Because of the presence of lower-level automation and efficiency in the backing welding of medium–thick plates,pulse-metalactive-gas–metal-inert-gas(MAG–MIG)dual-arc welding was applied to backing welding of 24-mm-...Because of the presence of lower-level automation and efficiency in the backing welding of medium–thick plates,pulse-metalactive-gas–metal-inert-gas(MAG–MIG)dual-arc welding was applied to backing welding of 24-mm-thick Q235-B plate and the process and mechanism of root welding with back formation were investigated.The heating position of the MAG-arc at the front of the molten pool could be adjusted by using the electromagnetic force between the MAG-arc and the MIG-arc,and part of the arc energy could work on the root face directly.By combining the arc-discharge behaviour and analysis of flow in the molten pool,the shear stress of a tungsten inert gas(TIG)arc to the molten pool could make the liquid metal flow backwards.Thus,the quality of the front and bottom liquid metal were reduced,which favored the balance and stability.Continuous and stable back formation with uniform penetration could be achieved by using the pulse MAG–TIG dual-arc welding technology.展开更多
We investigate the effect of the formation process under pulse and dc modes on the performance of one transistor and one resistor (1 T1R) resistance random access memory (RRAM) device. All the devices are operated...We investigate the effect of the formation process under pulse and dc modes on the performance of one transistor and one resistor (1 T1R) resistance random access memory (RRAM) device. All the devices are operated under the same test conditions, except for the initial formation process with different modes. Based on the statistical results, the high resistance state (FIRS) under the dc forming mode shows a lower value with better distribution compared with that under the pulse mode. One of the possible reasons for such a phenomenon originates from different properties of conductive filament (CF) formed in the resistive switching layer under two different modes. For the dc forming mode, the formed filament is thought to be continuous, which is hard to be ruptured, resulting in a lower HRS. However, in the case of pulse forming, the filament is discontinuous where the transport mechanism is governed by hopping. The low resistance state (LRS) can be easily changed by removing a few trapping states from the conducting path. Hence, a higher FIRS is thus observed. However, the HRS resistance is highly dependent on the length of the gap opened. A slight variation of the gap length will cause wide dispersion of resistance.展开更多
In view of the unstable welding process of Tri-Arc DE,surfacing test with Q235 steel plate was completed with the help of the self-built high-speed camera and waveform synchronous acquisition system using the Tri-Arc ...In view of the unstable welding process of Tri-Arc DE,surfacing test with Q235 steel plate was completed with the help of the self-built high-speed camera and waveform synchronous acquisition system using the Tri-Arc DE technology. The effects of pulsed M-Arc frequency on Tri-Arc DE droplet transfer and weld formation were analyzed. The results show that while the gradual increase of pulse frequency,the droplet transfer frequency gradually decreases,which is followed by several drops per pulse,one drop per pulse,and one drop within several pulses. The most ideal transfer form is one drop per pulse,of which the welding process is the most stable,and the quality of weld formation is the most satisfied.展开更多
The object of this work is to investigate the influence of process parameters on drilling characteristics of an Al 1050 sheet with a thickness of 0.2 mm using a pulsed Nd:YAG laser through numerical analyses and exper...The object of this work is to investigate the influence of process parameters on drilling characteristics of an Al 1050 sheet with a thickness of 0.2 mm using a pulsed Nd:YAG laser through numerical analyses and experiments. By comparing the numerical analyses with the experiments, a proper numerical model was obtained. From the results of the numerical analyses and the experiments, the effects of process parameters on entrance diameters of drilled holes, shapes of the holes, taper angles of the holes and temperature distributions in the vicinity of the holes were examined quantitatively. In addition, the optimal drilling condition was estimated to improve the quality of the drilled holes.展开更多
The interfacial reaction control of SiC_p/2124Al composites was investigated during pulsed argon arc welding. Meanwhile, the mechanical properties, the metallographic structure and interfacial microstructure of the in...The interfacial reaction control of SiC_p/2124Al composites was investigated during pulsed argon arc welding. Meanwhile, the mechanical properties, the metallographic structure and interfacial microstructure of the induced welding joint were tested and detected, respectively. The results reveal that the joint with excellent properties could be achieved by the proper selection of the special filling material and the addition of the pulse during welding. Moreover, the formation mechanism of the welding joint was discussed and the corresponding measures on further improving the quality of the welding joint of SiC_p/2124Al composites were put forward in the condition of pulsed argon arc welding.展开更多
