Glucose molecules are of great significance being one of the most important molecules in metabolic chain.However,due to the small Raman scattering cross-section and weak/non-adsorption on bare metals,accurately obtain...Glucose molecules are of great significance being one of the most important molecules in metabolic chain.However,due to the small Raman scattering cross-section and weak/non-adsorption on bare metals,accurately obtaining their"fingerprint information"remains a huge obstacle.Herein,we developed a tip-enhanced Raman scattering(TERS)technique to address this challenge.Adopting an optical fiber radial vector mode internally illuminates the plasmonic fiber tip to effectively suppress the background noise while generating a strong electric-field enhanced tip hotspot.Furthermore,the tip hotspot approaching the glucose molecules was manipulated via the shear-force feedback to provide more freedom for selecting substrates.Consequently,our TERS technique achieves the visualization of all Raman modes of glucose molecules within spectral window of 400-3200 cm^(-1),which is not achievable through the far-field/surface-enhanced Raman,or the existing TERS techniques.Our TERS technique offers a powerful tool for accurately identifying Raman scattering of molecules,paving the way for biomolecular analysis.展开更多
Fiber-reinforced composites are an ideal material for the lightweight design of aerospace structures. Especially in recent years, with the rapid development of composite additive manufacturing technology, the design o...Fiber-reinforced composites are an ideal material for the lightweight design of aerospace structures. Especially in recent years, with the rapid development of composite additive manufacturing technology, the design optimization of variable stiffness of fiber-reinforced composite laminates has attracted widespread attention from scholars and industry. In these aerospace composite structures, numerous cutout panels and shells serve as access points for maintaining electrical, fuel, and hydraulic systems. The traditional fiber-reinforced composite laminate subtractive drilling manufacturing inevitably faces the problems of interlayer delamination, fiber fracture, and burr of the laminate. Continuous fiber additive manufacturing technology offers the potential for integrated design optimization and manufacturing with high structural performance. Considering the integration of design and manufacturability in continuous fiber additive manufacturing, the paper proposes linear and nonlinear filtering strategies based on the Normal Distribution Fiber Optimization (NDFO) material interpolation scheme to overcome the challenge of discrete fiber optimization results, which are difficult to apply directly to continuous fiber additive manufacturing. With minimizing structural compliance as the objective function, the proposed approach provides a strategy to achieve continuity of discrete fiber paths in the variable stiffness design optimization of composite laminates with regular and irregular holes. In the variable stiffness design optimization model, the number of candidate fiber laying angles in the NDFO material interpolation scheme is considered as design variable. The sensitivity information of structural compliance with respect to the number of candidate fiber laying angles is obtained using the analytical sensitivity analysis method. Based on the proposed variable stiffness design optimization method for complex perforated composite laminates, the numerical examples consider the variable stiffness design optimization of typical non-perforated and perforated composite laminates with circular, square, and irregular holes, and systematically discuss the number of candidate discrete fiber laying angles, discrete fiber continuous filtering strategies, and filter radius on structural compliance, continuity, and manufacturability. The optimized discrete fiber angles of variable stiffness laminates are converted into continuous fiber laying paths using a streamlined process for continuous fiber additive manufacturing. Meanwhile, the optimized non-perforated and perforated MBB beams after discrete fiber continuous treatment, are manufactured using continuous fiber co-extrusion additive manufacturing technology to verify the effectiveness of the variable stiffness fiber optimization framework proposed in this paper.展开更多
The lack of autonomous take-off and landing capabilities of bird-like flapping-wing aerial vehicles(BFAVs)seriously restricts their further development and application.Thus,combined with the current research results o...The lack of autonomous take-off and landing capabilities of bird-like flapping-wing aerial vehicles(BFAVs)seriously restricts their further development and application.Thus,combined with the current research results on the autonomous take-off and landing technology of unmanned aerial vehicles,four types of technologies are studied,including jumping take-off and landing technology,taxiing take-off and landing technology,gliding take-off and landing technology,and vertical take-off and landing(VTOL)technology.Based on the analytic hierarchy process(AHP)-comprehensive evaluation method,a fuzzy comprehensive evaluation model for the autonomous take-off and landing scheme of a BFAV is established,and four schemes are evaluated concretely.The results show that under the existing technical conditions,the hybrid layout VTOL scheme is the best.Furthermore,the detailed design and development of the prototype of a BFAV with a four-rotor hybrid layout are carried out,and the vehicle performance is tested.The results prove that through the four-rotor hybrid layout design,the BFAV has good autonomous take-off and landing abilities.The power consumption analysis shows that for a fixed-point reconnaissance mission,when the mission radius is less than 3.38 km,the VTOL type exhibits longer mission duration than the hand-launched type.展开更多
