In this study,the rotary movement of the tungsten needle in gas tungsten arc welding(GTAW)process was realized by direct current motor.The arc characteristics,the flow of molten pool and the microstructure and propert...In this study,the rotary movement of the tungsten needle in gas tungsten arc welding(GTAW)process was realized by direct current motor.The arc characteristics,the flow of molten pool and the microstructure and properties of the weld bead were studied.The results showed that the rotary motion of the tungsten needle transferred circumferential momentum to the arc as well as the molten pool,thereby conferring the latter with rotating fluid flow characteristics.Under the action of a relatively spiraling shielding gas,arc constriction occurred,and molten pool width dropped considerably.A finer and more uniform precipitated phase in the matrix,as well as a fewer large-medium pores,were achieved in the 5A06 aluminum alloy weld metal using this modified GTAW process,which noticeably increased the bending strength and tensile strength of weld metal and the microhardness of fusion zone.展开更多
Laser twin-arc GTAW(LTA-GTAW)process has been developed by using the synergic interaction effects of laser and a coupled arc in a weld pool to achieve higher energy efficiency.In this study,bead-on-plate welding was c...Laser twin-arc GTAW(LTA-GTAW)process has been developed by using the synergic interaction effects of laser and a coupled arc in a weld pool to achieve higher energy efficiency.In this study,bead-on-plate welding was conducted on 8-mm-thick Q235B work-pieces to investigate the variation of hybrid arc profile,the influence of hybrid arc profile on weld forming,microstructure and mech-anical properties of the joint during the LTA-GTAW process.The influence of Laser-GTAW and LTA-GTAW methods on weld surface appearance,heat input per unit length,and weld metal microstructure were also demonstrated systematically.The LTA-GTAW can make the distribution of arc energy more reasonable in welding depth and width.When defocus is 0,I_(f)is 330 A,I_(b)is 240 A,laser power is 2.4 kW,and spacing between heat sources of tungsten electrode is 10 mm,the weld shape is better.Compared with Laser-GTAW,LTA-GTAW can achieve lower heat input at the same penetration depth,and the microstructure of the weld is refined.The tensile strength of the welded joint is 121.8%of the base material,and the fracture mode of the welded joint is ductile fracture,the comprehensive mechanical properties are better.展开更多
因高度向分辨能力缺失,地基干涉雷达应用于建筑成像时会发生严重的高度向叠掩现象。层析合成孔径雷达(Tomographic Synthetic Aperture Radar,TomoSAR)技术具备高度向分辨能力,能够实现建筑三维成像。地基层析圆弧扫描合成孔径雷达(Grou...因高度向分辨能力缺失,地基干涉雷达应用于建筑成像时会发生严重的高度向叠掩现象。层析合成孔径雷达(Tomographic Synthetic Aperture Radar,TomoSAR)技术具备高度向分辨能力,能够实现建筑三维成像。地基层析圆弧扫描合成孔径雷达(Ground-based Tomographic Arc-scanning Synthetic Aperture Radar,GB-TomoArcSAR)通过双轴转台控制天线在不同俯仰角度的水平面内进行圆周扫描来获取高度向合成孔径,实现三维层析成像。本文提出了GB-TomoArcSAR的三维点云生成方法,首先构建了适用于高度向弧形采样条件的层析成像几何模型。其次利用基于巴特沃斯滤波器的奇异值分解(Singular Value Decomposition,SVD)方法进行谱估计,找出层析谱中的峰值及其对应的峰值位置,构成层析向目标候选集。随后利用自对消顺序广义似然比(Sequential Generalized Likelihood Ratio Test with Cancellation,SGLRTC)检测器估计散射体的数目与位置,通过设置检测门限将真实目标的峰值及对应的峰值位置从候选集中筛选出来。最后采用基于空间几何分布的点云优化方法剔除误差点,生成点云图像。文章通过点目标和面目标的仿真实验,验证了所提方法适用于GB-TomoArcSAR,能够有效解决高度向多散射体目标的叠掩问题;进一步开展了实测数据验证,基于所提方法获取了北京市一处建筑基坑的层析点云,其与实际场景几何特征一致。展开更多
The North Sulawesi arc(NSUA)constitutes the northern arm of Sulawesi Island and is characterized by complex Cenozoic records of magmatism and tectonics.Zircon U-Pb geochronological and Hf-O isotopic data,whole-rock ma...The North Sulawesi arc(NSUA)constitutes the northern arm of Sulawesi Island and is characterized by complex Cenozoic records of magmatism and tectonics.Zircon U-Pb geochronological and Hf-O isotopic data,whole-rock major oxides,trace elemental,and Sr-Nd-Pb isotopic data of the high-silica granites from the NSUA document their petrogenesis and tectonic setting.Zircon elemental analysis of the granitic samples shows a juvenile oceanic crust origin and the U-Pb geochronology indicates their Oligocene ages between 30.4 and 27.3 Ma.The samples have high SiO_(2)(75.05 wt.%-79.38 wt.%)and Na_(2)O(4.48 wt.%-5.67 wt.%),low K_(2)O(0.15 wt.%-1.34 wt.%)and MgO(0.07 wt.%-0.91 wt.