航空材料学报

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2021, 41(6): .

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Abstract:

Structural innovation of new fighter based on additive manufacturing

WU Bin, WANG Xiangming, XUAN Minghao, WANG Fuyu

2021, 41(6): 1-12.

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Abstract:
Based on the traditional manufacturing technology, the “classic” structure, which has a large mass and many weak parts of fatigue is difficult to satisfy the development needs of future fighter aircraft. The innovative structures ( three-dimensional bearing overall structure, bionic structure, gradient metal structure and micro truss lattice structure) based on the advantages of additive manufacturing technology characteristics, breaking through the shackles of traditional structures, with lightweight, long-life, low-cost and other characteristics, can greatly improve the quality of the body platform, providing an effective technical way for the future development of new fighter aircraft. Taking the fuel pipe joint, ring radiators and three-dimensional frame beam integral structure as examples, this paper expounded the whole process of integrated development of new additive structure design and manufacturing, and compared with the original traditional manufacturing scheme, achieved significant benefits, such as substantial weight loss, improvement of finished product rate, and reduction of fatigue weak parts. In addition, the reference significance of cross-domain technologies such as fiber optic sensing and construction structure to the innovation of aircraft structure was also discussed.

Progress of 3D printed microwave absorbers

WU Sai, ZHANG Youwei, CHEN Meng, HU Yue

2021, 41(6): 13-22.

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Abstract:
In recent years, as the 3D printing technology growing maturity and commercialization, the researchers have attempted to apply this emerging manufacturing technology to the design and fabrication of wave-absorbing materials. In this paper, the recent progress of 3D printing technology in fabrication of microwave absorbing materials, including 3D printing FSS and metamaterial absorbing materials, 3D printing honeycomb absorbing materials, 3D printing ceramics and other 3D printing microwave absorbing materials are reviewed. Furthermore, the limitations of 3D printing materials, the lack of mechanical properties of materials, the problems of testing and analysis of microstructure of 3D printing technology in microwave absorption materials manufacturing are also systematically expounded, at the same time, the future developing trend of 3D printing technology in the manufacturing field of microwave absorption materials, such as miniaturization, multi-function and intelligent is also prospected.

Research progress of solid propellant 3D printing technology

LIU Qingdong, WU Zhujun, LI Miaomiao, XU Yifeng, SUN Fei, REN Yang, SONG Xuefeng

2021, 41(6): 23-32.

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Abstract:
Solid propellant is an important source of power for rockets and missiles, and its performance improvement is of great significance for improving the combat capability of missile weapons. 3D printing technology as a focus on advanced manufacturing technology, able to complete high-precision, high-complexity device manufacturing that is difficult to achieve by traditional manufacturing processes, solve the problems of uneven mixing, poor product consistency, and low safety, which are difficult to solve by traditional solid propellant pouring process, has broad prospects in the field of solid propellant manufacture.. The slow progress of the research on the preparation of solid propellant by 3D printing is mainly due to the two major problems of safety and process bottleneck. In view of the safety issues of solid propellant 3D printing, solid propellant 3D printing and related work are divided into three stages: 3D printing of partial energetic components, 3D printing of mixed propellants, and 3D printing of solid propellants. The safe printability of energetic components should be demonstrated step by step. In review of the bottleneck problem of solid propellant 3D printing process, the development progress of 3D printing propellant special slurry and equipment is introduced. From the current achievements and development, the future research on solid propellant 3D printing should focus on the development of special formulation and the realization of large-scale printing.

Microstructures and mechanical properties of spray deposited Al-Cu-Li alloy through thermo-mechanical processing

TANG Qidong, XIAO Kai, GUAN Ruichun, JIANG Mang, XU Jinjun

2021, 41(6): 33-43.

