Abstract:The recent development of rigid aromatic polyimide foams is reviewed. The components, structures and properties as well as fabrication process of rigid aromatic polyimide foams are introduced. Moreover, properties and applications of rigid polyimide foams for commercialization are summarized. The problems found in the process and research of rigid polyimide foams are also analyzed. Its future research direction as well as the development trends is also pointed out.

Abstract:In order to overcome the disadvantages of dicyandiamide, such as high curing temperature, poor dispersion in epoxy resin and so on, the effects of chemical and physical modification methods on the curing activity and storage performance of dicyandiamide are reviewed. The curing mechanism of dicyandiamide, chemical and physical modification methods are summarized in this paper. The future development of dicyandiamide is also prospected.

Abstract:Numerical simulation and theoretical analysis were performed to explore the mechanical behavior of filament wound cylinders with rectangular defects. 3D-Hashin failure criterion was applied to distinguish the damage modes and predict the damage initiation, and damage evolution laws with parameters degradation were used. The VUMAT subroutines which was compiled by FORTRAN was established for ABAQUS/Explicit FE code. Selecting the filament wound cylinder with ［90°₂/18.9°₂/90°₂/28.9°₂/90°₂ ］winding order as the research object, the influence of defect depth on stress level was analyzed. Based on the influence of the defect depth on the circumferential and axial stress of each layer, the calculation formula for the blasting pressure of the filament wound cylinders containing defects was proposed with the adoption of the correction method. The results of this formula are in agreement with the numerical simulation results. This research reveals that when the defect depth is greater than 1.26mm, the burst pressure decreases rapidly, and affects the normal use of the cylinder.

Abstract:In this paper, a three-dimensional finite element model is established for the local deformation of the woven composite preforms during the draping. The commercial finite element software Abaqus is employed to predict the deformation of the carbon fiber preform in a spherical draping. The deformation process of the 0° and 45° carbon fabrics in the spherical draping process is studied. The results show that sliding between fibers and wrinkling of fibers are the typical deformation modes of the preform during the spherical draping. In the spherical draping deformation of 0° fabric, the shear deformation angle of the 0° and 90° fiber bundles is the smallest, and the shear deformation angle of the fiber bundle is the largest in the 45° direction; for the 45° fabric, the shear deformation angles of the 0° and 90° fiber bundles are the largest, and that of the fiber bundle in the 45° direction is the smallest.

Abstract:In order to solve the defects caused by the wear and corrosion of the slurry pump impeller, such as short life and poor reliability. In this paper, the numerical analysis of the wear characteristics of the slurry pump impeller was carried out by Fluent software. The main wear zone is inlet and outlet pressure surfaces of the blade, which is basically consistent with the actual wear. Combined with the wear resistance and corrosion resistance of ceramic coating，the surface sample of the high-chromium cast iron-base AT13 ceramic coating was prepared by cold spraying method. The test results show that the microhardness of the coating is 1020HV; the loss quality of the coating sample is only 5.1mg; X-ray diffraction analysis shows that the coating has good bonding with the matrix; and the average porosity is 1.25%. The surface hardness and wear resistance of the coating sample is higher than that of the high chromium cast iron. The coating quality is good. The coating process can provide technical reference for the protection of the slurry pump impeller.

Abstract:To understand the variation of their thermal conductivity, nano-porous thermal insulating materials loaded with carbon black and silica fiber were synthesized from tetraethylorthosilicate (TEOS) via a sol-gel process followed by supercritical drying, and they were characterized by thermal conductivity tester, nitrogen adsorption-desorption, SEM, laser particle size analyzer. Test results indicate that the thermal conductivity of the materials without carbon black at atmospheric pressure declines linearly and then rises linearly with increasing apparent density, and the lowest value appears at apparent density of 203 kg/m3. The variation rate of thermal conductivity in the rising region is higher than that in the declining region. With the increase of doped carbon black, the thermal conductivity of the resulting materials with the same porosity at atmospheric pressure decreases first and then increases slightly, their thermal conductivity under ultimate vacuum drops, and their gaseous thermal conductivity at atmospheric pressure grows. In semilogarithmic coordinate, the gaseous thermal conductivity reduction of the resulting material as a function of gas pressure can be divided into 3 stages according to decreasing rate, it decreases rapidly by 6 mW/(m·K) from 101.325 to 30 kPa and then decreases slowly by 2 mW/(m·K) from 30 to 0.1 kPa, while the reduction between 0.1 and 0.01 kPa can be neglected. The lowest thermal conductivity of these materials at atmospheric pressure is only 16.62 mW/(m·K) and it can be further reduced to 14.50 mW/(m·K) via doping 5 wt% carbon black into these materials.

