Within the bonded interface of metal bars joint produced by conventional solid state bonding process （ such as flash welding, resistance butt welding, friction welding and so on）, the inclusions are often present, w...Within the bonded interface of metal bars joint produced by conventional solid state bonding process （ such as flash welding, resistance butt welding, friction welding and so on）, the inclusions are often present, which degrade the ductility of joint. A new process of transformation-diffusion brazing is proposed, in which an amorphous foil containing melting point depressant is preplaced between the interfaces to be joined, and the assembly is repeatedly heated/cooled without holding time at peak temperature. A low carbon steel bars, BNi-2 amorphous foil and resistance butt welding machine were used. The results show that surfuce contamination can be disrupted by the dissolution of base metal into molten interlayer in comparison with conventional process, and the ductility of joint can be improved by increasing the times of temperature cycles on line. In addition, transformation-diffusion brazing can be done with relatively simple and inexpensive system in comparison with transient liquid phase bonding.展开更多
Tube and bar products of aluminum alloy composites reinforced by alumina short fiber were formed in a single process with liquid extrusion technology. The microstructure verifies that the reinforcing effect is obvious...Tube and bar products of aluminum alloy composites reinforced by alumina short fiber were formed in a single process with liquid extrusion technology. The microstructure verifies that the reinforcing effect is obvious in the deformation direction since fibers are distributed along this direction, which is resulted from the flow and crystallization under pressure of liquid metal and large plastic deformation of solidified metal in the process. The interface between fiber and matrix belongs to mechanical bonding. The fractograph demonstrates ductile mode. Liquid extrusion process opens up a new way for fabricating tube, bar and shaped products.展开更多
An elusive phenomenon is observed in previous investigations on dynamic fracture that the dynamic fracture toughness （DFT） of high strength metals always increases with the loading rate on the order of TPa.m1/2.s-1....An elusive phenomenon is observed in previous investigations on dynamic fracture that the dynamic fracture toughness （DFT） of high strength metals always increases with the loading rate on the order of TPa.m1/2.s-1. For the purpose of verification, variation of DFT with the loading rate for two high strength steels commonly used in the aviation industry, 30CrMnSiA and 40Cr, is studied in this work. Results of the experiments are compared, which were conducted on the modified split Hopkinson pressure bar （SHPB） apparatus, with striker velocities ranging from 9.2 to 24.1 m/s and a constant value of 16.3 m/s for 30CrMnSiA and 40Cr, respectively. It is observed that for 30CrMnSiA, the crack tip loading rate increases with the increase of the striker velocity, while the fracture initiation time and the DFT simultaneously decrease. However, in the tests of 40Cr, there is also an increasing tendency of DFT, similar to other reports. Through an in-depth investigation on the relationship between the dynamic stress intensity factor （DSIF） and the loading rate, it is concluded that the generally increasing tendency in previous studies could be false, which is induced from a limited striker velocity domain and the errors existing in the experimental and numerical processes. To disclose the real dependency of DFT on the loading rate, experimentsneed to be performed in a comparatively large striker velocity range.展开更多
