7075 aluminum alloy is often used as an important load-bearing structure in aircraft industry due to its superior mechanical properties.During the process of deep hole boring,the boring bar is prone to vibrate because...7075 aluminum alloy is often used as an important load-bearing structure in aircraft industry due to its superior mechanical properties.During the process of deep hole boring,the boring bar is prone to vibrate because of its limited machining space,bad environment and large elongation induced low stiffness.To reduce vibration and improve machined surface quality,a particle damping boring bar,filled with particles in its inside damping block,is designed based on the theory of vibration control.The theoretical damping coefficient is determined,then the boring bar structure is designed and trial-manufactured.Experimental studies through impact testing show that cemented carbide particles with a diameter of 5 mm and a filling rate of 70% achieve a damping ratio of 19.386%,providing excellent vibration reduction capabilities,which may reduce the possibility of boring vibration.Then,experiments are setup to investigate its vibration reduction performance during deep hole boring of 7075 aluminum alloy.To observe more obviously,severe working conditions are adopted and carried out to acquire the time domain vibration signal of the head of the boring bar and the surface morphologies and roughness values of the workpieces.By comparing different experimental results,it is found that the designed boring bar could reduce the maximum vibration amplitude by up to 81.01% and the surface roughness value by up to 47.09% compared with the ordinary boring bar in two sets of experiments,proving that the designed boring bar can effectively reduce vibration.This study can offer certain valuable insights for the machining of this material.展开更多
The centroid coordinate serves as a critical control parameter in motion systems,including aircraft,missiles,rockets,and drones,directly influencing their motion dynamics and control performance.Traditional methods fo...The centroid coordinate serves as a critical control parameter in motion systems,including aircraft,missiles,rockets,and drones,directly influencing their motion dynamics and control performance.Traditional methods for centroid measurement often necessitate custom equipment and specialized positioning devices,leading to high costs and limited accuracy.Here,we present a centroid measurement method that integrates 3D scanning technology,enabling accurate measurement of centroid across various types of objects without the need for specialized positioning fixtures.A theoretical framework for centroid measurement was established,which combined the principle of the multi-point weighing method with 3D scanning technology.The measurement accuracy was evaluated using a designed standard component.Experimental results demonstrate that the discrepancies between the theoretical and the measured centroid of a standard component with various materials and complex shapes in the X,Y,and Z directions are 0.003 mm,0.009 mm,and 0.105 mm,respectively,yielding a spatial deviation of 0.106 mm.Qualitative verification was conducted through experimental validation of three distinct types.They confirmed the reliability of the proposed method,which allowed for accurate centroid measurements of various products without requiring positioning fixtures.This advancement significantly broadened the applicability and scope of centroid measurement devices,offering new theoretical insights and methodologies for the measurement of complex parts and systems.展开更多
In this work,a heterogeneous structure(HS)with an alternating distribution of coarse and fineαlamella is fabricated in bimodal Ti6242 alloy via insufficient diffusion of alloying elements induced by fast heat-ing tre...In this work,a heterogeneous structure(HS)with an alternating distribution of coarse and fineαlamella is fabricated in bimodal Ti6242 alloy via insufficient diffusion of alloying elements induced by fast heat-ing treatment.Instead of a distinct interface between the primaryα_(p)hase(α_(p))andβ_(t)ransformation microstructure(β_(t))in the equiaxed microstructure(EM),allα_(p)/β_(t)interfaces are eliminated in the HS,and the largeα_(p)phases are replaced by coarseαlamella.Compared to the EM alloy,the heterostruc-tured alloy exhibits a superior strength-ductility combination.The enhanced strength is predominantly attributed to the increased interfaces ofα/βplates and hetero-deformation induced(HDI)strengthening caused by back stress.Meanwhile,good ductility is ascribed to its uniform distribution of coarse and fineαlamella,which effectively inhibits strain localization and generates an extra HDI hardening.This can be evidenced by the accumulated geometrically necessary dislocations(GNDs)induced by strain partitioning of the heterostructure.Significantly,the HDI causes extra<c+a>dislocations piling up in the coarseαlamella,which generates an extra strain hardening to further improve the ductility.Such hetero-interface coordinated deformation mechanism sheds light on a new perspective for tailoring bimodal titanium al-loys with excellent mechanical properties.展开更多
The development of new quality productivity has set new requirements for vocational education.Vocational colleges need to integrate ideological and political education into professional courses to cultivate high-quali...The development of new quality productivity has set new requirements for vocational education.Vocational colleges need to integrate ideological and political education into professional courses to cultivate high-quality talents with both technical capabilities and political literacy.This paper analyzes the connotation of new quality productivity and its reshaping of vocational education,explores the challenges faced by the educational mechanism of Curriculumbased Political and Ideological Education(CPIE),and proposes a“three-dimensional synergy”practical pathway.That is,to effectively promote CPIE through three dimensions:the deep integration of cases with professional content,the enhancement of teaching effects using digitization,and the optimization of the course evaluation system.It aims to provide theoretical support and practical references for the reform of ideological and political education in vocational colleges.展开更多
With the economic and social development of the country,vocational education is playing an increasingly significant role in cultivating highly skilled talents.However,the mechanical drawing courses in vocational colle...With the economic and social development of the country,vocational education is playing an increasingly significant role in cultivating highly skilled talents.However,the mechanical drawing courses in vocational colleges still face numerous challenges in the teaching process,such as outdated textbook content,inadequate practical resources,weak teaching staff,and low student interest.This paper aims to explore these issues and propose corresponding coping strategies.The findings of this study not only provide specific improvement suggestions for vocational colleges but also emphasize the importance of these strategies in enhancing students’comprehensive abilities and promoting the development of vocational education.By addressing these challenges,this paper contributes to the enhancement of teaching quality and the overall advancement of vocational skills education.展开更多