Abstract:In order to investigate the relations between microstructures and properties of SiC fibers, SiC fibers are annealed in air and Ar respectively at elevated temperatures in this study. The strength of SiC fibers annealed in air decreases as the temperature increases above 1100℃. When the temperature reaches 1 200℃, bubbles are formed in the silica layer. The strength of SiC fibers annealed in Ar decreases gradually as the temperature increases above 1100℃, while decreases sharply as the temperature increases above 1500℃. accompanied by the transition of β-SiC to α-SiC and the enhancement of SiC grain size

Abstract:TDE-85 was used to modify cyanate resin without affecting curing temperature. The modification was investigated by the test of viscosity-temperature characteristics, differential scanning calorimetry, fourier transform infrared spectroscopy, mechanical test, water absorption, and thermal gravimetric analysis.The results show that the viscosity of epoxy and catalyst mixture at 40℃ is less than 1Pa·s, and the sustaining time is longer than 214min that is suitable for the wet winding molding. When the epoxy content is less than 10%, the initial curing temperature does not exceed 77℃, and the gel time at 80℃ is about 30minutes that meet the requirements for low-temperature rapid curing. The modified cyanate ester resin castings with 10% of TDE-85 epoxy resin has the best overall performance and the tensile strength, flexible strength and impact strength are 46.2 MPa, 83.4 MPa and 10.8 kJ/ m 2 , respectively. However, the addition of epoxy has a negative effect on the moisture resistance and heat resistance of cyanate esters

Abstract:In order to get better thermo-mechanical treatment process of 2050 Al-Li alloy, the orthogonal experiment and range analysis were used to investigate the mechanical properties and structure of 2050 Al-Li alloy under different solution temperature, pre-deformation, aging temperature and aging time. The microstructure of materials under different processes was analyzed by TEM and metallography, and the relationship between the microstructure and mechanical properties was explored.The results show that selecting technological parameters of 525℃ solution temperature, 12% pre-deformation, 160℃ aging temperature and 48 h aging time can obtain better comprehensive mechanical properties.

Abstract:LS nylon 12 is used to design and produce a low-bearing capacity and thin-wall water retaining plate structure for the launch vehicle body.The mechanical, thermal, fracture microstructure and SLS processing parameters of SLS nylon 12 and its carbon fiber reinforced materials are emphatically studied. Studies have shown that using nylon 12 powder with the brand X1556 as the material of the water retaining plates,the unnotched impact strength of the material is 81.2 kJ/m² the elongation at break is 26.9%, and the temperature difference of the sintering window is 26.0℃. The material has good impact strength, fracture toughness and a wide range of sintering window temperatures. In addition, the forming process parameters are optimized, such as a pre-powder starting temperature of 155℃, a pre-powder holding temperature of 168℃, a processing temperature of 169℃, and a filling speed of 4 000 mm/s, whereby the formed water retaining plates have a good appearance. The plates have passed the assessment and verification of the water retaining and heat resistance tests, which have laid the foundation for the expansion and application of SLS nylon producing technology in the aerospace industry.

Abstract:The present paper investigated the influence of different solid solution time on the microstructure and micro-hardness of selective laser melting produced AlSi10Mg alloy at 535℃ solid solution temperature by using SEM, EDS and micro-hardness tester. The results showed that the microstructures of AlSi10Mg composed of nano-sized network Al-Si eutectic and the supersaturated α-Al solid solution are very sensitive to solid solution time at 535℃ solid solution temperature.After 2min of solid solution, the boundary of the molten bath and the nano-size network eutectic structure disappeared.After 5min of solid solution, the eutectic Si was obviously spherical， the size of eutectic Si increased with the prolongation of the solid solution time. With the change of microstructure, the micro-hardness of AlSi10Mg is rapidly reduced from (119±3.2)HV0.2for as-built SLM specimens before the solid solution, and with the prolongation of the solid solution time, the micro-hardness eventually stabilizes at about 57HV_0.2.

Abstract:Based on the Archard wear model, a mathematical wear rate model in the course of friction between brush and conducting ring was set up. A friction and wear test bench for conducting ring was built， the friction and wear performance of electro-contact of silver - based composite brush is verified experimentally. We can conclude that a large contact pressure makes micro-convexs on the surface to the state of plastic deformation and forming abrasive particles more easily.The carrying current forms corrugated abrasion marks on the surface of the brush material and produces powder abrasive particles.The wear rate increases first and then decreases at the beginning of wear due to the small contact area and the hardening effect of surface processing.The wear rate model is modified so that it is more accurate to predict the wear rate of silver base composite brush.This study provides theoretical guidance and experimental basis for further research and development of silver-based composite brush.

