Abstract:

For the poor machining performance of engineering ceramics， the surface/subsurface is prone to processing damage， which significantly impacts the service performance and fatigue life of engineering ceramic parts， the grinding damage formation and evolution mechanism of engineering ceramics are elaborated from the aspects of strain rate effect and material constitutive relation models. Based on this analysis， the influencing factors and the regulation of the grinding damages are analyzed. Then the suppression strategy of grinding damages is investigated in two aspects： grinding tools and processing technology. Finally，a brief outlook on the future development direction of key technologies for grinding damage suppression is presented.

Abstract:

Exit damages frequently occur during the drlling of titanium alloy， and the drilling quality is directly influenced by the axial force of drilling. This paper develops an analytical model to predict the axial drilling force of Ti6Al4V titanium alloy and conducts experiments to validate this model. The accuracy of prediction model is verified by experimental data， and the effects of cutting parameters on both the axial force and drilling quality are investigated. The results show that the maximum error between the predicted and experimental value of axial force is 12.8%. The predicted axial force values show good consistency with the experimental results，demonstrating that the model can effectively predict the drilling axial force for titanium alloys.The axial force and hole exit burr height decrease as spindle speed increases at a constant feed rate. The axial force increases with rising feed rate at a constant spindle speed， but the hole exit burr height decreases at first then increases. Except for the impact of drilling temperature at low feed rates， the hole exit burr height has a positive correlation with the axial force. The surface of hole exit is not burned and the burr height is relatively small under a spindle speed of 1000 r/min and a feed rate of 40 mm/min. And the better drilling quality is obtained.

Abstract:

In order to study the impact protection mode of 7075/T651 aluminum alloy （rocket body material）， the cushioning and energy absorption properties of artificial cartilage Biomimetic material （ACF material）， two new foam materials with different densities， were studied by combining experiment and numerical simulation. The material compression tests at different rates were carried out to obtain the mechanical properties of the material at different strain rates. The protective performance of ACF material against aluminum alloy was studied through low-speed impact experiments. The impact stress， model energy change and displacement of aluminum alloy were analyzed based on the numerical model of low-speed impact. The experimental and numerical simulation studies show that the mechanical properties of ACF material have strain rate effect and are related to density. The foam material significantly reduce the impact stress on the protected object and has good cushioning and energy absorption . In addition， it can be used as an excellent arrow body protection material because of its low density and good flexibility.

Abstract:

During the cutting process of Al-50wt% Si alloy， plastic deformation of aluminum matrix and brittle failure of reinforced silicon particles easily lead to crack， edge collapse， burr and other defects， which is a typical difficult to machine material. In order to solve the problem of poor drilling quality of Al-50wt% Si alloy， this paper adopts single factor experimental method to dry drill Al-50wt% Si alloy， and research on the morphology of hole wall and edge defects. The results show that when the drill feed rate is 0.08 mm/r， the cutting speed increases from 30 m/min to 70 m/min， the axial force increases by 15.8%， and the hole wall surface roughness increases by 19.8%. At lower cutting speeds， the edge appearance at the hole outlet is dominated by particle shedding and burrs. With the increase of cutting speed， the edge appearance at the hole outlet is dominated by matrix ductile fracture，the radial width of edge defect at hole outlet increases； When the drill cutting speed is 50 m/min， the feed rate increases from 0.04 mm/r to 0.12 mm/r， the axial force increases by 74.3% on the whole， and the hole wall surface roughness increases by 50.2%.At lower feed rates increasses，the convex deformation and matrix ductile fracture occur at the outlet side of the hole.As the feed rate， the convex deformation decreases，the radial width of the edge defect at the hole outlet decreases first and then increases，and the minimum radial width is obtained when the feed rate is 0.08 mm/r.