Rich-nickel layered ternary NCM811 has been widely used in the field of electric vehicles ascribed to its high theoretical specific capacity.However,poor cycling stability and rate-performance hindered its further dev...Rich-nickel layered ternary NCM811 has been widely used in the field of electric vehicles ascribed to its high theoretical specific capacity.However,poor cycling stability and rate-performance hindered its further development.Herein,different amounts of nitrogen-doped carbon were wrapped on the surface of NCM811 via a facile rheological phase method by regulating the amount of dopamine hydrochloride.The effects of the coating amounts on the structure and electrochemical performance are investigated.The DFT calculation,XRD,SEM and XPS reveal that an appropriate amount of nitrogen-doped carbon coating could uniformly form a protective layer on the NCM811 surface and the introduced N could anchor Ni atoms to inhibit the Li^(+)/Ni^(2+)mixing,but excessive amount would reduce Ni^(3+)to Ni^(2+)so as to conversely aggravate Li^(+)/Ni^(2+)mixing.Among the samples,the NCM811-CN0.75 sample exhibits the most excellent electrochemical performance,delivering a high-rate capacity of 151.6 mA·h/g at 10C,and long-term cyclability with 82.2%capacity retention after 300 cycles at 5C,exhibiting remarkable rate-performance and cyclability.展开更多
In this paper,a topology optimization method for coordinated stiffness and strength design is proposed under mass constraints,utilizing the Solid Isotropic Material with Penalization approach.Element densities are reg...In this paper,a topology optimization method for coordinated stiffness and strength design is proposed under mass constraints,utilizing the Solid Isotropic Material with Penalization approach.Element densities are regulated through sensitivity filtering tomitigate numerical instabilities associatedwith stress concentrations.Ap-norm aggregation function is employed to globalize local stress constraints,and a normalization technique linearly weights strain energy and stress,transforming the multi-objective problem into a single-objective formulation.The sensitivity of the objective function with respect to design variables is rigorously derived.Three numerical examples are presented,comparing the optimized structures in terms of strain energy,mass,and stress across five different mathematical models with varying combinations of optimization objectives.The results validate the effectiveness and feasibility of the proposed method for achieving a balanced design between structural stiffness and strength.This approach offers a new perspective for future research on stiffness-strength coordinated structural optimization.展开更多
This paper investigates a wireless powered communication network(WPCN)facilitated by an unmanned aerial vehicle(UAV)in Internet of Things(IoT)networks,where multiple IoT devices(IoTDs)gather energy from a terrestrial ...This paper investigates a wireless powered communication network(WPCN)facilitated by an unmanned aerial vehicle(UAV)in Internet of Things(IoT)networks,where multiple IoT devices(IoTDs)gather energy from a terrestrial energy station(ES)during the wireless energy transfer(WET)stage,followed by the UAV collecting data from these powered IoTDs with the time division multiple access(TDMA)protocol in the wireless information transfer(WIT)stage.To overcome the challenges of radio propagation caused by obstructions,we incorporate a reconfigurable intelligent surface(RIS)to enhance the link quality of the ES-IoTDs and IoTDs-UAV.The primary objective is to maximize the average sum rate of all IoTDs by jointly optimizing UAV trajectory,ES transmit power,and RIS phase shifts,along with the time allocation for WET and WIT.To this end,we reformulate the optimization problem as a markov decision process(MDP)and introduce a deep reinforcement learning(DRL)approach for addressing the formulated problem,called the proximal policy optimization(PPO)based energy harvesting with trajectory design and phase shift optimization(PPO-EHTDPS)algorithm.By continuously exploring within the environment,the PPO algorithm refines its policy to optimize the UAV trajectory,the energy phase shifts,ES transmit power,and WET/WIT time allocation.Additionally,a continuous phase shift optimization algorithm is employed to determine the information phase shifts for each IoTD to maximize average sum rate.Finally,numerical results demonstrate that the proposed PPOEHTDPS algorithm can significantly achieve higher average sum rate and show better convergence performance over the benchmark algorithms.展开更多
The remaining useful life prediction of rolling bearing is vital in safety and reliability guarantee.In engineering scenarios,only a small amount of bearing performance degradation data can be obtained through acceler...The remaining useful life prediction of rolling bearing is vital in safety and reliability guarantee.In engineering scenarios,only a small amount of bearing performance degradation data can be obtained through accelerated life testing.In the absence of lifetime data,the hidden long-term correlation between performance degradation data is challenging to mine effectively,which is the main factor that restricts the prediction precision and engineering application of the residual life prediction method.To address this problem,a novel method based on the multi-layer perception neural network and bidirectional long short-term memory network is proposed.Firstly,a nonlinear health indicator(HI)calculation method based on kernel principal component analysis(KPCA)and exponential weighted moving average(EWMA)is designed.Then,using the raw vibration data and HI,a multi-layer perceptron(MLP)neural network is trained to further calculate the HI of the online bearing in real time.Furthermore,The bidirectional long short-term memory model(BiLSTM)optimized by particle swarm optimization(PSO)is used to mine the time series features of HI and predict the remaining service life.Performance verification experiments and comparative experiments are carried out on the XJTU-SY bearing open dataset.The research results indicate that this method has an excellent ability to predict future HI and remaining life.展开更多
Developing high-efficiency catalyst is crucial for electrochemical conversion of carbon dioxide(CO_(2))to high-value products.In the present work,a three-chamber electrolysis cell has been developed for CO_(2)reductio...Developing high-efficiency catalyst is crucial for electrochemical conversion of carbon dioxide(CO_(2))to high-value products.In the present work,a three-chamber electrolysis cell has been developed for CO_(2)reduction to carbon monoxide(CO)in an organic electrolyte,with sodium hydroxide(NaOH)and chlorine(Cl_(2))produced as byproducts.In order to improve the performance of the three-chamber electrolyzer,a gallium-based(Ga-based)ternary-porous catalyst(Ga-In_(4)Ag_(9))has been fabricated.During the long-term electrolysis process,Ga-In_(4)Ag_(9)catalyst exhibits good performance toward CO_(2)reduction reaction(CO_(2)RR),the CO partial current density achieves to 139.21 mA·cm^(-2)at-2.4 V(vs.SHE),with the Faraday efficiency(FE)of CO formation stabled at 92.3%.Density functional theory(DFT)analysis reveals that the position of the d-band center of Ga-In_(4)Ag_(9)is regulated by silver(Ag)atoms,which is beneficial for enhancing the binding ability between the catalyst and the intermediate.Owing to the adsorption of Cl^(-)on the surface of Ga-In_(4)Ag_(9),the reconfiguration of electron density has been altered,which is beneficial for the stabilization of*CO_(2)-intermediate.This work provides valuable insights for designing Ga-based metal catalysts toward CO_(2)electrolysis to produce high-value chemicals.展开更多