Wingtip slots,where the outer primary feathers of birds split and spread vertically,are regarded as an evolved favorable feature that could effectively improve their aerodynamic performance.They have inspired many to ...Wingtip slots,where the outer primary feathers of birds split and spread vertically,are regarded as an evolved favorable feature that could effectively improve their aerodynamic performance.They have inspired many to perform experiments and simulations as well as to relate their results to aircraft design.This paper aims to provide guidance for the research on the aerodynamic mechanism of wingtip slots.Following a review of previous wingtip slot research,four imperfections are put forward:vacancies in research content,inconsistencies in research conclusions,limitations of early research methods,and shortage of the aerodynamic mechanism analysis.On this basis,further explorations and expansion of the influence factors for steady state are needed;more attention should be poured into the application of flow field integration method to decompose drag,and evaluation of variation in induced drag seems a more rational choice.Geometric and kinematic parameters of wingtip slot structure in the unsteady state,as well as the flexibility of wingtips,should be taken into account.As for the aerodynamic mechanism of wingtip slots,the emphasis can be placed on the study of the formation,development,and evolution of wingtip vortices on slotted wings.Besides,some research strategies and feasibility analyses are proposed for each part of the research.展开更多
The slotted wingtip structure of birds is considered to be the product of improving flight efficiency in the process of evolution. It can change the vortex structure of wingtip and improve aerodynamic efficiency. This...The slotted wingtip structure of birds is considered to be the product of improving flight efficiency in the process of evolution. It can change the vortex structure of wingtip and improve aerodynamic efficiency. This paper reports a numerical investigation of slotted wing configuration undergoing bio-inspired flapping kinematics(consisting of plunging and in-line movement)extracted from a free-flying bald eagle wing. The aim is to eluci-date the collective mechanism of the flow generated by slotted tips and the lift contribution of each tip. Specifi-cally, the objective of the study is to determine how changes in the wing spacing affect the resulting aerodynamic interaction between the slotted tips and how that affects the force generation and efficiency. Changes in the phase angle between the flapping motions of slotted tips, as well as the spacings among them,can affect the resulting vortex inter-actions. The rear tips often operates in the wake of the frontal tips and, meanwhile, the vortex generated by the movement of the rear tips promote the frontal tips.The interaction of vortices in time and space leads to wing-wing interference and the flow around slotted tips becomes complicated and unstable. The innovative study of wingtip slot in unsteady state leads us to find that the aerodynamic interaction among slotted tips makes the overall lift characteristic better than that of the unslotted wings. The slotted wing configuration can efficiently convert more energy into lift. As the flapping frequency increases, the collective feature of slotted wing with constantly changing gaps can be more advantageous to enhance lift-generation performance.展开更多
A ground girder is laid on the preprocessed subgrade by gravity compaction and integrally uniformly supported by subgrade in maglev transit.The settlement of the maglev subgrade inevitably affects the vibration state ...A ground girder is laid on the preprocessed subgrade by gravity compaction and integrally uniformly supported by subgrade in maglev transit.The settlement of the maglev subgrade inevitably affects the vibration state of the medium and low speed maglev coupled system by the additional deformation of the maglev track.This study investigated the dynamic properties of the coupled vibration system affected by the subgrade settlement.First,a theoretical coupled vibration model of a maglev train-track-ground girder system with uneven subgrade settlement was proposed and verified.Then,the effect mechanism of the coupled system caused by the uneven subgrade settlement was explored.Finally,settlement types and subgrade support voiding were examined.The analysis showed that the uneven subgrade settlement considerably increased the dynamic responses of the levitation control system and maglev vehicle while having a minor influence on those of the track-ground girder.The influence of a single ground girder settling was the strongest,and adjacent sides’settling of two ground girders was the weakest for the vibration of a maglev train.An extremely large uneven settlement exceeding 6 mm led to active levitation control system instability.The subgrade support voiding enlarged the vehicle-induced vibration of the track ground girder.展开更多
