Severe tool wear and poor surface quality are the main problems during micro machining of cemented carbide.In this work,an innovative hybrid process of laser-induced oxidation assisted micro milling(LOMM)was proposed ...Severe tool wear and poor surface quality are the main problems during micro machining of cemented carbide.In this work,an innovative hybrid process of laser-induced oxidation assisted micro milling(LOMM)was proposed to solve the problems.A nanosecond laser was utilized to induce oxidation of the WC-20%Co material,producing loose oxide which was easy to remove.The micro machinability of the material was improved by laser-induced oxidation.The oxidation mechanisms of cemented carbide were studied.A microgroove with a depth of 2.5 mm and aspect ratio of 5 was fabricated successfully.The milling force,surface quality and tool wear mechanisms were investigated.For comparison,a microgroove was also fabricated with conventional micro milling(COMM)using identical milling parameters.Results revealed that in LOMM the milling force and tool wear rate were extremely low during removing the oxide.The machined surface quality and dimensional accuracy achieved by LOMM were superior to those obtained by COMM.The surface roughness Saof the microgroove bottom reached 88 nm in LOMM,while the cross-sectional geometry of the microgroove was a trapezoid.Perpendicularity of the microgroove sidewall machined by LOMM was better than that by COMM.The tool wear forms in LOMM were coating spalling and slight tool nose breakage.Compared with COMM,the tool life in LOMM was prolonged significantly.It indicates that the proposed hybrid process is an effective and efficient way to fabricate high aspect ratio micro-features with high dimensional accuracy.展开更多
Bird-like flapping-wing vehicles with a high aspect ratio have the potential to fulfill missions given to micro air vehicles,such as high-altitude reconnaissance,surveillance,rescue,and bird group guidance,due to thei...Bird-like flapping-wing vehicles with a high aspect ratio have the potential to fulfill missions given to micro air vehicles,such as high-altitude reconnaissance,surveillance,rescue,and bird group guidance,due to their good loading and long endurance capacities.Biologists and aeronautical researchers have explored the mystery of avian flight and made efforts to reproduce flapping flight in bioinspired aircraft for decades.However,the cognitive depth from theory to practice is still very limited.The mechanism of generating sufficient lift and thrust during avian flight is still not fully understood.Moving wings with unique biological structures such as feathers make modeling,simulation,experimentation,and analysis much more difficult.This paper reviews the research progress on bird-like flapping wings from flight mechanisms to modeling.Commonly used numerical computing methods are briefly compared.The aeroelastic problems are also highlighted.The results of the investigation show that a leading-edge vortex can be found during avian flight.Its induction and maintenance may have a close relationship with wing configuration,kinematics and deformation.The present models of flapping wings are mainly two-dimensional airfoils or three-dimensional single root-jointed geometric plates,which still exhibit large differences from real bird wings.Aeroelasticity is encouraged to consider the nonignorable effect on aerodynamic performance due to large-scale nonlinear deformation.Introducing appropriate flexibility can improve the peak values and efficiencies of lift and thrust,but the detailed conclusions always have strong background dependence.展开更多
It is difficult to access exfoliated sepiolite(Sep)fibers with high aspect ratio from Sep ore.The traditional method used to purify Sep ore also reduces its aspect ratio.In this study,impurities in the Sep ore were re...It is difficult to access exfoliated sepiolite(Sep)fibers with high aspect ratio from Sep ore.The traditional method used to purify Sep ore also reduces its aspect ratio.In this study,impurities in the Sep ore were removed by acid activation followed by a cetyltrimethylammonium chloride(C16)treatment to organically modify the purified Sep by cation exchange.Then,the organically-modified Sep(O-Sep)was stripped and processed by an ultrasonic cell crusher to obtain Sep microfibers at a specific frequency for a given period.These Sep samples had relatively high aspect ratio,compared with the Sep fibers gotten by traditional method.Scanning electron microscopy(SEM)and transmission electron microscopy(TEM)demonstrate the micro-morphology of exfoliated Sep samples in an intuitive way.Moreover,pure inorganic membrane prepared only with the exfoliated Sep fibers exhibited excellent flexibility,further demonstrating the excellent properties of Sep fibers with high aspect ratio.展开更多
