Three-dimensional thermo-electrical finite element analyses were conducted to simulate the current density and temperature distributions in solder bump joints with different pad geometries.The effects of pad thickness...Three-dimensional thermo-electrical finite element analyses were conducted to simulate the current density and temperature distributions in solder bump joints with different pad geometries.The effects of pad thickness,diameter and shape on current density and temperate distributions were investigated respectively.It was found that pads with larger thickness or/and diameter could reduce current density and temperature in solder bump significantly.Pad shapes affected the current density and temperature distributions in solder bumps.The relatively low current density and temperature didn＇t occur in the bump joint with traditional rounded pad but occurred in bump joints with octagonal and nonagonal pads respectively.Therefore,optimized pad geometry may be designed to alleviate the current crowding effect and reduce the bump temperature,and therefore delay electromigration failure and increase the mean-time-to-failure.展开更多
Experiments were carried out with bypass-current MIG welding–brazing of magnesium alloy to galvanized steel to investigate the effect of heat input on the microstructure and mechanical properties of lap joints. Exper...Experiments were carried out with bypass-current MIG welding–brazing of magnesium alloy to galvanized steel to investigate the effect of heat input on the microstructure and mechanical properties of lap joints. Experimental results indicated that the joint efficiency tended to increase at first and then to reduce with the increase of heat input. The joint efficiency reached its maximum of about 70% when the heat input was 155 J/mm. The metallurgical bonding between magnesium alloy and steel was a thin continuous reaction layer, and the intermetallic compound layer consisted of Mg–Zn and slight Fe–Al phases. It is concluded that bypass-current MIG welding–brazing is a stable welding process, which can be used to achieve defect-free joining of magnesium alloy to steel with good weld appearances.展开更多
Sheets of aluminum 6061 alloy were welded using bypass-current double-sided arc welding with Al-Si filler wire to investigate the effect of Al-Si intermetallic compounds on the microstructure, microhardness and corros...Sheets of aluminum 6061 alloy were welded using bypass-current double-sided arc welding with Al-Si filler wire to investigate the effect of Al-Si intermetallic compounds on the microstructure, microhardness and corrosion behavior of weld joint. Experimental results indicated that the Al4.5FeSi phase in the topside of the weld joint was finer than that in the backside and newly formed phase of Al0.5Fe3Si0.5 was observed in the backside. The formation of reinforcing phases of Al-Fe-Si in the weld improved the microhardness of the weld by about 18%. The corrosion resistance of the weld zone was greater than that of the base metal, while the corrosion current displayed opposite, and the corrosion resistance of the weld region was better than that of the base metal.展开更多
The transverse shrinkage, mechanical and metallurgical properties of AISI: 310 S ASS weld joints prepared by P-GMAW and DP-GMAW processes were investigated. It was observed that the use of the DP-GMAW process improves...The transverse shrinkage, mechanical and metallurgical properties of AISI: 310 S ASS weld joints prepared by P-GMAW and DP-GMAW processes were investigated. It was observed that the use of the DP-GMAW process improves the aforementioned characteristics in comparison to that of the P-GMAW process. The enhanced quality of weld joints obtained with DP-GMAW process is primarily due to the combined effect of pulsed current and thermal pulsation(low frequency pulse). During the thermal pulsation period, there is a fluctuation of wire feed rate,which results in the further increase in welding current and the decrease in arc voltage. Because of this synchronization between welding current and arc voltage during the period of low frequency pulse, the DP-GMAW deposit introduces comparatively more thermal shock compared to the P-GMAW deposit, thereby reducing the heat input and improves the properties of weld joints.展开更多
This paper is dealing with the problem of tracking control for uncertain flexible joint manipulator robots driven by brushless direct current motor(BDCM). Flexibility of joint in the manipulator constitutes one of the...This paper is dealing with the problem of tracking control for uncertain flexible joint manipulator robots driven by brushless direct current motor(BDCM). Flexibility of joint in the manipulator constitutes one of the most important sources of uncertainties. In order to achieve high performance, all parts of the manipulator including actuator have been modeled. To cancel the tracking error, a hysteresis current controller and speed controllers have been developed. To evaluate the effectiveness of speed controllers, a comparative study between proportional integral(PI) and sliding mode controllers has been performed. Finally, simulation results carried out in the Matlab simulink environment demonstrate the high precision of sliding mode controller compared with PI controller in the presence of uncertainties of joint flexibility.展开更多
目的·探讨自动管电流调制(automatic tube current modulation,ATCM)降低髋关节机器人CT辐射剂量的可行性,并系统评估其对图像质量的影响。方法·纳入南京鼓楼医院2021年11月至2024年10月进行髋机器人CT检查的患者共106例。采...目的·探讨自动管电流调制(automatic tube current modulation,ATCM)降低髋关节机器人CT辐射剂量的可行性,并系统评估其对图像质量的影响。方法·纳入南京鼓楼医院2021年11月至2024年10月进行髋机器人CT检查的患者共106例。采用随机分组设计,将全部受检者随机分为2组,A组(56例)使用ACTM扫描,B组(50例)使用部分固定管电流扫描(髋关节)。以容积CT剂量指数(volume CT dose index,CTDIvol)和辐射长度乘积(dose-length product,DLP)作为辐射剂量评估指标,以图像信噪比(signal-to-noise ratio,SNR)、对比信噪比(contrast signal to ratio,CNR)和客观噪声作为图像质量评估指标。比较2组患者的年龄、性别、体质量指数(body mass index,BMI)、扫描长度、CTDIvol、DLP、SNR、CNR、客观噪声、建模图像合格率。结果·2组患者的性别、年龄、BMI、扫描长度、图像建模合格率、SNR、CNR、客观噪声比较,差异均无统计学意义(均P>0.05)。A组的髋关节CTDIvol和DLP低于B组,差异有统计学意义(均P<0.001)。结论·使用ACTM技术进行髋关节机器人术前CT扫描,可显著降低辐射剂量,同时保证CT图像质量满足髋关节机器人术前建模需要。展开更多
文摘Three-dimensional thermo-electrical finite element analyses were conducted to simulate the current density and temperature distributions in solder bump joints with different pad geometries.The effects of pad thickness,diameter and shape on current density and temperate distributions were investigated respectively.It was found that pads with larger thickness or/and diameter could reduce current density and temperature in solder bump significantly.Pad shapes affected the current density and temperature distributions in solder bumps.The relatively low current density and temperature didn＇t occur in the bump joint with traditional rounded pad but occurred in bump joints with octagonal and nonagonal pads respectively.Therefore,optimized pad geometry may be designed to alleviate the current crowding effect and reduce the bump temperature,and therefore delay electromigration failure and increase the mean-time-to-failure.