Molecular catalysts can effectively steer the electrocatalytic acetylene semihydrogenation into ethylene,but realizing high Faradaic efficiency(FE)at industrial current densities remains a challenge.Herein,we report a...Molecular catalysts can effectively steer the electrocatalytic acetylene semihydrogenation into ethylene,but realizing high Faradaic efficiency(FE)at industrial current densities remains a challenge.Herein,we report a ligand engineering strategy that utilizes polymeric N–heterocyclic carbene(NHC)as a hydrophobic ligand to modulate the microenvironment of Cu sites.This polymeric NHC imparts appropriate hydrophobic properties for the chelated Cu sites,thereby moderating the H_(2)O transport and enabling easy access of acetylene.Consequently,the polymeric NHC chelated Cu exhibits an FE_(ethylene)of~97%at a current density of 500 m A/cm^(2)in a flow cell.Particularly in a zero-gap reactor,the FE_(ethylene)consistently exceeds 86%across current densities from 100 m A/cm^(2)to 400 m A/cm^(2),reaching an optimal FEethyleneof 98%at 200 m A/cm^(2)and achieving durable operation for 155 h at 100 m A/cm^(2).This work provides a promising paradigm to regulate the microenvironment of molecular catalysts for improving electrocatalytic performances under industrial current densities.展开更多
Lead-tin(Pb-Sn)perovskites with an ideal bandgap of 1.34-1.40 eV show great promise in perovskite solar cells(PSCs).Recently,to address the environmental pollution and Sn^(2+)oxidation problems of dimethyl sulfoxide,m...Lead-tin(Pb-Sn)perovskites with an ideal bandgap of 1.34-1.40 eV show great promise in perovskite solar cells(PSCs).Recently,to address the environmental pollution and Sn^(2+)oxidation problems of dimethyl sulfoxide,methylammonium acetate(MAAc)ionic liquid has been developed as an alternative to fabricate ideal bandgap MAPb_(0.7)Sn_(0.3)I_(3)(1.36 eV)film via hot-casting in air.However,the spontaneous crystallization of Pb-Sn perovskite initiated by heat-induced supersaturation is fast and random,setting critical challenges in regulating crystal growth during the film-forming process.Herein,a lattice activation strategy is developed to control the crystallization dynamics of MAPb_(0.7)Sn_(0.3)I_(3)in MAAc to produce films with micrometer-sized grains in air.FA is shown to activate the crystal lattice that facilitates the formation of intermediates and balances the crystal growth of MAPb_(0.7)Sn_(0.3)I_(3),producing films with a grain size of 2.78±0.17μm.Furthermore,4-fluoro-phenethylammonium and phenethylammonium are adopted to passivate the defects in the film and promote the energy level alignment at the top interface,respectively.The optimized PSC device achieved an efficiency of 18.24%with a short-circuit current of 29.84 mA/cm^(2),which are both the highest values in 1.36 eV Pb-Sn PSCs to date.Notably,the unencapsulated devices show excellent storage and air stability under various conditions.展开更多
Hetero-structured thermally conductive spherical boron nitride and boron nitride nanosheets(BNN-30@BNNS)fillers were prepared via electro static self-assembly method.And the corresponding thermally conductive&elec...Hetero-structured thermally conductive spherical boron nitride and boron nitride nanosheets(BNN-30@BNNS)fillers were prepared via electro static self-assembly method.And the corresponding thermally conductive&electrically insulating BNN-30@BNNS/Si-GFs/E-44 laminated composites were then fabricated via hot compression.BNN-30@BNNS-Ⅲ(fBNN-30/fBNNS,1/2,wt/wt)fillers presented the optimal synergistic improvement effects on the thermal conductivities of epoxy composites.When the mass fraction of BNN-30@BNNS-Ⅲwas 15 wt%,λvalue of the BNN-30@BNNS-Ⅲ/E-44 composites was up to0.61 W m^(-1)K^(-1),increased by 2.8 times compared with pure E-44(λ=0.22 W m^(-1)K^(-1)),also higher than that of the 15 wt%BNN-30/E-44(0.56 W m^(-1)K^(-1)),15 wt%BNNS/E-44(0.42 W m^(-1)K^(-1)),and 15 wt%(BNN-30/BNNS)/E-44(direct blending BNN-30/BNNS hybrid fillers,1/2,wt/wt,0.49 W m^(-1)K^(-1))composites.Theλin-plane(λ//)andλcross-plane(λ_(⊥))of 15 wt%BNN-30@BNNS-Ⅲ/Si-GFs/E-44 laminated composites significantly reached 2.75 W m^(-1)K^(-1)and 1.32 W m^(-1)K^(-1),186.5%and 187.0%higher than those of Si-GFs/E-44 laminated composites(λ//=0.96 W m^(-1)K^(-1)andλ_(⊥)=0.46 W m^(-1)K^(-1)).Established models can well simulate heat transfer efficiency in the BNN-30@BNNS-Ⅲ/Si-GFs/E-44 laminated composites.Under the condition of point heat source,the introduction of BNN-30@BNNS-Ⅲfillers were conducive to accelerating heat flow trans fe r.BNN-30@BNNS-Ⅲ/Si-GFs/E-44 laminated composites also demonstrated outstanding electrical insulating properties(cross-plane withstanding voltage,breakdown strength,surface&volume resistivity of 51.3 kV,23.8 kV mm^(-1),3.7×10^(14)Ω&3.4×10^(14)Ω·cm,favorable mechanical properties(flexural strength of 401.0 MPa and ILSS of 22.3 MPa),excellent dielectric properties(εof 4.92 and tanδof 0.008)and terrific thermal properties(T_(g)of 167.3℃and T_(HRI)of 199.2℃).展开更多