As one of the alloy-type lithium-ion electrodes,Bi has outstanding application prospects for large volume capacity(3800 mAh·cm^(-3))and high electronic conductivity(1.4×10^(7)S·m^(-1)).However,the fast-...As one of the alloy-type lithium-ion electrodes,Bi has outstanding application prospects for large volume capacity(3800 mAh·cm^(-3))and high electronic conductivity(1.4×10^(7)S·m^(-1)).However,the fast-charging performance is hindered by significant volume expansion(>218%)and a low rate of phase diffusion.To overcome these two problems,an N-doped carbon nanoflower coating layer was elaborately in-situ reconstructed on a multiple-wall Bi microsphere by hydrothermal methods and subsequent calcination in this study.The carbon nanoflowers greatly increase specific surface area(40.0 m^(2)·g^(-1))and alleviate the volume expansion(130%).In addition,the incorporation of N-doped carbon nanoflowers leads to a gradual enhancement in the Li adsorption energy of Bi during the process of lithium insertion and improves the electrical conductivity.Therefore,the contribution rate of pseudo-capacitance reached 87.5%at the scan rate of 0.8 mV·s^(-1),and the Li-ion diffusion coefficient(D_(Li^(+)))was calculated in the range of 10^(-10)to 10^(-12)cm^(2)·s^(-1).The Bi@CNFs anode provided a high specific volumetric capacity of 2117.0 mAh·cm^(-3)at 5C and a high capacity retention ratio of 93.2%after 800 cycles.The Bi@CNFs//LiFePO_(4)full cell also displayed a stable capacity of 113.9 mAh·g^(-1)and energy density of 296.1 Wh·kg^(-1)after 100 cycles with a Coulombic efficiency of 97.6%.The mechanism of fast-charging lithium storage was verified by distribution of relaxation time analysis and density functional theory calculation.This paper provides a new strategy to increase the pseudo-capacitance and reduce the volume expansion for the preparation of alloy-type fast-charging electrodes.展开更多
The hot deformation behavior of 2707 hyper duplex stainless steel(HDSS)was investigated through a hot compression test at 950℃ to 1,250℃ at strain rates of 0.01 s^(-1) to 10 s^(-1).Observations from the flow stress ...The hot deformation behavior of 2707 hyper duplex stainless steel(HDSS)was investigated through a hot compression test at 950℃ to 1,250℃ at strain rates of 0.01 s^(-1) to 10 s^(-1).Observations from the flow stress curves reveal a balance between work hardening and dynamic recovery at the beginning of the deformation and subsequently demonstrate various softening mechanisms with the increase of strain.At high strain rates,dynamic recovery is the prevailing mechanism,whereas,at medium and low strain rates,dynamic recrystallization becomes dominant.The constitutive equation was constructed,and the deformation activation energy was calculated to be 645.46 kJ·mol^(-1).The hot processing map was drawn based on the dynamic material model at a strain of 0.8.The results indicate that the hot workability of 2707 HDSS decreases due to its high alloying content.The microstructure evolution of 2707 HDSS at 1,050℃ was identified by means of electron backscatter diffraction and transmission electron microscopy.The results demonstrate that the ferrite completes dynamic recrystallization at the strain rate of 1 s^(-1).The softening process of austenite is influenced by ferrite and mainly experiences dynamic recovery.The austenite located at the α/γ phase boundaries tends to undergo dynamic recrystallization.展开更多
In order to improve the corrosion and mechanical properties of AM50 magnesium alloy, 1 wt.% Gd was used to modify the AM50 magnesium alloy. The microstructure, corrosion and mechanical properties were evaluated by X-r...In order to improve the corrosion and mechanical properties of AM50 magnesium alloy, 1 wt.% Gd was used to modify the AM50 magnesium alloy. The microstructure, corrosion and mechanical properties were evaluated by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, energy dispersive spectroscopy （EDS）, electrochemical and mechanical stretch methods. The results indicated that β-Mg17Al12 phase decreased and Al2Gd3 and Al0.4GdMn1.6 phase existed after Gd addition. Because of the Gd addition, the grain of AM50 magnesium alloy was refined significantly, which improved the tensile strength of AM50 magnesium al-loy. The decreasing ofβ phase improved the corrosion resistance of the magnesium alloy. The fracture mechanism of the Gd modified AM50 magnesium alloy was quasi-cleavage fracture. The corrosion residual strength （CRS） of AM50 magnesium alloy was im-proved after 1 wt.% Gd addition.展开更多
Ball spinning is applied to manufacturing thin-walled tube with high precision and high mechanical properties.On the basis of plastic mechanics,by simplifying ball spinning of thin-walled tube as plane strain problem,...Ball spinning is applied to manufacturing thin-walled tube with high precision and high mechanical properties.On the basis of plastic mechanics,by simplifying ball spinning of thin-walled tube as plane strain problem,slab method is used for the purpose of calculating the contact deformation pressure.The spinning force components,the torsional moment,the deformation power and the deformation work are calculated further as well.The influence of the two important process parameters such as the feed ratio and the ball diameter on the spinning force components is analyzed in order to further control the spinning force components by regulating the two process variables during the ball spinning process.The stress and strain state in deformable zone as well as mechanics boundary conditions in ball spinning are obtained.The effect of the three spinning force components on the formability of the spun part is analyzed and validated through the ball spinning experiments.The theoretical and experimental results show that the radial spinning component plays a significant role in ball spinning of thin-walled tube,and the mechanics situation in backward ball spinning contributes to enhancing the plasticity of the metal material,but that in forward ball spinning contributes to advancing the axial flow of the metal material.展开更多
Based on the process experiments, micrography analysis was dedicated to advancing the understanding of plastic flow of the metal in backward ball spinning of thin-walled tubular part with longitudinal inner ribs. Micr...Based on the process experiments, micrography analysis was dedicated to advancing the understanding of plastic flow of the metal in backward ball spinning of thin-walled tubular part with longitudinal inner ribs. Micrography analysis reveals that severe plastic deformation leads to grain refinement, grain orientation and grain flow line of the spun part. Based on rigid-plastic finite element method, DEFORME3D finite element code was used to simulate and analyze multi-pass backward ball spinning of thin-walled tubular part with longitudinal inner ribs. Finite element simulation results involve the distributions of the strain, the shape variation of the inner ribs as well as the prediction of the spinning loading.展开更多