Abstract:

A cutting model for SiC_p/Al composite material with SiC particles as JH2 constitutive model was established based on finite element simulation software， and was compared with previous cutting experiments. The research studied the trends associated with various SiC particle constitutive models， as well as the chip， surface morphology， and cutting force. The results show that the chips produced when cutting the SiC particles usin the JH2 model in SiC_p/Al composite material are more fragmented， and the particles at different positions on the material surface are closer to the actual cutting experiment， where there are extrusion， fracture， and protrusion. The overall cutting force fluctuates more gently. It is concluded that the JH2 constitutive model of SiC particles is suitable for cutting simulation of SiC_p/Al composite material.

Abstract:

Due to the fragility， hydrophilicity and high cost， the application of aerogels in civil fields is limited. In this paper， the flexible and hydrophobic polysilsesquioxane aerogel has been prepared using dimethyldimethoxysilane （DMDMS） and vinyltrimethoxysilane （VTMS） as co-precursors through atmospheric pressure drying. The effects of different silicon source ratios on the structure and properties of aerogels were studied. When n （ DMDMS/VTMS ）=2∶3， the silicon-based aerogel exhibits a three-dimensional nanoporous structure， which has low density （0.13 g/cm³）， low thermal conductivity ［2.919×10^-2 W/（m·K）］ and superhydrophobicity （151°）. Its maximum stress shows no significan change after 500 compression cycles under 50% deformation . According to this simple preparation process， the flexible aerogel has promising application prospects in the field of thermal insulation.

Abstract:

A simple one-pot method for preparing phenolic aerogel （PA） was proposed. Resorcinol and formaldehyde were mixed and added to an alkaline solution， with cetyltrimethylammonium chloride included as a surfactant. PA was prepared by sol-gel and high-temperature aging reactions. The effects of phenolic precursor ratio and pH on the structure and properties of aerogels were investigated. The results show that as formaldehyde content increases， the shrinkage rate of PA decreased，while the density and thermal conductivity increases. When the ratio of phenol to formaldehyde is 1∶4， the aerogel has a typical three-dimensional network structure， with the lowest density of 0.32 g/cm³， good thermal insulation and thermal conductivity of 0.0318 W/（m·K）， and the average particle size of PA was 1.059 μm. The higher the pH of the alkaline solution is， the more methylene and methylene ether bonds are， the larger the gel particle size is， and the closer the neck connection is. The PA prepared with ammonia as a catalyst has the smallest shrinkage， the lowest density， and the better thermal insulation performance and thermal stability.

Abstract:

IIn this paper，a series of high resilience silicone-modified polyimide foams （IBPIF-Si） were prepared.The pore structure， mechanical properties， foaming principles and the highest operating temperature of IBPIF-Si were investigated.Compared to pure IBPIF， IBPIF-Si showed the low density ［（22.0±6.7）mg/cm³）］，high porosity（97.93%），excellent hydrophobic ［the water contact angle was （128±2.72）°］ and outstanding flexibility（with a linear elastic region was 0~14.77%）.This unique modification method broadened the potential application of polyimide foam in the aerospace sector，including heat insulation，noise reduction，insulation and other aspects.

Abstract:

This paper is based on a national key project stratospheric long-endurance fixed-wing UAV project， which studies the manufacturing technology of wing structural components for unmanned aerial vehicles. To meet the strength， stiffness and stability of the wing structure， the main beam and leading edge of the carbon fiber composite foam sandwich structure were solidified using external molding and internal pressure， combined with hot plate oven heating technology. Load test and finite element analysis were conducted on the main beam products. According to the analysis results，the surface of the main beam product was reinforced.The results indicate that the reinforced main beam product can withstand 2.5 times the rated load and bear atorque of 102N·m， and the total weight of the main beam products was 7.2kg and the leading edge products weighed 0.19kg，achieving the lightweight of the wing structural components.The developed products meet the requirements of various indicators， and provide a new technical approach for the forming of ultra-light carbon fiber composite structural parts.

