Novel hybrid refill friction stir spot welding （RFSSW） assisted with ultrasonic oscillation was introduced to 5A06 aluminum alloy joints. The metallographic structure and mechanical properties of 5A06 aluminum alloy...Novel hybrid refill friction stir spot welding （RFSSW） assisted with ultrasonic oscillation was introduced to 5A06 aluminum alloy joints. The metallographic structure and mechanical properties of 5A06 aluminum alloy RFSSW joints formed without ultrasonic assistance and with lateral and longitudinal ultrasonic assistance were compared, and the ultrasonic-assisted RFSSW process parameters were opti- mized. The results show that compared with lateral ultrasonic oscillation, longitudinal ultrasonic oscillation strengthens the horizontal bond- ing ligament in the joint and has a stronger effect on the joint＇s shear strength. By contrast, lateral ultrasonic oscillation strengthens the ver- tical bonding ligament and is more effective in increasing the joint＇s tensile strength. The maximum shear strength of ultrasonic-assisted RFSSW 5A06 aluminum alloy joints is as high as 8761 N, and the maximum tensile strength is 3679 N when the joints are formed at a tool rotating speed of 2000 r/rain, a welding time of 3.5 s, a penetration depth of 0.2 mm, and an axial pressure of 11 kN.展开更多
Several special mechanical properties,such as dilatancy and compressibility,of cemented paste backfill(CPB)are controlled by its internal microstructure and evolution.The mesoscopic structure changes of CPB during the...Several special mechanical properties,such as dilatancy and compressibility,of cemented paste backfill(CPB)are controlled by its internal microstructure and evolution.The mesoscopic structure changes of CPB during the development process were investigated.On the basis of the scanning electron microscopy(SEM)and mechanical test results of CPB,the particle size information of CPB was extracted,and a two-dimensional particle flow code(PFC)model of CPB was established to analyze the evolution rule of mesoscopic parameters during CPB development.The embedded FISH language in PFC was used to develop a program for establishing a PFC model on the basis of the SEM results.The mesoscopic parameters of CPB samples at different curing times,such as coordination number(C_(n)),contact force chain,and rose diagram,were obtained by recording and loading and used to analyze the intrinsic relationship between mesoscopic parameter variations and macroscopic mechanical response during CPB development.It is of considerable significance to establish the physical model of CPB using the PFC to reveal the mesoscopic structure of CPB.展开更多
Utilizing delayed expansion cemented paste backfill materials(DECPB) in mine backfill operations offers an effective solution to the challenge of achieving proper contact between the in-situ cemented backfill mass and...Utilizing delayed expansion cemented paste backfill materials(DECPB) in mine backfill operations offers an effective solution to the challenge of achieving proper contact between the in-situ cemented backfill mass and the roof in mined-out areas(backfill-roof contact).This article presents recent progress in both theoretical and experimental research concerning DECPB.The types and mechanisms of expansive additives,including expansive agents,foaming agents,and expansive mineral materials relevant to DECPB,are explained,along with their impact on the expansive properties and mechanical characteristics of DECPB.The composition,material characteristics,preparation methods,and controlled release mechanisms of microcapsules are analyzed.Two methods for measuring the volume change rate of paste backfill slurries are discussed.Research indicates that an appropriate content of expansive additives not only enhances the expansive properties of cemented paste backfill materials but also contributes to improving their mechanical properties.Chemical foaming agents and bentonite are found to be more suitable for preparing DECPB compared to expansive agents.The delayed expansion of cemented paste backfill material is influenced by microcapsules,with their wall materials,preparation parameters,and the alkaline slurry environment affecting their controlled release mechanism.Developing and optimizing precise measurement devices and methods forfor the volume change rate of cemented paste backfill materials is essential requirement for studying the performance of DECPB.Combining delayed expansion technology with retarding techniques in cemented paste backfill materials can provide a reliable solution for achieving proper backfill-roof contact in the future.展开更多
基金financially supported by Hunan Science and Technology Research Projects(Nos.2016GK2021 and 2016TP1023)Hunan Provincial Natural Science Foundation of China(No.2016JJ4082)
文摘Novel hybrid refill friction stir spot welding （RFSSW） assisted with ultrasonic oscillation was introduced to 5A06 aluminum alloy joints. The metallographic structure and mechanical properties of 5A06 aluminum alloy RFSSW joints formed without ultrasonic assistance and with lateral and longitudinal ultrasonic assistance were compared, and the ultrasonic-assisted RFSSW process parameters were opti- mized. The results show that compared with lateral ultrasonic oscillation, longitudinal ultrasonic oscillation strengthens the horizontal bond- ing ligament in the joint and has a stronger effect on the joint＇s shear strength. By contrast, lateral ultrasonic oscillation strengthens the ver- tical bonding ligament and is more effective in increasing the joint＇s tensile strength. The maximum shear strength of ultrasonic-assisted RFSSW 5A06 aluminum alloy joints is as high as 8761 N, and the maximum tensile strength is 3679 N when the joints are formed at a tool rotating speed of 2000 r/rain, a welding time of 3.5 s, a penetration depth of 0.2 mm, and an axial pressure of 11 kN.
