The microstructure of the as-cast 2D70 aluminum alloy and its evolution during homogenization were investigated by means of optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectrosco...The microstructure of the as-cast 2D70 aluminum alloy and its evolution during homogenization were investigated by means of optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and differential scanning calorimetry (DSC) analysis. The results indicate that the microstructure of the as-cast 2D70 aluminum alloy mainly consists of the dendritic network of aluminum solid solution and intermetallic compounds (Al2CuMg, Al2Cu, Al9FeNi, Cu2FeAl7, and Al7Cu4Ni). After conventional homogenization, Al/Al2CuMg eutectic phases are dissolved into the matrix, and a small amount of high melting-point eutectic Al/Al2Cu phases exist in the matrix, resulting in an increase in the starting melting temperature. Under double homogenization, the high melting point Al/Al2Cu phases are dissolved, and no obvious change is observed for the size and morphology of Al9FeNi, Cu2FeAl7, and Al7CuaNi compounds.展开更多
The effect of solution treatment on the microstructure and mechanical properties of a novel 7 A56 aluminum alloy plate was investigated by optical microscopy(OM),scanning electron microscopy(SEM),transmission electron...The effect of solution treatment on the microstructure and mechanical properties of a novel 7 A56 aluminum alloy plate was investigated by optical microscopy(OM),scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray diffraction(XRD),differential scanning calorimetry(DSC),conductivity,hardness and tensile tests.The results indicate that the coarse second phases in the hot-rolled plate mainly consist of AlZnMgCu quaternary phase and Al_(7) Cu_(2) Fe phase,and no Al_(2) CuMg phase is found.The amount of the second phases gradually reduces with the increase in temperature(450-480℃)and time(1-8 h)during the solution treatment,and the soluble particles are completely dissolved into the matrix after solution treatment at 470℃for 4 h,while the residual phases are mainly Fe-rich phase along the grain boundaries.The recrystallization fraction of the alloy gradually increases with the degree of solution treatment deepened.When the temperature exceeds480℃,over-burning takes place.The mechanical properties of samples treated at 470℃for various times were tested.After the solution treated at 470℃for 4 h,the quenching conductivity and peak-aged hardness of the alloy are 30.8%IACS and HV 204,respectively.The ultimate tensile strength and yield strength of the samples aged at 120℃for 24 h are 661 and 588 MPa,respectively.展开更多
The multilayered 7XXX series aluminum alloy was impacted by 7.62 mm ogival projectiles at velocities ranging from 787 to 851m·s^(-1). The deformed microstructure under various impacting velocities and fracture ...The multilayered 7XXX series aluminum alloy was impacted by 7.62 mm ogival projectiles at velocities ranging from 787 to 851m·s^(-1). The deformed microstructure under various impacting velocities and fracture surfaces of different sections were investigated at different physical scales to determine the process of failure.Optical microscopy(OM),electron back-scattered diffraction(EBSD) and scanning electron microscopy(SEM) were used in the investigation. The results show that crater is constrained in the 7B52 front layer and two types of adiabatic shear bands which are transformed bands and deformed bands and different types of cracks are observed.Spall fracture is the significant failure mode of 7B52 front layer, and the resulting delamination leads to the presence of bending tensile fracture instead of the shear plugging.The ductile 7A01 layer blunts and deflects the spall crack tips, preventing the targets from full spall, and induces a constraint of 7A52 rear layer. The level of the constraint determines different fracture modes of 7A52 layer,accounting for the asymmetry of damage.展开更多
Finite element method(FEM) simulations were employed to investigate the quenching residual stress distributions of 7085 aluminum alloy plates.The effect of dimensional variation on the quenching residual stress distri...Finite element method(FEM) simulations were employed to investigate the quenching residual stress distributions of 7085 aluminum alloy plates.The effect of dimensional variation on the quenching residual stress distributions was studied and discussed by using models with different dimensions(length,width,and thickness).The accuracy and efficiency of the models were verified by other numerical examples.The order of the dimension effects on the quenching residual stress distributions is:thickness> width=length.The maximum tensile stress and compressive stress increase from 33 to 190 and 39 to 270 MPa,respectively,as the thickness increases from 30 to 150 mm.The ultimate maximum tensile stress(about190 MPa) is equivalent to half of the quenching yield strength at 20℃,while the ultimate maximum compressive stress(about 300 MPa) is equivalent to 80 % of the quenching yield strength at 20℃.There are stress fluctuations at the edge of the large plate both in rolling and in transverse directions.The ratio of the fluctuation region along the rolling direction and transverse direction increases as the thickness increases,while it decreases as the length or width increases.The actual length of the fluctuation region is almost a constant value for the plates with a thickness of 115 mm(about 500 mm in length and 300 mm in width).展开更多