Low weight and good toughness thin plate parts are widely used in modem industry, but its flexibility seriously impacts the machinability. Plenty of studies locus on the influence of machine tool and cutting tool on t...Low weight and good toughness thin plate parts are widely used in modem industry, but its flexibility seriously impacts the machinability. Plenty of studies locus on the influence of machine tool and cutting tool on the machining errors. However, few researches focus on compensating machining errors through the fixture. In order to improve the machining accuracy of thin plate-shape part in face milling, this paper presents a novel method for compensating the surfacc errors by prebending the workpiece during the milling process. First, a machining error prediction model using finite element method is formulated, which simplifies the contacts between the workpiece and fixture with spring constraints. Milling fbrces calculated by the micro-unit cutting force model arc loaded on the error prediction model to predict the machining error. The error prediction results are substituted into the given formulas to obtain the prebending clamping forces and clamping positions. Consequently, the workpiece is prebent in terms of the calculated clamping forces and positions during the face milling operation to reduce the machining error. Finally, simulation and experimental tests are carried out to validate the correctness and efficiency of the proposed error compensation method. The experimental measured flatness results show that the flatness improves by approximately 30 percent through this error compensation method. The proposed mcthod not only predicts the machining errors in face milling thin plate-shape parts but also reduces the machining errors by taking full advantage of the workpiece prebending caused by fixture, meanwhile, it provides a novel idea and theoretical basis for reducing milling errors and improving the milling accuracy.展开更多
The(Cu−10Sn)−Ni−MoS2 composites,prepared by powder metallurgy,were studied for the effects of Ni-coated MoS2 on the microstructure,mechanical properties and lubricating properties.The mechanism of effects of Ni and Mo...The(Cu−10Sn)−Ni−MoS2 composites,prepared by powder metallurgy,were studied for the effects of Ni-coated MoS2 on the microstructure,mechanical properties and lubricating properties.The mechanism of effects of Ni and MoS2 on the properties of composites was analyzed through a comparative experiment by adding Ni and MoS2 separately.The results show that the nickel wrapping around the MoS2 particles decreases the reaction rate of MoS2 with the copper matrix,and greatly improves the bonding of the matrix.The composites with 12 wt.%Ni-coated MoS2(C12)show the optimum performance including the mechanical properties and tribological behaviors.Under oil lubrication conditions,the friction coefficient is 0.0075 with a pressure of 8 MPa and a linear velocity of 0.25 m/s.The average dry friction coefficient,sliding against 40Cr steel disc,is measured to be 0.1769 when the linear velocity and pressure are 0.25 m/s and 4 MPa,respectively.展开更多
Backward ball spinning was applied for manufacturing thin-walled tubular parts with longitudinal inner ribs. Rigid-plastic finite element method(FEM) was used for simulating the backward ball spinning process in order...Backward ball spinning was applied for manufacturing thin-walled tubular parts with longitudinal inner ribs. Rigid-plastic finite element method(FEM) was used for simulating the backward ball spinning process in order to calculate the height of the inner ribs. With a view to guarantee a better simulation accuracy, it is essential to enhance and improve some general problems of FEM, such as generation of initial velocity field, choice of penalty factor, determination of boundary conditions, treatment of rigid region and description of convergence criteria. It is evident that whether the problems with respect to FEM are dealt with appropriately or not, they have a significant influence on the modeling accuracy and efficiency. By reasonable solving the general problems, rigid-plastic FEM can successfully simulate the height of the inner ribs and the calculated values are in good agreement with the measured values.展开更多
The present work inainly focuses on tlie effect of minor cofiteut of Gd cicmcnt on the micrGstmcturc and mechanical properties of Mg Zn alloy.The Mg-4Zn-xGd(x=0,0.5,1,2)alloys were fabricated and subjected to extrusio...The present work inainly focuses on tlie effect of minor cofiteut of Gd cicmcnt on the micrGstmcturc and mechanical properties of Mg Zn alloy.The Mg-4Zn-xGd(x=0,0.5,1,2)alloys were fabricated and subjected to extrusion at 280℃with the ratio of 25:1.Results revealed that the addition of Gd could inhibit the dynamic recrystallization(DRX)of Mg-4Zn alloy,and both the size and volume fraction of DRXed grains demonstrated a decreasing tendency as the Gd content increased from 0.5 to 2 wt.%.It is the weakening effect on DRX behavior that lead to the smaller amount of fine precipitate and the stronger texture intensity.As compared with the Mg-4Zn alloy,the yield strength and ultimate tensile strength of Mg-4Zn-xGd alloys were improved obviously by the addition of minor content of Gd,however,at the expense of elongation.Excellent tensile properties with the yield strength of〜369.8 MPa and ultimate tensile strength of〜400.3 MPa were obtained when the Gd content was 2 wt.%.展开更多
The phenomenon of heat accumulation and transportation in the composite materials is a very typical and critical issue during drilling process.In this study,a three-dimensional temperature field prediction model is pr...The phenomenon of heat accumulation and transportation in the composite materials is a very typical and critical issue during drilling process.In this study,a three-dimensional temperature field prediction model is proposed using finite difference method,based on the partly homogenization hypothesis of material,to predict temperature field in the process of drilling unidirectional carbon fiber/epoxy(C/E)composites.According to the drilling feed motion,drilling process is divided into four stages to study the temperature distributing characteristics.The results show that the temperature distribution predicted by numerical study has a good agreement with the experimental results.The temperature increases with increasing the drilling depth,and the burn phenomena is observed due to the heat accumulation,especially at the drill exit.Due to the fiber orientation,an elliptical shape of the temperature field along the direction is found for both numerical and experimental studies of C/E composites drilling process.展开更多
基金supported by the Scientific Research Program of Tianjin Education Committee(No.2022ZD030)。
文摘7075 aluminum alloy is often used as an important load-bearing structure in aircraft industry due to its superior mechanical properties.During the process of deep hole boring,the boring bar is prone to vibrate because of its limited machining space,bad environment and large elongation induced low stiffness.To reduce vibration and improve machined surface quality,a particle damping boring bar,filled with particles in its inside damping block,is designed based on the theory of vibration control.The theoretical damping coefficient is determined,then the boring bar structure is designed and trial-manufactured.Experimental studies through impact testing show that cemented carbide particles with a diameter of 5 mm and a filling rate of 70% achieve a damping ratio of 19.386%,providing excellent vibration reduction capabilities,which may reduce the possibility of boring vibration.Then,experiments are setup to investigate its vibration reduction performance during deep hole boring of 7075 aluminum alloy.To observe more obviously,severe working conditions are adopted and carried out to acquire the time domain vibration signal of the head of the boring bar and the surface morphologies and roughness values of the workpieces.By comparing different experimental results,it is found that the designed boring bar could reduce the maximum vibration amplitude by up to 81.01% and the surface roughness value by up to 47.09% compared with the ordinary boring bar in two sets of experiments,proving that the designed boring bar can effectively reduce vibration.This study can offer certain valuable insights for the machining of this material.
