A new type of variable polarity welding power modulated with high-frequency pulse current is developed. Series of high-frequency pulse current is superimposed on direct-current-electrode-negative （DCEN）, which can i...A new type of variable polarity welding power modulated with high-frequency pulse current is developed. Series of high-frequency pulse current is superimposed on direct-current-electrode-negative （DCEN）, which can improve the crystallization process in the weld bead as a result of the electromagnetic force generated by pulse current. Digital signal processor （DSP） is used to realize the closed-loop control of the first inverter, variable polarity output of the second inverter and high-frequency pulse current superposition.展开更多
A novel two-dimensional （2D） simulation method of positive corona current pulses is proposed. A control-volume- based finite element method （CV-FEM） is used to solve continuity equations, and the Galerkin finite e...A novel two-dimensional （2D） simulation method of positive corona current pulses is proposed. A control-volume- based finite element method （CV-FEM） is used to solve continuity equations, and the Galerkin finite element method （FEM） is used to solve Poisson＇s equation. In the proposed method, photoionization is considered by adopting an exact Helmholtz photoionization model. Furthermore, fully implicit discretization and variable time step are used to ensure the time-efficiency of the present method. Finally, the method is applied to a positive rod-plane corona problem. The numerical results are in agreement with the experimental results, and the validity of the proposed method is verified.展开更多
The selection of process parameters for obtaining optimal tensile properties in the pulsed current gas tungsten arc welding is presented. The tensile properties include ultimate tensile strength, yield strength and no...The selection of process parameters for obtaining optimal tensile properties in the pulsed current gas tungsten arc welding is presented. The tensile properties include ultimate tensile strength, yield strength and notch tensile strength. All these characteristics are considered together in the selection of process parameters by modified taguchi method to analyse the effect of each welding process parameter on tensile properties. Experimental results are furnished to illustrate the approach.展开更多
The paper focuses on developing mathematical models to predict grain size and ul- timate tensile strength of pulsed current micro plasma arc welded Inconel 625 nickel alloy. Four factors, five levels, central composit...The paper focuses on developing mathematical models to predict grain size and ul- timate tensile strength of pulsed current micro plasma arc welded Inconel 625 nickel alloy. Four factors, five levels, central composite rotatable design matrix is used to op- timize the number of experiments. The mathematical models have been developed by response surface method. The adequacy of the models is checked by analysis of vari- ance technique. By using the developed mathematical models, grain size and ultimate tensile strength of the joints can be predicted with 99% confidence level. Contour plots are drawn to study the interaction effect of pulsed current micro plasma arc welding parameters on fusion zone grain size and ultimate tensile strength of Inconel 625 weld joints.展开更多
Though the preferred welding process to weld aluminium alloy is frequently constant current gas tungsten arc welding (CCGTAW),it resulted in grain coarsening at the fusion zone and heat affected zone(HAZ).Hence,pulsed...Though the preferred welding process to weld aluminium alloy is frequently constant current gas tungsten arc welding (CCGTAW),it resulted in grain coarsening at the fusion zone and heat affected zone(HAZ).Hence,pulsed current gas tungsten arc welding(PCGTAW) was performed,to yield finer fusion zone grains,which leads to higher strength of AA6061 (Al-Mg-Si) aluminium alloy joints.In order to determine the most influential control factors which will yield minimum fusion zone grain size and maximum tensile strength of the joints,the traditional Hooke and Jeeves pattern search method was used.The experiments were carried out based on central composite design with 31 runs and an algorithm was developed to optimize the fusion zone grain size and the tensile strength of pulsed current gas tungsten arc welded AA6061 aluminium alloy joints.The results indicate that the peak current (Ip) and base current (IB) are the most significant parameters,to decide the fusion zone grain size and the tensile strength of the AA6061 aluminum alloy joints.展开更多