Attribute-based encryption(ABE) has been a preferred encryption technology to solve the problems of data protection and access control, especially when the cloud storage is provided by third-party service providers.AB...Attribute-based encryption(ABE) has been a preferred encryption technology to solve the problems of data protection and access control, especially when the cloud storage is provided by third-party service providers.ABE can put data access under control at each data item level. However, ABE schemes have practical limitations on dynamic attribute revocation. We propose a generic attribute revocation system for ABE with user privacy protection. The attribute revocation ABE(AR-ABE) system can work with any type of ABE scheme to dynamically revoke any number of attributes.展开更多
Polystyrene membranes with precisely controlled and vertically oriented pores are fabricated by a bidirectional freezing process. In this process, the influence of polymer in growth of diphenyl sulfone (DPS) crystal...Polystyrene membranes with precisely controlled and vertically oriented pores are fabricated by a bidirectional freezing process. In this process, the influence of polymer in growth of diphenyl sulfone (DPS) crystals has been demonstrated by XRD and simulated by DFT based on the interaction between DPS crystal faces and polystyrene (PS). The influence of temperature gradient on membrane structures is also elucidated. Compared to the original membrane and modified traditional membranes, modified PS membranes with vertically oriented pores show large and stable fluxes in the processes of multiple oil and water separation.展开更多
At present,natural orifice specimen extraction surgery(NOSES)has attracted more and more attention worldwide,because of its great advantages including minimal cutaneous trauma and post-operative pain,fast post-operati...At present,natural orifice specimen extraction surgery(NOSES)has attracted more and more attention worldwide,because of its great advantages including minimal cutaneous trauma and post-operative pain,fast post-operative recovery,short hospital stay,and positive psychological impact.However,NOSES for the treatment of gastric cancer(GC)is still in its infancy,and there is great potential to improve its theoretical system and clinical practice.Especially,several key points including oncological outcomes,bacteriological concerns,indication selection,and standardized surgical procedures are raised with this innovative technique.Therefore,it is necessary to achieve an international consensus to regulate the implementation of GC-NOSES,which is of great significance for healthy and orderly development of NOSES worldwide.展开更多
文摘The microstructure of the as-cast 2D70 aluminum alloy and its evolution during homogenization were investigated by means of optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and differential scanning calorimetry (DSC) analysis. The results indicate that the microstructure of the as-cast 2D70 aluminum alloy mainly consists of the dendritic network of aluminum solid solution and intermetallic compounds (Al2CuMg, Al2Cu, Al9FeNi, Cu2FeAl7, and Al7Cu4Ni). After conventional homogenization, Al/Al2CuMg eutectic phases are dissolved into the matrix, and a small amount of high melting-point eutectic Al/Al2Cu phases exist in the matrix, resulting in an increase in the starting melting temperature. Under double homogenization, the high melting point Al/Al2Cu phases are dissolved, and no obvious change is observed for the size and morphology of Al9FeNi, Cu2FeAl7, and Al7CuaNi compounds.
基金financially supported by the National Key Research and Development Program of China(No.2016YFB0300803)the National Natural Science Foundation of China(No.51274046)the National Key Basic Research Program(No.2012CB619504)。
文摘The effect of solution treatment on the microstructure and mechanical properties of a novel 7 A56 aluminum alloy plate was investigated by optical microscopy(OM),scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray diffraction(XRD),differential scanning calorimetry(DSC),conductivity,hardness and tensile tests.The results indicate that the coarse second phases in the hot-rolled plate mainly consist of AlZnMgCu quaternary phase and Al_(7) Cu_(2) Fe phase,and no Al_(2) CuMg phase is found.The amount of the second phases gradually reduces with the increase in temperature(450-480℃)and time(1-8 h)during the solution treatment,and the soluble particles are completely dissolved into the matrix after solution treatment at 470℃for 4 h,while the residual phases are mainly Fe-rich phase along the grain boundaries.The recrystallization fraction of the alloy gradually increases with the degree of solution treatment deepened.When the temperature exceeds480℃,over-burning takes place.The mechanical properties of samples treated at 470℃for various times were tested.After the solution treated at 470℃for 4 h,the quenching conductivity and peak-aged hardness of the alloy are 30.8%IACS and HV 204,respectively.The ultimate tensile strength and yield strength of the samples aged at 120℃for 24 h are 661 and 588 MPa,respectively.
