Abstract:The main machining methods of ultra-fine grained cemented carbide, including traditional grinding, electrolytic in-process dressing grinding, electrical discharge machining, ultrasonic vibration assisted machining and laser heating assisted machining were introduced. And the machining mechanism and machining properties of ultra-fine grained cemented carbide were reviewed. The further researches of high efficiency and precision machining of ultra-fine cemented carbide were also prospected.

Abstract:SiC_p/Al composites have excellent comprehensive properties and have been widely used in the field of high and new technology. Meanwhile, the presence of SiC particles as reinforced phase in SiC_p/Al composites makes SiC_p/Al composites extremely difficult to cut, which easily causes a series of processing damage. In this paper, the machining defect types, defect formation mechanism, defect control strategy, tool wear mechanism and optimization strategy of SiC_p/Al composites were summarized. And the research prospect of processing damage of SiC_p/Al composites was discussed.

Abstract:Two different filling systems of ZL101 pump casting were designed in this paper, and the flowing field, solidification phase field and distribution of shrinkage were calculated by the FEM numerical simulation. The results show that the melt alloy fills smoothly and the gas inside the resin sand core exhaust effectively from the riser by adjusting the bottom injection casting system, which forms the solidification sequence from top to bottom and from inside to outside. The average tensile strength, yield strength and elongation of the bulk samples are 334.5MPa, 274MPa and 5.8% after the T5 treatment process, which meets the technical requirements of HB962-2001 Type II castings.

Abstract:To solve the delamination defect that was easy to occur in the traditional drilling process of carbon fiber reinforced plastics (CFRP), the analyses of delamination and suppression mechanism during ultrasonic vibration core drilling (UVCD) of CFRP were implemented based on the diamond core drill and ultrasonic vibration machining technology. The delamination mechanism and evaluation in traditional drilling of twist drill and common core drilling (CCD) of diamond core drill were analyzed by theoretical method, the delamination suppression mechanism of UVCD was also analyzed, which was verified by experimental method. The results show that compared with the CCD of CFRP, the UVCD can effectively improve the cutting performance and chip removal effects of diamond core drill, reduce the thrust force by 12.5%~19.2%, suppress the chip adhesion and rod jamming of diamond core drill, suppress the formation of delamination defect of CFRP as well as improve the surface quality of machined hole.

Abstract:Flexible silicone aerogels were prepared through sol-gel polymerization of methyltrimethoxysilane (MTMS) and dimethyldimethoxysilane (DMDMS), followed by ambient pressure drying. The effects of mole ratio of MTMS to DMDMS on the chemical composition and microstructure of silicone aerogels were analyzed. Furthermore, flexible aerogel composites with a low density of around 0.25 g/cm³ were prepared by using mullite fiber blanket as structure reinforced agent. The as-prepared composites have excellent flexibility, good thermal stability and low room-temperature thermal conductivity below 0.03 W/(m·K). When the ratio of MTMS to DMDMS was optimized to 3.8∶1.2, the resultant composites had the highest tensile elongation of 3.6% and char yield of 82%. After calcination of the composites, the silicone aerogels were convent into inorganic SiO₂ aerogels with similar microstructure and thermal insulation. In static assessment of quartz lamp heating for 500 s, the surface of composites occurred ceramic reaction without obvious shrinkage at thickness direction, and there was 81℃-rise of their back temperature, demonstrating the combined functions of organic ablator and inorganic insulation properties.

Abstract:The mechanical properties, survivability of space environment, and thermal properties of CCF700-12K carbon fibers and their composites, are studied based on the localization research of high-strength carbon fiber materials for a major product. The tensile strength of domestic CCF700-12K carbon fibers is 4 706 MPa, with a tensile modulus of 268 GPa. The tensile strength of one-way slabs containing CCF700-12K/F46 composite is 1958.8 MPa, and with a tensile modulus of 144.79 GPa. The results confirm that CCF700-12K carbon fibers show excellent mechanical properties, stable process performance, which can meet the requirements for structrural engineering applications of composite materials.

Abstract:A novel MT300 carbon fabrics/phthalonitrile composite was manufactured through autoclave processing. The effects of postcure temperature on mechanical properties of composites were systematically examined, especially for mechanics performance at 400℃. The results show that the flexural modulus and strengths at room temperature improve significantly with the postcure temperature increased from 315℃ to 330℃. As the postcure temperature raised to 375℃, the RT flexural strength decreases constantly, but the RT flexural modulus remains stable. The flexural properties and compressive strengths at 400°C are obviously enhanced by the higher postcure temperature. Moreover, the RT compressive strengths show a downward trend with increasing postucre temperature, but exhibite a remarkable increase for composites postcured at 350℃. The RT and 400°C interlaminar shear strengths both initially decrease but then increase with the postcure temperature increased from 315℃ to 375℃.