Semiconductor-based electronic devices usually work under multiphysics fields rendering complex electromagnetic-thermo-mechanical coupling.In this work,we develop a penalty function method based on a finite element an...Semiconductor-based electronic devices usually work under multiphysics fields rendering complex electromagnetic-thermo-mechanical coupling.In this work,we develop a penalty function method based on a finite element analysis to tackle this coupling behavior in a metal/semiconductor bilayer plate-the representative unit of semiconductor antenna,which receives strong and pulsed electromagnetic signals.Under these pulses,eddy current is generated,of which the magnitude varies remarkably from one plate to another due to the difference in electrical conductivity.In the concerned system,the metal layer generates much larger current,resulting in the large temperature rise and the nonnegligible Lorentz force,which could lead to delamination and failure of the semiconductor-based electronic device.This study provides theoretical guidance for the design and protection of semiconductor-based electronic devices in complex environments.展开更多
In this article, we apply the first elliptic function equation to find a new kind of solutions of nonlinear partial differential equations （PDEs） based on the ho- mogeneous balance method, the Jacobi elliptic expans...In this article, we apply the first elliptic function equation to find a new kind of solutions of nonlinear partial differential equations （PDEs） based on the ho- mogeneous balance method, the Jacobi elliptic expansion method and the auxiliary equation method. New exact solutions to the Jacobi elliptic functions of a nonlinear PDE describing pulse narrowing nonlinear transmission lines are given with the aid of computer program, e.g. Maple or Mathematica. Based on Kirchhoff＇s current law and Kirchhoff＇s voltage law, the given nonlinear PDE has been derived and can be reduced to a nonlinear ordinary differential equation （ODE） using a simple transformation. The given method in this article is straightforward and concise, and can be applied to other nonlinear PDEs in mathematical physics. Further results may be obtained.展开更多
Epoxy resin is widely used in high-temperature,high-electric-field power equipment owing to its stable physicochemical properties and excellent insulation performance.During prolonged operation,it undergoes thermal ag...Epoxy resin is widely used in high-temperature,high-electric-field power equipment owing to its stable physicochemical properties and excellent insulation performance.During prolonged operation,it undergoes thermal aging,making lifetime extension essential.The effects of thermal aging on insulation by comparing samples cured with anhydride curing agents under both air and non-air conditions are investigated.The Fourier transform infrared spectroscopy,current integrated charge,and pulsed electro-acoustic methods are used to analyze physicochemical characteristics and electrical performance.Control groups compared thermal aging in air versus an oil bath to examine atmospheric influences.Results show that air-aged samples turned yellow,while the oil bath-aged samples remained colorless.At temperatures above T_(g)(135℃),air-aged samples showed more positive hetero charge accumulation.Non-air-aged samples also accumulated space charge,but to a lesser extent,and sho wed better insulation breakdown resistance.These findings indicate that thermal aging in air may degrade insulation perform ance owing to oxidative effects.展开更多
文摘A new type of variable polarity welding power modulated with high-frequency pulse current is developed. Series of high-frequency pulse current is superimposed on direct-current-electrode-negative （DCEN）, which can improve the crystallization process in the weld bead as a result of the electromagnetic force generated by pulse current. Digital signal processor （DSP） is used to realize the closed-loop control of the first inverter, variable polarity output of the second inverter and high-frequency pulse current superposition.
基金Project supported by the National Basic Research Program of China(Grant No.2011CB209402)the National Natural Science Foundation of China(Grant No.51177041)the Fundamental Research Funds for the Central Universities,China(Grant No.12QX01)
文摘A novel two-dimensional （2D） simulation method of positive corona current pulses is proposed. A control-volume- based finite element method （CV-FEM） is used to solve continuity equations, and the Galerkin finite element method （FEM） is used to solve Poisson＇s equation. In the proposed method, photoionization is considered by adopting an exact Helmholtz photoionization model. Furthermore, fully implicit discretization and variable time step are used to ensure the time-efficiency of the present method. Finally, the method is applied to a positive rod-plane corona problem. The numerical results are in agreement with the experimental results, and the validity of the proposed method is verified.
文摘The selection of process parameters for obtaining optimal tensile properties in the pulsed current gas tungsten arc welding is presented. The tensile properties include ultimate tensile strength, yield strength and notch tensile strength. All these characteristics are considered together in the selection of process parameters by modified taguchi method to analyse the effect of each welding process parameter on tensile properties. Experimental results are furnished to illustrate the approach.