基金financially supported by the National Natural Science Foundation of China(No.51005049)
文摘Experiments were carried out with bypass-current MIG welding–brazing of magnesium alloy to galvanized steel to investigate the effect of heat input on the microstructure and mechanical properties of lap joints. Experimental results indicated that the joint efficiency tended to increase at first and then to reduce with the increase of heat input. The joint efficiency reached its maximum of about 70% when the heat input was 155 J/mm. The metallurgical bonding between magnesium alloy and steel was a thin continuous reaction layer, and the intermetallic compound layer consisted of Mg–Zn and slight Fe–Al phases. It is concluded that bypass-current MIG welding–brazing is a stable welding process, which can be used to achieve defect-free joining of magnesium alloy to steel with good weld appearances.
基金financially supported by the National Natural Science Foundation of China(No.51005049)
文摘Sheets of aluminum 6061 alloy were welded using bypass-current double-sided arc welding with Al-Si filler wire to investigate the effect of Al-Si intermetallic compounds on the microstructure, microhardness and corrosion behavior of weld joint. Experimental results indicated that the Al4.5FeSi phase in the topside of the weld joint was finer than that in the backside and newly formed phase of Al0.5Fe3Si0.5 was observed in the backside. The formation of reinforcing phases of Al-Fe-Si in the weld improved the microhardness of the weld by about 18%. The corrosion resistance of the weld zone was greater than that of the base metal, while the corrosion current displayed opposite, and the corrosion resistance of the weld region was better than that of the base metal.
文摘The transverse shrinkage, mechanical and metallurgical properties of AISI: 310 S ASS weld joints prepared by P-GMAW and DP-GMAW processes were investigated. It was observed that the use of the DP-GMAW process improves the aforementioned characteristics in comparison to that of the P-GMAW process. The enhanced quality of weld joints obtained with DP-GMAW process is primarily due to the combined effect of pulsed current and thermal pulsation(low frequency pulse). During the thermal pulsation period, there is a fluctuation of wire feed rate,which results in the further increase in welding current and the decrease in arc voltage. Because of this synchronization between welding current and arc voltage during the period of low frequency pulse, the DP-GMAW deposit introduces comparatively more thermal shock compared to the P-GMAW deposit, thereby reducing the heat input and improves the properties of weld joints.
文摘This paper is dealing with the problem of tracking control for uncertain flexible joint manipulator robots driven by brushless direct current motor(BDCM). Flexibility of joint in the manipulator constitutes one of the most important sources of uncertainties. In order to achieve high performance, all parts of the manipulator including actuator have been modeled. To cancel the tracking error, a hysteresis current controller and speed controllers have been developed. To evaluate the effectiveness of speed controllers, a comparative study between proportional integral(PI) and sliding mode controllers has been performed. Finally, simulation results carried out in the Matlab simulink environment demonstrate the high precision of sliding mode controller compared with PI controller in the presence of uncertainties of joint flexibility.
文摘目的·探讨自动管电流调制(automatic tube current modulation,ATCM)降低髋关节机器人CT辐射剂量的可行性,并系统评估其对图像质量的影响。方法·纳入南京鼓楼医院2021年11月至2024年10月进行髋机器人CT检查的患者共106例。采用随机分组设计,将全部受检者随机分为2组,A组(56例)使用ACTM扫描,B组(50例)使用部分固定管电流扫描(髋关节)。以容积CT剂量指数(volume CT dose index,CTDIvol)和辐射长度乘积(dose-length product,DLP)作为辐射剂量评估指标,以图像信噪比(signal-to-noise ratio,SNR)、对比信噪比(contrast signal to ratio,CNR)和客观噪声作为图像质量评估指标。比较2组患者的年龄、性别、体质量指数(body mass index,BMI)、扫描长度、CTDIvol、DLP、SNR、CNR、客观噪声、建模图像合格率。结果·2组患者的性别、年龄、BMI、扫描长度、图像建模合格率、SNR、CNR、客观噪声比较,差异均无统计学意义(均P>0.05)。A组的髋关节CTDIvol和DLP低于B组,差异有统计学意义(均P<0.001)。结论·使用ACTM技术进行髋关节机器人术前CT扫描,可显著降低辐射剂量,同时保证CT图像质量满足髋关节机器人术前建模需要。
