The friction coefficient between tube and die in guide zone of tube hydroforming was obtained. In hydroforming, the tube is expanded by an internal pressure against the tool wall. By pushing the tube through tool, a f...The friction coefficient between tube and die in guide zone of tube hydroforming was obtained. In hydroforming, the tube is expanded by an internal pressure against the tool wall. By pushing the tube through tool, a friction force at the contact surface between the tube and the tool occurs. In guiding zone, the friction coefficients between tube and die can be estimated from the measured axial feeding forces. In expansion zone, the friction coefficients between tube and die can be evaluated from the measured geometries of expanded tubes and FE analysis.展开更多
A pilot wire drawing machine as well as wire end-pointing roller was developed. Using these machines, a wire drawing test for four different coating materials and two different lubricants was performed as the reductio...A pilot wire drawing machine as well as wire end-pointing roller was developed. Using these machines, a wire drawing test for four different coating materials and two different lubricants was performed as the reduction ratio increased from 10% to 30%. Materials used for a substrate in this study are plain carbon steel (AISI1045) and ultra low carbon bainite steel. To compute the friction coefficient between the coating layer of wire and the surface of die for a specific lubricant, a series of finite element analyses were carried out. SEM observations were also conducted to investigate the surface defects of wire deformed. Results show that the behavior of drawing force varies with the lubricant-type at the initial stage of drawing. The powder-typed lubricant with a large particle causes the retardation of full lubrication on the entire contact surface and the local delamination of coating layer on the wire surface. As the flow stress of a substrate increases, the delamination becomes severe.展开更多
In order to transmit secure messages, a quantum secure direct communication protocol based on extended three-particle GHZ state was presented, in which the extended three-particle GHZ state was used to detect eave sdr...In order to transmit secure messages, a quantum secure direct communication protocol based on extended three-particle GHZ state was presented, in which the extended three-particle GHZ state was used to detect eave sdroppers. In the security analysis, the method of the entropy theory is introduced, and three detection strategies are compared quantitatively by using the constraint between the information eavesdroppers can obtain and the interference introduced. If the eavesdroppers intend to obtain all information, the detection rate of the original "Ping-pong" protocol is 50%; the second protocol used two particles of EPR pair as detection particles is also 50%; while the presented protocol is 58%. At last, the security of the proposed protocol is discussed. The analysis results indicate that the protocol in this paper is more secure than the other two.展开更多
AA5454-O aluminum alloy plates with the thicknesses of 1.4 and 1.0 mm were friction-spot-joined (FSJed).The plunge speed of the joining tool was changed in a range of 100 500 mm/min under a constant rotation speed of ...AA5454-O aluminum alloy plates with the thicknesses of 1.4 and 1.0 mm were friction-spot-joined (FSJed).The plunge speed of the joining tool was changed in a range of 100 500 mm/min under a constant rotation speed of 500 r/min.The plunge depth was ranged from 1.6 mm to 2.2 mm.The tool plunge speed did not make a remarkable effect on the surface appearance and macro-structure of the FSJed zone.The average hardness of the FSJed zone was greater than or equal to that of the base metal.However,there was no remarkable tendency in the average hardness change of the FSJed zone in spite of the variation in the tool plunge speed and tool plunge depth.The increase of the tool plunge depth resulted in the increase of the tensile shear load.However,the change of the tool plunge speed did not lead to the remarkable variation in the tensile shear load of the FSJed plates.It was noteworthy that the FSJed plate exhibited the highest tensile shear load of about 4.0 kN.展开更多
The deflection of rolls of Sendzimir mill with double AS-U-Roll was simulated by finite element method(FEM). The influences of rolling pressure, strip width and rolls-assignment on rolls deflection were analyzed. The ...The deflection of rolls of Sendzimir mill with double AS-U-Roll was simulated by finite element method(FEM). The influences of rolling pressure, strip width and rolls-assignment on rolls deflection were analyzed. The results show that the work roll deflection increases with the increase of rolling pressure and the reduction of work roll radius, but the rigid displacement of work roll slightly changes; the work roll end might appear negative displacement for the narrow strip width and high rolling pressure that might cause the contact of work rolls. The research results are significant for guiding production and theoretical analysis of the rolls system of Sendzimir mill.展开更多
Both wear and crack due to heat checking in hot work tool steel are major failure modes. It is desirable to find amethod to lengthen the tool life while reducing manufacturing cost. This paper suggests a method to imp...Both wear and crack due to heat checking in hot work tool steel are major failure modes. It is desirable to find amethod to lengthen the tool life while reducing manufacturing cost. This paper suggests a method to improve toollife for hot work tool steel (SKD6) with crack by laser-melting process. The method has been evaluated using theimpact and fatigue test results. It is demonstrated that a repair of the crack by a laser-melting process is effectivefor life extension of the damaged tool.展开更多
