In order to control welding stress and distortion, a new welding with trailing peening method based on the electromagnetic hammer was developed. This method uses the idea of constant frequency pulse width modulation f...In order to control welding stress and distortion, a new welding with trailing peening method based on the electromagnetic hammer was developed. This method uses the idea of constant frequency pulse width modulation for designing the control circuit of peening force and peening freqneney. The peening force can be adjusted between 0 and 1 000 N and the peening frequency ranges from 0 to 25 Hz. Peening force is applied to the weld metal and the weld toe during the welding by peening head. The experiments show that the method is portable and flexible, and it can adjust the distribution state of welding residual stress, making grain refinement. When the peening force is changed to 700 N and the peening frequency to 3 Hz, both the transverse and longitudinal residual stresses will drop obviously.展开更多
In this paper, a high-speed camera and an optical emission monitor were used to study the behavior of vapor/ plasma during CO2 laser welding of SUS304 stainless steel. Results of optical emission from vapor/plasma sho...In this paper, a high-speed camera and an optical emission monitor were used to study the behavior of vapor/ plasma during CO2 laser welding of SUS304 stainless steel. Results of optical emission from vapor/plasma show that two characteristic frequency bands exist, 100 -500 Hz and 1 500 -3 500 Hz. At the same time, the changing images of vapor/ plasma and bottom pool also confirm that there are two different fluctuation frequency bands. One of the frequency bands represents the characteristic of vapor/plasma within the keyhole, and it is within 167 -500 Hz. Another frequency band is within 1 500 - 3 500 Hz, and it obviously derives from the shielding gas. Some factors may cause these frequency differences between the keyhole plasma and the shielding gas plasma. One of them is that the vapor/plasma pressure within the keyhole will increase slowly.展开更多
A metal bellows-based fiber Bragg grating （FBG） accelerometer is proposed and experimentally demonstrated. The optical fiber （containing the FBG） is pre-tensioned, and the two ends of the optical fiber are fixed d...A metal bellows-based fiber Bragg grating （FBG） accelerometer is proposed and experimentally demonstrated. The optical fiber （containing the FBG） is pre-tensioned, and the two ends of the optical fiber are fixed directly from the shell to the inertial mass. In this design, the FBG is uniformly tensioned to obtain a constant strain distribution over it. By employing this configuration, the FBG always has a sharp reflection characteristic with no broadening in its reflection spectrum during wavelength shifting. Dynamic vibration measurements show that the proposed FBG accelerometer has a wide frequency response range （5-110 Hz） and an extremely high sensitivity （548.7 pro/g）. The two important indicators of FBG accelerometer can be tuned by the addition of mass to tailor the sensor performance to specific applications, identifying it as a good candidate for structural health monitoring.展开更多
The main objective of this investigation is to study the influence of arc constriction current frequency(ACCF)on tensile properties and microstructural evolution of aerospace Alloy 718 sheets(2 mm in thickness)joined ...The main objective of this investigation is to study the influence of arc constriction current frequency(ACCF)on tensile properties and microstructural evolution of aerospace Alloy 718 sheets(2 mm in thickness)joined by constricted arc TIG(CA-TIG)welding process.One variable at a time approach of design of experiments(DOE)was used,in which ACCF was varied from 4 to 20 kHz at an interval of 5 levels while other parameters were kept constant.The joints welded using ACCF of 4 kHz exhibited superior tensile properties extending joint efficiency up to 99.20%.It is attributed to the grain refinement in fusion zone leading to the evolution of finer,discrete Laves phase in interdendritic areas.An increase of ACCF above 12 kHz caused severe grain growth and evolution of coarser Laves phase in fusion zone.Alloy 718 welds showed more obvious tendency for Nb segregation and Laves phase formation at higher levels of ACCF due to the slower cooling rate.The volume fraction of Laves phase was increased by 62.31%at ACCF of 20 kHz compared to that at 4 kHz,thereby reducing the tensile properties of joints.This is mainly due to the stacking of heat input in weld thermal cycles at increased levels of ACCF.展开更多
基金The work was supported by the Natural Science Foundation of Hebei Province of China under Grant No. E2006000528.
