Abstract:Ultrahigh-temperature high entropy ceramics are composed of refractory metal carbides， borides and nitrides， which exhibit high hardness， high temperature strength and good thermal stability. Ultrahigh-temperature high entropy ceramics become one of the hot research directions in the field of ultrahigh temperature ceramics. Compared with traditional materials， ultrahigh-temperature high entropy ceramics involve complex component space， multiple scale dimensions and extreme multi-field coupling service environment. The efficiency of developing ultrahigh-temperature high entropy ceramics by traditional trial and error method is poor. Therefore， it is necessary to change the material research paradigm and improve the developing and application efficiency of ultrahigh-temperature high entropy ceramics by relying on multi-scale simulation calculation method. The representative multi-scale material calculation methods is briefly introduced， and the typical application achievement of multi-scale materials calculation methods in the research of ultrahigh-temperature high entropy ceramics are summerized. Finally， the prospect of multi-scale material calculation methods in the research of ultrahigh temperature high entropy ceramics is prospected.

Abstract:Aerogel materials have unique nano-scale holes and nano-particle skeleton structure， extremely low density and thermal conductivity， which can save space and weight resources of spacecraft. It is the optimal thermal insulation material in the field of space exploration under extreme low and high temperature environment （-230~1 800 ℃）. In this paper， the application progress of aerogel materials in the fields of device heat insulation， space power supply insulation， cryogenic storage box insulation and interstellar spacesuits in spacecraft at home and abroad is reviewed in detail， and the future development of aerogel in space exploration is prospected.

Abstract:The historical development of aromatic polyamide fiber at home and abroad is briefly introduced. The excellent thermo-mechanical properties， stability， and electrical insulation are summarized，and then the potential application in military and civil fields is classified and outlined. After that， the application of aromatic polyamide fiber and its composites in honeycomb materials， pressure bottles， aircraft tires， engines， and other aerospace fields are systematically elaborated. The analysis above can be concluded that China is facing the demand for high-performance and high productivity in developing aromatic polyamide fiber.

Abstract:The precursor impregnation pyrolysis process （PIP） was a near-net-shape preparation method for SiC/SiC composites， but the stress generated during the precursor pyrolysis process hindered the industrialization of the process. In this study， a chemical-mechanical couple model was proposed to study the mechanism of process stress and simulate the stress evolution during pyrolysis. The pyrolysis process of precursor was described by a kinetic model. An analytical model derived from the three-phase sphere model was developed to determine the homogenized properties and behavior of matrix. A finite element model integrating the kinetic model and the analytical model was established to compute the process stress of a microscale representative volume cell （RVC）. The results show that the matrix sustains significant tensile circumferential stress at the interface of matrix-poor area. For the matrix composed by pure precursor， the evolution of the process stress is dominated by the chemical shrink due to the pyrolysis process and slightly influenced by the thermal expansion due to the process temperature. With the increasing of PIP cycle numbers， the roles of chemical shrink and of thermal expansion inverse.

Abstract:XM23 glue was widely used in aerospace optical remote sensors for bonding optical lenses and metal structural parts， which could play a shock absorption role. At present， the research of the mechanical properties of XM23 glue was based on linear elastic theory. However， XM23 glue was a high polymer and exhibited nonlinear characteristics， which could not be accurately characterized by Young''s modulus and Poisson''s ratio of linear elastic materials. In this paper， the stress-strain data of XM23 glue was first tested by the uniaxial tensile test of XM23 glue. Based on the theory of hyperelasticity， three kinds of hyperelastic constitutive models were tried to fit the data. The analysis shows that the Mooney-Rivlin 3 parameter constitutive model is the most suitable for characterizing the mechanical properties of XM23 glue. In the constitutive model， the material parameters is -0.205 9 MPa， is 0.688 8 MPa and is 0.055 7 MPa. Using this constitutive model， the uniaxial tensile test of the adhesive is simulated with finite element software， and the simulated stress and strain data are consistent with the test data within the error range. The construction of hyperelastic constitutive model of XM23 glue provides theoretical and data support for the finite element simulation of XM23 glue bonded structures.