The split Hopkinson pressure bar （SHPB） was used to determine the dynamic compressive strength of the high-strength Zr38Ti17Cu10.5Co12Be22.5 bulk metallic glass at strain rate on the order of 102 s^-1. It is shown t...The split Hopkinson pressure bar （SHPB） was used to determine the dynamic compressive strength of the high-strength Zr38Ti17Cu10.5Co12Be22.5 bulk metallic glass at strain rate on the order of 102 s^-1. It is shown that at high strain rates beyond about 1 000 s^-1, uniform deformation within the metallic glass specimen could not be achieved and dispersion in the transmitted pulse can lead to discrepancies in measuring the dynamic failure strength of the present Zr-based bulk metallic glass. Based on these reasons, a copper insert was placed between the strike bar and the input bar to obtain reliable and consistent experimental data for testing of the Zr38Ti17Cu10.5Co12Be22.5 bulk metallic glass using the SHPB. Negative strain rate sensitivity was found in the present Zr-based bulk metallic glass.展开更多
The 3-D thermo-mechanical coupled elasto-plastic finite element method (FEM)was used for the simulation of the two-pass continuous hot rolling process of 60SiMnA spring steelbars and rods using MARC/AutoForge3.1 softw...The 3-D thermo-mechanical coupled elasto-plastic finite element method (FEM)was used for the simulation of the two-pass continuous hot rolling process of 60SiMnA spring steelbars and rods using MARC/AutoForge3.1 software. The simulated results visualize the metal flow andthe dynamic evolutions of the strain, stress and temperature during the continuous hot rolling,especially inside the work-piece. It is shown that the non-uniform distributions of the strain,stress and temperature on the longitudinal and transverse sections are a distinct characteristic ofthe continuous hot rolling, which can be used as basic data for improving the tool design,predicting and controlling the micro-structural evolution of a bar and rod.展开更多
目的探讨日间漏斗胸Nuss术后钢板取出术患儿围术期麻醉效果。方法选取2022—2023年首都医科大学附属北京儿童医院计划按照日间手术管理模式行漏斗胸Nuss术后钢板取出术患儿,收集患儿一般资料和临床资料,观察术中、术后患儿不良事件和恢...目的探讨日间漏斗胸Nuss术后钢板取出术患儿围术期麻醉效果。方法选取2022—2023年首都医科大学附属北京儿童医院计划按照日间手术管理模式行漏斗胸Nuss术后钢板取出术患儿,收集患儿一般资料和临床资料,观察术中、术后患儿不良事件和恢复情况。结果共纳入377例患儿,其中男286例、女91例;年龄6~18岁,平均(13.0±3.6)岁,体质量(45.3±14.6)kg;美国麻醉医师协会(American Society of Anesthesiologists,ASA)分级Ⅰ或Ⅱ级,均采用全身麻醉,麻醉诱导后置入气管插管33例,置入喉罩344例,术中出血量为(2.2±1.2)ml,手术时间(40.0±20.9)min,麻醉时间(56.7±22.5)min,停药至拔管时间(8.1±3.0)min,麻醉恢复室停留时间(13.0±2.9)min;术中均未出现低氧血症、高血压、低血压、心动过速、心动过缓、心律失常、术中知晓等不良事件;术后均未出现苏醒延迟、呼吸抑制、低氧血症、严重咽喉部不适、中重度疼痛、恶心呕吐、气胸、伤口出血或血肿等不良事件。结论日间漏斗胸Nuss术后钢板取出术患儿的手术操作时间短、手术及麻醉相关并发症少。术前麻醉门诊完成患儿全面评估和筛选、术中配合外科医生进行肺复张操作,术后早期识别因气胸引起的低氧血症,可提高日间漏斗胸Nuss术后钢板取出术患儿的术后恢复效果。展开更多
文摘Within the bonded interface of metal bars joint produced by conventional solid state bonding process （ such as flash welding, resistance butt welding, friction welding and so on）, the inclusions are often present, which degrade the ductility of joint. A new process of transformation-diffusion brazing is proposed, in which an amorphous foil containing melting point depressant is preplaced between the interfaces to be joined, and the assembly is repeatedly heated/cooled without holding time at peak temperature. A low carbon steel bars, BNi-2 amorphous foil and resistance butt welding machine were used. The results show that surfuce contamination can be disrupted by the dissolution of base metal into molten interlayer in comparison with conventional process, and the ductility of joint can be improved by increasing the times of temperature cycles on line. In addition, transformation-diffusion brazing can be done with relatively simple and inexpensive system in comparison with transient liquid phase bonding.
文摘Tube and bar products of aluminum alloy composites reinforced by alumina short fiber were formed in a single process with liquid extrusion technology. The microstructure verifies that the reinforcing effect is obvious in the deformation direction since fibers are distributed along this direction, which is resulted from the flow and crystallization under pressure of liquid metal and large plastic deformation of solidified metal in the process. The interface between fiber and matrix belongs to mechanical bonding. The fractograph demonstrates ductile mode. Liquid extrusion process opens up a new way for fabricating tube, bar and shaped products.