基金supported by National Natural Science Foundation of China(No.52176122).
文摘The centroid coordinate serves as a critical control parameter in motion systems,including aircraft,missiles,rockets,and drones,directly influencing their motion dynamics and control performance.Traditional methods for centroid measurement often necessitate custom equipment and specialized positioning devices,leading to high costs and limited accuracy.Here,we present a centroid measurement method that integrates 3D scanning technology,enabling accurate measurement of centroid across various types of objects without the need for specialized positioning fixtures.A theoretical framework for centroid measurement was established,which combined the principle of the multi-point weighing method with 3D scanning technology.The measurement accuracy was evaluated using a designed standard component.Experimental results demonstrate that the discrepancies between the theoretical and the measured centroid of a standard component with various materials and complex shapes in the X,Y,and Z directions are 0.003 mm,0.009 mm,and 0.105 mm,respectively,yielding a spatial deviation of 0.106 mm.Qualitative verification was conducted through experimental validation of three distinct types.They confirmed the reliability of the proposed method,which allowed for accurate centroid measurements of various products without requiring positioning fixtures.This advancement significantly broadened the applicability and scope of centroid measurement devices,offering new theoretical insights and methodologies for the measurement of complex parts and systems.
基金financially supported by the National Natural Science Foundation of China(Nos.52161019 and 52271054)the Science and Technology Project of Guizhou Province,China(No.[2023]047)+1 种基金the GuiZhou DIIT Innovation Project(No.[2023]153)the One Hundred Person Project of Guizhou Province,China(No.[2020]6006).
文摘In this work,a heterogeneous structure(HS)with an alternating distribution of coarse and fineαlamella is fabricated in bimodal Ti6242 alloy via insufficient diffusion of alloying elements induced by fast heat-ing treatment.Instead of a distinct interface between the primaryα_(p)hase(α_(p))andβ_(t)ransformation microstructure(β_(t))in the equiaxed microstructure(EM),allα_(p)/β_(t)interfaces are eliminated in the HS,and the largeα_(p)phases are replaced by coarseαlamella.Compared to the EM alloy,the heterostruc-tured alloy exhibits a superior strength-ductility combination.The enhanced strength is predominantly attributed to the increased interfaces ofα/βplates and hetero-deformation induced(HDI)strengthening caused by back stress.Meanwhile,good ductility is ascribed to its uniform distribution of coarse and fineαlamella,which effectively inhibits strain localization and generates an extra HDI hardening.This can be evidenced by the accumulated geometrically necessary dislocations(GNDs)induced by strain partitioning of the heterostructure.Significantly,the HDI causes extra<c+a>dislocations piling up in the coarseαlamella,which generates an extra strain hardening to further improve the ductility.Such hetero-interface coordinated deformation mechanism sheds light on a new perspective for tailoring bimodal titanium al-loys with excellent mechanical properties.
基金supported by the Beijing Municipal Commission of Education(Project Leader:Shang Wang,Project No.ZYJYDJ2024049).
文摘The development of new quality productivity has set new requirements for vocational education.Vocational colleges need to integrate ideological and political education into professional courses to cultivate high-quality talents with both technical capabilities and political literacy.This paper analyzes the connotation of new quality productivity and its reshaping of vocational education,explores the challenges faced by the educational mechanism of Curriculumbased Political and Ideological Education(CPIE),and proposes a“three-dimensional synergy”practical pathway.That is,to effectively promote CPIE through three dimensions:the deep integration of cases with professional content,the enhancement of teaching effects using digitization,and the optimization of the course evaluation system.It aims to provide theoretical support and practical references for the reform of ideological and political education in vocational colleges.
基金support from the Science and Technology Key Project of Beijing Polytechnic(Project Leader:Jinru Ma,No.2024X008-KXZ).
文摘With the economic and social development of the country,vocational education is playing an increasingly significant role in cultivating highly skilled talents.However,the mechanical drawing courses in vocational colleges still face numerous challenges in the teaching process,such as outdated textbook content,inadequate practical resources,weak teaching staff,and low student interest.This paper aims to explore these issues and propose corresponding coping strategies.The findings of this study not only provide specific improvement suggestions for vocational colleges but also emphasize the importance of these strategies in enhancing students’comprehensive abilities and promoting the development of vocational education.By addressing these challenges,this paper contributes to the enhancement of teaching quality and the overall advancement of vocational skills education.
