Abstract:Polymer matrix composites （PMCs） have become one kind of the most important structure materials in the aerospace field due to their advantages of high specific strength，high specific stiffness and excellent vibration damping performance.Structure-damping composites can be achieved by hybridization.In this review，the damping properties of structure-damping hybrid composites are summarized.Vibration damping properties of structure-damping hybrid composites are analyzed in details based on micro/nano material hybridization，intraply hybridization，interply hybridization and sandwich hybridization.In addition，this paper identifies some technical challenges and suggestions of further application for structure-damping hybrid composites in future.

Abstract:Large solid rocket motor （SRM） is well suited to space exploration mission because of simple architecture，large thrust， and high reliablity. Large throat is a key technology for the nozzle. This paper presents an overview of large SRM nozzle and throat international preparation，materials property， characterization of large SRM nozzle and throat in France， Japan，USA， India.Chinese large SRM throat technology was summarized， and directions for large throat design and material preparation are given.

Abstract:Five commonly used categories of characterization techniques in physical metallurgy employed for damage analysis of metallic materials were reviewed in this paper. The techniques with regards to microstructural characterization， physical property measurement， chemical composition analysis， residual stress measurement and in situ characterization were covered. Application of each technique for the analysis of damage in metallic materials was discussed in detail. Comprehensive comparison between various techniques was also made， and the advantages and limitations associated with the exploitation of the reviewed techniques were proposed. The major considerations in selection of these techniques for damage analysis were discussed as well， based on their specific applications.

Abstract:The cutting process of carbon fiber reinforced plastic （CFRP） contains the fracture of fibers and cracking failure of resin matrix and interfacial phases.Meanwhile，the chip formation mechanism is diverse from different fiber cutting angle.Thus predicting the cutting force of CFRP effectively has been proven difficult.Combined with the principle of minimum potential energy and winkler elastic foundation beam theory， the deflection equation of fiber is obtained by calculating the microelement based on the representative element of CFRP （RVE） in this paper. The mechanical behavior of three cutting deformation areas with different fiber orientation angle is analyzed ，respectively.The prediction of critical damage length of the fiber is completed， which formed the analytical model of the cutting force of CFRP with different fiber orientation angle.The cutting force model is verified by the milling experiment of CFRP with straight edge milling cutter.When the whole fiber orientation ranges from 0° to 180°， the theoretical value of the cutting force and the experimental data is consistent with the variation trend of fiber orientation angle， and the relative error is within 15%.The cutting force increases first and then decreases with the increase of the fiber orientation angle. Both of them convert variation trend near 90° and 45°，respectively. The cutting morphology shows that when the fiber orientation angle turns 135°， the milling surface quality of CFRP is poor and the critical damage length is tremendous.The established analytical model of cutting force can predict the orthogonal cutting force of CFRP accurately，which can also provide theoretical guidance for the analysis of mechanical behavior in the forming of CFRP chips.

Abstract:In order to satisfy the application requirements of the large space transportation systems in china， the 130 L helium cylinder is firstly developed by superplastic-isothermal forming method using Ti-5Al-2.5Sn ELI titanium alloy plate， and the cryogenic temperature deformation mechanism of Ti-5Al-2.5Sn ELI titanium alloy is also systematically investigated in this work. The experimental results indicate that Ti-5Al-2.5Sn ELI titanium alloy shows the cyclic deformation behavior of sliding and twinning modes under 20 K， and the incomplete re-crystallization of raw material can be eliminated by thermal forming process. Furthermore， the completely recrystallized grains with equiaxial characteristic and the curved grain boundaries of helium cylinder can coordinate cryogenic temperature deformation process nicely， inducing the excellent mechanical properties of Ti-5Al-2.5Sn ELI titanium alloy under cryogenic temperature. Therefore， the superplastic-isothermal forming method is a feasible technology to manufacture the large pressure vessel for the aerospace industry.