基金supported by the 111 Project (B07050)the National Natural Science Foundation of China (10932008)
文摘An elusive phenomenon is observed in previous investigations on dynamic fracture that the dynamic fracture toughness （DFT） of high strength metals always increases with the loading rate on the order of TPa.m1/2.s-1. For the purpose of verification, variation of DFT with the loading rate for two high strength steels commonly used in the aviation industry, 30CrMnSiA and 40Cr, is studied in this work. Results of the experiments are compared, which were conducted on the modified split Hopkinson pressure bar （SHPB） apparatus, with striker velocities ranging from 9.2 to 24.1 m/s and a constant value of 16.3 m/s for 30CrMnSiA and 40Cr, respectively. It is observed that for 30CrMnSiA, the crack tip loading rate increases with the increase of the striker velocity, while the fracture initiation time and the DFT simultaneously decrease. However, in the tests of 40Cr, there is also an increasing tendency of DFT, similar to other reports. Through an in-depth investigation on the relationship between the dynamic stress intensity factor （DSIF） and the loading rate, it is concluded that the generally increasing tendency in previous studies could be false, which is induced from a limited striker velocity domain and the errors existing in the experimental and numerical processes. To disclose the real dependency of DFT on the loading rate, experimentsneed to be performed in a comparatively large striker velocity range.
基金Sponsored by the Ministerial Level Research Foundation (00J12 1 7 BQ0123)
文摘The split Hopkinson pressure bar （SHPB） was used to determine the dynamic compressive strength of the high-strength Zr38Ti17Cu10.5Co12Be22.5 bulk metallic glass at strain rate on the order of 102 s^-1. It is shown that at high strain rates beyond about 1 000 s^-1, uniform deformation within the metallic glass specimen could not be achieved and dispersion in the transmitted pulse can lead to discrepancies in measuring the dynamic failure strength of the present Zr-based bulk metallic glass. Based on these reasons, a copper insert was placed between the strike bar and the input bar to obtain reliable and consistent experimental data for testing of the Zr38Ti17Cu10.5Co12Be22.5 bulk metallic glass using the SHPB. Negative strain rate sensitivity was found in the present Zr-based bulk metallic glass.
文摘The 3-D thermo-mechanical coupled elasto-plastic finite element method (FEM)was used for the simulation of the two-pass continuous hot rolling process of 60SiMnA spring steelbars and rods using MARC/AutoForge3.1 software. The simulated results visualize the metal flow andthe dynamic evolutions of the strain, stress and temperature during the continuous hot rolling,especially inside the work-piece. It is shown that the non-uniform distributions of the strain,stress and temperature on the longitudinal and transverse sections are a distinct characteristic ofthe continuous hot rolling, which can be used as basic data for improving the tool design,predicting and controlling the micro-structural evolution of a bar and rod.
文摘目的探讨日间漏斗胸Nuss术后钢板取出术患儿围术期麻醉效果。方法选取2022—2023年首都医科大学附属北京儿童医院计划按照日间手术管理模式行漏斗胸Nuss术后钢板取出术患儿,收集患儿一般资料和临床资料,观察术中、术后患儿不良事件和恢复情况。结果共纳入377例患儿,其中男286例、女91例;年龄6~18岁,平均(13.0±3.6)岁,体质量(45.3±14.6)kg;美国麻醉医师协会(American Society of Anesthesiologists,ASA)分级Ⅰ或Ⅱ级,均采用全身麻醉,麻醉诱导后置入气管插管33例,置入喉罩344例,术中出血量为(2.2±1.2)ml,手术时间(40.0±20.9)min,麻醉时间(56.7±22.5)min,停药至拔管时间(8.1±3.0)min,麻醉恢复室停留时间(13.0±2.9)min;术中均未出现低氧血症、高血压、低血压、心动过速、心动过缓、心律失常、术中知晓等不良事件;术后均未出现苏醒延迟、呼吸抑制、低氧血症、严重咽喉部不适、中重度疼痛、恶心呕吐、气胸、伤口出血或血肿等不良事件。结论日间漏斗胸Nuss术后钢板取出术患儿的手术操作时间短、手术及麻醉相关并发症少。术前麻醉门诊完成患儿全面评估和筛选、术中配合外科医生进行肺复张操作,术后早期识别因气胸引起的低氧血症,可提高日间漏斗胸Nuss术后钢板取出术患儿的术后恢复效果。