基金Project(2021H0028) supported by the Natural Scienceof Fujian Province,ChinaProject(JAT200455) supported by the Fujian Provincial Young and Middle-aged Teacher Education Project,ChinaProject(fma2023003) supported by the Open Fund of Fujian Provincial Key Laboratory of Functional Materials and Applications,China。
文摘Rich-nickel layered ternary NCM811 has been widely used in the field of electric vehicles ascribed to its high theoretical specific capacity.However,poor cycling stability and rate-performance hindered its further development.Herein,different amounts of nitrogen-doped carbon were wrapped on the surface of NCM811 via a facile rheological phase method by regulating the amount of dopamine hydrochloride.The effects of the coating amounts on the structure and electrochemical performance are investigated.The DFT calculation,XRD,SEM and XPS reveal that an appropriate amount of nitrogen-doped carbon coating could uniformly form a protective layer on the NCM811 surface and the introduced N could anchor Ni atoms to inhibit the Li^(+)/Ni^(2+)mixing,but excessive amount would reduce Ni^(3+)to Ni^(2+)so as to conversely aggravate Li^(+)/Ni^(2+)mixing.Among the samples,the NCM811-CN0.75 sample exhibits the most excellent electrochemical performance,delivering a high-rate capacity of 151.6 mA·h/g at 10C,and long-term cyclability with 82.2%capacity retention after 300 cycles at 5C,exhibiting remarkable rate-performance and cyclability.
基金funded by National Nature Science Foundation of China(92266203)National Nature Science Foundation of China(52205278)+1 种基金Key Projects of Shijiazhuang Basic Research Program(241791077A)Central Guide Local Science and Technology Development Fund Project of Hebei Province(246Z1022G).
文摘In this paper,a topology optimization method for coordinated stiffness and strength design is proposed under mass constraints,utilizing the Solid Isotropic Material with Penalization approach.Element densities are regulated through sensitivity filtering tomitigate numerical instabilities associatedwith stress concentrations.Ap-norm aggregation function is employed to globalize local stress constraints,and a normalization technique linearly weights strain energy and stress,transforming the multi-objective problem into a single-objective formulation.The sensitivity of the objective function with respect to design variables is rigorously derived.Three numerical examples are presented,comparing the optimized structures in terms of strain energy,mass,and stress across five different mathematical models with varying combinations of optimization objectives.The results validate the effectiveness and feasibility of the proposed method for achieving a balanced design between structural stiffness and strength.This approach offers a new perspective for future research on stiffness-strength coordinated structural optimization.
文摘This paper investigates a wireless powered communication network(WPCN)facilitated by an unmanned aerial vehicle(UAV)in Internet of Things(IoT)networks,where multiple IoT devices(IoTDs)gather energy from a terrestrial energy station(ES)during the wireless energy transfer(WET)stage,followed by the UAV collecting data from these powered IoTDs with the time division multiple access(TDMA)protocol in the wireless information transfer(WIT)stage.To overcome the challenges of radio propagation caused by obstructions,we incorporate a reconfigurable intelligent surface(RIS)to enhance the link quality of the ES-IoTDs and IoTDs-UAV.The primary objective is to maximize the average sum rate of all IoTDs by jointly optimizing UAV trajectory,ES transmit power,and RIS phase shifts,along with the time allocation for WET and WIT.To this end,we reformulate the optimization problem as a markov decision process(MDP)and introduce a deep reinforcement learning(DRL)approach for addressing the formulated problem,called the proximal policy optimization(PPO)based energy harvesting with trajectory design and phase shift optimization(PPO-EHTDPS)algorithm.By continuously exploring within the environment,the PPO algorithm refines its policy to optimize the UAV trajectory,the energy phase shifts,ES transmit power,and WET/WIT time allocation.Additionally,a continuous phase shift optimization algorithm is employed to determine the information phase shifts for each IoTD to maximize average sum rate.Finally,numerical results demonstrate that the proposed PPOEHTDPS algorithm can significantly achieve higher average sum rate and show better convergence performance over the benchmark algorithms.
基金supported by the National Key Research and Development Project(Grant Number 2023YFB3709601)the National Natural Science Foundation of China(Grant Numbers 62373215,62373219,62073193)+2 种基金the Key Research and Development Plan of Shandong Province(Grant Numbers 2021CXGC010204,2022CXGC020902)the Fundamental Research Funds of Shandong University(Grant Number 2021JCG008)the Natural Science Foundation of Shandong Province(Grant Number ZR2023MF100).
文摘The remaining useful life prediction of rolling bearing is vital in safety and reliability guarantee.In engineering scenarios,only a small amount of bearing performance degradation data can be obtained through accelerated life testing.In the absence of lifetime data,the hidden long-term correlation between performance degradation data is challenging to mine effectively,which is the main factor that restricts the prediction precision and engineering application of the residual life prediction method.To address this problem,a novel method based on the multi-layer perception neural network and bidirectional long short-term memory network is proposed.Firstly,a nonlinear health indicator(HI)calculation method based on kernel principal component analysis(KPCA)and exponential weighted moving average(EWMA)is designed.Then,using the raw vibration data and HI,a multi-layer perceptron(MLP)neural network is trained to further calculate the HI of the online bearing in real time.Furthermore,The bidirectional long short-term memory model(BiLSTM)optimized by particle swarm optimization(PSO)is used to mine the time series features of HI and predict the remaining service life.Performance verification experiments and comparative experiments are carried out on the XJTU-SY bearing open dataset.The research results indicate that this method has an excellent ability to predict future HI and remaining life.
基金supported by the National Natural Science Foundation of China(Nos.52164048 and 52067012)the Natural Science Foundation of Kunming University of Science and Technology(No.KKZ3202437105)the Analysis and Testing Foundation of Kunming University of Science and Technology(No.2023P20221102026).
文摘Developing high-efficiency catalyst is crucial for electrochemical conversion of carbon dioxide(CO_(2))to high-value products.In the present work,a three-chamber electrolysis cell has been developed for CO_(2)reduction to carbon monoxide(CO)in an organic electrolyte,with sodium hydroxide(NaOH)and chlorine(Cl_(2))produced as byproducts.In order to improve the performance of the three-chamber electrolyzer,a gallium-based(Ga-based)ternary-porous catalyst(Ga-In_(4)Ag_(9))has been fabricated.During the long-term electrolysis process,Ga-In_(4)Ag_(9)catalyst exhibits good performance toward CO_(2)reduction reaction(CO_(2)RR),the CO partial current density achieves to 139.21 mA·cm^(-2)at-2.4 V(vs.SHE),with the Faraday efficiency(FE)of CO formation stabled at 92.3%.Density functional theory(DFT)analysis reveals that the position of the d-band center of Ga-In_(4)Ag_(9)is regulated by silver(Ag)atoms,which is beneficial for enhancing the binding ability between the catalyst and the intermediate.Owing to the adsorption of Cl^(-)on the surface of Ga-In_(4)Ag_(9),the reconfiguration of electron density has been altered,which is beneficial for the stabilization of*CO_(2)-intermediate.This work provides valuable insights for designing Ga-based metal catalysts toward CO_(2)electrolysis to produce high-value chemicals.