Short-arc pulsed gas metal arc welding(P-GMAW)was used to solve the dificulties of molten pool spreading and droplet transfer of Ni-based welding wire.Suppression of short-circuit current was used to reduce spatter.Ar...Short-arc pulsed gas metal arc welding(P-GMAW)was used to solve the dificulties of molten pool spreading and droplet transfer of Ni-based welding wire.Suppression of short-circuit current was used to reduce spatter.Arc length stabilizer was used to acquire a proper and stable arc length maintained at the critical position where short circuit starts to occur.Short-arc P-GMAW with or without arc length stabilizer was compared.The droplet transfer,arc behaviors and weld bead profiles were investigated and compared based on the high-speed photography and observation of weld cross-section.When the arc length stabilizer was deactivated,the arc length was unstable and too short.The droplet transfer mode was mainly short circuit partial transfer,with only a small part of the droplet transferred into the molten pool,with the characteristics of no obvious necking,a few spatters,small droplet impact,long short circuit duration and high short-circuit current.There was also a small proportion of short circuit complete transfer with obvious necking,larger droplet impact,shorter short-circuit duration and lower short-circuit current.With arc length stabilizer,droplet transfer modes were short circuit complete transfer and spray transfer.The spray transfer had the largest droplet impact,no short circuit and no spatter.With the arc length stabilizer activated,a deep penetration,a high penetration ratio,a small reinforcement and a large reinforcement factor were acquired.This provides an innovative method to solve the difficulties of droplet transfer and molten pool spreading and eliminate the incomplete fusion in the GMAW of 9%Ni steel with nickel-based alloy welding wire.展开更多
Background A practical problem impeding clinical translation is the limited bone formation seen in artificial bone grafts.Low-pressure/vacuum seeding and dynamic culturing in bioreactors have led to a greater penetrat...Background A practical problem impeding clinical translation is the limited bone formation seen in artificial bone grafts.Low-pressure/vacuum seeding and dynamic culturing in bioreactors have led to a greater penetration into the scaffolds,enhanced production of bone marrow cells,and improved tissue-engineered bone formation.The goal of this study was to promote more extensive bone formation in the composites of porous ceramics and bone marrow stromal cells (BMSCs).Methods BMSCs/β-tricalcium phosphate (β-TCP) composites were subcultured for 2 weeks and then subcutaneously implanted into syngeneic rats that were split into a low-intensity pulsed ultrasound (LIPUS) treatment group and a control group.These implants were harvested at 5,10,25,and 50 days after implantation.The samples were then biomechanically tested and analyzed for alkaline phosphate (ALP) activity and osteocalcin (OCN) content and were also observed by light microscopy.Results The levels of ALP activity and OCN content in the composites were significantly higher in the LIPUS group than in the control group.Histomorphometric analysis revealed a greater degree of soft tissue repair,increased blood flow,better angiogenesis,and more extensive bone formation in the LIPUS groups than in the controls.No significant difference in the compressive strength was found between the two groups.Conclusion LIPUS treatment appears to enhance bone formation and angiogenesis in the BMSCs/β3-TCP composites.展开更多
A new technique for the generation of multi-channel optical pulse from a single laser diode (LD) is presented in this paper. 35 channel pulse source with 6.5 GHz repetition rate per channel and 32.5 GHz channel spacin...A new technique for the generation of multi-channel optical pulse from a single laser diode (LD) is presented in this paper. 35 channel pulse source with 6.5 GHz repetition rate per channel and 32.5 GHz channel spacing was generated from a subharmonically hybrid mode-locked two section monolithic laser with enhanced amplitude modulation. The obtained pulse source exhibits high extinction ratio (>10 dB) and low level of root mean square (RMS) phase noise (<0.11 rad) over all channels from 1556 nm to 1565...展开更多
基金Innovation Research Group Project of National Natural Science Foundation of China(51621064)The National Natural Science Foundation General Projects(11375038).