Friction stir butt welding (FSW) between A5052-O aluminum alloy plates with a thickness of 2 mm was performed.The rotation speeds of the welding tool were 2000 and 3000 r/min,respectively.The traverse speed was ranged...Friction stir butt welding (FSW) between A5052-O aluminum alloy plates with a thickness of 2 mm was performed.The rotation speeds of the welding tool were 2000 and 3000 r/min,respectively.The traverse speed was ranged from 100 mm/min to 900 mm/min.The defect-free welds with the very smooth surface morphology were successfully obtained,except for at the welding condition of 3000 r/min and 100 mm/min.The onion ring structure was observed in the friction-stir-welded zone (SZ) at the condition of 2000 r/min and 100 mm/min.For all the welding conditions,the grain size of the SZ was smaller than that of the base metal,and was decreased with the decrease of the tool rotation speed and with the increase of the tool traverse speed.The stir zone exhibited higher average hardness than the base metal.The decrease of the tool rotation speed and the increase of the tool traverse speed resulted in the increase in the average hardness of the SZ.The tensile strength of the FSWed plates was similar to that of the base metal,except for at the welding condition of 3000 r/min and 100 mm/min.The total elongation of the FSWed plates was lower than that of the base metal.展开更多
AA5454-O aluminum alloy plates with thicknesses of 1.4 and 1.0 mm were friction-stir-lap-welded (FSLWed).The influences of the tool plunge depth and welding distance on surface appearance,macrostructure and mechanical...AA5454-O aluminum alloy plates with thicknesses of 1.4 and 1.0 mm were friction-stir-lap-welded (FSLWed).The influences of the tool plunge depth and welding distance on surface appearance,macrostructure and mechanical properties of the FSLWed plates were experimentally investigated.The tensile shear load of the FSLWed plates was compared with that of the adhesive-bonded plates.Defect-free FSLWed zones were successfully obtained in all the tool plunge depths and the welding distances.The FSLWed zones exhibited the relatively smooth surface morphologies.Under all the FSLWed conditions,the FSLWed zone exhibited higher average hardness than the base metal.In addition,the upper plate exhibited a higher average hardness than the lower plate,although there was no special tendency in spite of the change in the tool plunge depth and the welding distance.The maximum tensile shear load of the FSLWed plates was much higher than that of the adhesive-bonded aluminum alloy plate.Especially,under the FSLW condition of the plunge depth of 1.8 mm and the welding distance of 40 mm,the tensile shear load of the FSLWed plate reached a level about 41% greater than that of the adhesive-bonded aluminum alloy plate.In addition,the maximum tensile shear load of the FSLWed plate was increased with the increase of the welding distance.展开更多
In order to solve the various privacy and security problems in RFID system, a new low-cost RFID mutual authentication protocol based on ID updating mechanics is proposed. In the proposed scheme, the backend server kee...In order to solve the various privacy and security problems in RFID system, a new low-cost RFID mutual authentication protocol based on ID updating mechanics is proposed. In the proposed scheme, the backend server keeps both the current ID and potential next ID for each tag, thus to solve the possible problem of de-synchronization attack in the most ID updating-based schemes. In the security analysis section, comparing several protocols in property required and attacker resistances, the comparison results show that the proposed protocol provides strong authentication and strong integrity of the transmissions and can withstand most the possible attacks that break the security of the previous schemes. In the performance evaluation section, the analysis results also indicate that, in terms of computational cost and storage requirement, the proposed scheme is safer, more efficient, more suitable for low-cost tag and more feasible in practice.展开更多
It is known that one of the causes of pitting corrosion of copper tubes is residual carbon on the inner surface. It was confirmed that type I” pitting corrosion of the copper tube is suppressed by keeping the residua...It is known that one of the causes of pitting corrosion of copper tubes is residual carbon on the inner surface. It was confirmed that type I” pitting corrosion of the copper tube is suppressed by keeping the residual carbon amount at 2 mg/m<sup>2</sup> or less, which is lower than that of the type I’ pitting corrosion, or by removing the fine particles that are the corrosion product of galvanized steel pipes. The developed water treatment chemical was evaluated using three types of copper tubes with residual carbon amounts of 0 mg/m<sup>2</sup>, 0.5 mg/m<sup>2</sup>, and 6.1 mg/m<sup>2</sup>. The evaluation was conducted for three months in an open-circulation cooling water system and compared with the current water treatment chemical. Under the current water treatment chemical conditions, only the copper tube with a residual carbon amount of 6.1 mg/m<sup>2</sup> showed a significant increase in the natural corrosion potential after two weeks, and pitting corrosion occurred. No pitting corrosion and no increase in the natural corrosion potential were observed in any of the copper tubes that were treated with the developed water treatment chemical. In addition, the polarization curve was measured using the cooling water from this field test, and the anodic polarization of two cooling waters was compared. For copper tubes with a large amount of residual carbon, the current density near 0 mV vs. Ag/AgCl electrode (SSE) increased when the developed water treatment chemical was added.展开更多
It is reported that laser-processing is effective to repair the heat checks, which are fine shallow cracks on a surfaceof die-casting dies. In this study, the rotating bending fatigue tests have been carried out to ev...It is reported that laser-processing is effective to repair the heat checks, which are fine shallow cracks on a surfaceof die-casting dies. In this study, the rotating bending fatigue tests have been carried out to evaluate the fatiguecharacteristics of laser-processed hot working tool steel. Because test results are scattered, S-N curves are decidedbased on the evaluation of fatigue strength distribution. As a result, the fatigue strength of the laser-processedspecimens decreases remarkably in comparison with that of base metal. However, it can be recovered to almostinitial value by heat treatment at secondary hardening temperature. This procedure is also effective to decrease thescatter of fatigue strength. The laser-processing can be carried out at low cost and this method is effective for theextension of the work life of dies.展开更多