Abstract:In this paper， the subsidence deformation processing of the thin-walled TC2 alloy profile was studied by thermal tensile tests and computer simulations. First， the hot tensile deformation behavior of the TC2 alloy profile was analyzed in the temperature range from room temperature to 600 ℃. Then， Johnson-Cook constitutive model was used to describe the hot tensile deformation behavior. Through computer simulations， the distributions of stress and stress triaxiality during subsidence deformation were analyzed. The results show that stress concentration is easy to occur at the corner of L in the subsidence area， and it is tensile stress due to the stress triaxial R_d＞0 of the area before deformation. With the increasing deformation， the crack extends in lengthwise direction of the profile. By optimizing the forming temperature， the length of the subsidence area and the transition radius， the best subsidence deformation processing parameters for the TC2 alloy profile are deformation temperature is 300 ℃， length of subsidence deformation zone is 21 mm， interim fillet radius is 49 mm.

Abstract:Silicone rubber-based radiant thermal protection coating was prepared by MoSi₂-YSZ filler and characterized with ablation resistance and thermal shock resistance. Compared with traditional ablation coating， the high-emissivity coating with MoSi₂-YSZ has an emissivity over 0.93 in the range of 0.3~2.5 μm， the temperature rise of the backboard of high-emissivity coating is reduced by 60% in static heating condition， while the temperature rise of the thermal shock test is reduced by 30%. High-emissivity coatings exhibit hysteresis in response to temperature due to the heat dissipation of radiation during high temperature testing， the peak temperature change rate of the backboard is reduced by 40%. In addition， the dense oxide layer formed by MoSi₂ oxidation also has good protection and self-healing properties for the inner structure， which greatly increases the stability and reliability of the coating under high temperature conditions.

Abstract:In order to explore the process of using the new toughness curing agent， the curing kinetics of tetraglycidyl—4，4''—diaminodiphenyl methane （AG-80）/ triglycidyl-p-aminophenol （AFG-90） and triamine terminated polyether curing agent （TAPE） were investigated by non-isothermal DSC method. Málek method and isoconversional method were conducted to study the kinetics model and curing reaction mechanism， and mechnical properties of two epoxy systems were also explored. The results show that the initial curing reaction temperature of two systems are nearly 50^oC with good reactivity. The curing reaction process of the systems suit the Sestak-Berggren kinetic ［SB（m，n）］ model. The strain at break of two systems is higher than 3.74%， which shows the two systems have good reactivity and toughness.

Abstract:In this paper， the welding process of helium arc bottoming + argon arc filling and covering was used to conduct TIG welding experiment on 15 mm thick plate of 2219-T87 aluminum alloy to study its weld formation，microstructure and mechanical properties. The results show that this process has good weld appearance， no visible welding defects， and good porosity inhibition effect. The average tensile strength of the joint is 278.22 MPa， the average elongation after fracture is 3.89%， and the average strength coefficient of the joint reaches 58.94%. The overall performance of the joint hardness is the lowest in the center of the weld. From the center of the weld to the base material， the hardness first increases， then decreases locally， and then increases； and the hardness of the filler layer in the center of the weld is higher than that of the bottom layer and the cover layer. The microstructure of the fusion zone is columnar dendrite and cellular dendrite， and grows perpendicular to the fusion line. Equiaxed fine grain bands appear on both sides of the fusion zone. There are many tearing edges and dimples on the cross section of the welded joint， and micropores and second phase particles are found locally. The fracture mechanism of the welded joint is typical ductile fracture.

Abstract:The welding crafts of 2195 aluminum-lithium alloy was investigated to solve the problems of high crack sensitivity， high porosity sensitivity， oxidation during welding of 2195 aluminum-lithium alloy. The crack sensitivity，mechanical properties and microstructure of the weld joints were analyzed. The results show that the increasing Cu content in fusion can effectively reduce the crack sensitivity of the weld joints， with K₁=0% and K₂=0%. The two pass welded joint display the best tensile properties. The tensile strength of joint is 376 MPa， while the elongation of joint is 5.5%. The problem of high porosity sensitivity is solved by increasing the cleaning depth of the welding plate.Using pure Ar gas for backward gas and root side purge gas can avoid the fusion welding from oxidation. The research of welding process provided technical support for the engineering application of 2195 aluminum-lithium alloy.