基金financially supported by the National Natural Science Foundation of China(Nos.51874229,52074212,51674188,51504182,51404191,and 51405381)the Natural Science Basic Research Plan of Shaanxi Province of China(Nos.2015JQ5187,2018JQ5183,and 2018JM5161)+3 种基金the Scientific Research Program funded by the Shaanxi Education Department(No.15JK1466)the China Postdoctoral Science Foundation(No.2015M582685)the Outstanding Youth Science Fund of Xi’an University of Science and Technology(No.2018YQ2-01)supported by the National Research Council of Science&and Technology(NST)grant by the Korea Korean government(MSIP)(No.CRC-16-38502-KICT)。
文摘Several special mechanical properties,such as dilatancy and compressibility,of cemented paste backfill(CPB)are controlled by its internal microstructure and evolution.The mesoscopic structure changes of CPB during the development process were investigated.On the basis of the scanning electron microscopy(SEM)and mechanical test results of CPB,the particle size information of CPB was extracted,and a two-dimensional particle flow code(PFC)model of CPB was established to analyze the evolution rule of mesoscopic parameters during CPB development.The embedded FISH language in PFC was used to develop a program for establishing a PFC model on the basis of the SEM results.The mesoscopic parameters of CPB samples at different curing times,such as coordination number(C_(n)),contact force chain,and rose diagram,were obtained by recording and loading and used to analyze the intrinsic relationship between mesoscopic parameter variations and macroscopic mechanical response during CPB development.It is of considerable significance to establish the physical model of CPB using the PFC to reveal the mesoscopic structure of CPB.
基金financially supported by the National Natural Science Foundation of China (No.52274122)the Research Fund of BGRIMM Technology Group (No.02-2136)the Youth Innovation Fund of BGRIMM Technology Group (Nos.04-2306,04-2342 and 04-2208)。
文摘Utilizing delayed expansion cemented paste backfill materials(DECPB) in mine backfill operations offers an effective solution to the challenge of achieving proper contact between the in-situ cemented backfill mass and the roof in mined-out areas(backfill-roof contact).This article presents recent progress in both theoretical and experimental research concerning DECPB.The types and mechanisms of expansive additives,including expansive agents,foaming agents,and expansive mineral materials relevant to DECPB,are explained,along with their impact on the expansive properties and mechanical characteristics of DECPB.The composition,material characteristics,preparation methods,and controlled release mechanisms of microcapsules are analyzed.Two methods for measuring the volume change rate of paste backfill slurries are discussed.Research indicates that an appropriate content of expansive additives not only enhances the expansive properties of cemented paste backfill materials but also contributes to improving their mechanical properties.Chemical foaming agents and bentonite are found to be more suitable for preparing DECPB compared to expansive agents.The delayed expansion of cemented paste backfill material is influenced by microcapsules,with their wall materials,preparation parameters,and the alkaline slurry environment affecting their controlled release mechanism.Developing and optimizing precise measurement devices and methods forfor the volume change rate of cemented paste backfill materials is essential requirement for studying the performance of DECPB.Combining delayed expansion technology with retarding techniques in cemented paste backfill materials can provide a reliable solution for achieving proper backfill-roof contact in the future.