文摘Because of the presence of lower-level automation and efficiency in the backing welding of medium–thick plates,pulse-metalactive-gas–metal-inert-gas(MAG–MIG)dual-arc welding was applied to backing welding of 24-mm-thick Q235-B plate and the process and mechanism of root welding with back formation were investigated.The heating position of the MAG-arc at the front of the molten pool could be adjusted by using the electromagnetic force between the MAG-arc and the MIG-arc,and part of the arc energy could work on the root face directly.By combining the arc-discharge behaviour and analysis of flow in the molten pool,the shear stress of a tungsten inert gas(TIG)arc to the molten pool could make the liquid metal flow backwards.Thus,the quality of the front and bottom liquid metal were reduced,which favored the balance and stability.Continuous and stable back formation with uniform penetration could be achieved by using the pulse MAG–TIG dual-arc welding technology.
基金Supported by the National Basic Research Program of China under Grant Nos 2011CBA00602,2010CB934200,2011CB921804,2011CB707600,2011AA010401,and 2011AA010402the National Natural Science Foundation of China under Grant Nos61322408,61334007,61376112,61221004,61274091,61106119,61106082,and 61006011
文摘We investigate the effect of the formation process under pulse and dc modes on the performance of one transistor and one resistor (1 T1R) resistance random access memory (RRAM) device. All the devices are operated under the same test conditions, except for the initial formation process with different modes. Based on the statistical results, the high resistance state (FIRS) under the dc forming mode shows a lower value with better distribution compared with that under the pulse mode. One of the possible reasons for such a phenomenon originates from different properties of conductive filament (CF) formed in the resistive switching layer under two different modes. For the dc forming mode, the formed filament is thought to be continuous, which is hard to be ruptured, resulting in a lower HRS. However, in the case of pulse forming, the filament is discontinuous where the transport mechanism is governed by hopping. The low resistance state (LRS) can be easily changed by removing a few trapping states from the conducting path. Hence, a higher FIRS is thus observed. However, the HRS resistance is highly dependent on the length of the gap opened. A slight variation of the gap length will cause wide dispersion of resistance.
基金Project was supported by the National Natural Science Foundation of China(Grant No.U1733125)Natural Science Foundation of Tianjin(Grant No.18JCYBJC19100,18JCYJC18700)
文摘In view of the unstable welding process of Tri-Arc DE,surfacing test with Q235 steel plate was completed with the help of the self-built high-speed camera and waveform synchronous acquisition system using the Tri-Arc DE technology. The effects of pulsed M-Arc frequency on Tri-Arc DE droplet transfer and weld formation were analyzed. The results show that while the gradual increase of pulse frequency,the droplet transfer frequency gradually decreases,which is followed by several drops per pulse,one drop per pulse,and one drop within several pulses. The most ideal transfer form is one drop per pulse,of which the welding process is the most stable,and the quality of weld formation is the most satisfied.
基金supported by a grant-in-aid of Regional Innovation Center(RIC),New Technology Development and Research Center of Laser Application in Chosun University,Korea.
文摘The object of this work is to investigate the influence of process parameters on drilling characteristics of an Al 1050 sheet with a thickness of 0.2 mm using a pulsed Nd:YAG laser through numerical analyses and experiments. By comparing the numerical analyses with the experiments, a proper numerical model was obtained. From the results of the numerical analyses and the experiments, the effects of process parameters on entrance diameters of drilled holes, shapes of the holes, taper angles of the holes and temperature distributions in the vicinity of the holes were examined quantitatively. In addition, the optimal drilling condition was estimated to improve the quality of the drilled holes.
