Permafrost on the Qinghai-Tibet Plateau (QTP) has experienced major shifts during theQuaternary. During the past 40 years, permafrost has been degrading extensively, due to climaticwarming. Simulations suggest signifi...Permafrost on the Qinghai-Tibet Plateau (QTP) has experienced major shifts during theQuaternary. During the past 40 years, permafrost has been degrading extensively, due to climaticwarming. Simulations suggest significant degradation of permafrost both in extent and inthickness within the next 50-100 years. Freshwater wetlands on the QTP can contributesignificantly to the global budgets in the atmospheric greenhouse gases. Permafrost degradationon the QTP has caused destabilization of foundations of engineering structures, deterioration ofgrasslands and meadows, and weakening of permafrost control on water resources.展开更多
The current research of narrow-gap gas metal arc welding(NG-GMAW)primarily focuses on improving the sidewall fusion and avoiding the lack-of-fusion defect.However,the high cost and operation difficulty of the methods ...The current research of narrow-gap gas metal arc welding(NG-GMAW)primarily focuses on improving the sidewall fusion and avoiding the lack-of-fusion defect.However,the high cost and operation difficulty of the methods limit the industrial application.In this study,small amount of active gases CO_(2) and O_(2) were added into pure argon inert shielding gas to improve the weld formation of pulsed-current narrow-gap gas metal arc welding(NG-GMAW)of mild steel.Their effects on droplet transfer and arc behavior were investigated.A high-speed visual sensing system was utilized to observe the metal transfer process and arc morphology.When the proportion of CO_(2),being added into the pure argon shielding gas,changes from 5%to 25%,the metal transfer mode changes from pulsed spray streaming transfer to pulsed projected spray transfer,while it remains the pulsed spray streaming transfer when 2%to 10%O_(2) is added.Both CO2 and O_(2) are favorable to stabilizing arc and welding process.O_(2) is even more effective than CO_(2).However,O_(2) is more likely to cause slags on the weld surface,while CO_(2) can improve the weld appearance in some sense.The weld surface concavity in NG-GMAW is greatly influenced by the addition of active gas,but the weld width and weld penetration almost keep constant.This study proposes a new method which is beneficial to improving the weld bead formation and welding process stability.展开更多
基金This research was supported by Program No. KZ951-A1-204-03,Program No. Kj-b-2-201 and No. KZ952-S1-215
文摘Permafrost on the Qinghai-Tibet Plateau (QTP) has experienced major shifts during theQuaternary. During the past 40 years, permafrost has been degrading extensively, due to climaticwarming. Simulations suggest significant degradation of permafrost both in extent and inthickness within the next 50-100 years. Freshwater wetlands on the QTP can contributesignificantly to the global budgets in the atmospheric greenhouse gases. Permafrost degradationon the QTP has caused destabilization of foundations of engineering structures, deterioration ofgrasslands and meadows, and weakening of permafrost control on water resources.
文摘The current research of narrow-gap gas metal arc welding(NG-GMAW)primarily focuses on improving the sidewall fusion and avoiding the lack-of-fusion defect.However,the high cost and operation difficulty of the methods limit the industrial application.In this study,small amount of active gases CO_(2) and O_(2) were added into pure argon inert shielding gas to improve the weld formation of pulsed-current narrow-gap gas metal arc welding(NG-GMAW)of mild steel.Their effects on droplet transfer and arc behavior were investigated.A high-speed visual sensing system was utilized to observe the metal transfer process and arc morphology.When the proportion of CO_(2),being added into the pure argon shielding gas,changes from 5%to 25%,the metal transfer mode changes from pulsed spray streaming transfer to pulsed projected spray transfer,while it remains the pulsed spray streaming transfer when 2%to 10%O_(2) is added.Both CO2 and O_(2) are favorable to stabilizing arc and welding process.O_(2) is even more effective than CO_(2).However,O_(2) is more likely to cause slags on the weld surface,while CO_(2) can improve the weld appearance in some sense.The weld surface concavity in NG-GMAW is greatly influenced by the addition of active gas,but the weld width and weld penetration almost keep constant.This study proposes a new method which is beneficial to improving the weld bead formation and welding process stability.