Abstract:

Composite structures made of woven composites undergo both physical and chemical changes during the curing process， and will produce deformation after demolding， which significantly impacts the accuracy of the parts. In order to accurately predict the deformation， this paper first establishes a multiscale analysis model for the curing deformation of woven composites parts， and combines the meso-mechanical method to obtain the evolution of mechanical and thermal properties of woven composites during the curing process. Then， the effects of curvature and thickness parameters on the curing characteristics of woven composite parts were further analyzed using the sequential thermo-mechanical coupling analysis method to simulate the thin shell parts of variable curvature and laminates with different curvature.The results showed that woven composite parts with a lower thickness have a lower temperature gradient during curing and a more uniform curing degree. The curvature parameters influence on the curing deformation of woven parts， and the thinner the member thickness， the more significant the effect of curvature on deformation. After the thin shell parts of variable curvature was cured and demolded， the maximum displacement in the warp and weft directions is greater than that in the thickness direction at the same curvature.

Abstract:

A laser welding process test was conducted on the lap joint of 0.40mm 0Cr17Ni4Cu4Nb and 0.26mm 3Cr19Ni9Mo2N stainless steel to investigate the microstructure and properties of the welded joint. The structure of the welded specimen was composed of three longitudinal welds created through lap welding. The HKQW-300 laser welding machine was utilized to perform welding joints in an argon atmosphere. The microstructure and mechanical properties of the welded joints were analyzed through tests. The results indicate that，when welding under the process parameters of a laser power of 20W， a defocusing amount of +8mm， a speed of 180mm/min， and argon protection， the weld of the 0Cr17Ni4Cu4Nb and 3Cr19Ni9Mo2N laser welded lap joint exhibits a ferritic weisman structure， with the weld width ranging from 335.3 to 404.0μm. The heat affected zone （HAZ） is narrow. The tensile force of the welded joint exceeds 5.493 9kN， which is better than 73.7% of the tensile force after 3Cr19Ni9Mo2N base metal strengthening， and meets the welding performance requirements of the product. The welding joint demonstrates excellent performance， and the welding seam has no phenomena such as virtual welding and welding penetration. This process has been extensively applied in the development of the pressing belt of the solar wing pressing and releasing mechanism for a satellite.

Abstract:

Two batches of cracked 50CrVA springs are analyzed by means of fracture analysis， chemical composition analysis， microstructure analysis and hardness test. The fracture mode and mechanism are revealed as well as the effective improvement measures. The results indicate that the fracture mode of the two batches of springs are both delayed brittle fracture. The fracture mechanism of the first batch is attributed tohydrogen embrittlement. The risk of hydrogen embrittlement can be reduced by increasing the tempering temperature and reducing the pickling time. The fracture mechanism of the second batch of springs is cadmium embrittlement. Zinc plating process can be used to enhance the heat resistance temperature of the springs coating and decrease the risk of embrittlement caused by low melting point metal.

Abstract:

For the verification of industrial CT detection sensitivity of micro-scale defects in metal additive manufacturing samples， an assembled structural specimen block， which includes a reference specimen， was designed and manufactured to evaluate detection performance in the target region of the part. Using the test block， the variation in defect detection sensitivity within its region of interest was preliminarily investigated under varying geometric magnifications and eccentricity distances. Results show that， with the reduction of the detection geometry magnification， and the increasing eccentricity distance， the size of the undetectable defects gradually increases， and the detectability of the defects and the accuracy of the identification gradually decreases.

Abstract:

The carbon fiber reinforced epoxy resin-based laminates （CFREL） were prepared using hot press tank molding process. The laminates were subjected to UV aging experiments under different temperature cycles through an artificial accelerated aging test， and the mechanical properties of the specimens were evaluated at different temperatures and times intervals and the microscopic morphology was observed by scanning electron microscope （SEM）. Studying the bending strength and interlaminar shear strength of CFREL subjected to UV aging. The life prediction was based on the residual strength model and the kinetic curve model. The results show that the calculated life prediction model aligns well with the experimental results， and the service life of the CFREL under natural light can be calculated with different strength retention rates.

