Friction stir welding(FSW)is a relatively new welding technique that has significant advantages compared to the fusion welding techniques in joining non weld able alloys by fusion,such as aluminum alloys.Three FSW sea...Friction stir welding(FSW)is a relatively new welding technique that has significant advantages compared to the fusion welding techniques in joining non weld able alloys by fusion,such as aluminum alloys.Three FSW seams of AA6061-T6 plates were made us-ing different FSW parameters.The structure of the FSW seams was investigated using X-ray diffraction(XRD),scanning electron mi-croscope(SEM)and non destructive testing(NDT)techniques and their hardness was also measured.The dominated phase in the AA6061-T6 alloy and the FSW seams was theα-Al.The FSW seam had lower content of the secondary phases than the AA6061-T6 al-loy.The hardness of the FSW seams was decreased by about 30%compared to the AA6061-T6 alloy.The temperature distributions in the weld seams were also studied experimentally and numerically modeled and the results were in a good agreement.展开更多
The difference in the microstructure,texture in the stir zone(SZ)of the AZ31(Mg-3 Al-1 Zn,wt.%)alloy after friction stir welding(FSW)and subsequent annealing at 400℃for 1 h was characterized by scanning electron micr...The difference in the microstructure,texture in the stir zone(SZ)of the AZ31(Mg-3 Al-1 Zn,wt.%)alloy after friction stir welding(FSW)and subsequent annealing at 400℃for 1 h was characterized by scanning electron microscopy(SEM)with electron backscatter diffraction(EBSD)measurements at the surface and core regions.The findings indicate that FSW produced grain refinement where the mean grain size decreases from 19μm(base metal)to 5.1 and 3.5μm at the surface and core regions,respectively.The c-axis of the grains at the surface region was aligned with the normal direction(<0001>//ND)due to the additional strain of the tool shoulder.In contrast,the core region shows a typical shear texture,where the c-axis tends to be oriented parallel to the welding direction(<0001>//WD).The Vickers microhardness mapping across the SZ revealed that the core region was soften than the surface region due to the dynamic recrystallization and texture weakening.The microstructure of the SZ remains principally deformed after annealing treatment except for the development of massive Mg_(17)Al_(12)precipitates and the abnormal grain growth of a few grains with<11-20>//WD orientation at the upper side of the surface region.The c-axis of the grains at the surface region was tilted about 10°toward WD,while an inclined<0001>//WD orientation about 30°from WD was developed at the core region.Consequently,the distribution of microhardness values across the SZ was more heterogeneous than the FSW sample.The results were discussed in the light of grain boundary misorientation,dislocation density and the pinning effect of Mg_(17)Al_(12)precipitates.Additionally,Schmid factor analysis was used to examine the activation of the basal slip mode to characterize the associated mechanical response.展开更多
目的:了解女性性工作者(female sex workers,FSWs)与不同性伴侣间安全套使用状况及其影响因素。方法:采用同伴推举抽样方法对上海市521名FSWs进行了匿名面对面问卷调查。结果:FSWs最近1个月与固定性伴侣、常客和一次客每次性行为都使用...目的:了解女性性工作者(female sex workers,FSWs)与不同性伴侣间安全套使用状况及其影响因素。方法:采用同伴推举抽样方法对上海市521名FSWs进行了匿名面对面问卷调查。结果:FSWs最近1个月与固定性伴侣、常客和一次客每次性行为都使用安全套的比例分别为24.0%、54.3%和72.6%;与上述对象最后1次性行为使用安全套的比例分别为33.3%、73.9%和87.3%。FSWs与固定性伴侣不使用安全套的主要原因是"从未想过要用"(28.3%)和"已上环"(28.3%);与常客不使用安全套的主要原因是"对方反对"(26.4%)和"没有安全套"(21.6%);与一次客不使用安全套的主要原因是"对方反对"(62.3%)。安全套使用的影响因素分析显示,来自农村、使用新型毒品、使用了除安全套以外的其他避孕措施、从事性工作年限较长、性伴数较多的FSWs与客人坚持使用安全套的可能性较小;桑拿场所的FSWs与客人坚持使用安全套的可能性显著高于其他场所类型的对象;来自于农村、使用了除安全套以外其他避孕措施的对象与固定性伴侣坚持使用安全套的可能性也较小。结论:女性性工作者坚持使用安全套的比例较低,特别是与固定性伴侣。应在娱乐场所及FSWs中大力倡导100%安全套使用;提高男性顾客对STDs/AIDS的危害及安全套能有效预防STDs/AIDS的认识,使商业性行为中安全套的使用率得以根本性地提高。展开更多
The buckling behavior of stiffened panels is significantly influenced by material and geometric defects,making it a critical factor in ensuring structural integrity and safety.These panels are widely used in mechanica...The buckling behavior of stiffened panels is significantly influenced by material and geometric defects,making it a critical factor in ensuring structural integrity and safety.These panels are widely used in mechanical,aerospace,marine,and civil engineering applications due to their ability to enhance bending stiffness with minimal additional weight.Under high loads or stress concentrations,localized structural failures can initiate global buckling in stiffened panels.This study investigates how such defects affect the critical buckling load,stiffness,and thickness of stiffened panels.Two finite element analyses were conducted:a linear analysis to identify the initial buckling mode and a nonlinear analysis using the Riks algorithm in Abaqus CAE,incorporating localized imperfections.The simulations show that material and geometric defects can reduce buckling resistance depending on their severity.展开更多