The high aspect ratio(HAR)micro-electro-mechanical system trench array is a key component for the miniaturization of micro sensors,actuators,and other advanced precision equipment,with broad application prospects in d...The high aspect ratio(HAR)micro-electro-mechanical system trench array is a key component for the miniaturization of micro sensors,actuators,and other advanced precision equipment,with broad application prospects in defense,security,aerospace,energy,and other fields.Therefore,accurate and efficient measurement of the aspect ratio of microstructures will become a crucial method for monitoring and ensuring the reliability and stability of the device fabrication process.This paper presents a novel method that combines the lattice light field generated by a microaxicon array with microscopic imaging technology to accurately measure the width and depth of HAR micro-trench structures.We designed and constructed a dedicated experimental system,initially using monochromatic microscopic imaging and edge extraction algorithms to obtain the width information of the trenches.Subsequently,the trench depth was measured using the diffraction lattice light field generated by the micro-axicon array.Experimental results indicate that as the light field propagates from the top to the bottom of the trench,the light spots in the lattice light field shift in position due to the presence of diffraction angles,with the displacement being closely related to the trench depth.A mapping between the displacement and depth is established through geometric relationships,enabling the calculation of the trench depth.We tested nine trench samples with different aspect ratios,with the maximum aspect ratio reaching 58.12.The experimental results,compared with the scanning electron microscope measurement values,show that the measurement errors are all<9%.展开更多
High-aspect-ratio metallic surface microstructures are increasingly demanded in breakthrough applications,such as high-performance heat transfer enhancement and surface plasmon devices.However,the fast and cost-effect...High-aspect-ratio metallic surface microstructures are increasingly demanded in breakthrough applications,such as high-performance heat transfer enhancement and surface plasmon devices.However,the fast and cost-effective fabrication of high-aspect-ratio microstructures on metallic surfaces remains challenging for existing techniques.This study proposes a novel cutting-based process,namely elliptical vibration chiseling(EV-chiseling),for the high-efficiency texturing of surface microstructures with an ultrahigh aspect ratio.Unlike conventional cutting,EV-chiseling superimposes a microscale EV on a backward-moving tool.The tool chisels into the material in each vibration cycle to generate an upright chip with a high aspect ratio through material deformation.Thanks to the tool’s backward movement,the chip is left on the material surface to form a microstructure rather than falling off.Since one microstructure is generated in one vibration cycle,the process can be highly efficient using ultrafast(>1 kHz)tool vibration.A finite element analysis model is established to explore the process mechanics of EV-chiseling.Next,a mechanistic model of the microstructured surface generation is developed to describe the microstructures’aspect ratio dependency on the process parameters.Then,surface texturing tests are performed on copper to verify the efficacy of EV-chiseling.Uniformed micro ribs with a spacing of 1–10μm and an aspect ratio of 2–5 have been successfully textured on copper.Compared with the conventional EV-cutting that uses a forward-moving tool,EV-chiseling can improve the aspect ratio of textured microstructure by up to 40 times.The experimental results also verify the accuracy of the developed surface generation model of microstructures.Finally,the effects of elliptical trajectory,depth of cut,tool shape,and tool edge radius on the surface generation of micro ribs have been discussed.展开更多
Nanoimprint lithography(NIL)has attracted attention recently as a promising fabrication method for dielectric metalenses owing to its low cost and high throughput,however,high aspect ratio(HAR)nanostructures are requi...Nanoimprint lithography(NIL)has attracted attention recently as a promising fabrication method for dielectric metalenses owing to its low cost and high throughput,however,high aspect ratio(HAR)nanostructures are required to manipulate the full 2πphase of light.Conventional NIL using a hard-polydimethylsiloxane(h-PDMS)mold inevitably incurs shear stress on the nanostructures which is inversely proportional to the surface area parallel to the direction of detachment.Therefore,HAR structures are subjected to larger shear stresses,causing structural failure.Herein,we propose a novel wet etching NIL method with no detachment process to fabricate flawless HAR metalenses.The water-soluble replica mold is fabricated with polyvinyl alcohol(PVA)which is simpler than an h-PDMS mold,and the flexibility of the PVA mold is suitable for direct printing as its high tensile modulus allows high-resolution patterning of HAR metalenses.The diffraction-limited focusing of the printed metalenses demonstrates that it operates as an ideal lens in the visible regime.This method can potentially be used for manufacturing various nanophotonic devices that require HAR nanostructures at low cost and high throughput,facilitating commercialization.展开更多
