Abstract:Aramid fiber-reinforced polymer （AFRP） is a high-performance fiber-reinforced composite with high specific strength， high modulus and light weight， and is widely used in aerospace， military equipment， automobile manufacturing and other fields. The characteristics of AFRP anisotropy and inhomogeneity lead to problems such as delamination， linting， and excessive heat-affected zone during processing， and the existing processing technology cannot reach the processing accuracy required for application in the aerospace field， which constitutes the technical bottleneck of current precision processing AFRP. This paper reviews the research status of AFRP processing， compares and discusses the advantages， disadvantages and shortcomings of traditional machining， abrasive waterjet processing， continuous laser and long pulse laser processing and ultrashort pulse laser processing， discusses the feasibility of using femtosecond laser fine processing to overcome this technical bottleneck according to the principle of femtosecond laser "cold processing"， and gives the corresponding research content and related technical approaches. This paper points out the direction for precision machining AFRP， which has obvious research significance and potential application value.

Abstract:Establishing a reasonable interface model for composites and systematically analyzing the fiber debonding process were the key to analyzing the microscopic mechanism of damage and failure in heat resistant C_f/C composite. This study was based on experimental literature reports， considering the submicron scale interfacial transition zone between fiber and matrix， and proposed an interface model that includes fiber， interphase and matrix. The exponential gradient model was used to calibrate the average mechanical properties of the interphase， and the differences between the traditional two-phase and improved three-phase interface treatments were compared and analyzed in predicting the effective elastic properties of the material. The simulation results show that the three-phase model can simulate the overall mechanical response behavior of the material more accurately than that of the two-phase model. Further， the three-phase model was used to simulate single fiber push-out experiment to analyze the effect of interfacial parameters on the progressive debonding process of the fiber. The results indicate that when the release rate of interficial critical fracture energy and cohesive strength are 0.001~0.006 N/mm and 13~33 MPa， respectively， the maximum ejection force of the fiber is positively correlated with these two parameters； beyond this range， the enhancement effect is no longer significant. Increasing the release rate of interficial critical fracture energy or decreasing the cohesive strength can delay the premature occurrence of complete damage at the interface and improve the fracture toughness of the interface. In addition， the cohesive parameters are calibrated by a combined experimental-simulation approach. The analysis results will provide theoretical support for the subsequent multi-scale research on the interfacial damage mechanism of C_f/C composites.

Abstract:Aiming at the problem of high-speed milling force prediction of aerospace materials such as TC4 titanium alloy， 7574 aluminum alloy， AISI304 stainless steel， and 45^# steel in the process of high-speed milling， this paper introduced the grey wolf algorithm （GWO） to improve the extreme learning machine （ELM） model to build the high-speed milling force prediction model， the second-order multiple regression model was used to analyze and determine the number of hidden layer nodes， the prediction results were compared with seven prediction models and experimental results， such as BP， RBF， ELM， etc. The research results show that the number of hidden layer nodes of the high-speed milling force prediction model based on GWO-ELM can be determined by the second-order multiple regression model， the accuracy of the prediction model is 98.8%， and the determination coefficient of 0.988 71 is better than other prediction models. Therefore， the high-speed milling force prediction model based on GWO-ELM is feasible and accurate. The research results of this paper provide a reference for the determination of the number of hidden layer nodes of the GWO-ELM model and the selection of the high-speed milling force prediction model.

Abstract:W-Ti［w（Ti）=10%］ alloy was prepared， and the influence of powder purity and W powder size on the density and microstructure of W-Ti［w（Ti）=10%］ alloy was studied. It is found that the higher the purity of powder， the higher the density of W-Ti［w（Ti）=10%］ alloy， and the lower the Ti rich phase proportion. The W-Ti［w（Ti）=10%］ alloy with 3N purity will retain pure Ti， and the proportion of Ti-rich phase is 31.28%. The W-Ti［w（Ti）=10%］ alloy with 4N and 4N5 purity does not have pure Ti， and the proportion of Ti-rich phase is 28.41% and 21.67%， respectively. The influence of W powder particle size is reflected in two aspects： the larger the W powder particle size， the better the mixing effect with Ti powder， the more conducive to diffusion； but the smaller the specific surface area， the less conducive to diffusion. With the increase of W particle size， the Ti-rich phase content of W-Ti［w（Ti）=10%］ alloy decreases first and then increases. In this experiment， when the particle size of W powder is 4~5 μm and the particle size of Ti powder is 44 μm， the microstructure properties of W-Ti［w（Ti）=10%］ alloy are the best， and the proportion of Ti-rich phase is 28.79%.

