The brazing of 55% SiCp/A356 (volume fraction) composites in air using Zn-Al alloy as a filler metal was investigated.During the brazing process,ultrasonic vibrations were applied to samples for bonding and a signific...The brazing of 55% SiCp/A356 (volume fraction) composites in air using Zn-Al alloy as a filler metal was investigated.During the brazing process,ultrasonic vibrations were applied to samples for bonding and a significant dissolution of the filler metal into the matrix alloy in the base materials occurred.As brazing temperatures were increased,the thickness of the partial melting layers in the base material increased.SiC particles in the partial melting layer of the base material were transferred into the liquid filler under ultrasonic action and a bond with homogeneously distributed reinforcements was obtained after solidification.The volume fraction of SiC particles in the bonds could be varied by changing the brazing temperature.The maximum SiC particle volume fraction of the bond material reached 37% at a brazing temperature of 500 ℃.The shear strength of the brazed bonds was improved at pressures up to 244 MPa (at 20 ℃) and increased by 133.8% (at 200 ℃) compared with the filler of the Zn-based alloy.展开更多
The transmitting models of ultrasonic vibration in ultrasonic transducer and capillary were presented according to the propagating mechanism of ultrasonic wave in elastic body. The coupling characteristics of ultrason...The transmitting models of ultrasonic vibration in ultrasonic transducer and capillary were presented according to the propagating mechanism of ultrasonic wave in elastic body. The coupling characteristics of ultrasonic longitudinal-complex transverse vibration system were simulated by Matlab software. The ultrasonic vibration displacement and the velocity of high frequency were measured by using the PSV-400-M2(1.5MHz) laser Doppler vibrometer. The vibration locus shapes driven by the same frequency and different frequencies were tested by using GDS-820S dual channel digital oscilloscope. The microstructures at bonding interface were observed by means of KYKY2800 scanning electron microscope. The results show that ultrasonic vibration displacement or velocity and energy density increase with the decrease of section area in the transmitting process. The vibration locus shapes driven simultaneously by the same frequency and different frequencies are elliptical (or circular) loci and rectangular (or square) loci, respectively. And the characteristics at bonding interface are improved by coupling loci.展开更多
The paper explains the comparison of magnetic pulse welding method which belongs to non-conventional machining methods with other conventional and non-conventional welding methods which include brazing, explosive weld...The paper explains the comparison of magnetic pulse welding method which belongs to non-conventional machining methods with other conventional and non-conventional welding methods which include brazing, explosive welding, ultrasonic welding, tungsten and metal inert gas and roll bonding. Magnetic pulse welding differs completely in technology when compared with conventional welding processes because the process is done with high velocity and without heat or consumable materials. It is better than other methods because it＇s cold process and can be done without any heat affect zone. In addition, there is no need for rework and post welding cleaning and there is no scrap problem. Magnetic pulse welding is a green process used to design and build light structure with high strength to reduce the weight and the energy. Magnetic pulse welding reduces the risk of corrosion by limiting the metallic interaction to just the two metals welded; therefore, it replaces the brazing method. Also, it is better than the explosive welding method because there is no risk of handling the explosive material and there is no noise. The part assembly by magnetic pulse welding is stronger than the parts assembly by tungsten and metal inert gas welding and it is easy to achieve a good aesthetic with high speed. Therefore, using magnetic pulse welding technology will not affect the environment.展开更多
Power ultrasound is finding widespread applications in assisting conventional processes yielding products of better quality at lower processing power and temperature. Transmission of ultrasound is known to be affected...Power ultrasound is finding widespread applications in assisting conventional processes yielding products of better quality at lower processing power and temperature. Transmission of ultrasound is known to be affected by the boundaries between layers of different materials or same material but in different states （solid or liquid or gas）. This paper investigates the effects of ultrasound （US） on the surface of the solidified weld which has been subjected to ultrasonic vibrations of 20 kHz frequency during laser welding. Vibrations due to ultrasound normally exert a very high force which is usually hundred or thousand times the gravity. The transverse waves will also cause movement of molten material in the weld. As the surface of the weld beads were of interest and not the mechanical properties and the microstructure, investigation of bead on plate welds were found to be sufficient. High carbon steel plate was held at one end by the ultrasonic horn through which ultrasound was injected. A bead on plate weld using a CO2 laser （1 kW） was then performed along the center of the plate using three different welding speeds namely, 400, 1200 and 2000 mm per minute. The ultrasonic powers selected were 3 W and 6 W respectively for each welding speed as higher acoustical power was causing ejection of molten metal from the pool during welding. 3D surface measurements and analysis were then made on a section of length 20 mm using a Talysurf machine. The results show that the surface of the weld was affected to different extent depending on the positions being considered in the weld. Some regions were similar to the reference weld whereas some specific regions were heavily disrupted with deep valleys followed by high peak/s. This shows that US vibration of weld pools, even at very small acoustical power, is a more complex problem than other similar processes such as casting because of the very small volume of molten metal involved.展开更多