A near-infrared femtosecond laser is focused by a 100 mm-focal-length plano-convex lens to form a laser filament,which is employed to drill holes on copper targets.By shifting or rotating the focusing lens,additional ...A near-infrared femtosecond laser is focused by a 100 mm-focal-length plano-convex lens to form a laser filament,which is employed to drill holes on copper targets.By shifting or rotating the focusing lens,additional aberration is imposed on the focused laser beam,and significant influence is produced on the aspect ratio and cross-sectional shape of the micro-holes.Experimental results show that when proper aberration is introduced,the copper plate with a thickness of 3 mm can be drilled through with an aspect ratio of 30,while no through-holes can be drilled on 3-mm-thickness copper plates by femtosecond laser with minimized aberration.In addition,when femtosecond laser filament with large astigmatism is used,micro-holes that had a length to width ratio up to 3.3 on the cross-section are obtained.Therefore,the method proposed here can be used to fabricate long oval holes with high aspect ratios.展开更多
A rapid,simple and cost-effective polyol method has been developed for the synthesis of silver nanowires with high aspect ratio and high purity.The aspect ratios of the silver nanowires as high as ca.1000(average leng...A rapid,simple and cost-effective polyol method has been developed for the synthesis of silver nanowires with high aspect ratio and high purity.The aspect ratios of the silver nanowires as high as ca.1000(average length 40μm and some even as long as 80μm,diameter 50-100 nm)were obtained via optimizing the reaction conditions.Transparent electrodes with excellent optoelectronic performances(optical transmittance of 90%,sheet resistance of 23.2Ω/□and optical transmittance of 87%,sheet resistance of 19.7Ω/□)comparable to commercial ITO were fab-ricated via simple spin coating the resulting silver nanowires onto the glass substrates.The high optoelectronic per-formances and the facile all-solution process of the as-prepared transparent electrodes render them rather promising candidates for use in cost-effective large-area optoelectronic devices.展开更多
A theoretical nonlinear aeroelastic response analysis for a flexible high-aspect ratio wing excited by harmonic gust load is presented along with a companion wind tunnel test. A multidisci- plinary coupled numerical c...A theoretical nonlinear aeroelastic response analysis for a flexible high-aspect ratio wing excited by harmonic gust load is presented along with a companion wind tunnel test. A multidisci- plinary coupled numerical calculation is developed to simulate the flexible model wing undergoing gust load in the time domain via discrete nonlinear finite element structural dynamic analysis and nonplanar unsteady vortex lattice aerodynamic computation. A dynamic perturbation analysis about a nonlinear static equilibrium is also used to determine the small perturbation flutter bound- ary. A novel noncontact 3-D camera measurement analysis system is firstly used in the wind tunnel test to obtain the spatial large deformation and responses. The responses of the flexible wing under different static equilibrium states and frequency gust loads are discussed. The fair to good quanti- tative agreements between the theoretical and experimental results demonstrate that the presented analysis method is an acceptable way to predict the geometrically nonlinear gust response for flex- ible wings.展开更多
In order to analyze the effects of forward-swept angle and skin ply-orientation on the static and dynamic aeroelastic characteristics, the aeroelastic modeling and calculation for high-aspect-ratio composite wings wit...In order to analyze the effects of forward-swept angle and skin ply-orientation on the static and dynamic aeroelastic characteristics, the aeroelastic modeling and calculation for high-aspect-ratio composite wings with different forward-swept angles and skin ply-orientation are performed. This paper presents the results of a design study aiming to optimize wings with typical forward-swept angles and skin ply-orientation in an aeroelastic way by using the genetic/sensitivity-based hybrid algorithm. Under the conditions of satiated multiple constraints including strength, displacements, divergence speeds and flutter speeds, the studies are carried out in a bid to minimize the structural weight of a wing with the lay-up thicknesses of wing components as design variabies. In addition, the effects of the power of spanwise variation function of lay-up thicknesses of skins and iugs on the optimized weights are also analyzed.展开更多
A unified structural model for high-aspect-ratio composite wing with arbitrary cross-section is developed. Two types of lay-ups of the composite wing, namely, circumferentially uniform stiffness （CUS） configuration ...A unified structural model for high-aspect-ratio composite wing with arbitrary cross-section is developed. Two types of lay-ups of the composite wing, namely, circumferentially uniform stiffness （CUS） configuration and circumferentially asymmetric stiffness （CAS） configuration, are investigated. The present structural modeling method is validated through ANSYS FEM software for the case of a composite box beam. Then, the case of a single-cell composite wing with NACA0012 airfoil shape is considered. To investigate the aeroelastic problem of high-aspect-ratio composite wings, the linear ONERA aerodynamic model is used to model the unsteady aerodynamic loads under the case of small angle of attack. Finally, flutter speeds of the high-aspect-ratio wing with various composite ply angles are determined by using U-g method.展开更多