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Abstract:
The microstructure evolution and mechanical properties of spray formed Al-Cu-Li alloy during thermomechanical treatment were studied by a series of experimental methods combining microstructure observation and mechanical properties testing. The results show that the grains in the spray formed aluminum lithium alloy are typical equiaxial crystals. The coarse crystalline phase at the grain boundary of the alloy is Al₇Cu₂Fe phase, and the thin crystal phase in the grain is AlCu phase. After homogenization treatment, the width of grain boundary in the alloy decreases and the distribution of elements in the inner grain tends to be uniform. Only a small amount of massive Al₇Cu₂Fe phase and punctate AlCu and AlZr phases are not dissolved in the alloy. After solution treatment, the grain structure of the alloy is still equiaxed, and there are dispersed second phases (β′ and δ′) in the alloy. Compared with direct artificial aging treatment, the pre-deformation treatment before aging can accelerate the aging process and improve the mechanical properties of peak aging alloy. Pre-deformation treatment before aging can promote the dense precipitation of T₁ phase in the grain, inhibit the formation of coarse grain boundary phase and intragranular phase δ′, so the stress concentration effect is weakened effectively. Moreover, the deformation of grain boundary and intragranular is more uniform , which can improve the strength and toughness of the alloy at the same time.

Analysis of deformation behavior and microstructure evolution for GH4133B superalloy based on isothermal compression test

LIU Zhaozhao, WANG Miao, LIU Yanhui

2021, 41(6): 44-50.

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Abstract:
The deformation behavior of the GH4133B Ni-base superalloy in hot working process was investigated by the isothermal compression tests carried out at the temperature of 940-1060℃ and the strain rate of 0.001-1.0 s⁻¹ with the height reduction of 50%. The microstructure of the deformed samples under different processing parameters was observed. Combined with Arrhenius hyperbolic sine equation and Zener-Hollomon parameter, the constitutive model of hot deformation of the alloy was established, and the hot working diagram was drawn. The activation energy of hot deformation of the alloy was 448 kJ/mol. the power dissipation reached its peak at 1020 ℃ and strain rate of 1 s⁻¹. Based on the establishment of constitutive model and processing map, the results of isothermal compression simulation and microstructure test analysis show that the best hot working deformation temperature of GH4133B nickel base superalloy is 1020-1060 ℃ and the strain rate is 0.01-0.1 s⁻¹.

Effect of brazing thermal cycles on microstructure of single crystal alloy DD6

FENG Hongliang, CHEN Bo, REN Haishui, LI Wenwen, MAO Wei, XIONG Huaping, CHENG Yaoyong, CHEN Hao

2021, 41(6): 51-58.

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Abstract:
In this paper, repeated brazing thermal cycles were carried out for the single crystal superalloy DD6 at 1220 ℃ for 30 min. The dendrite segregation was analyzed . The microstructural evolution and mechanical property of the alloy DD6 after thermal cycles were studied in detail. The results showed that the segregation coefficient didn’t change obviously after brazing thermal cycles in comparison with the original state. After one brazing thermal cycle, the γ′ phases grew up visibly, but they still kept a certain degree of cubitization. After two or three brazing thermal cycles, the cubitization of the γ′ phases decreased obviously. Therefore, the brazing repair times should not be more than one in this condition. With the increase of brazing thermal cycles, the original γ′ phases not only became larger and connected, but also a small part of the γ′ phase edge changed from straight state to uneven state, and gradually a large number of serrated state. It was also found that the fine secondary γ′ phases were formed in some of γ matrix during each cycle either in the dendritic core or interdendritic region. After each thermal cycle, the alloy DD6 can keep 100 h at 980 ℃ with the initial stress of 250 MPa. After that, the stress was increased by 25 MPa every 10 h until the sample fractured. The stress rupture life was similar to that without thermal cycle, but the elongation and redution of area were increased gradually.

Theoretical calculation of characteristics on titanium fire in aero-engine

LIANG Xianye, MI Guangbao, LI Peijie, HUANG Xu, CAO Chunxiao

2021, 41(6): 59-67.