In this study,the authors proposed a new algorism which can simultaneously meets the strip shape control criterion and the strip crown control criterion.Based on the new algorism,the pass schedule is optimized to maxi...In this study,the authors proposed a new algorism which can simultaneously meets the strip shape control criterion and the strip crown control criterion.Based on the new algorism,the pass schedule is optimized to maximize the allowable PC angle range.To calculate the objective value for optimization of pass schedule,a slab method has been integrated with the roll stack deformation to simulate the strip profile.展开更多
Modification of the carbide characteristics through the grain boundary serration is investigated, using an AISI 316 and 304 stainless steels. In both steels, triangular carbides were observed at straight grain boundar...Modification of the carbide characteristics through the grain boundary serration is investigated, using an AISI 316 and 304 stainless steels. In both steels, triangular carbides were observed at straight grain boundaries while planar carbides were observed at the serrated grain boundaries. The serrated grain boundary energy is observed to be much lower than that of the straight one. Therefore, the carbide morphology is found to be changed from triangular to planar along the serrated boundary to reduce the interfacial energy between the carbide and the matrix. The creep-fatigue properties of these steels at 873K have been investigated. The creep-fatigue life of the sample with planar carbide at the serrated grain boundary was found to be much longer than that with triangular carbide at the straight one. These results imply that the planar carbides with lower interfacial energy have higher cavitation resistance, resulting in the retardation of cavity nucleation and growth to increase creep-fatigue life.展开更多
We performed corrosion case study and corrosion tests to assess the corrosion resistance of stainless steel type 304 pipes in tap water and hot water facilities. Circulating test equipment used for corrosion tests and...We performed corrosion case study and corrosion tests to assess the corrosion resistance of stainless steel type 304 pipes in tap water and hot water facilities. Circulating test equipment used for corrosion tests and two types of sample, plates and straight pipe specimens, were examined under different conditions of residual chlorine concentration in the test water. The results of case study analysis indicated that high degrees of pitting corrosion occurred on straight pipes with inner diameter < 50 mm. The results of corrosion tests showed that the residual chlorine concentration around the pitting corrosion of stainless steel type 304 was greater than 0.3 mg/L in the plate, regardless of the remaining chlorine concentration in the straight pipe specimens. These results suggest that straight pipes have higher corrosion susceptibility because of bending during production.展开更多
It has been reported that pitting corrosion in copper tubes occurs due to the effect of a carbon film produced by the influence of undergoing an oil and heat treatment. As a quantitative method for determining the res...It has been reported that pitting corrosion in copper tubes occurs due to the effect of a carbon film produced by the influence of undergoing an oil and heat treatment. As a quantitative method for determining the residual carbon amount, it has been reported that the inner surface of a copper tube can be dissolved with a mixed acid to collect and analyze the adhering carbon;however, this method is dangerous and difficult. Therefore, two methods were examined as a simple quantitative method for obtaining the residual carbon amount using copper tubes with known residual carbon amounts. One method utilizes X-ray photoelectron spectroscopy (XPS), and the other method utilizes the potential difference between the carbon film-adhered surface and carbon film-removed surface. In regard to XPS measurement, a linear correlation was found between the spectral intensity of C and the residual carbon amount;therefore, XPS measurements were considered to be effective as a simple measurement method for the carbon film on the inner surface of a copper tube. In the evaluation method by measuring the corrosion potential, a correlation was observed between the potential difference ΔE and the residual carbon amount of the inner surface of the tube and the outer surface of the polished tube. It is considered possible to estimate the residual carbon amount from the prepared calibration curve. Through these studies, it is suggested that the carbon film was non-uniformly present on the surface of the copper tube. Therefore, the galvanic current was measured, and the effect of a non-uniform carbon film on corrosion behavior was investigated. As a result, in the measurement of galvanic current, the current flowed from the copper tube with a large amount of residual carbon (cathode) to the copper tube with a small amount of residual carbon (anode). In addition, the higher the area ratio of the carbon film was, the larger the galvanic current tended to be.展开更多