The stall flutter characters of high-aspect-ratio composite wing are investigated, and the effects of structure geometric nonlinearity and stiffness couple created by composite anisotropy on them also are discussed. F...The stall flutter characters of high-aspect-ratio composite wing are investigated, and the effects of structure geometric nonlinearity and stiffness couple created by composite anisotropy on them also are discussed. Firstly, the high-aspect-ratio wing is modeled as a composite thin-walled closed section Euler beam whose displacement and rotation both could be of finite value, and the nonlinear dynamic equations is build up on it with all the effects of geometric nonlinearity, aerodynamic nonlinearity and anisotropy of material being considered. Then vibration equations are deduced through perturbing the dynamic equations at wing＇s equilibrium position, and coupled with unsteady stall aerodynamic model and ONERA model, to obtain the nonlinear stall flutter analysis equations of wing. Finally, the flutter stabilities with various wind speeds are determined by the harmonic balance method. With several exampies, the validity of the stall flutter model is proved, and the significant effects of geometric nonlinearity on the stall flutter various characters as wall as the effects of ply angle on the stall flutter speed and frequency also are discussed.展开更多
A high-aspect-ratio microchannel heat exchanger based on multi-tool milling process was developed. Several slotting cutters were stacked together for simultaneously machining several high-aspect-ratio microchannels wi...A high-aspect-ratio microchannel heat exchanger based on multi-tool milling process was developed. Several slotting cutters were stacked together for simultaneously machining several high-aspect-ratio microchannels with manifold structures. On the basis of multi-tool milling process, the structural design of the manifold side height, microchannel length, width, number, and interval were analyzed. The heat transfer performances of high-aspect-ratio microchannel heat exchangers with two different manifolds were investigated by experiments, and the influencing factors were analyzed. The results indicate that the magnitude of heat transfer area per unit volume dominates the heat transfer performances of plate-type micro heat exchanger, while the velocity distribution between microchannels has little effects on the heat transfer performances.展开更多
The relationship between stiffness distribution and aeroelastic performance for a beam-frame model and a3-D model is investigated based on aeroelastic optimization of global stiffness design for high-aspect-ratio wing...The relationship between stiffness distribution and aeroelastic performance for a beam-frame model and a3-D model is investigated based on aeroelastic optimization of global stiffness design for high-aspect-ratio wings.The sensitivity information of wing spanwise stiffness distribution with respect to the twist angle at wing tip,the vertical displacement at wing tip,and the flutter speed are obtained using a sensitivity method for both models.Then the relationship between stiffness distribution and aeroelastic performance is summarized to guide the design procedure.By using the genetic/sensitivity-based hybrid algorithm,an optimal solution satisfying the strength,aeroelastic and manufacturing constraints is obtained.It is found that the summarized guidance is well consistent with the optimal solution,thus providing a valuable design advice with efficiency.The study also shows that the aeroelastic-optimization-based global stiffness design procedure can obtain the optimal solution under multiple constraints with high efficiency and precision,thereby having a strong application value in engineering.展开更多
Filling high-aspect-ratio trenches with gold is a frequent requirement in the fabrication of X-ray optics as well as micro-electronic components and other fabrication processes. Conformal electrodeposition of gold in ...Filling high-aspect-ratio trenches with gold is a frequent requirement in the fabrication of X-ray optics as well as micro-electronic components and other fabrication processes. Conformal electrodeposition of gold in sub-micron-width silicon trenches with an aspect ratio greater than 35 over a grating area of several square centimeters is challenging and has not been described in the literature previously. A comparison of pulsed plating and constant current plating led to a gold electroplating protocol that reliably filled trenches for such structures.展开更多