Distribution control and formation mechanism of gas inclusions formed in directionally solidified Al2O3-Er3Al5O12-ZrO2 eutectic ceramic rods are explored during laser floating zone melting. In atmospheric environment,...Distribution control and formation mechanism of gas inclusions formed in directionally solidified Al2O3-Er3Al5O12-ZrO2 eutectic ceramic rods are explored during laser floating zone melting. In atmospheric environment, highly-dense bubble-free eutectic rods are well fabricated at low solidification rate(<25μm/s). Gas inclusions form intermittently when the solidification rate is in the range of 25-50 μm/s,but produce continuously at higher solidification rates(100-200 μm/s). The gas inclusions exhibit an elongated finger-like pattern along the growth direction, which of the maximum value of diameter first increases and then decreases with increasing the solidification rate. Meanwhile, the volume fraction of gas inclusions increased gradually with the solidification rate. Based on the effect of surface tension gradient, heterogeneous nucleation of gas bubbles is evaluated to be the primary formation mechanism of gas inclusions.展开更多
The bent double-ridged rectangular tube(DRRT)with high forming quality is helpful to improve the microwave transmission accuracy.For reducing the cross-sectional deformation in the H-typed bending process,in addition ...The bent double-ridged rectangular tube(DRRT)with high forming quality is helpful to improve the microwave transmission accuracy.For reducing the cross-sectional deformation in the H-typed bending process,in addition to using rigid mandrel to support the inside of tube,ridge groove fillers are also added to restrict the deformation of ridge grooves.Because of the change of stress and strain state of bent tube in bending,rigid mandrel retracting and specially twicespringback stages,and the springback of fillers,the cross-sectional deformation of tube in each stage may be different.Therefore,based on the ABAQUS platform,the finite element models(FEM)for H-typed bending,mandrel retracting and twice-springback stages of H96 DRRT with fillers were established and validated.It is found that,for the height and width deformation of tube and spacing deformation of ridge grooves,retraction of mandrel can make the distribution of these deformations more uniform along the bending direction.The first springback can reduce these deformations significantly,which should be emphasized.But the second springback only increases them by less amount,which can be ignored.The smaller height deformation of ridge groove and filler can be neglected.展开更多
The force-generation mechanism of a dovelike flapping-wing micro air vehicle was studied by numerical simulation and experiment.To obtain the real deformation pattern of the flapping wing,the digital image correlation...The force-generation mechanism of a dovelike flapping-wing micro air vehicle was studied by numerical simulation and experiment.To obtain the real deformation pattern of the flapping wing,the digital image correlation technology was used to measure the dynamic deformation of the wing.The dynamic deformation data were subsequently interpolated and embedded into the CFD solver to account for the aeroelastic effects.The dynamic deformation data were further used to calculate the inertial forces by regarding the wing as a system of particles to take into account the wing flexibility.The temporal variation of the forces produced by the flapping wing was measured by a miniature load cell.The numerical results provide more flow details of the unsteady aerodynamics of the flapping wing in terms of vortex formation and evolution.The calculated results of the inertial forces are analyzed and compared with the CFD results which represent the aerodynamic forces.In addition,the total forces,i.e.,the sum of the CFD result and inertial result,are compared with the experimental results,and an overall good agreement is obtained.展开更多
Natural flyers have extraordinary flight skills and their prominent aerodynamic performance has attracted a lot of attention.However,the aerodynamic mechanism of birds’flapping wing kinematics still lacks in-depth un...Natural flyers have extraordinary flight skills and their prominent aerodynamic performance has attracted a lot of attention.However,the aerodynamic mechanism of birds’flapping wing kinematics still lacks in-depth understanding.In this paper,the aerodynamic performance of owl-like airfoil undergoing bio-inspired flapping kinematics extracted from a free-flying owl wing has been numerically investigated.The overset mesh technique is used to deal with the large range movements of flapping airfoils.The bio-inspired kinematics consist of plunging and pitching movement.A pure sinusoidal motion and a defined motion composed of plunging of sinusoidal motion and pitching of the bio-inspired kinematics are selected for comparison.The other two NACA