Abstract:The rheological behavior of 6818 high temperature epoxy resin system for resin transfer molding process (RTM) was studied, according to the differential scanning calorimetry analysis (DSC) and viscosity experiments. The curing process of 6818 resin system was determined by extrapolation. A rheological model based on dual-Arrhenius equation was established. The curve tallied exactly with the experimental results. The results showed that the viscosity of the 6818 resin was under 200 mPa·s within the temperature range from 80℃ to 100℃, and the viscosity maintaining time more than 12 hours. The model could reflect the viscosity change of 6818 resin and predict the RTM process window of the resin system.

Abstract:Tantalum hafnium carbide (Ta₄HfC₅) ultra pure and fine powders were fabricated by the pyrolysis of ceramic precursor. By co-hydrolysis with tantalum alkoxide and hafnium alkoxide as starting materials, blending phenolic resin (PF) as carbon source, the precursor PHT was successfully prepared as transparent stable light brown solution in xylene solvent. After the precursor was cured and mineralized, ceramic products were obtained at various pyrolysis conditions. Crystalline phase of the ceramic products was studied by XRD and SEM. Pure Ta₄HfC₅ solid solution was obtained when 3.25 wt% PF (weight ratio 100 % PHT supposed) was used and the sample was calcinated at 1450 ℃ for 1.5 h. Morphology, element and particle size analysis were conducted by SEM, TEM, ICP and laser particle analyzer. Particle size of the powder was 25 to 50 nm, and uniform fine particles were obtained with narrow size distribution, 100-200 nm with Dv(50)=136 nm. Viscosity of the PHT samples changed little after 3 months duration at atmospheric temperature with light avoided, which is favorable for the precursor impregnation pyrolysis manufacturing process.

Abstract:The mechanical properties, grain structures and precipitates of 2050 Al-Li alloy cold-rolled sheet in T8 temper with different annealing prior to solution treatment were investigated by tensile tests, electron backscattering diffraction analysis (EBSD), scanning lectron microscope (SEM) and transmission electron microscope (TEM). The results show that the number of incomplete recrystallization, the aspect ratio of the grains and the number of the low angle grain boundaries and the fraction of Goss texture increase in 2050 Al-Li alloy cold-rolled sheet with annealing prior to solution treatment. The main strengthening precipitates are T1 and θ' phase. The annealing prior to solution treatment leads to the precipitation differences of T₁ phase on different {111}_Al surfaces during T8 aging process. T₁ phase number on some {111}_Al surfaces decreases, while it increases on some {111}_Al surfaces with high shear stress during pre-tensile deformation. This therefore changes the mechanical properties of the alloy. The annealing at 300℃ for 4 h prior to solution treatment enhances the yield strength and the tensile strength of the alloy cold-rolled sheet with T8 ageing, but the elongation is kept unchanged.

Abstract:The burrs and the delamination defects are easy to be generated during the drilling of carbon fiber reinforced plastics (CFRP). In this paper, two types of new drills with the similar structures are designed and manufactured by employing the tungsten carbide material and the PCD material. The defects formations and the variations of the thrust forces as well as the defects under different drilling conditions are investigated. The results show that the drilling processes of these two structures can be obviously distinguished eight stages, according to the time-variable thrust forces. Both of the thrust forces in the drilling period of reamer edge and in the drilling period of the 2^nd counterboring edge are minimal. Additionally, the 2^nd counterboring edges Ⅳ of the two structures play an extremely crucial role for reducing the defects. The drilling effect of the linear drill structure is better than that of the arc-shaped drill structure, but the ability to restrain the burrs may be weakened with the increasing of the spindle speed and the feed speed. Compared to the carbide drill bits, the PCD drill bits have the absolute advantage for suppressing the defects.

Abstract:In order to study the influence of fiber orientation on temperature field distribution and hole-wall quality of CFRP, theoretical analysis and ABAQUS simulation analysis of cutting forms at different fiber orientation angles are studied. Through the drilling temperature distribution test and simulation analysis of drilling temperature field for CFRP unidirectional plate, orthogonal plate and quasi-isotropic plate, it was found that, the direction of carbon fiber has a great influence on the distribution of drilling temperature field. By comparing the quality of the pore wall at different fiber orientation angles observed by electron microscopy and confocal microscopy, it was found that the quality of the pore wall at 0 degree, 45 degree and 90 degree was better than the quality of the pore wall at 135 degree.