For the strong coupling among the channels of bank-to-turn （BTT） missile with high-aspect-ratio wing, an autopilot is designed with a two loop control structure robust autopilot design methods. By the inner loop des...For the strong coupling among the channels of bank-to-turn （BTT） missile with high-aspect-ratio wing, an autopilot is designed with a two loop control structure robust autopilot design methods. By the inner loop design, the question of pole-zero cancellation is solved, and the stabilization of structured uncertainty is achieved. Through the outer loop of H∞ controller design, the flying performance and robustness can be guaranteed. The nonlinear simulation results show that the autopilot designed has perfect time domain response, and can suppress bad influence of the inertial and kinematics couplings. It can make the missile fly stably in the large flying areas. The control is very effective.展开更多
基金the National Natural Science Foundation of China(No.51705249)the China Postdoctoral Science Foundation(No.2019M661823)+1 种基金the Aeronautical Science Foundation of China(No.2017ZE52047)the 111 Project on Key Technology in Sustainable Manufacturing(No.B16024)。
文摘Severe tool wear and poor surface quality are the main problems during micro machining of cemented carbide.In this work,an innovative hybrid process of laser-induced oxidation assisted micro milling(LOMM)was proposed to solve the problems.A nanosecond laser was utilized to induce oxidation of the WC-20%Co material,producing loose oxide which was easy to remove.The micro machinability of the material was improved by laser-induced oxidation.The oxidation mechanisms of cemented carbide were studied.A microgroove with a depth of 2.5 mm and aspect ratio of 5 was fabricated successfully.The milling force,surface quality and tool wear mechanisms were investigated.For comparison,a microgroove was also fabricated with conventional micro milling(COMM)using identical milling parameters.Results revealed that in LOMM the milling force and tool wear rate were extremely low during removing the oxide.The machined surface quality and dimensional accuracy achieved by LOMM were superior to those obtained by COMM.The surface roughness Saof the microgroove bottom reached 88 nm in LOMM,while the cross-sectional geometry of the microgroove was a trapezoid.Perpendicularity of the microgroove sidewall machined by LOMM was better than that by COMM.The tool wear forms in LOMM were coating spalling and slight tool nose breakage.Compared with COMM,the tool life in LOMM was prolonged significantly.It indicates that the proposed hybrid process is an effective and efficient way to fabricate high aspect ratio micro-features with high dimensional accuracy.
文摘Bird-like flapping-wing vehicles with a high aspect ratio have the potential to fulfill missions given to micro air vehicles,such as high-altitude reconnaissance,surveillance,rescue,and bird group guidance,due to their good loading and long endurance capacities.Biologists and aeronautical researchers have explored the mystery of avian flight and made efforts to reproduce flapping flight in bioinspired aircraft for decades.However,the cognitive depth from theory to practice is still very limited.The mechanism of generating sufficient lift and thrust during avian flight is still not fully understood.Moving wings with unique biological structures such as feathers make modeling,simulation,experimentation,and analysis much more difficult.This paper reviews the research progress on bird-like flapping wings from flight mechanisms to modeling.Commonly used numerical computing methods are briefly compared.The aeroelastic problems are also highlighted.The results of the investigation show that a leading-edge vortex can be found during avian flight.Its induction and maintenance may have a close relationship with wing configuration,kinematics and deformation.The present models of flapping wings are mainly two-dimensional airfoils or three-dimensional single root-jointed geometric plates,which still exhibit large differences from real bird wings.Aeroelasticity is encouraged to consider the nonignorable effect on aerodynamic performance due to large-scale nonlinear deformation.Introducing appropriate flexibility can improve the peak values and efficiencies of lift and thrust,but the detailed conclusions always have strong background dependence.
基金Fundamental Research Funds for the Central Universities of ministry of Education of China(No.2232020G-04)National Key Research&Development Program of China(No.2018YFC1801500)。
文摘It is difficult to access exfoliated sepiolite(Sep)fibers with high aspect ratio from Sep ore.The traditional method used to purify Sep ore also reduces its aspect ratio.In this study,impurities in the Sep ore were removed by acid activation followed by a cetyltrimethylammonium chloride(C16)treatment to organically modify the purified Sep by cation exchange.Then,the organically-modified Sep(O-Sep)was stripped and processed by an ultrasonic cell crusher to obtain Sep microfibers at a specific frequency for a given period.These Sep samples had relatively high aspect ratio,compared with the Sep fibers gotten by traditional method.Scanning electron microscopy(SEM)and transmission electron microscopy(TEM)demonstrate the micro-morphology of exfoliated Sep samples in an intuitive way.Moreover,pure inorganic membrane prepared only with the exfoliated Sep fibers exhibited excellent flexibility,further demonstrating the excellent properties of Sep fibers with high aspect ratio.