%)contents,belonging to calc-alkaline I-type high-silica granites.They have enriched LREE and LILE,and depleted HREE and HFSE,showing significant Eu,Sr,Nb,and Ta negative anomalies.These high-silica granites have low(^(87)Sr/^(86)Sr)_i ratios(0.704412-0.704592),positiveε_(Nd)(t)values(from+5.1 to+6.6),positive zirconε_(Hf)(t)values(from+10.1 to+18.8),low zirconδ^(18)O values(4.20‰-5.02‰),and similar Pb isotope compositions to the Indian Ocean MORB.Such signatures suggest that these high-silica granites were derived by partial melting process of the juvenile arc crust in an intra-oceanic setting.The felsic magmatism in the NSUA was likely driven by mantle upwelling and decompression melting during the Oligocene,in response to slab roll-back linked with the convergence of the East Sulawesi ophiolitic crust or the microcontinental fragments.展开更多
Heat and mass transfer within an electric arc furnace are strongly influenced by extreme temperatures and complex electromagnetic fields.Variations in temperature distribution play a crucial role in determining melt f...Heat and mass transfer within an electric arc furnace are strongly influenced by extreme temperatures and complex electromagnetic fields.Variations in temperature distribution play a crucial role in determining melt flow patterns and in the formation of stagnant regions,commonly referred to as dead zones.To better understand the internal flow dynamics and thermal behavior of the furnace,this study develops a multiphysics coupled model that integrates fluid heat transfer with Maxwell’s electromagnetic field equations.Numerical simulations are conducted to systematically examine how key operational parameters,such as electric current and arc characteristics,affect the heat transfer performance inside the furnace.The analysis reveals that arc length is the dominant factor governing both current density and heat distribution in the molten bath.Specifically,increasing the arc length from 200 mm to 400 mm results in a 16.1%rise in maximum current density within the titanium slag layer,from 7128 A/m^(2) to 8270 A/m^(2).However,a longer arc also introduces higher interfacial thermal resistance,which impedes heat transfer efficiency and leads to a significant drop in the peak temperature of the titanium slag,from 2618 K to 2125 K.These findings underscore the dual impact of arc length on both electrical and thermal behavior,highlighting the need for careful optimization.展开更多
Si-containing Mg alloys solidified at conventional rates often contain coarse and sharp Mg_(2)Si phases,which can result in inferior material properties.In this study,Mg-6wt.%Si(Mg-6Si)alloy was prepared by wire arc a...Si-containing Mg alloys solidified at conventional rates often contain coarse and sharp Mg_(2)Si phases,which can result in inferior material properties.In this study,Mg-6wt.%Si(Mg-6Si)alloy was prepared by wire arc additive manufacturing(WAAM),employing the gas tungsten arc welding technique with rapid cooling.The microstructures and mechanical properties of the WAAM alloy were investigated and compared with those of the as-cast samples produced using a metal mold.The results indicate that the WAAM Mg-6Si is harder and stronger than the as-cast samples.The microhardness of the WAAM Mg-6Si increases by 36.6% in comparison to that of as-cast Mg-6Si alloy.Furthermore,the average tensile strengths at room temperature and 150℃ increases by 63.4% and 21.3%,respectively.WAAM refines both the Mg_(2)Si phase and the overall grains,resulting in a homogeneous morphology and improved mechanical properties.The granular Mg_(2)Si phase,characterized by fine particles with a diffused distribution,shows a significant increase in concentration.The acicular Mg_(2)Si phase is distributed along the grain boundaries,and its concentration significantly decreases.The average grain size of the Mg_(2)Si phase is about 9.20μm,about 5 times smaller.The refinement and distribution of the granular Mg_(2)Si phase,as well as the reduction in the amount of needle-like Mg_(2)Si particles,are the key factors for improving the mechanical properties of WAAM Mg-6Si alloy.展开更多
基金supported by National Natural Science Foundation of China(52175305)National Natural Science Foundation of China(U22B20127)Taishan Scholars Project(tstp20230618).