In dry storage,spent fuel is typically stored in casks constructed from neutron absorbing materials(NAMs).The(B_(4)C+Al_(2)O_(3))/Al composite,which incorporates in-situ amorphous Al_(2)O_(3)(am-Al_(2)O_(3))formed on ...In dry storage,spent fuel is typically stored in casks constructed from neutron absorbing materials(NAMs).The(B_(4)C+Al_(2)O_(3))/Al composite,which incorporates in-situ amorphous Al_(2)O_(3)(am-Al_(2)O_(3))formed on fine aluminum powder as a reinforcing phase,can serve as an integrated structural and functional NAM for dry storage applications.Welding is crucial in the fabrication of these casks.In this study,friction stir welding was performed on(B_(4)C+Al_(2)O_(3))/Al composite sheets at a welding speed of 50 mm/min and rotation rates ranging from 500 to 1000 r/min.The microstructure of the weld joints was analyzed,and the intrinsic relationship between fracture behavior and microstructure was elucidated.Results showed that defect-free joints were achieved at rotation rates of 500 and 750 r/min,while tunnel defects were observed at 1000 r/min.The ultimate tensile strength of the joint welded at 500 r/min was 205.7 MPa,with a strength efficiency of 82%.Microstructural analysis revealed that the grains within the nugget zones(NZs)coarsened and the Al_(2)O_(3)network was disrupted due to the welding thermo-mechanical effect,resulting in softening within the NZs.Fracture locations for all three joints were consistently observed at the NZ boundary on the advancing side(AS).Finite element simulations confirmed that cracks propagated along the NZ boundary on the AS,where stress concentration occurred during tensile testing.展开更多
文摘Friction stir welding(FSW)is a relatively new welding technique that has significant advantages compared to the fusion welding techniques in joining non weld able alloys by fusion,such as aluminum alloys.Three FSW seams of AA6061-T6 plates were made us-ing different FSW parameters.The structure of the FSW seams was investigated using X-ray diffraction(XRD),scanning electron mi-croscope(SEM)and non destructive testing(NDT)techniques and their hardness was also measured.The dominated phase in the AA6061-T6 alloy and the FSW seams was theα-Al.The FSW seam had lower content of the secondary phases than the AA6061-T6 al-loy.The hardness of the FSW seams was decreased by about 30%compared to the AA6061-T6 alloy.The temperature distributions in the weld seams were also studied experimentally and numerically modeled and the results were in a good agreement.
基金supported by the PHC-Tassili program No.24MDU114。
文摘The difference in the microstructure,texture in the stir zone(SZ)of the AZ31(Mg-3 Al-1 Zn,wt.%)alloy after friction stir welding(FSW)and subsequent annealing at 400℃for 1 h was characterized by scanning electron microscopy(SEM)with electron backscatter diffraction(EBSD)measurements at the surface and core regions.The findings indicate that FSW produced grain refinement where the mean grain size decreases from 19μm(base metal)to 5.1 and 3.5μm at the surface and core regions,respectively.The c-axis of the grains at the surface region was aligned with the normal direction(<0001>//ND)due to the additional strain of the tool shoulder.In contrast,the core region shows a typical shear texture,where the c-axis tends to be oriented parallel to the welding direction(<0001>//WD).The Vickers microhardness mapping across the SZ revealed that the core region was soften than the surface region due to the dynamic recrystallization and texture weakening.The microstructure of the SZ remains principally deformed after annealing treatment except for the development of massive Mg_(17)Al_(12)precipitates and the abnormal grain growth of a few grains with<11-20>//WD orientation at the upper side of the surface region.The c-axis of the grains at the surface region was tilted about 10°toward WD,while an inclined<0001>//WD orientation about 30°from WD was developed at the core region.Consequently,the distribution of microhardness values across the SZ was more heterogeneous than the FSW sample.The results were discussed in the light of grain boundary misorientation,dislocation density and the pinning effect of Mg_(17)Al_(12)precipitates.Additionally,Schmid factor analysis was used to examine the activation of the basal slip mode to characterize the associated mechanical response.