airfoils are also selected to figure out the advantages of the owl-like airfoil.It is found that the cambered owl-like airfoil can enhance lift during the downstroke.The bio-inspired kinematics have an obvious advantage in lift generation with a presence of higher peak lift and positive lift over a wider proportion of the flapping cycle.Meanwhile,the bio-inspired motion is more economical for a lower power consumption compared with the sinusoidal motion.The sinusoidal flapping motion is better for thrust generation for a higher peak thrust value in both upstroke and downstroke,while the bio-inspired kinematics mainly generate thrust during the downstroke but produce more drag during the upstroke.The defined motion has similar lift performance with the bio-inspired kinematics,while it consumes more energy and generates less thrust.The unsteady flow field around airfoils is also analyzed to explain the corresponding phenomenon.The research in this paper is helpful to understand the flight mechanism of birds and to design a micro air vehicle with higher performance.展开更多
This paper establishes and analyzes a high-fidelity nonlinear time-periodic dynamic model and the corresponding state observer for flapping vibration suppression of a novel tailless Flapping Wing Micro Air Vehicle(FWM...This paper establishes and analyzes a high-fidelity nonlinear time-periodic dynamic model and the corresponding state observer for flapping vibration suppression of a novel tailless Flapping Wing Micro Air Vehicle(FWMAV),named NPU-Tinybird.Firstly,a complete modeling of NPU-Tinybird is determined,including the aerodynamic model based on the quasi-steady method,the kinematic and dynamic model about the mechanism of flapping and attitude control,combined with the single rigid body dynamic model.Based on this,a linearized longitudinal pitch dynamic cycle-averaged model is obtained and analyzed through the methods of neural network fitting and system identification,preparing for the design of flapping vibration suppression observer.Flapping vibration is an inherent property of the tailless FWMAV,which arises from the influence of time-periodic aerodynamic forces and moments.It can be captured by attitude and position sensors on the plane,which impairs the flight performance and efficiency of flight controller and actuators.To deal with this problem,a novel state observer for flapping vibration suppression is designed.A robust optimal controller based on the linear quadratic theory is also designed to stabilize the closed-loop system.Simulation results are given to verify the performance of the observer,including the closed loop responses combined with robust optimal controller,the comparison of different parameters of observer and the comparison with several classic methods,such as Kalman filter,H-infinity filter and low-pass filter,which prove that the novel observer owns a fairly good suppression effect on flapping vibration and benefits for the improvement of flight performance and control efficiency.展开更多
A novel AlCoCrFeNi2.1 eutectic high entropy alloy(EHEA)composite doped with SiC particles was designed and fabricated by laser powder bed fusion(LPBF).Its microstructure characteristic,tensile properties,and metallurg...A novel AlCoCrFeNi2.1 eutectic high entropy alloy(EHEA)composite doped with SiC particles was designed and fabricated by laser powder bed fusion(LPBF).Its microstructure characteristic,tensile properties,and metallurgical defects,with an emphasis on cracking behavior,have been investigated.The results showed that the addition of SiC particles into the AlCoCrFeNi_(2.1)matrix enabled the development of a{100}texture and highly elongated columnar grains,which were the main contributors to mechanical behavior anisotropy.The ultimate tensile strength of 1466±26 MPa and elongation of 9%±3%achieved in the as-deposited EHEA composite surpassed those of advanced metal alloys subjected to additive manufacturing processes.Unfortunately,severe horizontal and longitudinal cracks,as well as a few micro-cracks were observed in the as-deposited bulk samples.Micro-cracks were verified to be associated with the aggregation of carbon and oxide particles.They formed in the final stage of solidification owing to insufficient liquid feeding ability and solidification contraction.The formation of macroscopic cracking was induced by the tensile stress accumulations at sample edges,and the stress concentration areas where microcracks and pores were located were the predominant propagation location.This work provides guidelines for defect control in SiC-reinforced EHEA,assisting in the high-performance design and integrated manufacturing of EHEA composite components.展开更多