文摘In this study,the rotary movement of the tungsten needle in gas tungsten arc welding(GTAW)process was realized by direct current motor.The arc characteristics,the flow of molten pool and the microstructure and properties of the weld bead were studied.The results showed that the rotary motion of the tungsten needle transferred circumferential momentum to the arc as well as the molten pool,thereby conferring the latter with rotating fluid flow characteristics.Under the action of a relatively spiraling shielding gas,arc constriction occurred,and molten pool width dropped considerably.A finer and more uniform precipitated phase in the matrix,as well as a fewer large-medium pores,were achieved in the 5A06 aluminum alloy weld metal using this modified GTAW process,which noticeably increased the bending strength and tensile strength of weld metal and the microhardness of fusion zone.
基金supported by the Industrial Innovation Major Technology Global Unveiling Project of Jining City(2022JBZP004)Taishan Scholars Project.
文摘Laser twin-arc GTAW(LTA-GTAW)process has been developed by using the synergic interaction effects of laser and a coupled arc in a weld pool to achieve higher energy efficiency.In this study,bead-on-plate welding was conducted on 8-mm-thick Q235B work-pieces to investigate the variation of hybrid arc profile,the influence of hybrid arc profile on weld forming,microstructure and mech-anical properties of the joint during the LTA-GTAW process.The influence of Laser-GTAW and LTA-GTAW methods on weld surface appearance,heat input per unit length,and weld metal microstructure were also demonstrated systematically.The LTA-GTAW can make the distribution of arc energy more reasonable in welding depth and width.When defocus is 0,I_(f)is 330 A,I_(b)is 240 A,laser power is 2.4 kW,and spacing between heat sources of tungsten electrode is 10 mm,the weld shape is better.Compared with Laser-GTAW,LTA-GTAW can achieve lower heat input at the same penetration depth,and the microstructure of the weld is refined.The tensile strength of the welded joint is 121.8%of the base material,and the fracture mode of the welded joint is ductile fracture,the comprehensive mechanical properties are better.
文摘因高度向分辨能力缺失,地基干涉雷达应用于建筑成像时会发生严重的高度向叠掩现象。层析合成孔径雷达(Tomographic Synthetic Aperture Radar,TomoSAR)技术具备高度向分辨能力,能够实现建筑三维成像。地基层析圆弧扫描合成孔径雷达(Ground-based Tomographic Arc-scanning Synthetic Aperture Radar,GB-TomoArcSAR)通过双轴转台控制天线在不同俯仰角度的水平面内进行圆周扫描来获取高度向合成孔径,实现三维层析成像。本文提出了GB-TomoArcSAR的三维点云生成方法,首先构建了适用于高度向弧形采样条件的层析成像几何模型。其次利用基于巴特沃斯滤波器的奇异值分解(Singular Value Decomposition,SVD)方法进行谱估计,找出层析谱中的峰值及其对应的峰值位置,构成层析向目标候选集。随后利用自对消顺序广义似然比(Sequential Generalized Likelihood Ratio Test with Cancellation,SGLRTC)检测器估计散射体的数目与位置,通过设置检测门限将真实目标的峰值及对应的峰值位置从候选集中筛选出来。最后采用基于空间几何分布的点云优化方法剔除误差点,生成点云图像。文章通过点目标和面目标的仿真实验,验证了所提方法适用于GB-TomoArcSAR,能够有效解决高度向多散射体目标的叠掩问题;进一步开展了实测数据验证,基于所提方法获取了北京市一处建筑基坑的层析点云,其与实际场景几何特征一致。
基金supported by the National Natural Science Foundation of China(No.42330302)the National Key Research and Development Program of China(No.2023YFF0803701)+1 种基金the Southern Marine Science and Engineering Guangdong Laboratory(Zhuhai)(No.SML2023SP206)the Australian Research Council(No.FL160100168)。
文摘The North Sulawesi arc(NSUA)constitutes the northern arm of Sulawesi Island and is characterized by complex Cenozoic records of magmatism and tectonics.Zircon U-Pb geochronological and Hf-O isotopic data,whole-rock major oxides,trace elemental,and Sr-Nd-Pb isotopic data of the high-silica granites from the NSUA document their petrogenesis and tectonic setting.Zircon elemental analysis of the granitic samples shows a juvenile oceanic crust origin and the U-Pb geochronology indicates their Oligocene ages between 30.4 and 27.3 Ma.The samples have high SiO_(2)(75.05 wt.%-79.38 wt.%)and Na_(2)O(4.48 wt.%-5.67 wt.%),low K_(2)O(0.15 wt.%-1.34 wt.%)and MgO(0.07 wt.%-0.91 wt.