文摘目的:了解女性性工作者(female sex workers,FSWs)与不同性伴侣间安全套使用状况及其影响因素。方法:采用同伴推举抽样方法对上海市521名FSWs进行了匿名面对面问卷调查。结果:FSWs最近1个月与固定性伴侣、常客和一次客每次性行为都使用安全套的比例分别为24.0%、54.3%和72.6%;与上述对象最后1次性行为使用安全套的比例分别为33.3%、73.9%和87.3%。FSWs与固定性伴侣不使用安全套的主要原因是"从未想过要用"(28.3%)和"已上环"(28.3%);与常客不使用安全套的主要原因是"对方反对"(26.4%)和"没有安全套"(21.6%);与一次客不使用安全套的主要原因是"对方反对"(62.3%)。安全套使用的影响因素分析显示,来自农村、使用新型毒品、使用了除安全套以外的其他避孕措施、从事性工作年限较长、性伴数较多的FSWs与客人坚持使用安全套的可能性较小;桑拿场所的FSWs与客人坚持使用安全套的可能性显著高于其他场所类型的对象;来自于农村、使用了除安全套以外其他避孕措施的对象与固定性伴侣坚持使用安全套的可能性也较小。结论:女性性工作者坚持使用安全套的比例较低,特别是与固定性伴侣。应在娱乐场所及FSWs中大力倡导100%安全套使用;提高男性顾客对STDs/AIDS的危害及安全套能有效预防STDs/AIDS的认识,使商业性行为中安全套的使用率得以根本性地提高。
文摘The buckling behavior of stiffened panels is significantly influenced by material and geometric defects,making it a critical factor in ensuring structural integrity and safety.These panels are widely used in mechanical,aerospace,marine,and civil engineering applications due to their ability to enhance bending stiffness with minimal additional weight.Under high loads or stress concentrations,localized structural failures can initiate global buckling in stiffened panels.This study investigates how such defects affect the critical buckling load,stiffness,and thickness of stiffened panels.Two finite element analyses were conducted:a linear analysis to identify the initial buckling mode and a nonlinear analysis using the Riks algorithm in Abaqus CAE,incorporating localized imperfections.The simulations show that material and geometric defects can reduce buckling resistance depending on their severity.
基金support of the National Natural Science Foundation of China(Grant Nos.52171056 and 52203385)the Joint Funds of the National Natural Science Foundation of China(Grant Nos.U2341255 and U22A20114)+1 种基金the Young Elite Scientists Sponsorship Program by CAST(Grant No.YESS20220225)the IMR Innovation Fund(Grant No.2021-ZD02).
文摘In dry storage,spent fuel is typically stored in casks constructed from neutron absorbing materials(NAMs).The(B_(4)C+Al_(2)O_(3))/Al composite,which incorporates in-situ amorphous Al_(2)O_(3)(am-Al_(2)O_(3))formed on fine aluminum powder as a reinforcing phase,can serve as an integrated structural and functional NAM for dry storage applications.Welding is crucial in the fabrication of these casks.In this study,friction stir welding was performed on(B_(4)C+Al_(2)O_(3))/Al composite sheets at a welding speed of 50 mm/min and rotation rates ranging from 500 to 1000 r/min.The microstructure of the weld joints was analyzed,and the intrinsic relationship between fracture behavior and microstructure was elucidated.Results showed that defect-free joints were achieved at rotation rates of 500 and 750 r/min,while tunnel defects were observed at 1000 r/min.The ultimate tensile strength of the joint welded at 500 r/min was 205.7 MPa,with a strength efficiency of 82%.Microstructural analysis revealed that the grains within the nugget zones(NZs)coarsened and the Al_(2)O_(3)network was disrupted due to the welding thermo-mechanical effect,resulting in softening within the NZs.Fracture locations for all three joints were consistently observed at the NZ boundary on the advancing side(AS).Finite element simulations confirmed that cracks propagated along the NZ boundary on the AS,where stress concentration occurred during tensile testing.
