查看更多>>摘要：A new thermal protection design method for hypersonic vehicle's leading edge is pro-posed,which can effectively reduce temperature of the leading edge without additional cooling mea-sures.This method reduces the leading-edge's temperature by the multi-scale collaborative design of the macroscopic thermal optimization and the mesoscopic woven structures of Three-dimensional Orthogonal Woven Ceramic Matrix Composites(TOCMC).The macroscopic thermal optimization is achieved by designing different mesoscopic woven structures in different regions to create com-bined heat transfer channels to dredge the heat.The combined heat transfer channel is macroscop-ically represented by the anisotropic thermal conductivity of TOCMC.The thermal optimization multiple linear regression model is established to optimize the heat transport channel,which pre-dicts Theoretical Optimal Thermal Conductivity Configuration(TOTCC)in different regions to achieve the lowest leading-edge temperature.The function-oriented mesostructure design method is invented to design the corresponding mesostructure of TOCMC according to the TOTCC,which consists of universal thermal conductivity prediction formulas for TOCMC.These universal formu-las are firstly derived based on the thermal resistance network method,which is verified by exper-iments with an error of 6.25％.The results show that the collaborative design method can effectively reduce the leading edge temperature by about 12.8％without adding cooling measures.
查看更多>>摘要：This paper introduces an improvement to electrochemical drilling process by coupling flow field and electric field in pulsating state.A novel tube with half-wedged shape at the end(HW-tube)is prepared,with both sidewall and wedged part of the HW-tube insulated.Only the flat part is utilized to provide electric field for electrochemical drilling.By rotating the HW-tube,both flow field and electric field in pulsating state are generated,alternating in different positions within the inter-electrode gap(IEG).The pulsating flow field enhances the mass transfer process,while pul-sating electric field disperses material dissolution process and distribution of electrolytic by-products.Both pulsating fields are coupled at the same frequency,further enhancing the electro-chemical drilling process.Simulation results indicate that both flow field and electric field in pulsat-ing state are generated.Compared to the traditional tube,the HW-tube significantly reduces the number of residual particles in IEG,and this number is further reduced by increasing the rotation speed.Experimental results reveal that the surface quality and dimensional uniformity of small hole are improved with HW-tube.With feed rate of 2.22 mm/min,a small hole with diameter of 1.52 ±0.017 mm is drilled,resulting in a surface roughness of 0.331 μm.
查看更多>>摘要：To improve the service and machining performance of the workpiece,the tool wear mechanisms,surface machining quality,and wear resistance in conventional side milling(CSM)and longitudinal-torsional ultrasonic vibration side milling(LTUVSM)of GH4169 superalloy at different cutting lengths are investigated systematically.Tool wear mechanisms are revealed and the correlation between machined surface quality with tool wear is analyzed correspondingly.Tool wear patterns mainly include adhesive wear,diffusion wear,abrasive wear,and chipping sticking.Better surface quality is achieved in LTUVSM due to a maximum reduction of flank wear band-width and wear rate by 71.9％and 71.5％,respectively,compared to CSM.The friction coefficient,initial wear stage time,and wear volume of dry sliding wear were measured to evaluate the work-piece wear resistance.The maximum reductions in friction coefficient and wear volume in LTUVSM are 18.2％and 15.8％compared to CSM.The regular ultrasonic vibration textures sup-press the friction and the growth of contact nodes in the contact area,decreasing the degree of sur-face wear,which is demonstrated by a 38.8％increase in initial wear stage time compared to CSM.In conclusion,the workpiece in LTUVSM exhibits higher wear resistance because of the improve-ment of tool wear and the guarantee of surface quality.