Abstract:According to the honeycomb sandwich structure of CFRP grid panel and the forming technology and application environment,a test block containing typical defects is designed and made, aiming at effectively detecting the internal debonding, lamination and fiber fracture defects. The detection parameters such as phase-locked period and frequency of lock-in infrared thermography are determined by the test method, and the detection method of lock-in infrared thermography is established. The experimental results show that this method can detect and separate the debonding defects, delamination defects and fiber fracture in the honeycomb sandwich structure of CFRP grid panels.

Abstract:In order to provide essential data for aircraft designing, loading test and environmental performance test on PEEK clamp, both in P and saddle type, were finished. The effects on product properties after vibration, impact, temperature age, liquid immersion, humidity and salt were discussed. The direction that the most easily to damage in and the fracture load values in different installation angle and environmental temperature was obtained.It is shown that the tensile property of PEEK clamp is stable at room temperature.The clamp is easily broken in glue in hot and humid environment.The PEEK clamp can keep complete structure and stable perfonnance under the environmental load such as vibration, impact, and temperature aging and can replace metal clamp in certain conditions.

Abstract:Based on the quasi-static transverse bending test, the bending resistance and energy absorption characteristics of CFRP/Al hybrid tube manufactured by winding process were studied, and the failure modes of the hybrid tube were analyzed. Based on the three-point bending test results of CFRP-Al hybrid tube with different filament winding angles, the influence of filament winding angle on its transverse bending resistance and energy absorption was studied by finite element simulation method. The experimental results showed that the failure modes and damage modes of CFRP-Al hybrid tube under transverse load are basically the same as those of pure aluminum tube, but the failure morphologies are slightly different under the influence of filament winding angle. The smaller the filament winding angle, the better the bending resistance and energy absorption of CFRP-Al hybrid tube, and the lower the crushing efficiency (CFE). Based on the validated finite element model, the effect of different angle filament winding inner layer on the stress transfer of surface filament layer is studied. The restraint of small angle filament winding inner layer on the axial tension deformation of the tube increases the peak load and energy absorption of the whole tube, and the improvement of ring stiffness of the tube by large angle filament winding inner layer increases the overall crushing efficiency. The analysis can provide an effective basis for the reasonable design of CFRP-Al hybrid tube.

Abstract:The Material features and the machinability of PEEK/CA450 were analysed in this paper. The typical thin-wall parts technics characteristics, cutting parameters, and the heat treatment process of this material were studied. Then the optimum technological parameters were decided. The experiment results show three points. First, optimization of parts structure can decrease the internal stress and machining difficulty. Second the PCA tool and proper cutting parameters can ensure the machining quality of the thin-wall parts. Third the heat treatment in the machining process can improve parts finished rates and dimension accuracy. The PEEK/CA450 thin-wall parts that qualified complex design performance requirements is machined by the optimized machining process.

Abstract:For the use requirements of spacecraft, a lightweight and highly efficient aerogel composite material with a density of less than 30 kg/m³ was developed. In the light of the application environment of deep space exploration, the thermal conductivity under different conditions, thermal cycling, thermal vacuum, and total ionizing dose experiment were conducted. The result shows that the service temperature of low-density aerogel composite covers -145~85°C and the thermal conductivity under 1 kPa CO₂ atmosphere can be as low as 6.6 mW/(m·K). The change law of thermal conductivity in different atmosphere and different temperature and different pressure in same atmosphere is studied. The thermal conductivity of aerogels from different batches is also tested, and the result shows that batch stability is good. The variation of the dimension and thermal conductivity after various thermal cycling and total ionizing dose experiment is zero,which indicates that low-density aerogel composite maintains good structure and stable thermal insulation in the deep space environment.

Abstract:In traditional aerospace power modules, tin-lead solder with poor reliability is used for large-area substrate connections. In this work, sintered silver is used to join the large-area substrates. The mechanical properties, fracture mode and microstructure of large-area sintered silver joints are studied. The results show that the mechanical properties of the joints are good, and the average shear strength of the sample is 45.18 MPa, showing a cohesive failure and ductile fracture mode. No defects such as voids, cracks or delamination are found in the sintered silver bond-line. The microstructure of the bond-line is dense and uniform with a porosity of 4.82%. It is shown that the improved large-area sintered silver process requires only single printing. By increasing the heating rate to enhance the density of sintered silver and reducing sintering pressure to 2 MPa, the modified process can meet the requirements of substrate bonding in aerospace power modules.