Poppet valves have become increasingly significant in ensuring precise digital flow rate and pressure control in hydraulic systems,necessitating a more profound understanding of the geometrical properties of cavitatio...Poppet valves have become increasingly significant in ensuring precise digital flow rate and pressure control in hydraulic systems,necessitating a more profound understanding of the geometrical properties of cavitation in them,as well as associated flow-choking conditions.Through a comparative analysis with experimentally observed cavity images,we found that large eddy simulation(LES)turbulence modeling effectively replicates the geometrical properties of cavitation in these valves.The analysis demonstrated that cavitation is generated from vortices that result from the interaction between the notch contracta flow and the surrounding fluid structure.Variations in the internal or external vena contracta conditions result in fixed or discrete cavities,and the length-to-diameter ratio serves as a measure of the transition between internal and external vena contracta flow properties.This study establishes a threshold length-to-diameter ratio of approximately 2 for the tested poppet valves.More specifically,in notch structures with a smaller valve opening,longer sealing length,and smaller throttling angle(corresponding to a larger length-to-diameter ratio),the liquid-to-vapor transfer process is more evident than that in the reverse direction.A long-standing vapor cavity becomes fixed inside the notch,leading to a more pronounced flow-choking phenomenon.In contrast,for structures with a smaller length-to-diameter ratio,the cavitation process for discrete vapor cavities is more complete,ensuring fluid flow continuity and significantly reducing the occurrence of the flow-choking phenomenon.展开更多
The acting force on the roll system of Sendzimir mill was analyzed using 3D FEM.The roll gap pressure distribution and the acting force between rolls S and O,rolls O and I,rolls O and J,rolls I and A,rolls I and B,as ...The acting force on the roll system of Sendzimir mill was analyzed using 3D FEM.The roll gap pressure distribution and the acting force between rolls S and O,rolls O and I,rolls O and J,rolls I and A,rolls I and B,as well as rolls J and B were analyzed.The results showed that the roll gap pressure mainly affected the roll surface layer,50 mm for backup roll;the roll gap pressure distribution is of double peaks among the work roll,the 1st intermediate roll(IMR),and the 2nd IMR;the maximum value of the roll gap pressure between the backup roll and the second IMR appears on the edge of the barrel of rolls;the component force presents the in-para-curve distribution.These are important for reducing the wear of rolls and the break of the backup roll and guiding for production.展开更多
High-speed rolling (HSR) is known to improve the workability of Mg alloys significantly, which makes it possible to impose a large reduction in a single pass without fracture. In the present study, dynamic recrystal...High-speed rolling (HSR) is known to improve the workability of Mg alloys significantly, which makes it possible to impose a large reduction in a single pass without fracture. In the present study, dynamic recrystallization (DRX) behavior and microstructural and textural variations of Mg alloy AZ31 dur-ing a HSR process were investigated by conducting rolling with different imposed reductions in the range of 20%-80% at a high rolling speed of 470 m/min and 400℃. High-strain-rate deformation during HSR suppresses dislocation slips but promotes twinning, which results in the formation of numer-ous twins of several types, i.e., {10-12} extension twins, {10-11} and {10-13} contraction twins, and {10-11}-{10-12} double twins. After twinning, high strain energy is accumulated in twin bands because their crystallographic orientations are favorable for basal slips, leading to subsequent DRX at the twin bands. Accordingly, twinning activation and twinning-induced DRX behavior play crucial roles in accommodating plastic deformation during HSR and in varying microstructure and texture of the high- speed-rolled (HSRed) sheets. Area fraction of fine DRXed grains formed at the twin bands increases with increasing rolling reduction, which is attributed to the combined effects of increased strain, strain rate, and deformation temperature and a decreased critical strain for DRX. Size, internal strain, and texture intensity of the DRXed grains are smaller than those of unDRXed grains. Therefore, as rolling reduction increases, average grain size, stored internal energy, microstructural inhomogeneity, and basal texture intensity of the HSRed sheets gradually decrease owing to an increase in the area fraction of the DRXed grains.展开更多
In the continuous hot-dip galvanizing process, the gas-jet wiping is used to control the coating thickness of moving steel strip. The high speed gas-jet discharged from the nozzle slot impinges on the strip, and at th...In the continuous hot-dip galvanizing process, the gas-jet wiping is used to control the coating thickness of moving steel strip. The high speed gas-jet discharged from the nozzle slot impinges on the strip, and at this moment, wipes the liquid coating layer dragged by a moving strip. The coating thickness is generally influenced on the flow characteristics of wiping gas-jet such as the impinging pressure distribution, pressure gradient and shear stress distribution on the surface of strip. The flow characteristics of wiping gas-jet mentioned above depends upon considerably both the process operating conditions such as the nozzle pressure, nozzle-to-strip distance and line speed, and the geometry of gas-jet wiping apparatus such as the height of nozzle slot. In the present study, the effect of the geometry of nozzle on the coating thickness is investigated with the help of a computational fluid dynamics method. The height of nozzle slot is varied in the range of 0.6mm to 1.7mm. A finite volume method (FVM) is employed to solve two-dimensional, steady, compressible Navier-Stokes equations. Based upon the results obtained, the effect of the height of nozzle slot in the gas-jet wiping process is discussed in detail. The computational results show that for a given standoff distance between the nozzle to the strip, the effective height of nozzle slot exists in achieving thinner coating thickness.展开更多
基金supported by grants-in-aid for the National Core Research Center Program from MEST/KOSEF
文摘The friction coefficient between tube and die in guide zone of tube hydroforming was obtained. In hydroforming, the tube is expanded by an internal pressure against the tool wall. By pushing the tube through tool, a friction force at the contact surface between the tube and the tool occurs. In guiding zone, the friction coefficients between tube and die can be estimated from the measured axial feeding forces. In expansion zone, the friction coefficients between tube and die can be evaluated from the measured geometries of expanded tubes and FE analysis.