Abstract:

The aging behavior of carboxy nitroso fluororubber in a liquid dinitrogen tetroxide （N₂O₄） medium was investigated using several analytical techniques. The results indicated that the glass transition temperature （T_g） of the samples did not change significantly with the increase of aging days， but the thermal stability of the samples decreased and swelling ratio increased. Meanwhile， microcracks gradually appeared on the surface of the samples. These results indicate the samples gradually aged in the liquid medium. X-ray photoelectron spectroscopy （XPS） results revealed that compared to the unaged samples， the proportion of elements on the surface of the aged samples did not change significantly，but some crosslinking points were destroyed. The thermogravimetric analysis-Fourier transform infrared spectroscopy-gas chromatography/mass spectrometry （TGA-IR-GC/MS） result showed that the surface modifier of silica filler undergo oxidation in N₂O₄ medium during the aging process， thus reducing the thermal stability of the samples.

Abstract:

This study investigates the free shape curve and calibration process of piston rings to address the differences between their assembly state and free state in isolation valves.This article adopts static reverse research to obtain the opening size of the piston ring in the free state of the isolation valve，and conducts mechanical tests on its opening size.The results indicate that the opening size meets the requirements of assembly mechanics.Additionally，the formula for the free state curve of the piston ring under isobaric conditions.A calibration method for isolation valve piston rings was proposed， and a reasonable calibration scheme was verified and optimized using finite element static simulation technology.These findings provide a fundamental method for small batch processing of piston rings.

Abstract:

In order to meet the accuracy of drilling workpieces of difficult-to-machine materials， such as titanium alloys，while improving processing efficiency and reducing production costs，this paper presents a combination of theoretical analysis， numerical simulation and experiment.he chip breaker structure is designed for the chip breaking problem in the drilling process， and the thrust force， chip breaking process， strain state and chip shape under different machining parameters are studied. The results show that the maximum thrust force error between the experimental and simulated data ranges from 10% to 20%， and the chip fracture morphology aligns closely，confirming the reliability of the finite element model. The chip length decreases as the feed decreases； Under different processing parameters， the thrust force of the drill bit with chip breaker is less than that without groove； The interaction between the chip and the chip surface leads to curling，with both the degree of curl and the stress increasing as the tool feed rate rises.

Abstract:

The research focuses on analyzing the deformation of workpieces induced by residual stresses，the three-dimensional finite element milling model is established， taking into account the influence of residual stress caused by the rate of the back-cutting amount on the deformation，the simulated residual stress is integrated into the model，the relationship between the simulated residual stress and deformation is examined， and the simulation reliability is verified through experiments. The results indicate that as the tooth increases， the residual compressive stress on the surface of the workpiece（d=0） in the X and Y directions correspindingly increases， and the residual stress remains relatively unchanged when the distance between the test point and the surface exceeds 10μm. Wthe the increase in the number of baak-cutting tools，the residual stress on the surface of the workpiece in the X and Y directions increases accordingly. The deformation of the surface layer escalates with the rise in the feed rate of each tooth and also increases with the amount of back-cutting. A comparison of simulation and test results indicates that the maching deformation trends are fundamentally similar，thereby confirming the reliablity of the modeling.

Abstract:

Due to the high ambient temperature and humidity associated with a specific type of fairing， the product performance may be adversely affected if the fairing is stored for an extended period. In order to verify the influence of hot and humid environment on the properties of aluminum honeycomb sandwich structure composites， the samples were subjected to conditions of 80 ℃ and 85% relative humidity， and the relationship between storage time and moisture absorption was investigated，along with the effects of the hot and humid environment on the properties of flatwise tension strength， double compression shear and edgewise compressive strength. The test results show that the water absorption reaches equilibrium when the storage time reaches 8 days， the double compression shear strength remains relativel unchanged， and the flatwise tension strength decreases by 11.08%.Additionally，the edgewise compressive strength and edgewise compressive modulus decreas by 11.04% and 13.94% respectively. An analysis of the damage morphology reveals that after the water absorption reached equilibrium， the Al/Mg ratio on the surface of aluminum honeycomb increases from 42.11% to 48.79%， and the honeycomb appearance did not change significantly. At this time， the failure morphology of the flatwise tensile specimen transitions from aluminum honeycomb failure to aluminum honeycomb and aluminum honeycomb/panel interface mixed failure mode.