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Abstract:
Titanium fire is a typical catastrophic failure of modern aero-engine. The local heating of titanium alloy in the high-pressure compressor is the main ignition source. In this study, the ignition process of aero-engine titanium alloy isothermal heating, non-isothermal linear heating and non-isothermal friction heating were modeled to study the influence of factors such as the initial heating temperature, heating rate, oxygen concentration and flow rate on the ignition parameters, and then the recommendations on the flame-retardant design of titanium fire were given. The results show that during the isothermal heating process, the critical ignition temperature is about 958 K. When the heating surface temperature is 1941 K, the ignition delay time is 0.2 s. In the non-isothermal linear heating process, the ignition delay time of the heating rate of 28 K/s, 58 K/s and 100 K/s are 1.5 s, 1.1s and 0.9 s respectively, and the critical ignition temperature is basically maintained at about 950 K; When the microconvex is 16.5 μm, the critical ignition temperature is about 765 K, which is consistent with the experimental results reported in the literature. In the non-isothermal friction heating process, the ignition delay time decreases with the increase of contact stress. When the contact stress is 26.5 kPa, the heating rate is 130 K/s, and the ignition delay time is 1.4 s; When the flow rate is 300 m/s, the critical ignition temperature is 1040 K, and the ignition delay time is 2.8 s; When the oxygen concentration in the airflow is 50%, the critical ignition temperature is 920 K, and the ignition delay time is 1.5 s. The flame retardancy in low- speed environment should be considered when designing anti-titanium fire structures.

Damping properties of carbon fiber reinforced composites modified with cellulose nanofiber

ZHU Xuerui, LI Yan, YU Tao, ZHANG Zhongsen

2021, 41(6): 68-73.

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Abstract:
Cellulose is considered as the most abundant natural polymer from biomass. Cellulose nanofiber (CNF) is derived from natural cellulose. Compared with the other nanomaterials, CNF has the characteristics of low density, large specific surface area and high specific modulus, moreover, it has the advantages of renewable and biodegradable, etc. It is a new type of functional material with outstanding performance and economical practicality. Carbon fiber reinforced polymer composites (CFRPs) have been widely used in recent years due to their low density and high specific strength. However, the damping properties of CFRPs are poor since they have a high sensitivity to damage. In this paper, CNF was used to improve the damping properties of CFRP, which was proposed to provide new ideas and methods for the design and application of CNF in CFRP. A combination of mechanical and chemical methods was used to extract CNF from softwood pulp. The micron-level flocculent fibers were obtained by high-speed shearing treatment, then the impurities were removed by alkali pretreatment. The suspension liquid was grinded by a grinder until the diameters of fibers less than 1 μm. The effect of mechanical grinding time on the size of the cellulose product was studied. The obtained CNF suspension liquid was freeze-dried to obtain a three-dimensional networked film with low density and high porosity, which could be added as an interleaf to the CFRP. The hydrophilic characteristics of CNF maked it poorly compatible with the hydrophobic matrix, and the poor interface bonding greatly affected the mechanical properties of CFRP. In this paper, waterborne epoxy (WE) was used to modify the surface of CNF to reduce the hydrophilicity, which could effectively improve the interface between CNF and epoxy resin. The effect of CNF on the damping properties of CFRP was studied. The dynamic mechanical analysis (DMA) method was used to test the loss factor which could evaluate the damping properties of composite laminates. The results show that the addition of CNF films can slightly increase the loss factor of CFRP, because CNF are derived from plant fibers, and their damping properties are better than that of carbon fibers. The viscoelasticity of CNF helps to improve the loss factor of CFRP. In addition, the stick-slip motion occurs between CNF and resin, and friction generates energy consumption, therefore, the damping properties of CFRP were improved. After surface modification, the loss factor is further improved. The stronger interface bonding makes the surface of CNF debonded become rougher, which produces greater interface friction, thereby, the frictional energy consumption is increased. With the increase of amplitude, the loss factor of the cellulose nanofiber modified composite also increases.

Effects of temperature on moisture absorption and diffusion behavior of glass fiber/epoxy composites

ZHU Libao, LI Yongqing, ZHU Xi

2021, 41(6): 74-80.