Al–Co–Cr–Fe–Ni high entropy alloy(HEA) system is a newly developed category of metallic materials possessing unique microstructure, mechanical and functional properties, which presents many promising industrial ap...Al–Co–Cr–Fe–Ni high entropy alloy(HEA) system is a newly developed category of metallic materials possessing unique microstructure, mechanical and functional properties, which presents many promising industrial applications. In recent years, additive manufacturing technology has given rise to a great potential for fabricating HEA parts of ultra-fine grains and geometrical complexity, thereby attracting great interest of researchers. Herein, a comprehensive review emphasizes on the recent developments in high-energy beam additive manufacturing of Al–Co–Cr–Fe–Ni HEA, in the aspects of their printing processes, microstructures, properties, defects, and post treatments. The technical characteristics of three typical high-energy beam additive manufacturing technologies for printing HEA, namely, selective laser melting(SLM), selective electron beam melting(SEBM), and directed energy deposition(DED) are systematically summarized. Typical crystal structure, grain, microstructure, as well as corresponding properties of Al–Co–Cr–Fe–Ni HEA manufactured by those technologies are primarily presented and discussed. It also elaborates the formation mechanisms of harmful defects related to the rapid solidification and complex thermal cycle during high-energy beam additive manufacturing. Furthermore, several kinds of post treatments with an aim to improve performance of HEA are illustrated. Finally, future research directions for HEA by additive manufacturing are outlined to tackle current challenges and accelerate their applications in industrial fields.展开更多
Polymer-dispersed liquid crystal(PDLC)films comprising polyvinyl alcohol(PVA)and liquid crystal monomer(LCM)were successfully obtained by the method of solution casting&thermal compressing.LCM was distributed orde...Polymer-dispersed liquid crystal(PDLC)films comprising polyvinyl alcohol(PVA)and liquid crystal monomer(LCM)were successfully obtained by the method of solution casting&thermal compressing.LCM was distributed orderly in PVA matrix by hydrogen bond interaction,to form PVA-LCM interpe net rating-layered networks.When the mass fraction of LCM was up to 35 wt%,the corresponding in-plane thermal conductivity coefficient(λ//)of PDLC film was significantly increased to 1.41 W m^(-1)K^(-1),about 10.8 times that of neat PVA(0.13 W m^(-1)K^(-1)).High intrinsicλ//values of PDLC films were mainly attributed to the formed microscopic-ordered structures from ordered stacking of LCM,ordered arrangement of PVA chains,and their hydrogen bond interaction.This work would offer a new way to design and prepare novel intrinsic high thermal conductive polymers.展开更多
Crystallographic texture control is a major challenge in directionally solidified multiphase eutectic ceramics with complex faceted growth characteristics.In this study,the Czochralski(CZ)technique is proposed to prep...Crystallographic texture control is a major challenge in directionally solidified multiphase eutectic ceramics with complex faceted growth characteristics.In this study,the Czochralski(CZ)technique is proposed to prepare eutectic single crystal ceramic with large size(30 mm×125 mm).A highly oriented and unique texture of Al_(2)O_(3)/Y_(3)Al_(5)O_(12)(YAG)eutectic ceramic is formed via the 112¯0Al_(2)O_(3) single crystal seed induction based on crystallographic orientation tailoring.The orientations of Al_(2)O_(3)/YAG eutectic are more strictly constrained by single crystal seed induction on the basis of the minimum interface energy principle,resulting in a defined single orientation relationship along the solidification direction.In particular,the single crystallographic orientation can be obtained in a short competitive solidification distance under the influence of epitaxial solidification from single crystal seed.Therefore,it has been confirmed that the orientations of 112¯0Al_(2)O_(3) and 111YAG are preferentially stabilized with the minimum under-cooling during directional solidification.Crystallographic orientation disturbances and instabilities due to polycrystalline crystal seed are avoided.Finally,the successful texture control inducted by 112¯0Al_(2)O_(3) single crystal seed can provide a promising orientation design pathway for faced oxide eutectic solidification.展开更多
This paper presents the results of a numerical study of the effects of swirling flow in coolant jets on film cooling performance.Some combined-hole designs with swirling coolant flow entering the delivery hole are pro...This paper presents the results of a numerical study of the effects of swirling flow in coolant jets on film cooling performance.Some combined-hole designs with swirling coolant flow entering the delivery hole are proposed and analyzed.Adiabatic film cooling effectiveness values for cases with various blowing ratios are compared.Detailed flow structures and underlying mechanisms are discussed.The results show that film cooling effectiveness is improved with jet swirl at high blowing ratios,and that swirl strength has significant influence on film cooling performance.Combined-hole designs can further improve film cooling performance using swirling jets due to mixing of coolant flows and interaction of vortices.The largest improvements of area-averaged film cooling effectiveness for a single-hole swirl case and a combined-hole swirl case over corresponding non-swirling case results are 157%and 173%,respectively.展开更多
基金supported by National Natural Science Foundation of China(12374358,91950207)Guangdong Basic and Applied Basic Research Foundation(2024A1515010420).
