A novel three-dimensional numerical model is proposed to investigate the effect of tool eccentricity on the coupled thermal and material flow characteristics in friction stir welding(FSW) process.An asymmetrical bound...A novel three-dimensional numerical model is proposed to investigate the effect of tool eccentricity on the coupled thermal and material flow characteristics in friction stir welding(FSW) process.An asymmetrical boundary condition at the tool-workpiece interface,and the dynamic mesh technique are both employed for the consideration of the tool eccentricity during tool rotating.It is found that tool eccentricity induces the periodical variation of the heat densities both at the tool-workpiece interface and inside the shear layer,but the fluctuation amplitudes of the heat density variations are limited.However,it is demonstrated that tool eccentricity results in significant variation of the material flow behavior in one tool rotating period.Moreover,the material velocity variation at the retreating side is particularly important for the formation of the periodic characteristics in FSW.The modeling result is found to be in good agreement with the experimental one.展开更多
An accurate description of the contact condition between the tool and the workpiece material is one of the most important issues for expounding the underlying multi-physics coupled mechanism during friction stir weldi...An accurate description of the contact condition between the tool and the workpiece material is one of the most important issues for expounding the underlying multi-physics coupled mechanism during friction stir welding(FSW)process.In the present study,a novel asymmetrical boundary condition around the tool-workpiece contact interface is proposed for the FSW of AA2024-T4 alloy.A three-dimensional computational fluid dynamics model is employed for the comparison of the coupled thermal and plastic material flow behavior between asymmetrical and symmetrical boundary conditions.Numerical results of heat generation,temperature distribution,tunnel defect formation and material flow streamline during the welding process are quantitatively analyzed.Besides,various experimental measuring methods are utilized to obtain information about temperature,thermal cycle,tool torque and horizontal cross-section around the exiting keyhole.It is revealed that the modeling results of heat flux density and temperature distribution around the pin,as well as material flow characteristics all change significantly for the two models with different boundary conditions.Particularly,the asymmetrical boundary condition is more capable of predicting temperature fluctuation,plastic material flow along the vertical direction,as well as tunnel defect formation during FSW.Therefore,the superiority of the model with asymmetrical boundary condition over the symmetrical one during the numerical simulation of FSW is elucidated.展开更多
A clinical trial is a systematic investigation or study in or on one or more human subjects,undertaken to assess the safety,clinical performance,and/or effectiveness of a medical device.[1]In this paper,“overseas cli...A clinical trial is a systematic investigation or study in or on one or more human subjects,undertaken to assess the safety,clinical performance,and/or effectiveness of a medical device.[1]In this paper,“overseas clinical trial data”refers to data generated from a clinical trial(s)conducted in a foreign country or jurisdiction and proposed to be used as clinical evidence for a pre-market registration application in China.展开更多
It is of great significance to obtain a thorough understanding of the physical mechanisms responsible for humping bead phenomenon in high speed gas metal arc welding （GMAW） in order to raise welding efficiency. Expe...It is of great significance to obtain a thorough understanding of the physical mechanisms responsible for humping bead phenomenon in high speed gas metal arc welding （GMAW） in order to raise welding efficiency. Experiments were conducted to observe the weld pool behaviors in high speed GMAW, and it was found that both the severely deformed weld pool surface and strong backward flowing play a dominant role in humping bead formation. In this study, a mathematical model is developed to quantitatively analyze the forming mechanism of humping beads for high speed GMAW through considering both the momentum and heat content distribution of the backward flowing molten metal inside the weld pool. The transient development of temperature profiles in the weld pool with severe deformation demonstrates the humping bead forming process under some welding conditions. The predicted and measured humping bead dimensions are in agreement.展开更多
Welding has become the most important materials processing technology in manufacturing, and has critical effects on the quality, reliability and life of products as well as production cost, efficiency and response spe...Welding has become the most important materials processing technology in manufacturing, and has critical effects on the quality, reliability and life of products as well as production cost, efficiency and response speed to market. As various kinds of high performance metallic materials are widely used in engineering, there are more demands in manufacturing industry for advanced welding technology.展开更多