基金supported by research funds from Dong-A University, Korea
文摘A pilot wire drawing machine as well as wire end-pointing roller was developed. Using these machines, a wire drawing test for four different coating materials and two different lubricants was performed as the reduction ratio increased from 10% to 30%. Materials used for a substrate in this study are plain carbon steel (AISI1045) and ultra low carbon bainite steel. To compute the friction coefficient between the coating layer of wire and the surface of die for a specific lubricant, a series of finite element analyses were carried out. SEM observations were also conducted to investigate the surface defects of wire deformed. Results show that the behavior of drawing force varies with the lubricant-type at the initial stage of drawing. The powder-typed lubricant with a large particle causes the retardation of full lubrication on the entire contact surface and the local delamination of coating layer on the wire surface. As the flow stress of a substrate increases, the delamination becomes severe.
基金Acknowledgements The project was supported by the Specialized Research Found for the Doctoral Program of Higher Education of China under Grant No. 20060013007 the National Natural Science Foundation of Beijing under Caant No. 4092029 and the National Natural Science Foundation of China under Grant No. 61100205, No. 60873001.
文摘In order to transmit secure messages, a quantum secure direct communication protocol based on extended three-particle GHZ state was presented, in which the extended three-particle GHZ state was used to detect eave sdroppers. In the security analysis, the method of the entropy theory is introduced, and three detection strategies are compared quantitatively by using the constraint between the information eavesdroppers can obtain and the interference introduced. If the eavesdroppers intend to obtain all information, the detection rate of the original "Ping-pong" protocol is 50%; the second protocol used two particles of EPR pair as detection particles is also 50%; while the presented protocol is 58%. At last, the security of the proposed protocol is discussed. The analysis results indicate that the protocol in this paper is more secure than the other two.
基金financially supported by the Ministry of Education,Science Technology(MEST)and National Research Foundation of Korea(NRF)through the Human Resource Training Project for Regional Innovationby the development program of local science park funded by the ULSAN Metropolitan City and the Ministry of Education,Science and Technology(MEST)
文摘AA5454-O aluminum alloy plates with the thicknesses of 1.4 and 1.0 mm were friction-spot-joined (FSJed).The plunge speed of the joining tool was changed in a range of 100 500 mm/min under a constant rotation speed of 500 r/min.The plunge depth was ranged from 1.6 mm to 2.2 mm.The tool plunge speed did not make a remarkable effect on the surface appearance and macro-structure of the FSJed zone.The average hardness of the FSJed zone was greater than or equal to that of the base metal.However,there was no remarkable tendency in the average hardness change of the FSJed zone in spite of the variation in the tool plunge speed and tool plunge depth.The increase of the tool plunge depth resulted in the increase of the tensile shear load.However,the change of the tool plunge speed did not lead to the remarkable variation in the tensile shear load of the FSJed plates.It was noteworthy that the FSJed plate exhibited the highest tensile shear load of about 4.0 kN.
基金Project(2011-0030058) supported by the National Research Foundation of Korea(NRF)Project(20134030200220) supported by the Human Resources Development Program of the Korea Institute of Energy Technology Evaluation,Korea+1 种基金Project supported by the Planning (KETEP) Grant Funded by the Korea Government Ministry of Trade,Industry and Energy and POSCO 2012,KoreaProject(10043795) supported by the Technology Innovation Program of the Ministry of Knowledge Economy Korea
基金Project(50534020) supported by the National Natural Science Foundation of China
文摘The deflection of rolls of Sendzimir mill with double AS-U-Roll was simulated by finite element method(FEM). The influences of rolling pressure, strip width and rolls-assignment on rolls deflection were analyzed. The results show that the work roll deflection increases with the increase of rolling pressure and the reduction of work roll radius, but the rigid displacement of work roll slightly changes; the work roll end might appear negative displacement for the narrow strip width and high rolling pressure that might cause the contact of work rolls. The research results are significant for guiding production and theoretical analysis of the rolls system of Sendzimir mill.