文摘The high aspect ratio(HAR)micro-electro-mechanical system trench array is a key component for the miniaturization of micro sensors,actuators,and other advanced precision equipment,with broad application prospects in defense,security,aerospace,energy,and other fields.Therefore,accurate and efficient measurement of the aspect ratio of microstructures will become a crucial method for monitoring and ensuring the reliability and stability of the device fabrication process.This paper presents a novel method that combines the lattice light field generated by a microaxicon array with microscopic imaging technology to accurately measure the width and depth of HAR micro-trench structures.We designed and constructed a dedicated experimental system,initially using monochromatic microscopic imaging and edge extraction algorithms to obtain the width information of the trenches.Subsequently,the trench depth was measured using the diffraction lattice light field generated by the micro-axicon array.Experimental results indicate that as the light field propagates from the top to the bottom of the trench,the light spots in the lattice light field shift in position due to the presence of diffraction angles,with the displacement being closely related to the trench depth.A mapping between the displacement and depth is established through geometric relationships,enabling the calculation of the trench depth.We tested nine trench samples with different aspect ratios,with the maximum aspect ratio reaching 58.12.The experimental results,compared with the scanning electron microscope measurement values,show that the measurement errors are all<9%.
基金support for this research provided by the National Natural Science Foundation of China(Grant No.52105458)Beijing Natural Science Foundation(Grant No.3222009)+1 种基金Huaneng Group Science and Technology Research Project(No:HNKJ22-H105)China Postdoctoral Science Foundation(Grant No.2022M711807)。
文摘High-aspect-ratio metallic surface microstructures are increasingly demanded in breakthrough applications,such as high-performance heat transfer enhancement and surface plasmon devices.However,the fast and cost-effective fabrication of high-aspect-ratio microstructures on metallic surfaces remains challenging for existing techniques.This study proposes a novel cutting-based process,namely elliptical vibration chiseling(EV-chiseling),for the high-efficiency texturing of surface microstructures with an ultrahigh aspect ratio.Unlike conventional cutting,EV-chiseling superimposes a microscale EV on a backward-moving tool.The tool chisels into the material in each vibration cycle to generate an upright chip with a high aspect ratio through material deformation.Thanks to the tool’s backward movement,the chip is left on the material surface to form a microstructure rather than falling off.Since one microstructure is generated in one vibration cycle,the process can be highly efficient using ultrafast(>1 kHz)tool vibration.A finite element analysis model is established to explore the process mechanics of EV-chiseling.Next,a mechanistic model of the microstructured surface generation is developed to describe the microstructures’aspect ratio dependency on the process parameters.Then,surface texturing tests are performed on copper to verify the efficacy of EV-chiseling.Uniformed micro ribs with a spacing of 1–10μm and an aspect ratio of 2–5 have been successfully textured on copper.Compared with the conventional EV-cutting that uses a forward-moving tool,EV-chiseling can improve the aspect ratio of textured microstructure by up to 40 times.The experimental results also verify the accuracy of the developed surface generation model of microstructures.Finally,the effects of elliptical trajectory,depth of cut,tool shape,and tool edge radius on the surface generation of micro ribs have been discussed.
基金H.L.acknowledges the Technology Innovation program(20016234)funded by the Ministry of Trade and Industry&Energy(MOTIE)and the National Research Foundation(NRF)grants(NRF-2019K1A4A7A02113032,NRF-2022M3H4A1A02046445,NRF-2018M3D1A1058997)funded by the Ministry of Science and ICT(MSIT)of the Korean governmentJ.R.acknowledges the POSCO-POSTECH-RIST Convergence Research Center program funded by POSCO,an industry-university strategic grant funded by Samsung Display,and the NRF grants(NRF-2022M3C1A3081312,NRF-2022M3H4A1A02074314,NRF-2019R1A5A8080290,CAMM-2019M3A6B3030637)funded by the MSIT of the Korean government+1 种基金C.W.Q.acknowledges the support by AME Individual Research Grant(IRG)funded by A*STAR,Singapore(Grant No.A2083c0060).J.K.acknowledges the POSTECH Alchemist fellowship.
文摘Nanoimprint lithography(NIL)has attracted attention recently as a promising fabrication method for dielectric metalenses owing to its low cost and high throughput,however,high aspect ratio(HAR)nanostructures are required to manipulate the full 2πphase of light.Conventional NIL using a hard-polydimethylsiloxane(h-PDMS)mold inevitably incurs shear stress on the nanostructures which is inversely proportional to the surface area parallel to the direction of detachment.Therefore,HAR structures are subjected to larger shear stresses,causing structural failure.Herein,we propose a novel wet etching NIL method with no detachment process to fabricate flawless HAR metalenses.The water-soluble replica mold is fabricated with polyvinyl alcohol(PVA)which is simpler than an h-PDMS mold,and the flexibility of the PVA mold is suitable for direct printing as its high tensile modulus allows high-resolution patterning of HAR metalenses.The diffraction-limited focusing of the printed metalenses demonstrates that it operates as an ideal lens in the visible regime.This method can potentially be used for manufacturing various nanophotonic devices that require HAR nanostructures at low cost and high throughput,facilitating commercialization.