文摘Glucose molecules are of great significance being one of the most important molecules in metabolic chain.However,due to the small Raman scattering cross-section and weak/non-adsorption on bare metals,accurately obtaining their"fingerprint information"remains a huge obstacle.Herein,we developed a tip-enhanced Raman scattering(TERS)technique to address this challenge.Adopting an optical fiber radial vector mode internally illuminates the plasmonic fiber tip to effectively suppress the background noise while generating a strong electric-field enhanced tip hotspot.Furthermore,the tip hotspot approaching the glucose molecules was manipulated via the shear-force feedback to provide more freedom for selecting substrates.Consequently,our TERS technique achieves the visualization of all Raman modes of glucose molecules within spectral window of 400-3200 cm^(-1),which is not achievable through the far-field/surface-enhanced Raman,or the existing TERS techniques.Our TERS technique offers a powerful tool for accurately identifying Raman scattering of molecules,paving the way for biomolecular analysis.
基金supports for this research were provided by the National Natural Science Foundation of China(No.12272301,12002278,U1906233)the Guangdong Basic and Applied Basic Research Foundation,China(Nos.2023A1515011970,2024A1515010256)+1 种基金the Dalian City Supports Innovation and Entrepreneurship Projects for High-Level Talents,China(2021RD16)the Key R&D Project of CSCEC,China(No.CSCEC-2020-Z-4).
文摘Fiber-reinforced composites are an ideal material for the lightweight design of aerospace structures. Especially in recent years, with the rapid development of composite additive manufacturing technology, the design optimization of variable stiffness of fiber-reinforced composite laminates has attracted widespread attention from scholars and industry. In these aerospace composite structures, numerous cutout panels and shells serve as access points for maintaining electrical, fuel, and hydraulic systems. The traditional fiber-reinforced composite laminate subtractive drilling manufacturing inevitably faces the problems of interlayer delamination, fiber fracture, and burr of the laminate. Continuous fiber additive manufacturing technology offers the potential for integrated design optimization and manufacturing with high structural performance. Considering the integration of design and manufacturability in continuous fiber additive manufacturing, the paper proposes linear and nonlinear filtering strategies based on the Normal Distribution Fiber Optimization (NDFO) material interpolation scheme to overcome the challenge of discrete fiber optimization results, which are difficult to apply directly to continuous fiber additive manufacturing. With minimizing structural compliance as the objective function, the proposed approach provides a strategy to achieve continuity of discrete fiber paths in the variable stiffness design optimization of composite laminates with regular and irregular holes. In the variable stiffness design optimization model, the number of candidate fiber laying angles in the NDFO material interpolation scheme is considered as design variable. The sensitivity information of structural compliance with respect to the number of candidate fiber laying angles is obtained using the analytical sensitivity analysis method. Based on the proposed variable stiffness design optimization method for complex perforated composite laminates, the numerical examples consider the variable stiffness design optimization of typical non-perforated and perforated composite laminates with circular, square, and irregular holes, and systematically discuss the number of candidate discrete fiber laying angles, discrete fiber continuous filtering strategies, and filter radius on structural compliance, continuity, and manufacturability. The optimized discrete fiber angles of variable stiffness laminates are converted into continuous fiber laying paths using a streamlined process for continuous fiber additive manufacturing. Meanwhile, the optimized non-perforated and perforated MBB beams after discrete fiber continuous treatment, are manufactured using continuous fiber co-extrusion additive manufacturing technology to verify the effectiveness of the variable stiffness fiber optimization framework proposed in this paper.
基金supported in part by the National Key Research and Development Program of China(No.2017YFB1300102)the Key R&D Program in Shaanxi Province of China(No.2020ZDLGY06-05,No 2021ZDLGY09-10)the National Natural Science Foundation of China(No.11902103,No.11872314).