Fatigue is usually the cause for the cracks identified at bridge elements in service. With an increase in the introduction of corrugated steel web girders in recent highway bridge construction, the understanding of th...Fatigue is usually the cause for the cracks identified at bridge elements in service. With an increase in the introduction of corrugated steel web girders in recent highway bridge construction, the understanding of the fatigue behaviour of welded details in such structures becomes an important issue for the design. The typical welded details were represented as welded joints assembled by longitudinal corrugated plates. All the experiments were performed under fatigue loading using a servo-control testing machine. The test results from the failure mode observation with the aid of infrared thermo-graph technology show that the failure manner of these welded joints is comparable to that of the corrugated steel web beams reported previously. It is indicated from the stiffness degradation analysis that the welded joints with larger corrugation angle have higher stiffness and greater stiffness degradation in the notable stiffness degradation range. It is shown from the test S-N relations based on the free regression and forced regression analyses that there is a good linear dependence between lg(N) and lg(ΔS). It is also demonstrated that the proposed fracture mechanics analytical model is able to give a prediction slightly lower but on the safe side for the mean stresses at 2 million cycles of the test welded joints.展开更多
It is due to the need to ensure the security and integrity of equipment, that the non-destructive tests have been increasingly used in the industrial sector. Among these, the ultrasonic pulse echo technique is the mos...It is due to the need to ensure the security and integrity of equipment, that the non-destructive tests have been increasingly used in the industrial sector. Among these, the ultrasonic pulse echo technique is the most used in industry, mainly for its simplicity and efficiency. With one transducer only, it is possible to emit the ultrasonic and receive the echo pulse. The ANNs （artificial neural networks） are artificial intelligence techniques that, when properly trained, align themselves to inspection tests becoming a powerful tool in the detection and fault identification. In this work, the echo pulse technique was used to detect discontinuities in welds, where ANNs were fed from the information obtained by digital signal processing techniques （Fourier transform）, to identify and classify three distinct classes of defects. Results showed that with the combination of feature extraction by Fourier transformation and classification with neural networks, it is possible to obtain an automatic defect detection system in welded joints with average efficiency.展开更多
基金Project(50375039) supported by the National Natural Science Foundation of ChinaProject supported by the Excellence Team Program at the Harbin Institute of Technology,China
文摘The brazing of 55% SiCp/A356 (volume fraction) composites in air using Zn-Al alloy as a filler metal was investigated.During the brazing process,ultrasonic vibrations were applied to samples for bonding and a significant dissolution of the filler metal into the matrix alloy in the base materials occurred.As brazing temperatures were increased,the thickness of the partial melting layers in the base material increased.SiC particles in the partial melting layer of the base material were transferred into the liquid filler under ultrasonic action and a bond with homogeneously distributed reinforcements was obtained after solidification.The volume fraction of SiC particles in the bonds could be varied by changing the brazing temperature.The maximum SiC particle volume fraction of the bond material reached 37% at a brazing temperature of 500 ℃.The shear strength of the brazed bonds was improved at pressures up to 244 MPa (at 20 ℃) and increased by 133.8% (at 200 ℃) compared with the filler of the Zn-based alloy.
文摘The transmitting models of ultrasonic vibration in ultrasonic transducer and capillary were presented according to the propagating mechanism of ultrasonic wave in elastic body. The coupling characteristics of ultrasonic longitudinal-complex transverse vibration system were simulated by Matlab software. The ultrasonic vibration displacement and the velocity of high frequency were measured by using the PSV-400-M2(1.5MHz) laser Doppler vibrometer. The vibration locus shapes driven by the same frequency and different frequencies were tested by using GDS-820S dual channel digital oscilloscope. The microstructures at bonding interface were observed by means of KYKY2800 scanning electron microscope. The results show that ultrasonic vibration displacement or velocity and energy density increase with the decrease of section area in the transmitting process. The vibration locus shapes driven simultaneously by the same frequency and different frequencies are elliptical (or circular) loci and rectangular (or square) loci, respectively. And the characteristics at bonding interface are improved by coupling loci.