文摘Both wear and crack due to heat checking in hot work tool steel are major failure modes. It is desirable to find amethod to lengthen the tool life while reducing manufacturing cost. This paper suggests a method to improve toollife for hot work tool steel (SKD6) with crack by laser-melting process. The method has been evaluated using theimpact and fatigue test results. It is demonstrated that a repair of the crack by a laser-melting process is effectivefor life extension of the damaged tool.
基金financially supported by the Ministry of Education,Science Technology(MEST)and National Research Foundation of Korea(NRF)through the Human Resource Training Project for Regional Innovationby the development program of local science park funded by the ULSAN Metropolitan City and the Ministry of Education,Science and Technology(MEST)
文摘Friction stir butt welding (FSW) between A5052-O aluminum alloy plates with a thickness of 2 mm was performed.The rotation speeds of the welding tool were 2000 and 3000 r/min,respectively.The traverse speed was ranged from 100 mm/min to 900 mm/min.The defect-free welds with the very smooth surface morphology were successfully obtained,except for at the welding condition of 3000 r/min and 100 mm/min.The onion ring structure was observed in the friction-stir-welded zone (SZ) at the condition of 2000 r/min and 100 mm/min.For all the welding conditions,the grain size of the SZ was smaller than that of the base metal,and was decreased with the decrease of the tool rotation speed and with the increase of the tool traverse speed.The stir zone exhibited higher average hardness than the base metal.The decrease of the tool rotation speed and the increase of the tool traverse speed resulted in the increase in the average hardness of the SZ.The tensile strength of the FSWed plates was similar to that of the base metal,except for at the welding condition of 3000 r/min and 100 mm/min.The total elongation of the FSWed plates was lower than that of the base metal.
基金financially supported by the Ministry of Education,Science Technology(MEST)and National Research Foundation of Korea(NRF)through the Human Resource Training Project for Regional Innovationby the development program of local science park funded by the ULSAN Metropolitan City and the MEST(Ministry of Education,Science and Technology)
文摘AA5454-O aluminum alloy plates with thicknesses of 1.4 and 1.0 mm were friction-stir-lap-welded (FSLWed).The influences of the tool plunge depth and welding distance on surface appearance,macrostructure and mechanical properties of the FSLWed plates were experimentally investigated.The tensile shear load of the FSLWed plates was compared with that of the adhesive-bonded plates.Defect-free FSLWed zones were successfully obtained in all the tool plunge depths and the welding distances.The FSLWed zones exhibited the relatively smooth surface morphologies.Under all the FSLWed conditions,the FSLWed zone exhibited higher average hardness than the base metal.In addition,the upper plate exhibited a higher average hardness than the lower plate,although there was no special tendency in spite of the change in the tool plunge depth and the welding distance.The maximum tensile shear load of the FSLWed plates was much higher than that of the adhesive-bonded aluminum alloy plate.Especially,under the FSLW condition of the plunge depth of 1.8 mm and the welding distance of 40 mm,the tensile shear load of the FSLWed plate reached a level about 41% greater than that of the adhesive-bonded aluminum alloy plate.In addition,the maximum tensile shear load of the FSLWed plate was increased with the increase of the welding distance.
基金supported by National Natural Science Foundation of China under Grant No. 61100205Foundation of China Information Technology Security Evaluation Center under Grant No. CNITSEC-KY-0910-019/5
文摘In order to solve the various privacy and security problems in RFID system, a new low-cost RFID mutual authentication protocol based on ID updating mechanics is proposed. In the proposed scheme, the backend server keeps both the current ID and potential next ID for each tag, thus to solve the possible problem of de-synchronization attack in the most ID updating-based schemes. In the security analysis section, comparing several protocols in property required and attacker resistances, the comparison results show that the proposed protocol provides strong authentication and strong integrity of the transmissions and can withstand most the possible attacks that break the security of the previous schemes. In the performance evaluation section, the analysis results also indicate that, in terms of computational cost and storage requirement, the proposed scheme is safer, more efficient, more suitable for low-cost tag and more feasible in practice.
文摘It is known that one of the causes of pitting corrosion of copper tubes is residual carbon on the inner surface. It was confirmed that type I” pitting corrosion of the copper tube is suppressed by keeping the residual carbon amount at 2 mg/m<sup>2</sup> or less, which is lower than that of the type I’ pitting corrosion, or by removing the fine particles that are the corrosion product of galvanized steel pipes. The developed water treatment chemical was evaluated using three types of copper tubes with residual carbon amounts of 0 mg/m<sup>2</sup>, 0.5 mg/m<sup>2</sup>, and 6.1 mg/m<sup>2</sup>. The evaluation was conducted for three months in an open-circulation cooling water system and compared with the current water treatment chemical. Under the current water treatment chemical conditions, only the copper tube with a residual carbon amount of 6.1 mg/m<sup>2</sup> showed a significant increase in the natural corrosion potential after two weeks, and pitting corrosion occurred. No pitting corrosion and no increase in the natural corrosion potential were observed in any of the copper tubes that were treated with the developed water treatment chemical. In addition, the polarization curve was measured using the cooling water from this field test, and the anodic polarization of two cooling waters was compared. For copper tubes with a large amount of residual carbon, the current density near 0 mV vs. Ag/AgCl electrode (SSE) increased when the developed water treatment chemical was added.