基金the National KeyResearch and Development Program (No. 2018YFB0504400)。
文摘A near-infrared femtosecond laser is focused by a 100 mm-focal-length plano-convex lens to form a laser filament,which is employed to drill holes on copper targets.By shifting or rotating the focusing lens,additional aberration is imposed on the focused laser beam,and significant influence is produced on the aspect ratio and cross-sectional shape of the micro-holes.Experimental results show that when proper aberration is introduced,the copper plate with a thickness of 3 mm can be drilled through with an aspect ratio of 30,while no through-holes can be drilled on 3-mm-thickness copper plates by femtosecond laser with minimized aberration.In addition,when femtosecond laser filament with large astigmatism is used,micro-holes that had a length to width ratio up to 3.3 on the cross-section are obtained.Therefore,the method proposed here can be used to fabricate long oval holes with high aspect ratios.
基金support from the National Key Basic Research Program of China (973 Program,2014CB648300)the National Natural Science Foundation of China (21422402,20904024,51173081,61136003,61106036)+7 种基金the Natural Science Foundation of Jiangsu Province (BK20140060,BK20130037,BK2011760)Program for New Century Excellent Talents in University (NCET-13-0872)Specialized Research Fund for the Doctoral Program of Higher Education (20133223110008)the Ministry of Education of China (IRT1148)the NUPT Scientific Foundation (NY213119)the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD)the Six Talent Plan (2012XCL035)Qing Lan Project of Jiangsu Province.
文摘A rapid,simple and cost-effective polyol method has been developed for the synthesis of silver nanowires with high aspect ratio and high purity.The aspect ratios of the silver nanowires as high as ca.1000(average length 40μm and some even as long as 80μm,diameter 50-100 nm)were obtained via optimizing the reaction conditions.Transparent electrodes with excellent optoelectronic performances(optical transmittance of 90%,sheet resistance of 23.2Ω/□and optical transmittance of 87%,sheet resistance of 19.7Ω/□)comparable to commercial ITO were fab-ricated via simple spin coating the resulting silver nanowires onto the glass substrates.The high optoelectronic per-formances and the facile all-solution process of the as-prepared transparent electrodes render them rather promising candidates for use in cost-effective large-area optoelectronic devices.
基金supported by the National Natural Science Foundation of China(Nos.11302011,11172025)the National Natural Science Foundation for Youth of China(No.11402013)
文摘A theoretical nonlinear aeroelastic response analysis for a flexible high-aspect ratio wing excited by harmonic gust load is presented along with a companion wind tunnel test. A multidisci- plinary coupled numerical calculation is developed to simulate the flexible model wing undergoing gust load in the time domain via discrete nonlinear finite element structural dynamic analysis and nonplanar unsteady vortex lattice aerodynamic computation. A dynamic perturbation analysis about a nonlinear static equilibrium is also used to determine the small perturbation flutter bound- ary. A novel noncontact 3-D camera measurement analysis system is firstly used in the wind tunnel test to obtain the spatial large deformation and responses. The responses of the flexible wing under different static equilibrium states and frequency gust loads are discussed. The fair to good quanti- tative agreements between the theoretical and experimental results demonstrate that the presented analysis method is an acceptable way to predict the geometrically nonlinear gust response for flex- ible wings.
文摘In order to analyze the effects of forward-swept angle and skin ply-orientation on the static and dynamic aeroelastic characteristics, the aeroelastic modeling and calculation for high-aspect-ratio composite wings with different forward-swept angles and skin ply-orientation are performed. This paper presents the results of a design study aiming to optimize wings with typical forward-swept angles and skin ply-orientation in an aeroelastic way by using the genetic/sensitivity-based hybrid algorithm. Under the conditions of satiated multiple constraints including strength, displacements, divergence speeds and flutter speeds, the studies are carried out in a bid to minimize the structural weight of a wing with the lay-up thicknesses of wing components as design variabies. In addition, the effects of the power of spanwise variation function of lay-up thicknesses of skins and iugs on the optimized weights are also analyzed.