文摘The paper explains the comparison of magnetic pulse welding method which belongs to non-conventional machining methods with other conventional and non-conventional welding methods which include brazing, explosive welding, ultrasonic welding, tungsten and metal inert gas and roll bonding. Magnetic pulse welding differs completely in technology when compared with conventional welding processes because the process is done with high velocity and without heat or consumable materials. It is better than other methods because it＇s cold process and can be done without any heat affect zone. In addition, there is no need for rework and post welding cleaning and there is no scrap problem. Magnetic pulse welding is a green process used to design and build light structure with high strength to reduce the weight and the energy. Magnetic pulse welding reduces the risk of corrosion by limiting the metallic interaction to just the two metals welded; therefore, it replaces the brazing method. Also, it is better than the explosive welding method because there is no risk of handling the explosive material and there is no noise. The part assembly by magnetic pulse welding is stronger than the parts assembly by tungsten and metal inert gas welding and it is easy to achieve a good aesthetic with high speed. Therefore, using magnetic pulse welding technology will not affect the environment.
文摘Power ultrasound is finding widespread applications in assisting conventional processes yielding products of better quality at lower processing power and temperature. Transmission of ultrasound is known to be affected by the boundaries between layers of different materials or same material but in different states （solid or liquid or gas）. This paper investigates the effects of ultrasound （US） on the surface of the solidified weld which has been subjected to ultrasonic vibrations of 20 kHz frequency during laser welding. Vibrations due to ultrasound normally exert a very high force which is usually hundred or thousand times the gravity. The transverse waves will also cause movement of molten material in the weld. As the surface of the weld beads were of interest and not the mechanical properties and the microstructure, investigation of bead on plate welds were found to be sufficient. High carbon steel plate was held at one end by the ultrasonic horn through which ultrasound was injected. A bead on plate weld using a CO2 laser （1 kW） was then performed along the center of the plate using three different welding speeds namely, 400, 1200 and 2000 mm per minute. The ultrasonic powers selected were 3 W and 6 W respectively for each welding speed as higher acoustical power was causing ejection of molten metal from the pool during welding. 3D surface measurements and analysis were then made on a section of length 20 mm using a Talysurf machine. The results show that the surface of the weld was affected to different extent depending on the positions being considered in the weld. Some regions were similar to the reference weld whereas some specific regions were heavily disrupted with deep valleys followed by high peak/s. This shows that US vibration of weld pools, even at very small acoustical power, is a more complex problem than other similar processes such as casting because of the very small volume of molten metal involved.
基金Projects(51308363,11327801)supported by the National Natural Science Foundation of ChinaProject(2013-1792-9-4)supported by the Scientific Research Foundation for the Returned Overseas Chinese ScholarsProject(YJ201307)supported by the Start-up Research Fund for Introduced Talents of Sichuan University,China
文摘Fatigue is usually the cause for the cracks identified at bridge elements in service. With an increase in the introduction of corrugated steel web girders in recent highway bridge construction, the understanding of the fatigue behaviour of welded details in such structures becomes an important issue for the design. The typical welded details were represented as welded joints assembled by longitudinal corrugated plates. All the experiments were performed under fatigue loading using a servo-control testing machine. The test results from the failure mode observation with the aid of infrared thermo-graph technology show that the failure manner of these welded joints is comparable to that of the corrugated steel web beams reported previously. It is indicated from the stiffness degradation analysis that the welded joints with larger corrugation angle have higher stiffness and greater stiffness degradation in the notable stiffness degradation range. It is shown from the test S-N relations based on the free regression and forced regression analyses that there is a good linear dependence between lg(N) and lg(ΔS). It is also demonstrated that the proposed fracture mechanics analytical model is able to give a prediction slightly lower but on the safe side for the mean stresses at 2 million cycles of the test welded joints.
文摘It is due to the need to ensure the security and integrity of equipment, that the non-destructive tests have been increasingly used in the industrial sector. Among these, the ultrasonic pulse echo technique is the most used in industry, mainly for its simplicity and efficiency. With one transducer only, it is possible to emit the ultrasonic and receive the echo pulse. The ANNs （artificial neural networks） are artificial intelligence techniques that, when properly trained, align themselves to inspection tests becoming a powerful tool in the detection and fault identification. In this work, the echo pulse technique was used to detect discontinuities in welds, where ANNs were fed from the information obtained by digital signal processing techniques （Fourier transform）, to identify and classify three distinct classes of defects. Results showed that with the combination of feature extraction by Fourier transformation and classification with neural networks, it is possible to obtain an automatic defect detection system in welded joints with average efficiency.