文摘It is reported that laser-processing is effective to repair the heat checks, which are fine shallow cracks on a surfaceof die-casting dies. In this study, the rotating bending fatigue tests have been carried out to evaluate the fatiguecharacteristics of laser-processed hot working tool steel. Because test results are scattered, S-N curves are decidedbased on the evaluation of fatigue strength distribution. As a result, the fatigue strength of the laser-processedspecimens decreases remarkably in comparison with that of base metal. However, it can be recovered to almostinitial value by heat treatment at secondary hardening temperature. This procedure is also effective to decrease thescatter of fatigue strength. The laser-processing can be carried out at low cost and this method is effective for theextension of the work life of dies.
文摘In this study,the authors proposed a new algorism which can simultaneously meets the strip shape control criterion and the strip crown control criterion.Based on the new algorism,the pass schedule is optimized to maximize the allowable PC angle range.To calculate the objective value for optimization of pass schedule,a slab method has been integrated with the roll stack deformation to simulate the strip profile.
文摘Modification of the carbide characteristics through the grain boundary serration is investigated, using an AISI 316 and 304 stainless steels. In both steels, triangular carbides were observed at straight grain boundaries while planar carbides were observed at the serrated grain boundaries. The serrated grain boundary energy is observed to be much lower than that of the straight one. Therefore, the carbide morphology is found to be changed from triangular to planar along the serrated boundary to reduce the interfacial energy between the carbide and the matrix. The creep-fatigue properties of these steels at 873K have been investigated. The creep-fatigue life of the sample with planar carbide at the serrated grain boundary was found to be much longer than that with triangular carbide at the straight one. These results imply that the planar carbides with lower interfacial energy have higher cavitation resistance, resulting in the retardation of cavity nucleation and growth to increase creep-fatigue life.
文摘We performed corrosion case study and corrosion tests to assess the corrosion resistance of stainless steel type 304 pipes in tap water and hot water facilities. Circulating test equipment used for corrosion tests and two types of sample, plates and straight pipe specimens, were examined under different conditions of residual chlorine concentration in the test water. The results of case study analysis indicated that high degrees of pitting corrosion occurred on straight pipes with inner diameter < 50 mm. The results of corrosion tests showed that the residual chlorine concentration around the pitting corrosion of stainless steel type 304 was greater than 0.3 mg/L in the plate, regardless of the remaining chlorine concentration in the straight pipe specimens. These results suggest that straight pipes have higher corrosion susceptibility because of bending during production.
文摘It has been reported that pitting corrosion in copper tubes occurs due to the effect of a carbon film produced by the influence of undergoing an oil and heat treatment. As a quantitative method for determining the residual carbon amount, it has been reported that the inner surface of a copper tube can be dissolved with a mixed acid to collect and analyze the adhering carbon;however, this method is dangerous and difficult. Therefore, two methods were examined as a simple quantitative method for obtaining the residual carbon amount using copper tubes with known residual carbon amounts. One method utilizes X-ray photoelectron spectroscopy (XPS), and the other method utilizes the potential difference between the carbon film-adhered surface and carbon film-removed surface. In regard to XPS measurement, a linear correlation was found between the spectral intensity of C and the residual carbon amount;therefore, XPS measurements were considered to be effective as a simple measurement method for the carbon film on the inner surface of a copper tube. In the evaluation method by measuring the corrosion potential, a correlation was observed between the potential difference ΔE and the residual carbon amount of the inner surface of the tube and the outer surface of the polished tube. It is considered possible to estimate the residual carbon amount from the prepared calibration curve. Through these studies, it is suggested that the carbon film was non-uniformly present on the surface of the copper tube. Therefore, the galvanic current was measured, and the effect of a non-uniform carbon film on corrosion behavior was investigated. As a result, in the measurement of galvanic current, the current flowed from the copper tube with a large amount of residual carbon (cathode) to the copper tube with a small amount of residual carbon (anode). In addition, the higher the area ratio of the carbon film was, the larger the galvanic current tended to be.
基金supported by the National Natural Science Foundation of China(Nos.52075387 and 52375060)the Shanghai Natural Science Foundation of China(No.22ZR1464400)+2 种基金the National Key R&D Program of China(No.2019YFB2005102)the Shanghai Municipal Science and Technology Major Project(No.2021SHZDZX0100)the Fundamental Research Funds for the Central Universities(No.2022-1-ZD-04),China.