Abstract:Silicon carbide fiber reinforced silicon carbide matrix （SiC_f/SiC） composite had an important application in hot-section componets in aeroengines.SiC_f/SiC composite was fabricated by melt infiltration （MI） technique using SiC fibers as reinforcement. Physical and mechanical properties of the composite were evaluated and the microstructure and cross section was studied by Micro-CT and SEM.The results show that the bulk density of SiC_f/SiC composite is 2.78 g/cm³ and the apparent porosity is lower than 2.0%. The transverse thermal conductivity at 1 200 ℃ is 14.30 W/（m∙K） for the prepared composite. The linear expansion rates in thickness direction and in-plane direction are 0.59% and 0.56% and the average coefficient of thermal expansion are 5.02×10^-6/K and 4.73×10^-6/K， respectively. The representative values of in-plane tensile strength， flexural strength and interlaminar tensile strength of SiC_f/SiC composite are 317 MPa，794 MPa and 49 MPa， respectively.It is clearly observed that many fibers are pull out of the ceramic matrix from the SEM image of fracture surface of tensile specimen.

Abstract:In view of the poor absorbing effect of traditional honeycomb absorbing materials at low frequency， a composite absorbing structure of honeycomb inner wall loaded with zigzag wire is designed. The two-dimensional array is a frequency selective surface with near zero permeability. The height of honeycomb absorbing structure is 30 mm and the thickness of absorbing coating is 0.024 2 mm. The simulation results show that compared with the original honeycomb， the composite absorption structure loaded with the loop line has an absorption peak in the range of 0.4 to 2 GHz， the bandwidth of < - 10 dB increases by 10% to 50%， and has good absorption stability in the range of 0° to 60 ° incidence angle. By adjusting the geometrical parameters of the loop and the square resistance of the material， the position and the bandwidth of the low-frequency peak absorption can be adjusted.

Abstract:Two molding press processes with different cooling methods were adopted to manufacture poly-trifluorochloroethylene （PCTFE） seat sealing ring for ball valve. The results of cryogenic experiments show that internal micro-cracks would occur in the PCTFE product prepared by press process with natural cooling， while the one prepared by press process with pressurized cooling will not generate intrinsic micro-cracks. The results of characterizations and performance tests indicate that molding press process with natural cooling leads to occurrence of micro-cracks in the product， resulting in the subsurface defects during the cryogenic experiments and seal failure. Pressurizing the product during cooling will inhibit the occurrence of micro-cracks，avoiding the appearance of aggravated cracks due to the internal stress generated by the room-low temperature cycle condition.

Abstract:The Ti-1Al-8V-5Fe （Ti-185） alloys were prepared by powder metallurgy process based on TiH₂ powders and different sizes of element powders.The effect of compaction process on the microstructure and mechanical properties of Ti-185 alloys prepared by different particle sizes of element powders was investigated. The results indicate that the Ti-185 alloy has the highest green density under the following conditions：a pressing pressure of 800 MPa， a dwell time of 80 s and a pressing rate of 1 mm/s，which can be considered to be the optimum pressing process. The smaller particale size of Ti-185 alloy is， the higher sintering density of alloy is.The smaller particle size element powder is favorable to shorten the atoms diffusion distance of alloying elements during the sintering process， resulting in enhancing mechanical properties of Ti-185 alloy.Consequently，the sample with the minimum particle size displays the highest hardness （43 HRC） and strength （1 438 MPa）.

Abstract:Multi-diameter vascular system was studied to realize the multi-point self-healing of the scratch on the surface of composite material. The main pipeline， secondary pipeline and micro-nano porous structure were embedded in the superficial part of the coating to form the multi-diameter microvascular healing agent delivery system. The research indicated that three-diameter microvasculature system had the best effect of conveying repair agent， and the diffusion of repair agent was more uniform and faster. The horizontal layout of the main pipeline could prevent the pipeline from blocking， and the delivery of the repair agent was more smooth. The main pipeline was embedded in the substrate， which could reduce its impact on the coating performance. Further study on micro-nano porous structure showed that the diversion network was better than that of the porous nickel foam. Therefore， the three-diameter micropipette system， which was embedded the main pipe horizontally into the substrate and used the guide net structure micro-nano porous structure ， was expected to be applied to the self-healing of the scratch on the surface of composite material.