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Abstract:
In order to investigate the effects of temperature on the moisture absorption and diffusion behavior of composites, the moisture absorption tests for unidirectional glass fiber/epoxy composites under 35 ℃、50 ℃ and 70 ℃ were carried out. The storage modulus and glass transition temperature (T_g) of composites were studied by DMA, and functional group changes were study by FTIR. The results show that when the temperature is 35 ℃ and 50 ℃, the moisture absorption and diffusion behavior of the composite can be described by Fick model, and the three-dimensional diffusion coefficient of the composite can be fitted by Fick formula. When the temperature is 70 ℃, the moisture absorption and diffusion behavior of the composite can be described by Fick - relaxation coupled model. T_g of saturated composites increases with the increase of moisture absorption test temperature, and degradation and physical aging of the composites occur when the temperature is 70 ℃, resulting in mass loss. The moisture diffusion coefficients of the composites perpendicular to the fiber direction at different moisture absorption test temperatures satisfy the Arrhenius equation, and the activation energy is 78.15 kJ•K⁻¹•mol⁻¹. The diffusion coefficient along the fiber direction increases significantly at the moisture absorption test temperature of 70 ℃. The reason is that the high temperature significantly enhances the water diffusion in the fiber / matrix interface along fiber direction.

Dynamic response analysis on bird impacted composite honeycomb sandwich structure

HUO Yujia

2021, 41(6): 81-88.

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Abstract:
The finite element model of composite honeycomb sandwich structure subjected to gelatin bird impact was established．The effects of different layering methods of the fiber, the change of honeycomb core height on the anti-bird impact and energy absorption of sandwich plate were studied. The validity of the model was proved by the comparison with experimental results．The results show that the numerical simulation results are in good agreement with the experimental results. Part of the impact energy was converted into the internal energy of bird, part of the impact energy was continued to be stored in the remains of the gelatin bird which is not completely broken, the rest of the energy is converted into the internal energy of the structure．It is also found that the sandwich plate with ±45° fiber layer absorbed the energy more than the sandwich plate with ±90° fiber layer in the front panel．With the increase of the height of honeycomb core, the deformation of sandwich plate decreases, the variation of plate internal energy decreases, and the absorption of impact energy decreases．

Z-pins reinforced K-Cor foam sandwich structure and its strengthening mechanism

ZHENG Yingying, XIAO Jun

2021, 41(6): 89-97.

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Abstract:
Due to its excellent toughness and the cross-linking reaction for co-curing, partially-cured Z-pins currently are used as “Z”-directional reinforcing bat to strengthen foam-matrix sandwich structures. Through heat curing of the integrally-forming process to achieve a lightweight and high-strength foam sandwich structure which is widely used in spacecraft and missile shells to increase local bearing capacity and resistance to high-altitude electromagnetic radiation. The research of this paper was to explore a new -type K-Cor foam sandwich structure, as well as to study its strengthening mechanism of the as-received Z-pin within different curing degrees. The as-received K-Cor structures were fabricated by inserting Z-pin into Rohacell-51WF foam, using NHZP-1 and 5429/HT7 bismaleimides as pultrusion resin and pre-impregnated medium respectively. The experimental results show that Z-pin with a 45.59% curing degree had a cross-linking and co-curing reaction with skin panel during hot pressing, and the integrity of the foam sandwich structure was significantly improved. The results from shear tests indicate that as the Z-pin implantation angle at 45° and the implantation density as [5mm×5mm] (abbreviated as 45° [5mm ×5mm]), the shear strength and modulus of the K-Cor structures are 1.02 and 2.06 times higher than that of the blank foam. Great improvements on compression performance than tensile, this is mainly due to itself high strength of Rohacell-51WF foam core carrying some stress instead of Z-pin payload during the compression process. During the horizontal tensile test, as Z-pin implant angle at 70°, its tensile strength and modulus of K-Cor structure are 1.65 and 56.19 MPa, much higher than those at 60° and 45°, which is mainly attributed to the larger value of implantation angle to reduce the axial force along “Z” direction and increase the resistance to Z-pin failure during high load tensile processes. Overall, the lightweight and high-strength K-Cor foam sandwich structure is easily integrated with thermoforming and co-curing processes, currently being used in spacecraft rudder and missile shells under heavy loading conditions.

2021 Vol. 41, No. 6