Abstract:Based on the failure criteria including COD design curves and net section yield, engineering critical assessment (ECA) on 2219 aluminum alloy structure welded by friction stir welding (FSW) was carried out. Critical crack sizes of Nugget zone (NZ), thermo-mechanically affected zone (TMAZ), heat affected zone (HAZ) and base material (BM) of 2219 aluminum alloy FSW joint were calculated. The surface defect tolerances of friction-stir-welded 2219 aluminum alloy structure under different stress-level were obtained, and ECA on longitudinal FSW joint of launch vehicle tank under a certain pressure inside the cylinder was executed. ECA method in this study provides a reference for fracture control of friction-stir-welded aluminum alloy structure. Results show that HAZ at the longitudinal advancing side is the key area for the fracture control of the 2219 aluminum alloy FSW joint. The given surface defects are acceptable under specific internal pressure

Abstract:In order to solve the problem that there is prone to edge cracking of engineering ceramics with common processing, this paper studies the boundary damage prediction system of ultrasonic internal grinding. The experiment was carried out independently under the conditions of 35 kHz axial ultrasonic grinding and ordinary grinding. The support vector machine was used to study the influence of the process parameters to boundary damage. The improved particle swarm optimization algorithm was used to optimize the support vector machine and the hybrid kernel function AHPSO-SVM predict model was established . The results show that the reduction of boundary damage of the specimen under ultrasonic is 10.05%~21.23%, the MSE of the AHPSO-SVM prediction model is 0.3784, the average relative error is 1.3690%, and the standard deviation of the 30-time fitness value is 0.0202. Compared with ordinary grinding, ultrasonic grinding can significantly reduce the boundary damage value of ZTA ceramics.The established AHPSO-SVM model has better learning ability, generalization performance and good stability.

Abstract:In order to master damage mechanism of UHMWPE/LDPE composite material，training sample of acoustic emission signal with different damage modes was established by clustering analysis and acoustic emission technology. Acoustic emission signal generated from different damage modes were identified by neural network. The factors affecting the recognition accuracy of network such as training function, transfer function and network architecture were discussed respectively. The results revealed pattern characteristic consisting of amplitude, peak frequency and duration can be selected by hierarchical clustering method. The training sample consisting of 583 signals with 11 classes can be established by K-means clustering method. Using the confusion matrix as the recognition accuracy index, when the training function is traingdx, the hidden layer/output layer transfer function is tansig/logsig, and the number of hidden layer neurons is 70, the recognition accuracy of the network is 97.2%. The results provide reference for the damage identification of thermoplastic matrix composites based on acoustic emission technology.

Abstract:In order to obtain a complete set of materials performance data, and provide support for part manufacturability, and determine whether to meet the requirements of the civil aircraft design and application, the high temperature cured epoxy resin impregnated carbon fiber composites were fabricated by hot press process with two groups of three batches respectively. The prepreg and composite physical properties, basic mechanical properties under three different environment conditions were investigate. The results show that the resin volatiles of this two group prepregs are small, the resin flow and gel time are moderate,so the processes are good. The porosities of two group composites are small, and the fiber volumes are moderate, the temperature resistance, humidity resistance and interface adhesion property of this two group composites are relatively good. The overall mechanical property under three different environment conditions of M21 system composite are better than these of CYCOM 977-2 system composite. The results are all basic to satisfy a certain type of civil aircraft tail box’s design and use requirements, and it provide the basis for the subsequent application of this composites development.

Abstract:For the problem that the machining precision of film cooling hole of aero-engine turbine blade is low and the recast layer is difficult to be removed. A new film cooling hole process which is mainly based on the thought of using EDM to drill and using grinding to expand is proposed. Grinding experiment was carried out on the film cooling hole machined by EDM using the special fine CBN grinding wheel. The result shows that after the grinding process, the roundness of the film hole is reduced by 50.9%, the standard deviation of the hole size is reduced by 90.7%, the surface roughness is reduced by 65.9%, and the recast layer is completely removed, proving the feasibility of the grinding approach of film cooling hole of aero-engine turbine blade

Abstract:The process characteristics of J-133 adhesive sandwich plate at room temperature were compared and analyzed. The suitable process method was selected. The effects of brushing amount, thickness of pressure equalizing plate and pressing pressure on the quality of bonding were studied by orthogonal test. Screen out the optimal process parameters and produced verification parts successfully. The research shows that the best way to apply glue is to “apply the glue on the panel’s adhesive surface, then put a layer of 30 g/ m² carbon fiber felt on the glue and brush the remaining glue”; the maximum effects on 90°peeling strength of honeycomb sandwich plate is the thickness of the plate, the second effects is the amount of brush and the pressure is the least; the best process parameters is that the amount of brush glue is 350 g/m²,the thickness of plate is 1.5 mm, the pressure is 0.15 MPa. According to the optimum process parameters, the quality of the honeycomb plate bonding at the room temperature meet the requirements of aerospace, which is similar to that bonding with heating.