文摘Poppet valves have become increasingly significant in ensuring precise digital flow rate and pressure control in hydraulic systems,necessitating a more profound understanding of the geometrical properties of cavitation in them,as well as associated flow-choking conditions.Through a comparative analysis with experimentally observed cavity images,we found that large eddy simulation(LES)turbulence modeling effectively replicates the geometrical properties of cavitation in these valves.The analysis demonstrated that cavitation is generated from vortices that result from the interaction between the notch contracta flow and the surrounding fluid structure.Variations in the internal or external vena contracta conditions result in fixed or discrete cavities,and the length-to-diameter ratio serves as a measure of the transition between internal and external vena contracta flow properties.This study establishes a threshold length-to-diameter ratio of approximately 2 for the tested poppet valves.More specifically,in notch structures with a smaller valve opening,longer sealing length,and smaller throttling angle(corresponding to a larger length-to-diameter ratio),the liquid-to-vapor transfer process is more evident than that in the reverse direction.A long-standing vapor cavity becomes fixed inside the notch,leading to a more pronounced flow-choking phenomenon.In contrast,for structures with a smaller length-to-diameter ratio,the cavitation process for discrete vapor cavities is more complete,ensuring fluid flow continuity and significantly reducing the occurrence of the flow-choking phenomenon.
基金Item Sponsored by National Natural Science Foundation of China(50534020)
文摘The acting force on the roll system of Sendzimir mill was analyzed using 3D FEM.The roll gap pressure distribution and the acting force between rolls S and O,rolls O and I,rolls O and J,rolls I and A,rolls I and B,as well as rolls J and B were analyzed.The results showed that the roll gap pressure mainly affected the roll surface layer,50 mm for backup roll;the roll gap pressure distribution is of double peaks among the work roll,the 1st intermediate roll(IMR),and the 2nd IMR;the maximum value of the roll gap pressure between the backup roll and the second IMR appears on the edge of the barrel of rolls;the component force presents the in-para-curve distribution.These are important for reducing the wear of rolls and the break of the backup roll and guiding for production.
基金supported and by the National Research Foundation of Korea(NRF) grants funded by the Korean government(MSIP,South Korea)(No.2016R1C1B2012140 and No.2017R1A4A1015628)by the Korean Institute of Industrial Technology(KITECH JA180001)
文摘High-speed rolling (HSR) is known to improve the workability of Mg alloys significantly, which makes it possible to impose a large reduction in a single pass without fracture. In the present study, dynamic recrystallization (DRX) behavior and microstructural and textural variations of Mg alloy AZ31 dur-ing a HSR process were investigated by conducting rolling with different imposed reductions in the range of 20%-80% at a high rolling speed of 470 m/min and 400℃. High-strain-rate deformation during HSR suppresses dislocation slips but promotes twinning, which results in the formation of numer-ous twins of several types, i.e., {10-12} extension twins, {10-11} and {10-13} contraction twins, and {10-11}-{10-12} double twins. After twinning, high strain energy is accumulated in twin bands because their crystallographic orientations are favorable for basal slips, leading to subsequent DRX at the twin bands. Accordingly, twinning activation and twinning-induced DRX behavior play crucial roles in accommodating plastic deformation during HSR and in varying microstructure and texture of the high- speed-rolled (HSRed) sheets. Area fraction of fine DRXed grains formed at the twin bands increases with increasing rolling reduction, which is attributed to the combined effects of increased strain, strain rate, and deformation temperature and a decreased critical strain for DRX. Size, internal strain, and texture intensity of the DRXed grains are smaller than those of unDRXed grains. Therefore, as rolling reduction increases, average grain size, stored internal energy, microstructural inhomogeneity, and basal texture intensity of the HSRed sheets gradually decrease owing to an increase in the area fraction of the DRXed grains.
文摘In the continuous hot-dip galvanizing process, the gas-jet wiping is used to control the coating thickness of moving steel strip. The high speed gas-jet discharged from the nozzle slot impinges on the strip, and at this moment, wipes the liquid coating layer dragged by a moving strip. The coating thickness is generally influenced on the flow characteristics of wiping gas-jet such as the impinging pressure distribution, pressure gradient and shear stress distribution on the surface of strip. The flow characteristics of wiping gas-jet mentioned above depends upon considerably both the process operating conditions such as the nozzle pressure, nozzle-to-strip distance and line speed, and the geometry of gas-jet wiping apparatus such as the height of nozzle slot. In the present study, the effect of the geometry of nozzle on the coating thickness is investigated with the help of a computational fluid dynamics method. The height of nozzle slot is varied in the range of 0.6mm to 1.7mm. A finite volume method (FVM) is employed to solve two-dimensional, steady, compressible Navier-Stokes equations. Based upon the results obtained, the effect of the height of nozzle slot in the gas-jet wiping process is discussed in detail. The computational results show that for a given standoff distance between the nozzle to the strip, the effective height of nozzle slot exists in achieving thinner coating thickness.