Double?roller clamping spinning(DRCS) is a new process for forming a thin?walled cylinder with a complex surface flange. The process requires a small spinning force,and can visibly improve forming quality and producti...Double?roller clamping spinning(DRCS) is a new process for forming a thin?walled cylinder with a complex surface flange. The process requires a small spinning force,and can visibly improve forming quality and production e ciency. However,the deformation mechanism of the process has not been completely understood. Therefore,both a finite element numerical simulation and experimental research on the DRCS process are carried out. The results show that both radial force and axial force dominate the forming process of DRCS. The deformation area elongates along the radial direction and bends along the axial direction under the action of the two forces. Both the outer edge and round corner of the flange show the tangential tensile stress and radial compressive stress. The middle region shows tensile tangential stress and radial stress,while the inner edge shows compressive tangential stress and radial stress. Tan?gential tensile strain causes a wall thickness reduction in the outer edge and middle regions of the flange. The large compressive thickness strain causes material accumulation and thus,an increase in the wall thickness of the round corner. Because of bending deformation,the round corner shows a large radial tensile strain in addition. The inner edge of the flange shows small radial compressive strain and tensile strain in thickness. Thus,the wall thickness on the inner edge of the flange continues to increase,although the increment is small. Furthermore,microstructure analysis and tensile test results show that the flanged thin?walled cylinder formed by DRCS has good mechanical properties. The results provide instructions for the application of the DRCS process.展开更多
Compared with the conventional single-roller spinning process, the double-roller clamping spinning（DRCS） process can effectively prevent the sheet metal surface wrinkling and improve the the production efficiency an...Compared with the conventional single-roller spinning process, the double-roller clamping spinning（DRCS） process can effectively prevent the sheet metal surface wrinkling and improve the the production efficiency and the shape precision of final spun part. Based on ABAQUS/Explicit nonlinear finite element software, the finite element model of the multi-pass DRCS for the sheet metal is established, and the material model, the contact definition, the mesh generation, the loading trajectory and other key technical problems are solved. The simulations on the multi-pass DRCS of the ordinary Q235A steel cylindrical part with the arc-shaped surface flange are carried out. The effects of number of spinning passes on the production efficiency, the spinning moment, the shape error of the workpiece, and the wall thickness distribution of the final part are obtained. It is indicated definitely that with the increase of the number of spinning passes the geometrical precision of the spun part increases while the production efficiency reduces. Moreover, the variations of the spinning forces and the distributions of the stresses, strains, wall thickness during the multi-pass DRCS process are revealed. It is indicated that during the DRCS process the radical force is the largest, and the whole deformation area shows the tangential tensile strain and the radial compressive strain, while the thickness strain changes along the generatrix directions from the compressive strain on the outer edge of the flange to the tensile strain on the inner edge of the flange. Based on the G-CNC6135 NC lathe, the three-axis linkage computer-controlled experimental device for DRCS which is driven by the AC servo motor is developed. And then using the experimental device, the Q235A cylindrical parts with the arc-shape surface flange are formed by the DRCS. The simulation results of spun parts have good consistency with the experimental results, which verifies the feasibility of DRCS process and the reliability of the finite element model for DRCS.展开更多
A double-clamped piezoelectric energy harvester subjected to random excitation is presented,for which corresponding analytical model is established to predict its output characteristics.With the presented theoretical ...A double-clamped piezoelectric energy harvester subjected to random excitation is presented,for which corresponding analytical model is established to predict its output characteristics.With the presented theoretical natural frequency and equivalent stiffness of vibrator,the closed-form expressions of mean power and voltage acquired from the double-clamped piezoelectric energy harvester under random excitation are derived.Finally theoretical analysis is conducted for the output performance of the doubleclamped energy harvester with the change of spectrum density（SD）of acceleration,load resistance,piezoelectric coefficient and natural frequency value,which is found to closely agree with Monte Carlo simulation and experimental results.展开更多