基金supported by the National Natural Science Foundation of China (Nos. 51905309, 52035005, 52275349)the State Key Laboratory of Solidification Processing, China (No. SKLSP201912)。
基金the financial support from the National Natural Science Foundation of China (Nos. 52005297, 52035005)the Key Research and Development Program of Shandong Province, China (No. 2021ZLGX01)。
文摘A novel three-dimensional numerical model is proposed to investigate the effect of tool eccentricity on the coupled thermal and material flow characteristics in friction stir welding(FSW) process.An asymmetrical boundary condition at the tool-workpiece interface,and the dynamic mesh technique are both employed for the consideration of the tool eccentricity during tool rotating.It is found that tool eccentricity induces the periodical variation of the heat densities both at the tool-workpiece interface and inside the shear layer,but the fluctuation amplitudes of the heat density variations are limited.However,it is demonstrated that tool eccentricity results in significant variation of the material flow behavior in one tool rotating period.Moreover,the material velocity variation at the retreating side is particularly important for the formation of the periodic characteristics in FSW.The modeling result is found to be in good agreement with the experimental one.
基金The authors are grateful for the financial support from the National Natural Science Foundation of China(Grant Nos.52005297 and 52035005).
文摘An accurate description of the contact condition between the tool and the workpiece material is one of the most important issues for expounding the underlying multi-physics coupled mechanism during friction stir welding(FSW)process.In the present study,a novel asymmetrical boundary condition around the tool-workpiece contact interface is proposed for the FSW of AA2024-T4 alloy.A three-dimensional computational fluid dynamics model is employed for the comparison of the coupled thermal and plastic material flow behavior between asymmetrical and symmetrical boundary conditions.Numerical results of heat generation,temperature distribution,tunnel defect formation and material flow streamline during the welding process are quantitatively analyzed.Besides,various experimental measuring methods are utilized to obtain information about temperature,thermal cycle,tool torque and horizontal cross-section around the exiting keyhole.It is revealed that the modeling results of heat flux density and temperature distribution around the pin,as well as material flow characteristics all change significantly for the two models with different boundary conditions.Particularly,the asymmetrical boundary condition is more capable of predicting temperature fluctuation,plastic material flow along the vertical direction,as well as tunnel defect formation during FSW.Therefore,the superiority of the model with asymmetrical boundary condition over the symmetrical one during the numerical simulation of FSW is elucidated.
文摘A clinical trial is a systematic investigation or study in or on one or more human subjects,undertaken to assess the safety,clinical performance,and/or effectiveness of a medical device.[1]In this paper,“overseas clinical trial data”refers to data generated from a clinical trial(s)conducted in a foreign country or jurisdiction and proposed to be used as clinical evidence for a pre-market registration application in China.
文摘It is of great significance to obtain a thorough understanding of the physical mechanisms responsible for humping bead phenomenon in high speed gas metal arc welding （GMAW） in order to raise welding efficiency. Experiments were conducted to observe the weld pool behaviors in high speed GMAW, and it was found that both the severely deformed weld pool surface and strong backward flowing play a dominant role in humping bead formation. In this study, a mathematical model is developed to quantitatively analyze the forming mechanism of humping beads for high speed GMAW through considering both the momentum and heat content distribution of the backward flowing molten metal inside the weld pool. The transient development of temperature profiles in the weld pool with severe deformation demonstrates the humping bead forming process under some welding conditions. The predicted and measured humping bead dimensions are in agreement.
文摘Welding has become the most important materials processing technology in manufacturing, and has critical effects on the quality, reliability and life of products as well as production cost, efficiency and response speed to market. As various kinds of high performance metallic materials are widely used in engineering, there are more demands in manufacturing industry for advanced welding technology.