基金financially supported by the National Basic Research Program of China(No.2012CB619504)the National Natural Science Foundation of China(No.51274046)
文摘The multilayered 7XXX series aluminum alloy was impacted by 7.62 mm ogival projectiles at velocities ranging from 787 to 851m·s^(-1). The deformed microstructure under various impacting velocities and fracture surfaces of different sections were investigated at different physical scales to determine the process of failure.Optical microscopy(OM),electron back-scattered diffraction(EBSD) and scanning electron microscopy(SEM) were used in the investigation. The results show that crater is constrained in the 7B52 front layer and two types of adiabatic shear bands which are transformed bands and deformed bands and different types of cracks are observed.Spall fracture is the significant failure mode of 7B52 front layer, and the resulting delamination leads to the presence of bending tensile fracture instead of the shear plugging.The ductile 7A01 layer blunts and deflects the spall crack tips, preventing the targets from full spall, and induces a constraint of 7A52 rear layer. The level of the constraint determines different fracture modes of 7A52 layer,accounting for the asymmetry of damage.
基金financially supported by the National Basic Research Program of China(No.2012CB619504)the National Natural Science Foundation of China(No.51274046)
文摘Finite element method(FEM) simulations were employed to investigate the quenching residual stress distributions of 7085 aluminum alloy plates.The effect of dimensional variation on the quenching residual stress distributions was studied and discussed by using models with different dimensions(length,width,and thickness).The accuracy and efficiency of the models were verified by other numerical examples.The order of the dimension effects on the quenching residual stress distributions is:thickness> width=length.The maximum tensile stress and compressive stress increase from 33 to 190 and 39 to 270 MPa,respectively,as the thickness increases from 30 to 150 mm.The ultimate maximum tensile stress(about190 MPa) is equivalent to half of the quenching yield strength at 20℃,while the ultimate maximum compressive stress(about 300 MPa) is equivalent to 80 % of the quenching yield strength at 20℃.There are stress fluctuations at the edge of the large plate both in rolling and in transverse directions.The ratio of the fluctuation region along the rolling direction and transverse direction increases as the thickness increases,while it decreases as the length or width increases.The actual length of the fluctuation region is almost a constant value for the plates with a thickness of 115 mm(about 500 mm in length and 300 mm in width).
基金Project supported by the Ningbo eHealth Project,China(No.2016C11024)
文摘Attribute-based encryption(ABE) has been a preferred encryption technology to solve the problems of data protection and access control, especially when the cloud storage is provided by third-party service providers.ABE can put data access under control at each data item level. However, ABE schemes have practical limitations on dynamic attribute revocation. We propose a generic attribute revocation system for ABE with user privacy protection. The attribute revocation ABE(AR-ABE) system can work with any type of ABE scheme to dynamically revoke any number of attributes.
基金financially supported by the National Natural Science Foundation of China (Nos. 51522305 and 21374100)the Fundamental Research Funds for the Central Universities (No. 2015XZZX004-26)
文摘Polystyrene membranes with precisely controlled and vertically oriented pores are fabricated by a bidirectional freezing process. In this process, the influence of polymer in growth of diphenyl sulfone (DPS) crystals has been demonstrated by XRD and simulated by DFT based on the interaction between DPS crystal faces and polystyrene (PS). The influence of temperature gradient on membrane structures is also elucidated. Compared to the original membrane and modified traditional membranes, modified PS membranes with vertically oriented pores show large and stable fluxes in the processes of multiple oil and water separation.
文摘At present,natural orifice specimen extraction surgery(NOSES)has attracted more and more attention worldwide,because of its great advantages including minimal cutaneous trauma and post-operative pain,fast post-operative recovery,short hospital stay,and positive psychological impact.However,NOSES for the treatment of gastric cancer(GC)is still in its infancy,and there is great potential to improve its theoretical system and clinical practice.Especially,several key points including oncological outcomes,bacteriological concerns,indication selection,and standardized surgical procedures are raised with this innovative technique.Therefore,it is necessary to achieve an international consensus to regulate the implementation of GC-NOSES,which is of great significance for healthy and orderly development of NOSES worldwide.