文摘The paper focuses on developing mathematical models to predict grain size and ul- timate tensile strength of pulsed current micro plasma arc welded Inconel 625 nickel alloy. Four factors, five levels, central composite rotatable design matrix is used to op- timize the number of experiments. The mathematical models have been developed by response surface method. The adequacy of the models is checked by analysis of vari- ance technique. By using the developed mathematical models, grain size and ultimate tensile strength of the joints can be predicted with 99% confidence level. Contour plots are drawn to study the interaction effect of pulsed current micro plasma arc welding parameters on fusion zone grain size and ultimate tensile strength of Inconel 625 weld joints.
基金Naval Research Board (NRB),Ministry of Defence,New Delhi for the financial support to carry out this investigation through sponsored project No.DNRD/05/4003/NRB/67.
文摘Though the preferred welding process to weld aluminium alloy is frequently constant current gas tungsten arc welding (CCGTAW),it resulted in grain coarsening at the fusion zone and heat affected zone(HAZ).Hence,pulsed current gas tungsten arc welding(PCGTAW) was performed,to yield finer fusion zone grains,which leads to higher strength of AA6061 (Al-Mg-Si) aluminium alloy joints.In order to determine the most influential control factors which will yield minimum fusion zone grain size and maximum tensile strength of the joints,the traditional Hooke and Jeeves pattern search method was used.The experiments were carried out based on central composite design with 31 runs and an algorithm was developed to optimize the fusion zone grain size and the tensile strength of pulsed current gas tungsten arc welded AA6061 aluminium alloy joints.The results indicate that the peak current (Ip) and base current (IB) are the most significant parameters,to decide the fusion zone grain size and the tensile strength of the AA6061 aluminum alloy joints.
基金the National Natural Science Foundation of China(Grant nos.11772294,11621062)the Fundamental Research Funds for the Central Universities(Grant no.2017QNA4031).
文摘Semiconductor-based electronic devices usually work under multiphysics fields rendering complex electromagnetic-thermo-mechanical coupling.In this work,we develop a penalty function method based on a finite element analysis to tackle this coupling behavior in a metal/semiconductor bilayer plate-the representative unit of semiconductor antenna,which receives strong and pulsed electromagnetic signals.Under these pulses,eddy current is generated,of which the magnitude varies remarkably from one plate to another due to the difference in electrical conductivity.In the concerned system,the metal layer generates much larger current,resulting in the large temperature rise and the nonnegligible Lorentz force,which could lead to delamination and failure of the semiconductor-based electronic device.This study provides theoretical guidance for the design and protection of semiconductor-based electronic devices in complex environments.
文摘In this article, we apply the first elliptic function equation to find a new kind of solutions of nonlinear partial differential equations （PDEs） based on the ho- mogeneous balance method, the Jacobi elliptic expansion method and the auxiliary equation method. New exact solutions to the Jacobi elliptic functions of a nonlinear PDE describing pulse narrowing nonlinear transmission lines are given with the aid of computer program, e.g. Maple or Mathematica. Based on Kirchhoff＇s current law and Kirchhoff＇s voltage law, the given nonlinear PDE has been derived and can be reduced to a nonlinear ordinary differential equation （ODE） using a simple transformation. The given method in this article is straightforward and concise, and can be applied to other nonlinear PDEs in mathematical physics. Further results may be obtained.
文摘Epoxy resin is widely used in high-temperature,high-electric-field power equipment owing to its stable physicochemical properties and excellent insulation performance.During prolonged operation,it undergoes thermal aging,making lifetime extension essential.The effects of thermal aging on insulation by comparing samples cured with anhydride curing agents under both air and non-air conditions are investigated.The Fourier transform infrared spectroscopy,current integrated charge,and pulsed electro-acoustic methods are used to analyze physicochemical characteristics and electrical performance.Control groups compared thermal aging in air versus an oil bath to examine atmospheric influences.Results show that air-aged samples turned yellow,while the oil bath-aged samples remained colorless.At temperatures above T_(g)(135℃),air-aged samples showed more positive hetero charge accumulation.Non-air-aged samples also accumulated space charge,but to a lesser extent,and sho wed better insulation breakdown resistance.These findings indicate that thermal aging in air may degrade insulation perform ance owing to oxidative effects.