The double flapper-nozzle servo valve is widely used to launch and guide the equipment. Due to the large instantaneous flow rate of servo valve working under specific operating conditions, the temperature of servo val...The double flapper-nozzle servo valve is widely used to launch and guide the equipment. Due to the large instantaneous flow rate of servo valve working under specific operating conditions, the temperature of servo valve would reach 120℃ and the valve core and valve sleeve deform in a short amount of time. So the control precision of servo valve significantly decreases and the clamping stagnation phenomenon of valve core appears. In order to solve the problem of degraded control accuracy and clamping stagnation of servo valve under large temperature difference circumstance, the numerical simulation of heat-fluid-solid coupling by using finite element method is done. The simulation result shows that zero position leakage of servo valve is basically impacted by oil temperature and change of fit clearance. The clamping stagnation is caused by warpage-deformation and fit clearance reduction of the valve core and valve sleeve. The distribution roles of the temperature and thermal-deformation of shell, valve core and valve sleeve and the pressure, velocity and temperature field of flow channel are also analyzed. Zero position leakage and electromagnet＇s current when valve core moves in full-stroke are tested using Electro-hydraulic Servo-valve Characteristic Test-bed of an aerospace sciences and technology corporation. The experimental results show that the change law of experimental current at different oil temperatures is roughly identical to simulation current. The current curve of the electromagnet is smooth when oil temperature is below 80℃, but the amplitude of current significantly increases and the hairy appears when oil temperature is above 80℃. The current becomes smooth again after the warped valve core and valve sleeve are reground. It indicates that clamping stagnation is caused by warpage-deformation and fit clearance reduction of valve core and valve sleeve. This paper simulates and tests the heat-fluid-solid coupling of double flapper-nozzle servo valve, and the obtained results provide the reference value for the design of double flapper-nozzle force feedback servo valve.展开更多
基金Supported by National Natural Science Foundation of China(Grant No.51305333)Shaanxi Provincial Key Science and Technology Industrial Research Plan of China(Grant No.2014K07-23)Shaanxi Provincial Cooperation Project of China(Grant No.2014SJ-15)
文摘Double?roller clamping spinning(DRCS) is a new process for forming a thin?walled cylinder with a complex surface flange. The process requires a small spinning force,and can visibly improve forming quality and production e ciency. However,the deformation mechanism of the process has not been completely understood. Therefore,both a finite element numerical simulation and experimental research on the DRCS process are carried out. The results show that both radial force and axial force dominate the forming process of DRCS. The deformation area elongates along the radial direction and bends along the axial direction under the action of the two forces. Both the outer edge and round corner of the flange show the tangential tensile stress and radial compressive stress. The middle region shows tensile tangential stress and radial stress,while the inner edge shows compressive tangential stress and radial stress. Tan?gential tensile strain causes a wall thickness reduction in the outer edge and middle regions of the flange. The large compressive thickness strain causes material accumulation and thus,an increase in the wall thickness of the round corner. Because of bending deformation,the round corner shows a large radial tensile strain in addition. The inner edge of the flange shows small radial compressive strain and tensile strain in thickness. Thus,the wall thickness on the inner edge of the flange continues to increase,although the increment is small. Furthermore,microstructure analysis and tensile test results show that the flanged thin?walled cylinder formed by DRCS has good mechanical properties. The results provide instructions for the application of the DRCS process.