Abstract:Due to excellent physical and mechanical properties， carbon fiber reinforced plastics（CFRP） and titanium alloys （TC4） were often widely used in the aerospace industry as laminated structures. Since CFRP and TC4 were both typical difficult-to-machine materials， and had different mechanical and thermal properties， the tool wear was rapid during the hole-making process， which affected the machining quality. In order to ensure the quality of drilling and timely replacement of cutting tools， a tool wear condition monitoring model based on convolution neural network-long short time memory（CNN-LSTM） was established. The model took the feature of force and acoustic emission signals with strong correlation to tool wear as input and the tool wear condition labels as output to realize tool wear monitoring. The results show that the model has an accuracy rate of 97.222%， which can effectively monitor the tool wear status during the drilling process of CFRP/TC4 laminated structures.

Abstract:SiC particle reinforced aluminum matrix composites （SiC_p/Al） had excellent physical and mechanical properties and were widely used in aerospace， electronics， military and other high-end fields. In this paper， SiC_p/Al composites with a volume fraction of 20% were taken as the research object， and the dry milling test was carried out by using the single factor test method. The effects of the cutting edge radius and the cutting speed on the cutting force， surface morphology， surface roughness（Ra） and chip morphology were analyzed. The results show that the cutting force decreases with the increase of the cutting edge radius， and decreases first and then increases with the increase of the cutting speed. With the increase of the cutting edge radius， the pits and furrows on the machined surface decrease， and the Ra tends to decrease.With the increase of cutting speed， the scratch defects on the machined surface increase， and the Ra increases first and then decreases； Under different cutting edge radius and different cutting speed， the chip shapes appear irregular sawtooth. The micro morphology of non free surface of the chip gradually becomes smooth with the increase of the cutting edge radius， and more serious cracks appear with the increase of the cutting speed.

Abstract:This paper prepared and evaluated an epoxy resin system （V601） and its composite materials for a low-cost vacuum assisted resin infusion （VARI） molding process. This paper evaluated the resin matrix and its composite materials through DSC curves， rheological curves， and mechanical tests. The results show that the V601 epoxy resin system can be completely cured under a curing system of 120 ℃/2h； the process applicability period of resin is long （viscosity ≤ 500 mPa·s， 225 min）； the tensile strength of the resin cured material is 77.7 MPa， the tensile modulus is 3.25 GPa， the bending strength is 137.7 MPa， and the bending modulus is 3.37 GPa. The fiber volume content of SW280F/V601 composite material prepared by VARI method is 67.7%， the longitudinal tensile strength is 626 MPa， the longitudinal tensile modulus is 25.8 GPa， the longitudinal bending strength is 727.4 MPa， and the longitudinal bending modulus is 11.7 GPa. The results indicate that the V601 resin system has good applicability to VARI molding process， and the prepared composite materials also have high mechanical properties.

Abstract:Vacuum assisted resin transfer molding （VARTM） was a cost-effective method for fabricating wing T-shaped stringer， but the cross-section characteristics of the stringer were not conducive to the balanced resin flow during the molding process. Aiming at the problem of resin enrichment in triangle area of T-shaped stringer but insufficient wetting in edge area， the fiber filling method of corner triangle area of mold was adopted in this paper to optimize VARTM process parameters and improve the mechanical properties of T-shaped stringer. The influence of process scheme on the thickness uniformity of each part of stringer was studied. Optical microscope was used to observe the microstructure of the stringer. Moreover， the void content and fiber volume fractions were quantitatively analyzed by burning method. Besides， the mechanical properties of the stringer were tested by universal material testing machine. The results show that the T-shaped stringer formed by VARTM process has good thickness uniformity， high fiber volume fractions， low void content and good mechanical properties， the bending resistance of the stringer is increased by 15.72% and the void content is less than 1% （0.9%）.

Abstract:To improve the manufacturing accuracy of composite stiffened panels， this paper study the structural composition of composite stiffened panels based on the co-bonded forming process of composite stiffened panels. A calculation model is derived for the amount of prepreg required to fill the R region of the stiffeners， achieving precise filling of the R zone of co-bonded composite stiffened panels. The structural design of the molding fixture for composite stiffened panels is optimized， improving the positioning accuracy of the positioning pins and achieving precise control of the stiffener axis line position. A cutting template is made for the outline of the stiffener to achieve accurate cutting of the stiffener edge distance. By precisely filling the R zone of the stiffeners， precisely controlling the stiffener axis line position， and accurately cutting the stiffener edge distance， the precise manufacturing of composite stiffened panels with stiffeners is achieved.

