abnormal aggregate phase shows that the main constituent elements of the aggregate phase are Al and Cu,and the atomic percentage is approximately 2∶1.It is determined that the main component of the aggregate phase is Al₂Cu.Analyzing the causes of the aggregate phase,the generation of aggregate phase is mainly affected by the welding heat input and the mechanical agitation of the mixing head.During the welding process,Al₂Cu in the plastic softened metal shows aggregation behavior in the process of filling the cavity behind the stirring needle,solidification with metal,aggregation behavior begins to slow down and ends.