基金supported by the project of the National Natural Science Foundation of China(NSFC,Nos.5216040127,52164048 and U1802256)Central Guidance for Local Science and Technology Development Funds(No.202107AB110011)the Analysis and Test Funds of Kunming University of Science and Technology(No.2021M0202230188).
文摘As one of the alloy-type lithium-ion electrodes,Bi has outstanding application prospects for large volume capacity(3800 mAh·cm^(-3))and high electronic conductivity(1.4×10^(7)S·m^(-1)).However,the fast-charging performance is hindered by significant volume expansion(>218%)and a low rate of phase diffusion.To overcome these two problems,an N-doped carbon nanoflower coating layer was elaborately in-situ reconstructed on a multiple-wall Bi microsphere by hydrothermal methods and subsequent calcination in this study.The carbon nanoflowers greatly increase specific surface area(40.0 m^(2)·g^(-1))and alleviate the volume expansion(130%).In addition,the incorporation of N-doped carbon nanoflowers leads to a gradual enhancement in the Li adsorption energy of Bi during the process of lithium insertion and improves the electrical conductivity.Therefore,the contribution rate of pseudo-capacitance reached 87.5%at the scan rate of 0.8 mV·s^(-1),and the Li-ion diffusion coefficient(D_(Li^(+)))was calculated in the range of 10^(-10)to 10^(-12)cm^(2)·s^(-1).The Bi@CNFs anode provided a high specific volumetric capacity of 2117.0 mAh·cm^(-3)at 5C and a high capacity retention ratio of 93.2%after 800 cycles.The Bi@CNFs//LiFePO_(4)full cell also displayed a stable capacity of 113.9 mAh·g^(-1)and energy density of 296.1 Wh·kg^(-1)after 100 cycles with a Coulombic efficiency of 97.6%.The mechanism of fast-charging lithium storage was verified by distribution of relaxation time analysis and density functional theory calculation.This paper provides a new strategy to increase the pseudo-capacitance and reduce the volume expansion for the preparation of alloy-type fast-charging electrodes.
基金funded by the Major Science and Technology Program of Luoyang,China(Grant No.2101005A)Provincial and Ministerial Co-construction of Collaborative Innovation Center for Non-ferrous Metal New Materials and Advanced Processing Technology.
文摘The hot deformation behavior of 2707 hyper duplex stainless steel(HDSS)was investigated through a hot compression test at 950℃ to 1,250℃ at strain rates of 0.01 s^(-1) to 10 s^(-1).Observations from the flow stress curves reveal a balance between work hardening and dynamic recovery at the beginning of the deformation and subsequently demonstrate various softening mechanisms with the increase of strain.At high strain rates,dynamic recovery is the prevailing mechanism,whereas,at medium and low strain rates,dynamic recrystallization becomes dominant.The constitutive equation was constructed,and the deformation activation energy was calculated to be 645.46 kJ·mol^(-1).The hot processing map was drawn based on the dynamic material model at a strain of 0.8.The results indicate that the hot workability of 2707 HDSS decreases due to its high alloying content.The microstructure evolution of 2707 HDSS at 1,050℃ was identified by means of electron backscatter diffraction and transmission electron microscopy.The results demonstrate that the ferrite completes dynamic recrystallization at the strain rate of 1 s^(-1).The softening process of austenite is influenced by ferrite and mainly experiences dynamic recovery.The austenite located at the α/γ phase boundaries tends to undergo dynamic recrystallization.
基金Project supported by National Natural Science Foundation of China(51201068)Science and Technology Development Projects of Jilin Province(201201032)Science and Technology Development of Changchun City(11KZ31)
文摘In order to improve the corrosion and mechanical properties of AM50 magnesium alloy, 1 wt.% Gd was used to modify the AM50 magnesium alloy. The microstructure, corrosion and mechanical properties were evaluated by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, energy dispersive spectroscopy （EDS）, electrochemical and mechanical stretch methods. The results indicated that β-Mg17Al12 phase decreased and Al2Gd3 and Al0.4GdMn1.6 phase existed after Gd addition. Because of the Gd addition, the grain of AM50 magnesium alloy was refined significantly, which improved the tensile strength of AM50 magnesium al-loy. The decreasing ofβ phase improved the corrosion resistance of the magnesium alloy. The fracture mechanism of the Gd modified AM50 magnesium alloy was quasi-cleavage fracture. The corrosion residual strength （CRS） of AM50 magnesium alloy was im-proved after 1 wt.% Gd addition.
基金supported by Overseas Returnee Foundation of Heilongjiang Province,China(lc01c13).
文摘Ball spinning is applied to manufacturing thin-walled tube with high precision and high mechanical properties.On the basis of plastic mechanics,by simplifying ball spinning of thin-walled tube as plane strain problem,slab method is used for the purpose of calculating the contact deformation pressure.The spinning force components,the torsional moment,the deformation power and the deformation work are calculated further as well.The influence of the two important process parameters such as the feed ratio and the ball diameter on the spinning force components is analyzed in order to further control the spinning force components by regulating the two process variables during the ball spinning process.The stress and strain state in deformable zone as well as mechanics boundary conditions in ball spinning are obtained.The effect of the three spinning force components on the formability of the spun part is analyzed and validated through the ball spinning experiments.The theoretical and experimental results show that the radial spinning component plays a significant role in ball spinning of thin-walled tube,and the mechanics situation in backward ball spinning contributes to enhancing the plasticity of the metal material,but that in forward ball spinning contributes to advancing the axial flow of the metal material.