文摘A unified structural model for high-aspect-ratio composite wing with arbitrary cross-section is developed. Two types of lay-ups of the composite wing, namely, circumferentially uniform stiffness （CUS） configuration and circumferentially asymmetric stiffness （CAS） configuration, are investigated. The present structural modeling method is validated through ANSYS FEM software for the case of a composite box beam. Then, the case of a single-cell composite wing with NACA0012 airfoil shape is considered. To investigate the aeroelastic problem of high-aspect-ratio composite wings, the linear ONERA aerodynamic model is used to model the unsteady aerodynamic loads under the case of small angle of attack. Finally, flutter speeds of the high-aspect-ratio wing with various composite ply angles are determined by using U-g method.
文摘The stall flutter characters of high-aspect-ratio composite wing are investigated, and the effects of structure geometric nonlinearity and stiffness couple created by composite anisotropy on them also are discussed. Firstly, the high-aspect-ratio wing is modeled as a composite thin-walled closed section Euler beam whose displacement and rotation both could be of finite value, and the nonlinear dynamic equations is build up on it with all the effects of geometric nonlinearity, aerodynamic nonlinearity and anisotropy of material being considered. Then vibration equations are deduced through perturbing the dynamic equations at wing＇s equilibrium position, and coupled with unsteady stall aerodynamic model and ONERA model, to obtain the nonlinear stall flutter analysis equations of wing. Finally, the flutter stabilities with various wind speeds are determined by the harmonic balance method. With several exampies, the validity of the stall flutter model is proved, and the significant effects of geometric nonlinearity on the stall flutter various characters as wall as the effects of ply angle on the stall flutter speed and frequency also are discussed.
基金Projects(50675070 50805052) supported by the National Nature Science Foundation of China+1 种基金Projects(07118064 8451064101000320) supported by the Natural Science Foundation of Guangdong Province
文摘A high-aspect-ratio microchannel heat exchanger based on multi-tool milling process was developed. Several slotting cutters were stacked together for simultaneously machining several high-aspect-ratio microchannels with manifold structures. On the basis of multi-tool milling process, the structural design of the manifold side height, microchannel length, width, number, and interval were analyzed. The heat transfer performances of high-aspect-ratio microchannel heat exchangers with two different manifolds were investigated by experiments, and the influencing factors were analyzed. The results indicate that the magnitude of heat transfer area per unit volume dominates the heat transfer performances of plate-type micro heat exchanger, while the velocity distribution between microchannels has little effects on the heat transfer performances.
基金supported by the National Natural Science Foundation of China (Nos.11302011,11372023, 11172025)
文摘The relationship between stiffness distribution and aeroelastic performance for a beam-frame model and a3-D model is investigated based on aeroelastic optimization of global stiffness design for high-aspect-ratio wings.The sensitivity information of wing spanwise stiffness distribution with respect to the twist angle at wing tip,the vertical displacement at wing tip,and the flutter speed are obtained using a sensitivity method for both models.Then the relationship between stiffness distribution and aeroelastic performance is summarized to guide the design procedure.By using the genetic/sensitivity-based hybrid algorithm,an optimal solution satisfying the strength,aeroelastic and manufacturing constraints is obtained.It is found that the summarized guidance is well consistent with the optimal solution,thus providing a valuable design advice with efficiency.The study also shows that the aeroelastic-optimization-based global stiffness design procedure can obtain the optimal solution under multiple constraints with high efficiency and precision,thereby having a strong application value in engineering.
文摘Filling high-aspect-ratio trenches with gold is a frequent requirement in the fabrication of X-ray optics as well as micro-electronic components and other fabrication processes. Conformal electrodeposition of gold in sub-micron-width silicon trenches with an aspect ratio greater than 35 over a grating area of several square centimeters is challenging and has not been described in the literature previously. A comparison of pulsed plating and constant current plating led to a gold electroplating protocol that reliably filled trenches for such structures.
文摘For the strong coupling among the channels of bank-to-turn （BTT） missile with high-aspect-ratio wing, an autopilot is designed with a two loop control structure robust autopilot design methods. By the inner loop design, the question of pole-zero cancellation is solved, and the stabilization of structured uncertainty is achieved. Through the outer loop of H∞ controller design, the flying performance and robustness can be guaranteed. The nonlinear simulation results show that the autopilot designed has perfect time domain response, and can suppress bad influence of the inertial and kinematics couplings. It can make the missile fly stably in the large flying areas. The control is very effective.