文摘The interfacial reaction control of SiC_p/2124Al composites was investigated during pulsed argon arc welding. Meanwhile, the mechanical properties, the metallographic structure and interfacial microstructure of the induced welding joint were tested and detected, respectively. The results reveal that the joint with excellent properties could be achieved by the proper selection of the special filling material and the addition of the pulse during welding. Moreover, the formation mechanism of the welding joint was discussed and the corresponding measures on further improving the quality of the welding joint of SiC_p/2124Al composites were put forward in the condition of pulsed argon arc welding.
基金the MARK III Materials Research Project of Ministry of Industry and Information Technology of China。
文摘Short-arc pulsed gas metal arc welding(P-GMAW)was used to solve the dificulties of molten pool spreading and droplet transfer of Ni-based welding wire.Suppression of short-circuit current was used to reduce spatter.Arc length stabilizer was used to acquire a proper and stable arc length maintained at the critical position where short circuit starts to occur.Short-arc P-GMAW with or without arc length stabilizer was compared.The droplet transfer,arc behaviors and weld bead profiles were investigated and compared based on the high-speed photography and observation of weld cross-section.When the arc length stabilizer was deactivated,the arc length was unstable and too short.The droplet transfer mode was mainly short circuit partial transfer,with only a small part of the droplet transferred into the molten pool,with the characteristics of no obvious necking,a few spatters,small droplet impact,long short circuit duration and high short-circuit current.There was also a small proportion of short circuit complete transfer with obvious necking,larger droplet impact,shorter short-circuit duration and lower short-circuit current.With arc length stabilizer,droplet transfer modes were short circuit complete transfer and spray transfer.The spray transfer had the largest droplet impact,no short circuit and no spatter.With the arc length stabilizer activated,a deep penetration,a high penetration ratio,a small reinforcement and a large reinforcement factor were acquired.This provides an innovative method to solve the difficulties of droplet transfer and molten pool spreading and eliminate the incomplete fusion in the GMAW of 9%Ni steel with nickel-based alloy welding wire.
基金the National Natural Science Foundation of China,the Natural Science Foundation of Beijing,China
文摘Background A practical problem impeding clinical translation is the limited bone formation seen in artificial bone grafts.Low-pressure/vacuum seeding and dynamic culturing in bioreactors have led to a greater penetration into the scaffolds,enhanced production of bone marrow cells,and improved tissue-engineered bone formation.The goal of this study was to promote more extensive bone formation in the composites of porous ceramics and bone marrow stromal cells (BMSCs).Methods BMSCs/β-tricalcium phosphate (β-TCP) composites were subcultured for 2 weeks and then subcutaneously implanted into syngeneic rats that were split into a low-intensity pulsed ultrasound (LIPUS) treatment group and a control group.These implants were harvested at 5,10,25,and 50 days after implantation.The samples were then biomechanically tested and analyzed for alkaline phosphate (ALP) activity and osteocalcin (OCN) content and were also observed by light microscopy.Results The levels of ALP activity and OCN content in the composites were significantly higher in the LIPUS group than in the control group.Histomorphometric analysis revealed a greater degree of soft tissue repair,increased blood flow,better angiogenesis,and more extensive bone formation in the LIPUS groups than in the controls.No significant difference in the compressive strength was found between the two groups.Conclusion LIPUS treatment appears to enhance bone formation and angiogenesis in the BMSCs/β3-TCP composites.
文摘A new technique for the generation of multi-channel optical pulse from a single laser diode (LD) is presented in this paper. 35 channel pulse source with 6.5 GHz repetition rate per channel and 32.5 GHz channel spacing was generated from a subharmonically hybrid mode-locked two section monolithic laser with enhanced amplitude modulation. The obtained pulse source exhibits high extinction ratio (>10 dB) and low level of root mean square (RMS) phase noise (<0.11 rad) over all channels from 1556 nm to 1565...