查看更多>>摘要：In flat jet electrochemical milling,the electrolyte forms a backward parallel flow after impacting the workpiece,resulting in a weak current density distribution on the workpiece.Poor surface quality usually occurs on the machined titanium alloy surface because it inevitably suffers from the weak current density.In this study,a method of flat jet electrochemical milling with tai-loring the backward parallel flow was proposed to eliminate the negative effects caused by the weak current density.Multiphysics simulations are carried out to comprehend the mechanism of flat jet-EC milling with tailoring backward parallel flow and better construct the novel tool electrode.Experiments on flat jet electrochemical milling of TC4 alloy with and without tailoring backward parallel flow are conducted.The results reveal that,compared with flat jet electrochemical milling without tailoring backward parallel flow,the recommended tool reduces the surface roughness by 86％to 93％,and improves the material removal rate by 93％to 163％with different feed rates.Additionally,the recommended tool is more conducive to maintaining the inherent hardness of the material.Finally,a surface with low Sa of 0.37 μm is obtained.
查看更多>>摘要：To obtain final parts with the desired dimensional accuracy and repeatability via electro-chemical machining(ECM),the machining process must enter an ECM balanced state.However,for the ECM processing of blisk,a key component of aerospace engines,the surface of the blade blank often has an uneven allowance distribution due to the narrow passage of the cascade.It is difficult to remedy this issue in subsequent processing steps,which is necessary to ensure the dimen-sional accuracy and repeatability of the final blade profile.To solve this problem,electrolytic machining must be preceded by electrolytic shaping,which requires cathode tools with large leveling ratios to quickly homogenize the blank surface of the blade.In this study,to obtain a cathode tool with an extremely high leveling ratio,a design method based on the variation in the electrode gap in the non-equilibrium electrolytic state is proposed,and a dissolution model based on the non-equilibrium state is established.In this design method,the allowance on the blank to be machined is first divided into many discrete allowances with the normal direction.The initial machining clear-ance,feed rate,and total machining time are then calculated using classical ECM equilibrium state theory based on the maximum allowance.Meanwhile,the point coordinates of the cathode tool at maximum allowance can be determined.The non-equilibrium model can then be used to calculate the relative coordinate positions corresponding to the remaining discrete allowances.Finally,the entire cathode tool profile is designed.Simulations,fundamental experiments,and blisk unit work-piece experiments were carried out to validate the design approach.In the simulated processing of the plane workpiece,the leveling ratio of the cathode tool designed by the proposed method(0.77)was 83％higher than that of the cathode tool designed using the traditional method.The simulation results were confirmed by processing experiments.In the machining of blisk unit workpieces with complex curved surfaces,the leveling ratios of the convex and concave parts of the blade machined using the proposed cathode tool respectively reached 0.75 and 0.54,which are 75％and 38％higher than those obtained using the traditional method.This new cathode design method and machining technology can significantly improve the surface allowance distribution of blank before electrolytic finishing.It is helpful for finishing machine to enter electrolytic equilibrium state.Finally,the final blade profile accuracy can be guaranteed and repeated errors can be reduced.
查看更多>>摘要：Numerical simulation and experimental research on Linear Friction Welding(LFW)for GH4169 superalloy were carried out.Based on the joint microstructure and mechanical properties,a suitable welding process was determined,which provided an important theoretical basis for the manufacture and repair of aeroengine components such as the superalloy blisk.The results show that the joint strain rate gradually increases with the increase of welding frequency,and the defor-mation resistance of the thermoplastic metal increases in the welding process,resulting in the inter-face thermoplastic metal not being extruded in time to form a flash,so the joint shortening amount gradually decreases.The thermoplastic metal in the center of the welding surface is kept at high welding temperature for a long time,resulting in the decrease of the joint strength.The microhard-ness of the joint shows a"W"distribution perpendicular to the weld,and most of the joints break in the Thermo-Mechanically Affected Zone(TMAZ)with high tensile strength and low elongation.When the welding area is increased without changing the aspect ratio of the welding surface,the interface peak temperature increases gradually,and the joint shortening amount decreases with the increase of the welding interface size.
NETL
NSTL
万方数据