基金Project(3236301154) supported by Postdoctoral Foundation of Heilongjiang Province, China
文摘Based on the process experiments, micrography analysis was dedicated to advancing the understanding of plastic flow of the metal in backward ball spinning of thin-walled tubular part with longitudinal inner ribs. Micrography analysis reveals that severe plastic deformation leads to grain refinement, grain orientation and grain flow line of the spun part. Based on rigid-plastic finite element method, DEFORME3D finite element code was used to simulate and analyze multi-pass backward ball spinning of thin-walled tubular part with longitudinal inner ribs. Finite element simulation results involve the distributions of the strain, the shape variation of the inner ribs as well as the prediction of the spinning loading.
基金Supported by National Natural Science Foundation of China(Grant No.51175304)Shandong Provincial Science and Technology Development Plan of China(Grant No.2013GHZ30305)
文摘Low weight and good toughness thin plate parts are widely used in modem industry, but its flexibility seriously impacts the machinability. Plenty of studies locus on the influence of machine tool and cutting tool on the machining errors. However, few researches focus on compensating machining errors through the fixture. In order to improve the machining accuracy of thin plate-shape part in face milling, this paper presents a novel method for compensating the surfacc errors by prebending the workpiece during the milling process. First, a machining error prediction model using finite element method is formulated, which simplifies the contacts between the workpiece and fixture with spring constraints. Milling fbrces calculated by the micro-unit cutting force model arc loaded on the error prediction model to predict the machining error. The error prediction results are substituted into the given formulas to obtain the prebending clamping forces and clamping positions. Consequently, the workpiece is prebent in terms of the calculated clamping forces and positions during the face milling operation to reduce the machining error. Finally, simulation and experimental tests are carried out to validate the correctness and efficiency of the proposed error compensation method. The experimental measured flatness results show that the flatness improves by approximately 30 percent through this error compensation method. The proposed mcthod not only predicts the machining errors in face milling thin plate-shape parts but also reduces the machining errors by taking full advantage of the workpiece prebending caused by fixture, meanwhile, it provides a novel idea and theoretical basis for reducing milling errors and improving the milling accuracy.
基金Projects(51371099,51501091)supported by the National Natural Science Foundation of China。
文摘The(Cu−10Sn)−Ni−MoS2 composites,prepared by powder metallurgy,were studied for the effects of Ni-coated MoS2 on the microstructure,mechanical properties and lubricating properties.The mechanism of effects of Ni and MoS2 on the properties of composites was analyzed through a comparative experiment by adding Ni and MoS2 separately.The results show that the nickel wrapping around the MoS2 particles decreases the reaction rate of MoS2 with the copper matrix,and greatly improves the bonding of the matrix.The composites with 12 wt.%Ni-coated MoS2(C12)show the optimum performance including the mechanical properties and tribological behaviors.Under oil lubrication conditions,the friction coefficient is 0.0075 with a pressure of 8 MPa and a linear velocity of 0.25 m/s.The average dry friction coefficient,sliding against 40Cr steel disc,is measured to be 0.1769 when the linear velocity and pressure are 0.25 m/s and 4 MPa,respectively.
文摘Backward ball spinning was applied for manufacturing thin-walled tubular parts with longitudinal inner ribs. Rigid-plastic finite element method(FEM) was used for simulating the backward ball spinning process in order to calculate the height of the inner ribs. With a view to guarantee a better simulation accuracy, it is essential to enhance and improve some general problems of FEM, such as generation of initial velocity field, choice of penalty factor, determination of boundary conditions, treatment of rigid region and description of convergence criteria. It is evident that whether the problems with respect to FEM are dealt with appropriately or not, they have a significant influence on the modeling accuracy and efficiency. By reasonable solving the general problems, rigid-plastic FEM can successfully simulate the height of the inner ribs and the calculated values are in good agreement with the measured values.
基金This work was supported by"National Natural Science Foundation of China"(Grant nos.51771128,51771129 and 51201112)Projects of International Cooperation in Shanxi(Grant no.201703D421039)+1 种基金Shanxi province science and technology major projects(20181101008)The authors also thank to the Support from Program for the Outstanding Innovative Teams of Higher Learning Institutions of Shanxi,and the Special Fund Project for Guiding Local Science and Technology Development by the Central Government(YDZX20191400002734).
文摘The present work inainly focuses on tlie effect of minor cofiteut of Gd cicmcnt on the micrGstmcturc and mechanical properties of Mg Zn alloy.The Mg-4Zn-xGd(x=0,0.5,1,2)alloys were fabricated and subjected to extrusion at 280℃with the ratio of 25:1.Results revealed that the addition of Gd could inhibit the dynamic recrystallization(DRX)of Mg-4Zn alloy,and both the size and volume fraction of DRXed grains demonstrated a decreasing tendency as the Gd content increased from 0.5 to 2 wt.%.It is the weakening effect on DRX behavior that lead to the smaller amount of fine precipitate and the stronger texture intensity.As compared with the Mg-4Zn alloy,the yield strength and ultimate tensile strength of Mg-4Zn-xGd alloys were improved obviously by the addition of minor content of Gd,however,at the expense of elongation.Excellent tensile properties with the yield strength of〜369.8 MPa and ultimate tensile strength of〜400.3 MPa were obtained when the Gd content was 2 wt.%.
基金Projects(51475073,51605076,51875079)supported by the National Natural Science Foundation of ChinaProject(2017YFB1301701)supported by the National Key Research and Development Program of China
文摘The phenomenon of heat accumulation and transportation in the composite materials is a very typical and critical issue during drilling process.In this study,a three-dimensional temperature field prediction model is proposed using finite difference method,based on the partly homogenization hypothesis of material,to predict temperature field in the process of drilling unidirectional carbon fiber/epoxy(C/E)composites.According to the drilling feed motion,drilling process is divided into four stages to study the temperature distributing characteristics.The results show that the temperature distribution predicted by numerical study has a good agreement with the experimental results.The temperature increases with increasing the drilling depth,and the burn phenomena is observed due to the heat accumulation,especially at the drill exit.Due to the fiber orientation,an elliptical shape of the temperature field along the direction is found for both numerical and experimental studies of C/E composites drilling process.