文摘In order to control welding stress and distortion, a new welding with trailing peening method based on the electromagnetic hammer was developed. This method uses the idea of constant frequency pulse width modulation for designing the control circuit of peening force and peening freqneney. The peening force can be adjusted between 0 and 1 000 N and the peening frequency ranges from 0 to 25 Hz. Peening force is applied to the weld metal and the weld toe during the welding by peening head. The experiments show that the method is portable and flexible, and it can adjust the distribution state of welding residual stress, making grain refinement. When the peening force is changed to 700 N and the peening frequency to 3 Hz, both the transverse and longitudinal residual stresses will drop obviously.
文摘In this paper, a high-speed camera and an optical emission monitor were used to study the behavior of vapor/ plasma during CO2 laser welding of SUS304 stainless steel. Results of optical emission from vapor/plasma show that two characteristic frequency bands exist, 100 -500 Hz and 1 500 -3 500 Hz. At the same time, the changing images of vapor/ plasma and bottom pool also confirm that there are two different fluctuation frequency bands. One of the frequency bands represents the characteristic of vapor/plasma within the keyhole, and it is within 167 -500 Hz. Another frequency band is within 1 500 - 3 500 Hz, and it obviously derives from the shielding gas. Some factors may cause these frequency differences between the keyhole plasma and the shielding gas plasma. One of them is that the vapor/plasma pressure within the keyhole will increase slowly.
基金supported by the International S&T Cooperation Project of China by the MOST of China (No. 2009DFG13050)the National "863" Program of China (Nos. 2007AA06Z413 and 2009AA06Z203)+1 种基金the Key Scientific and Technological Research Project of Shaanxi Province (Nos. 20092KC01-19 and 2008ZDGC-14)the National Natural Science Foundation of China ( Nos. 60727004 and 61077060)
文摘A metal bellows-based fiber Bragg grating （FBG） accelerometer is proposed and experimentally demonstrated. The optical fiber （containing the FBG） is pre-tensioned, and the two ends of the optical fiber are fixed directly from the shell to the inertial mass. In this design, the FBG is uniformly tensioned to obtain a constant strain distribution over it. By employing this configuration, the FBG always has a sharp reflection characteristic with no broadening in its reflection spectrum during wavelength shifting. Dynamic vibration measurements show that the proposed FBG accelerometer has a wide frequency response range （5-110 Hz） and an extremely high sensitivity （548.7 pro/g）. The two important indicators of FBG accelerometer can be tuned by the addition of mass to tailor the sensor performance to specific applications, identifying it as a good candidate for structural health monitoring.
基金This work was supported by the Indian Space Research Organization(ISRO),Department of Space,India,under ISRO RESPOND scheme(Project No.ISRO/RES/3/728/16-17).
文摘The main objective of this investigation is to study the influence of arc constriction current frequency(ACCF)on tensile properties and microstructural evolution of aerospace Alloy 718 sheets(2 mm in thickness)joined by constricted arc TIG(CA-TIG)welding process.One variable at a time approach of design of experiments(DOE)was used,in which ACCF was varied from 4 to 20 kHz at an interval of 5 levels while other parameters were kept constant.The joints welded using ACCF of 4 kHz exhibited superior tensile properties extending joint efficiency up to 99.20%.It is attributed to the grain refinement in fusion zone leading to the evolution of finer,discrete Laves phase in interdendritic areas.An increase of ACCF above 12 kHz caused severe grain growth and evolution of coarser Laves phase in fusion zone.Alloy 718 welds showed more obvious tendency for Nb segregation and Laves phase formation at higher levels of ACCF due to the slower cooling rate.The volume fraction of Laves phase was increased by 62.31%at ACCF of 20 kHz compared to that at 4 kHz,thereby reducing the tensile properties of joints.This is mainly due to the stacking of heat input in weld thermal cycles at increased levels of ACCF.