Abstract:Continuous and discontinuous dual degree of freedom resonance sound absorption structures were prepared by using aramid paper honeycombs， embedded resin partitions and micro-perforated panels. The mechanical properties and sound absorption coefficients of the two resonance sound absorption structures were compared. The results show that： the compression and tensile performances of the resonance absorption structure of the continuous honeycomb core material are higher that of discontinuous honeycomb core material. Among them， the unstabilized compressive strength and tensile strength are 19% higher， the stable compressive strength is 32% higher， the stable compressive modulus is 43% higher， and the shear performance of the structure is basically equal. At the same time， the two-layer honeycomb core material is prone to cell dislocation （discontinuous resonance sound absorption structure）， which causes the micropores blocking in the dislocation area， and the peak of the resonance absorption structure is greatly different from the theoretical value.

Abstract:In order to solve the unidirectional shape memory effect problem of most current shape memory polymers， a shape memory polymer composite with laminated structure is prepared by combining TDE-86 epoxy resin modified hydrogenated bisphenol A epoxy resin and polyurethane elastomer with polybutadiene as soft segment. The composite exhibits two-way shape memory behavior under stress-free condition because of the balance between the restoring force generated by the shape memory epoxy resin and the contraction force generated by the pre-stretched polyurethane elastomer. It demonstrates reverse bending when heated and cooled in the temperature range of 90~ 110 ℃. The results show that the greater the pre-stretched strain of the polyurethane elastomer， the larger the degree of bending in the entire temperature range. When the recovery temperature is at or above the glass transition temperature of the shape memory epoxy resin， the degree of recovery is greater. The thickness of the elastomer will increase the initial degree of bending but reduce the degree of deformation and recovery during the two-way shape memory process.

Abstract:2219， 2A14 and 2195 alloys were three kinds of structural materials for aerospace application. Particularly， 2195 alloy was more and more widely used in aerospace industry because of its low density， high specific strength and rigidity and etc. By using the in-situ observation system of high temperature metallography， the microstructure evolution and phase transformation of three kinds of aluminum alloys in strengthened condition from room temperature （about 25 ℃） to zero strength temperature （about 600~660 ℃） at a heating rate of 50K/min was investigated. The results show that three kinds of aluminum alloys melt at a temperature higher than the solidus curve， the first melting position lies around the spherical phase （containing Al， Cu）， and that the massive phases （containing Al， Cu， Fe， etc） melt at last. After the cycled-water solidification process， the micro-hardness of the re-solidified materials decreases by about 50%， indicating that the strengthening phase in the matrix decreases. The Cu content of primary α phase decreases， and most of the Cu element remains at the grain boundaries， forming net-like Cu-rich phase whose composition is close to eutectic composition， and a few massive phases that do not dissolve completely are forced to the grain boundaries. As a result of the comparison of three alloys， the conclusion is drawn that 2195 alloy， which has the smallest solid-liquid temperature interval， is susceptible to thermal cracks since the Cu-rich liquid films are easily torn apart by thermal stress.

Abstract:The high density inclusions （HDI） in high temperature titanium alloy were studied by means of X-ray test， OM and EDS. The microstructure photos show that the normal microstructure of high temperature titanium alloy is duplex microstructure with α phase content of about 15% after heat treatment， the structure around the inclusion is different from the normal structure. It is widmanstatten structure， high content of β phase， acicular α phase precipitates at grain boundary and in crystal of β phase. The inclusion is obviously different from the matrix， the EDS results shows that the HDI are Ta inclusions. The main reason for the formation of HDI： when batching， high melting point element are mixed in the form of pure element powder and added to the electrode block by manual distribution. It leads to the agglomeration and increases the size of high melting point metal powder. During material melting， the DC arc are can not melt all the powder with large size， the agglomerated powder falls into the molten pool and then enters the solidified ingot to become HDI. It can be improved by changing the distribution mode or selecting multi-component alloy. HDI are not found in the forgings after adding refractory metals by mixing method.

Abstract:Combined with ultrasonic phased array， metallographic observation and mechanical test analysis technology， the influence of welding gap caused by different milling angles on the welding quality and mechanical properties of friction stir welding seam on tank dome cover was studied. The results show that when the welding gap caused by the difference of milling angle is greater than 1.30 mm， there are void volume defects in the weld. The larger the welding gap is， the more serious the defect is. The existence of welding gap reduces the density of the weld and the elongation of the weld. When the welding gap is greater than 1.30 mm， the tensile strength of the weld decreases greatly.