基金supported by National Natural Science Foundation of China(Grant Nos.50905137,50975222)China Postdoctoral Science Foundation(Grant No.2012M521757)Natural Science Foundation of Shaanxi for Youths,China(Grant No.2012JQ7032)
文摘Compared with the conventional single-roller spinning process, the double-roller clamping spinning（DRCS） process can effectively prevent the sheet metal surface wrinkling and improve the the production efficiency and the shape precision of final spun part. Based on ABAQUS/Explicit nonlinear finite element software, the finite element model of the multi-pass DRCS for the sheet metal is established, and the material model, the contact definition, the mesh generation, the loading trajectory and other key technical problems are solved. The simulations on the multi-pass DRCS of the ordinary Q235A steel cylindrical part with the arc-shaped surface flange are carried out. The effects of number of spinning passes on the production efficiency, the spinning moment, the shape error of the workpiece, and the wall thickness distribution of the final part are obtained. It is indicated definitely that with the increase of the number of spinning passes the geometrical precision of the spun part increases while the production efficiency reduces. Moreover, the variations of the spinning forces and the distributions of the stresses, strains, wall thickness during the multi-pass DRCS process are revealed. It is indicated that during the DRCS process the radical force is the largest, and the whole deformation area shows the tangential tensile strain and the radial compressive strain, while the thickness strain changes along the generatrix directions from the compressive strain on the outer edge of the flange to the tensile strain on the inner edge of the flange. Based on the G-CNC6135 NC lathe, the three-axis linkage computer-controlled experimental device for DRCS which is driven by the AC servo motor is developed. And then using the experimental device, the Q235A cylindrical parts with the arc-shape surface flange are formed by the DRCS. The simulation results of spun parts have good consistency with the experimental results, which verifies the feasibility of DRCS process and the reliability of the finite element model for DRCS.
基金Supported by National High Technology R&D Program(SS2013AA041104)
文摘A double-clamped piezoelectric energy harvester subjected to random excitation is presented,for which corresponding analytical model is established to predict its output characteristics.With the presented theoretical natural frequency and equivalent stiffness of vibrator,the closed-form expressions of mean power and voltage acquired from the double-clamped piezoelectric energy harvester under random excitation are derived.Finally theoretical analysis is conducted for the output performance of the doubleclamped energy harvester with the change of spectrum density（SD）of acceleration,load resistance,piezoelectric coefficient and natural frequency value,which is found to closely agree with Monte Carlo simulation and experimental results.
基金Supposed by National Natural Science Foundation of China(Grant No.51075348)Hebei Provincial Natural Science Foundation of China(Grant No.E2011203151)Research Fund for Doctoral Program of Higher Education of China(Grant No.20101333110002)
文摘The double flapper-nozzle servo valve is widely used to launch and guide the equipment. Due to the large instantaneous flow rate of servo valve working under specific operating conditions, the temperature of servo valve would reach 120℃ and the valve core and valve sleeve deform in a short amount of time. So the control precision of servo valve significantly decreases and the clamping stagnation phenomenon of valve core appears. In order to solve the problem of degraded control accuracy and clamping stagnation of servo valve under large temperature difference circumstance, the numerical simulation of heat-fluid-solid coupling by using finite element method is done. The simulation result shows that zero position leakage of servo valve is basically impacted by oil temperature and change of fit clearance. The clamping stagnation is caused by warpage-deformation and fit clearance reduction of the valve core and valve sleeve. The distribution roles of the temperature and thermal-deformation of shell, valve core and valve sleeve and the pressure, velocity and temperature field of flow channel are also analyzed. Zero position leakage and electromagnet＇s current when valve core moves in full-stroke are tested using Electro-hydraulic Servo-valve Characteristic Test-bed of an aerospace sciences and technology corporation. The experimental results show that the change law of experimental current at different oil temperatures is roughly identical to simulation current. The current curve of the electromagnet is smooth when oil temperature is below 80℃, but the amplitude of current significantly increases and the hairy appears when oil temperature is above 80℃. The current becomes smooth again after the warped valve core and valve sleeve are reground. It indicates that clamping stagnation is caused by warpage-deformation and fit clearance reduction of valve core and valve sleeve. This paper simulates and tests the heat-fluid-solid coupling of double flapper-nozzle servo valve, and the obtained results provide the reference value for the design of double flapper-nozzle force feedback servo valve.