Abstract:This study aimed to investigated the effects of steady magnetic fields with different intensities on laser cladding of Inconel 718 superalloy. Laser cladding experiments were conducted under four different magnetic field strengths （0，100，300，500 mT）， and numerical simulation combined with typical experiments was used to study the surface morphology， keyhole mode temperature field changes， microstructure， and mechanical properties of the cladding layer. The results show that when B=300 mT， the melting and evaporation latent heat barrier of the material is significantly suppressed， the morphology between the keyhole solid-liquid interface is most uniform， and the surface morphology of the cladding layer is optimal， with an average surface roughness Ra of about 4.1 μm. The microstructure is mainly composed of equiaxed grains with an average grain size of about 5.1 μm. Although the change in hardness is not significant， the average tensile strength of the cladding layer can be increased to 1.122 GPa， with an average elongation of 29.9%. The study demonstrates that a steady magnetic field of appropriate strength can significantly improve the comprehensive performance of the Inconel 718 laser cladding layer， providing theoretical basis and experimental data support for the application of magnetic-controlled laser cladding technology in related industrial fields.

Abstract:Based on Box-Behnken Design （BBD） method， the experimental research of alumina particles reinforced bonding was carried out. The multivariate regression models between bond characteristic parameters （particle size， adhesive layer thickness and mass fraction） and response values （failure load， energy absorption value） were established， and the models were verified by experiments. The RVE （representative volume element） model was established to verify the failure mechanism of adhesive layer fracture. The results indicate that the greatest impact on the failure load of the joint is particle size. The greatest impact on energy absorption value of the joint is particle mass fraction. The optimal process parameters are particle size of 46 μm， adhesive layer thickness of 0.6 mm and mass fraction of 5%. Finite element analysis shows that the addition of alumina particles changes the cracks propagation path， which increases the crack length and the fracture energy of adhesive layer， thus enhance the mechanical properties of adhesive joints.

Abstract:In order to investigate the influence of the precise control and time-varying coupling effect of the process parameters of tape winding on the performance and internal quality of composite with conical structure， this paper conducted optimization research on the key process parameters of tape winding forming for nozzle diffusion section products through design experiments and response surface methodology. The results show when using 50 mm wide carbon cloth tape for winding forming， the winding temperature and pressure were controlled at （60~65）℃/（700~800） N， and the interlayer shear strength can research 21 MPa， with fluctuation of 5% in the dB difference defected by ultrasound. Under these process conditions， there is a significant improvement in the internal quality of the product， with can meet the requirements of engineering and speed increase.

Abstract:The fused deposition 3D printing technology was used to print the pyramid structure. The printing material was PLA （thermoplastic plastic）， and the composite absorbing material of pyramid structure was prepared. The prepared pyramid samples were hollow structures， with a single pyramid wall thickness of 1 mm， a height of 20 mm， and a total base area of 200 mm×200 mm. The influence of the angle and height of the pyramid on the absorption performance was studied. The reflectance of the 4~18 GHz band range was measured by the bow method. Because the angular pyramid absorbing material had gradient structure， it also had many absorbing mechanisms such as dielectric loss and interference cancellation. The results show that the angular pyramid structure has excellent absorbing performance. The absorbing performance of the angular pyramid structure increases with the decrease of the angular cone angle （33°~73°）. Different angular pyramid structure parameters have different effects on the absorbing performance at C， X and Ku bands.

Abstract:In order to study the relationship between strain rate and mechanical performance of 2219 aluminum alloy， through the uniaxial tensile test in 6 different strain rates in 0.05、0.10、0.15、0.20、0.30、0.40 mm·s^-1， the stress-strain curve of 2219 aluminum alloy was obtained under different strain rates. In order to accord with the actual production situation， selected 4 larger strain rate in 0.075、0.30、0.40、0.55 mm·s^-1， changed the material state， conducted the uniaxial tensile test and metallographic analysis， the variation trend of mechanical performance of 2219 aluminum alloy was tested and verified under different strain rates. The results show that mechanical performance of 2219 aluminum alloy is insensitive in yield strength and tensile strength. As the strain rate goes up， percentage elongation has an upward trend. According to the actual situation of processing equipment， a higher deformation rate （recommended not to exceed 0.4 mm·s^-1） is chose to improve processing efficiency.