%)contents,belonging to calc-alkaline I-type high-silica granites.They have enriched LREE and LILE,and depleted HREE and HFSE,showing significant Eu,Sr,Nb,and Ta negative anomalies.These high-silica granites have low(^(87)Sr/^(86)Sr)_i ratios(0.704412-0.704592),positiveε_(Nd)(t)values(from+5.1 to+6.6),positive zirconε_(Hf)(t)values(from+10.1 to+18.8),low zirconδ^(18)O values(4.20‰-5.02‰),and similar Pb isotope compositions to the Indian Ocean MORB.Such signatures suggest that these high-silica granites were derived by partial melting process of the juvenile arc crust in an intra-oceanic setting.The felsic magmatism in the NSUA was likely driven by mantle upwelling and decompression melting during the Oligocene,in response to slab roll-back linked with the convergence of the East Sulawesi ophiolitic crust or the microcontinental fragments.
基金support from National Natural Science Foundation of China under Contract(NO.51966005)Yunnan Fundamental Research Projects(NO.202301AT070469)Yunnan Major Scientific and Technological Projects(NO.202202AG050002).
文摘Heat and mass transfer within an electric arc furnace are strongly influenced by extreme temperatures and complex electromagnetic fields.Variations in temperature distribution play a crucial role in determining melt flow patterns and in the formation of stagnant regions,commonly referred to as dead zones.To better understand the internal flow dynamics and thermal behavior of the furnace,this study develops a multiphysics coupled model that integrates fluid heat transfer with Maxwell’s electromagnetic field equations.Numerical simulations are conducted to systematically examine how key operational parameters,such as electric current and arc characteristics,affect the heat transfer performance inside the furnace.The analysis reveals that arc length is the dominant factor governing both current density and heat distribution in the molten bath.Specifically,increasing the arc length from 200 mm to 400 mm results in a 16.1%rise in maximum current density within the titanium slag layer,from 7128 A/m^(2) to 8270 A/m^(2).However,a longer arc also introduces higher interfacial thermal resistance,which impedes heat transfer efficiency and leads to a significant drop in the peak temperature of the titanium slag,from 2618 K to 2125 K.These findings underscore the dual impact of arc length on both electrical and thermal behavior,highlighting the need for careful optimization.
基金supported by the National Natural Science Foundation of China(Grant Nos.52001037,U2037601,and U21A2048)the Science and Technology Program of Guangzhou,China(Grant No.2022BLC003).
文摘Si-containing Mg alloys solidified at conventional rates often contain coarse and sharp Mg_(2)Si phases,which can result in inferior material properties.In this study,Mg-6wt.%Si(Mg-6Si)alloy was prepared by wire arc additive manufacturing(WAAM),employing the gas tungsten arc welding technique with rapid cooling.The microstructures and mechanical properties of the WAAM alloy were investigated and compared with those of the as-cast samples produced using a metal mold.The results indicate that the WAAM Mg-6Si is harder and stronger than the as-cast samples.The microhardness of the WAAM Mg-6Si increases by 36.6% in comparison to that of as-cast Mg-6Si alloy.Furthermore,the average tensile strengths at room temperature and 150℃ increases by 63.4% and 21.3%,respectively.WAAM refines both the Mg_(2)Si phase and the overall grains,resulting in a homogeneous morphology and improved mechanical properties.The granular Mg_(2)Si phase,characterized by fine particles with a diffused distribution,shows a significant increase in concentration.The acicular Mg_(2)Si phase is distributed along the grain boundaries,and its concentration significantly decreases.The average grain size of the Mg_(2)Si phase is about 9.20μm,about 5 times smaller.The refinement and distribution of the granular Mg_(2)Si phase,as well as the reduction in the amount of needle-like Mg_(2)Si particles,are the key factors for improving the mechanical properties of WAAM Mg-6Si alloy.