Abstract:In order to determine the development of the radial heterogeneity of oxidative polyacrylonitrile fibers，it is urgent to develop a detection method for the evaluation of homogeneous oxidation of polyacrylonitrile fiber.In this paper，fiber samples are prepared by resin embedding and polishing technique for optical analysis.The evolution process of the radial heterogeneity of two kinds of oxidative polyacrylonitrile fibers were compared and analyzed by optical microscope.The evolution model was proposed for the radial heterogeneity of oxidative polyacrylonitrile fibers.The results proved that typical radial heterogeneity is present in TG300 oxidative polyacrylonitrile fibers.However，no obvious radial heterogeneity is found in TG800 oxidative polyacrylonitrile fibers.When the oxidation reaction proceed，the diameter and carbon content of fiber decrease and the oxygen content increase gradually.Therefore， the optical microscope can be applied in the evaluation of homogeneous oxidation of polyacrylonitrile fiber.A new detection method is provided for the manufacture of homogeneous oxidative polyacrylonitrile fibers.

Abstract:In order to obtain the molecular structure，the of polycarbosilanes relationship between molecular hydrodynamics and molecular mass and the concentration dependence of reduced viscosity have been investigated.The results indicated that for PCS，absolute weight-average molecular mass M_w=1.098×10⁴ g/mol，molecular weight distribution MWD=6.7，the second virial coefficient A₂=1.57×10^-3 cm³·mol/g²，Huggins constant k’=1.85，the scaling exponent b between hydrodynamic radius and molecular mass=0.21.At normal atmospheric temperature，tetrahydrofuran（THF） is a thermodynamically good solvent for PCS.And PCS macromolecules are characterized by compact structure which is not in according with the characteristics of linear polymers.

Abstract:According to the relevant testing standards of fiber mechanical properties，the testing method of tensile properties of high model PBO bundle fiber was studied systematically.The results show that the clamping fixture and ceramic material fixture body are suitable for the tensile test of PBO dry yarn.The twist coefficient has a great influence on the tensile properties of PBO，and the optimum value is 8.It is found that twisting will affect the orientation degree of fiber.The increase of the stretching speed will increase the fracture strength of the fiber.The pre-tension has little influence on the tensile properties of the PBO fiber within the testing range.The longer the clamping length is，the closer tensile deformation measured by the crossbeam is to the real value.

Abstract:In order to improve the detection efficiency of debonding defects in bonded structures and achieve rapid and automatic detection in large areas，air-coupled ultrasonic lamb wave detection technology is proposed to detect and study the defects of steel/resin/rubber bonded structures based on the leaky Lamb wave detection principle.The two-dimensional Fourier transform was used to analyze the Lamb wave modes，and the sensitivity of different modes of Lamb waves to debonding defects was analyzed. The defects of different sizes were quantitatively studied by the air-coupled detection system.Finally，the probability damage imaging algorithm was used to image the defects. The amplitude of the lamb wave increases with the size of the debonding defect.Different Lamb wave modes have different detection sensitivities，and the modal with high detection sensitivity has greater off-plane displacement.Using 800 kHz S₀ mode detection sensitivity is higher than A₀ mode，the Lamb wave imaging algorithm can quickly and accurately locate the debonding area.Air-coupled ultrasonic Lamb wave technology can quickly and effectively detect SRM debonding defects，improve detection efficiency，and provide beneficial exploration for the practical application of non-contact ultrasound.

Abstract:During the flight of the aerospace structure， the temperature and strain amplitude， etc. will change significantly. In order to study the effect of service environment on damping， the internal damping of Mg-6Gd-3Y-0.5Zr magnesium alloy and ZL114A aluminum alloy with the variation of service environment were studied by using DMA tester. The results show that the damping of both Mg-6Gd-3Y-0.5Zr and ZL114A materials gradually increases with the increase of strain amplitude， and under the same amplitude， the damping performance of Mg-6Gd-3Y-0.5Zr is better than that of ZL114A. In addition， the damping of both materials increases with the increase of temperature. The average damping values of Mg-6Gd-3Y-0.5Zr and ZL114A alloy at 330℃ are 2.1 and 1.3 times that at 30℃， respectively. It can be seen that Mg-6Gd-3Y-0.5Zr alloy is more sensitive to temperature rise， when the structure temperature rise is large， its damping should be considered as a variable.