2003,Vol.24,No.I TRANSACTIONS OF THE CHINA WELDING INSTITU TION length is put forward. The balance length should be designed between 0 Abstract Based on the macroscale and microscale mechanics me- mm and several millimeters (this numencal value is accordance to the thod a research on fatigue damage evolution of welded joint is conduct welding parameter). A type of wave-controlled CO] are welding inverter ed. The propagation trace of fatigue crack in welded joint is considered to arc is simulated to disclose the effect of the inverterarc system control be with a fractal characteristic within certain scale range, By use of frac- parameters on the CO2 welding process for optimizing the system design tal is established Key words are welding; carbon dioxide; power source; simulation in which the fracture mechanics theory is connected with fatigue damage evolution. An expression of fractal effective stress intensity and a equa Surface tension transformtion in (O, are welding ZHAN G Guang- ion of fatigue damage evolution are given. A new quantitative method is xian( Shandong University, Jinan 250061, China), ZOU Zeng-da, Yin provided for describing the characteristics on fatigue crack surfaces of Hai, LI sihai Li Zhong you. p80-84 Abstract The short-circuit transformation is always adopted in COz Key words :welded joint; fatigue damage; fractal model are welding process, which has disadvantages of high spatter and bad welding formation. Basing on the study of short-circuit transformation in Control system for electron beam scan GUO Guang- yao( Key Labor lgh Energy Density Beam Processin ters in each phase in surface tension tranformation(STT)and the wire Aeronautical Manufacturing Techology Research Institute, Beijing feed The method to test the welding voltage and the state of liquid 100024, China) LIU Fang jun, HAN Rurqing p91-93 bridge is also presented in this paper, The results show that th Abstract A flexible programmable electron beam deflection system out of control before liquid bridge breading, which increases th proposed which enables an electron beam to be controlled externally to ty of STT. with the variety of wire feed speed the interval of se a spot. With this system it is poss ble to produce calculate and oont rol of droplet transformation has a great influence on the breaking state most any desired deflecting figures in which each case comprises several liquid bridges. According to the requirement to the welding power individual spots. The gradient of temperature can be precisely adjusted STT, two designs, invert-loop control mode and output cont rol mode within very narrow tolerance. The system may be readily fitted to exist- ive been pre-sented. The limitation of the invert-loop control mode in ing electron beam units and is suitable for electron beam welding, hard- STT control is also put forward. The result shows that by adjusting the ening remelting surfacing and brazing current in each phase can improve the stability of the transformation in Key words electron beam; welding; brazing; scanning control STT. The project has been validated by experiment Key words :surface tension transformation; shorf circuit tiansfornar Effect of loading rate on mec hanical properties and fracture toughness tion; outat control invert-loop control of structural steel ZHAN GLi( Welding Division, College of Materr al Science and Engineering, Tianjin University, Tianjin 30072, China) Welda bility of activating flux in A-TIG welding for mild steel ZHANG Yurfeng, HUO Lrxing p94-96 HANG Rur hua( Gansu University of technology, Lanzhou 730050 Abstract: The dynamic tenson and fracture toughness tests on structural steels( 16Mn and Q235B steel)were carried out at room temr Abstract: The welding technology test is conducted by using actr perature, the results show that: for 16Mn and Q235B steel, both the vating flux of A- TIG welding tor mild steels. Evaluation includes appear yield strength and tensile strength increase and the plastic properties of the two kinds of material decrease a little under dynamic loading. The ical compositions of weld and base materal and mechanical properties toughness of the base metal and welded joints of 16Mn steel under dy The results indicate that the penetration has been increased 3 times cor namic loading is higher than under static loading at room temperature pared with the conventional TIG welding and for the plates of 12 mr The fracture toughness of welded joints for Q235B steel is poor unde thick the full penetration can be get in a single static loading at room temperature Dynamic loading has great effect on preparation. The appearance of weld is fine there is no effect on the mi- ss of base metal. The fracture toughness of base rostructure, the chemical compositions and mechanical properties. Weld- metal of Q235B under dynamic loading decreases to one fourth the ing current travel speed, are length, coating quantity and type of shidld toughness under static lording. All of the results show that the resis- ing gas have effect on penetration. tance to dynamic load such as earthquake of Q235B steel is rather poor Key words A- TIG welding; mild steel flux; weldability level toughness, the tensile prorperty of material should be considered ractal d elded j when studying the fracture behavior under dynamic loading WU Hurzhi( Nanjing University of Aeronautics and Astronautics Key words :dynamic loading:; fracture toughness; earthquake ress Nanjing 210016, China)Guo Harding, Gao De-ping. p88-90 fracture behavior 201994-2009ChinaAcademicJournalElectronicPublishingHouse.Allrightsreservedhttp:/www.cnki.netlength is put forward. The balance length should be designed between 0 mm and several millimeters (this numerical value is accordance to the welding parameter) . A type of wave2controlled CO2 arc welding inverter2 arc is simulated to disclose the effect of the inverter2arc system control parameters on the CO2 welding processfor optimizing the system design. Key words :arc welding ; carbon dioxide ; power source ; simulation Surface tension transformation in CO2 arc welding ZHAN G Guang2 xian( Shandong University ,Jinan 250061 , China) , ZOU Zeng2da , YIN Hai ,L I si2hai ,Li Zhong2you. p80～84 Abstract :The short2circuit transformation is always adopted in CO2 arc welding process , which has disadvantages of high spatter and bad welding formation.Basing on the study of short2circuit transformation in CO2 arc welding ,the paper presented the relation between the parame2 ters in each phase in surface tension tranformation (STT) and the wire feed. The method to test the welding voltage and the state of liquid bridge is also presented in this paper. The results show that the droplet is out of control before liquid bridge breading ,which increases the unstabli2 ty of STT. With the variety of wire feed speed ,the interval of each phase of droplet transformation has a great influence on the breaking state of liquid bridges. According to the requirement to the welding power in STT ,two designs ,invert2loop control mode and output control mode , have been pre2sented. The limitation of the invert2loop control mode in STT control is also put forward. The result shows that by adjusting the current in each phase can improve the stability of the transformation in STT. The project has been validated by experiment. Key words :surface tension transformation ; shorf circuit tiansforna2 tion ; outpat control ; invert2loop control Weldability of activating flux in A2TIG welding for mild steel ZHAN G Rui2hua ( Gansu University of technology , Lanzhou 730050 , China) ,FAN Ding . p85～87 ,90 Abstract :The welding technology test is conducted by using acti2 vating flux of A2TIG welding for mild steels. Evaluation includes appear2 ance of weld ,effect of flux on penetration ,microstructure of weld ,chem2 ical compositions of weld and base material and mechanical properties. The results indicate that the penetration has been increased 3 times com2 pared with the conventional TIG welding and for the plates of 12 mm thick the full penetration can be get in a single pass without groove preparation. The appearance of weld is fine ,there is no effect on the mi2 crostructure ,the chemical compositions and mechanical properties. Weld2 ing current ,travel speed ,arc length ,coating quantity and type of shidld2 ing gas have effect on penetration. Key words :A2TIG welding ; mild steel ; flux ; weldabilit y Fractal damage evolution model of low2cycled fatigue in welded joint WU Hua2zhi (Nanjing University of Aeronautics and Astronautics , Nanjing 210016 ,China) Guo Hai2ding , Gao De2ping. p88～90 Abstract :Based on the macroscale and microscale mechanics me2 thod ,a research on fatigue damage evolution of welded joint is conduct2 ed. The propagation trace of fatigue crack in welded joint is considered to be with a fractal characteristic within certain scale range.By use of frac2 tal geometry theory ,a model of fatigue crack propagation is established , in which the fracture mechanics theory is connected with fatigue damage evolution. An expression of fractal effective stress intensit y and a equa2 tion of fatigue damage evolution are given. A new quantitative method is provided for describing the characteristics on fatigue crack surfaces of welded joint from microscale. Key words :welded joint ; fatigue damage ; fractal model. Control system for electron beam scan GUO Guang2yao ( Key Labo2 ratory of High Energy Density Beam Processing Technology , Bejjing Aeronautical Manufacturing Technology Research Institute , Beijing 100024 ,China) ,L IU Fang2jun ,HAN Rui2qing. p91～93 Abstract :A flexible programmable electron beam deflection system is proposed which enables an electron beam to be controlled externally to a spot. With this system it is possible to produce ,calculate and control al2 most any desirded deflecting figures in which each case comprises several individual spots. The gradient of temperature can be precisely adjusted within very narrow tolerance. The system may be readily fitted to exist2 ing electron beam units and is suitable for electron beam welding ,hard2 ening remelting ,surfacing and brazing. Key words :electron beam ; welding ; brazing ; scanning control Effect of loading rate on mechanical properties and fracture toughness of structural steel ZHAN GLi (Welding Division ,College of Materi2 al Science and Engineering , Tianjin University , Tianjin 30072 ,China) , ZHAN G Yu2feng ,HUO Li2xing. p94～96 Abstract : The dynamic tension and fracture toughness tests on structural steels(16Mn and Q235B steel) were carried out at room tem2 perature ,the results show that : for 16Mn and Q235B steel , both the yield strength and tensile strength increase and the plastic properties of the two kinds of material decrease a little under dynamic loading. The toughness of the base metal and welded joints of 16Mn steel under dy2 namic loading is higher than under static loading at room temperature. The fracture toughness of welded joints for Q235B steel is poor under static loading at room temperature. Dynamic loading has great effect on the fracture toughness of base metal. The fracture toughness of base metal of Q235B under dynamic loading decreases to one fourth the toughness under static loa2ding. All of the results show that the resis2 tance to dynamic load such as earthquake of Q235B steel is rather poor. From the research in this paper ,we can conclude that for material of low level toughness , the tensile pro2perty of material should be considered when studying the fracture behavior under dynamic loading. Ⅶ Key words :dynamic loading ; fracture toughness; earthquake resis2 tance ; fracture behavior 2003 ,Vol. 24 ,No. 1 TRANSACTIONS OF THE CHINA WELDIN G INSTITU TION