文摘The lack of autonomous take-off and landing capabilities of bird-like flapping-wing aerial vehicles(BFAVs)seriously restricts their further development and application.Thus,combined with the current research results on the autonomous take-off and landing technology of unmanned aerial vehicles,four types of technologies are studied,including jumping take-off and landing technology,taxiing take-off and landing technology,gliding take-off and landing technology,and vertical take-off and landing(VTOL)technology.Based on the analytic hierarchy process(AHP)-comprehensive evaluation method,a fuzzy comprehensive evaluation model for the autonomous take-off and landing scheme of a BFAV is established,and four schemes are evaluated concretely.The results show that under the existing technical conditions,the hybrid layout VTOL scheme is the best.Furthermore,the detailed design and development of the prototype of a BFAV with a four-rotor hybrid layout are carried out,and the vehicle performance is tested.The results prove that through the four-rotor hybrid layout design,the BFAV has good autonomous take-off and landing abilities.The power consumption analysis shows that for a fixed-point reconnaissance mission,when the mission radius is less than 3.38 km,the VTOL type exhibits longer mission duration than the hand-launched type.
基金support from National Natural Science Foundation of China(Grant 11872314 and U1613227)Youth Program of Natural Science Basic Research Plan in Shaanxi Province of China(Grant 2019JQ-394)Key R&D Program in Shaanxi Province of China(Grant 2020GY-154).
文摘Wingtip slots,where the outer primary feathers of birds split and spread vertically,are regarded as an evolved favorable feature that could effectively improve their aerodynamic performance.They have inspired many to perform experiments and simulations as well as to relate their results to aircraft design.This paper aims to provide guidance for the research on the aerodynamic mechanism of wingtip slots.Following a review of previous wingtip slot research,four imperfections are put forward:vacancies in research content,inconsistencies in research conclusions,limitations of early research methods,and shortage of the aerodynamic mechanism analysis.On this basis,further explorations and expansion of the influence factors for steady state are needed;more attention should be poured into the application of flow field integration method to decompose drag,and evaluation of variation in induced drag seems a more rational choice.Geometric and kinematic parameters of wingtip slot structure in the unsteady state,as well as the flexibility of wingtips,should be taken into account.As for the aerodynamic mechanism of wingtip slots,the emphasis can be placed on the study of the formation,development,and evolution of wingtip vortices on slotted wings.Besides,some research strategies and feasibility analyses are proposed for each part of the research.
基金the support from the National Natural Science Foundation of China(Nos.11872314 and U1613227)the Key R&D Program in Shaanxi Province of China(No.2020GY-154)。
文摘The slotted wingtip structure of birds is considered to be the product of improving flight efficiency in the process of evolution. It can change the vortex structure of wingtip and improve aerodynamic efficiency. This paper reports a numerical investigation of slotted wing configuration undergoing bio-inspired flapping kinematics(consisting of plunging and in-line movement)extracted from a free-flying bald eagle wing. The aim is to eluci-date the collective mechanism of the flow generated by slotted tips and the lift contribution of each tip. Specifi-cally, the objective of the study is to determine how changes in the wing spacing affect the resulting aerodynamic interaction between the slotted tips and how that affects the force generation and efficiency. Changes in the phase angle between the flapping motions of slotted tips, as well as the spacings among them,can affect the resulting vortex inter-actions. The rear tips often operates in the wake of the frontal tips and, meanwhile, the vortex generated by the movement of the rear tips promote the frontal tips.The interaction of vortices in time and space leads to wing-wing interference and the flow around slotted tips becomes complicated and unstable. The innovative study of wingtip slot in unsteady state leads us to find that the aerodynamic interaction among slotted tips makes the overall lift characteristic better than that of the unslotted wings. The slotted wing configuration can efficiently convert more energy into lift. As the flapping frequency increases, the collective feature of slotted wing with constantly changing gaps can be more advantageous to enhance lift-generation performance.
基金National Natural Science Foundation of China under Grant Nos.52478467and 52108417Guangdong Basic and Applied Basic Research Foundation under Grant No.2024A1515012569the Natural Science Basic Research Program of Shaanxi under Grant No.2021JQ-101。
文摘A ground girder is laid on the preprocessed subgrade by gravity compaction and integrally uniformly supported by subgrade in maglev transit.The settlement of the maglev subgrade inevitably affects the vibration state of the medium and low speed maglev coupled system by the additional deformation of the maglev track.This study investigated the dynamic properties of the coupled vibration system affected by the subgrade settlement.First,a theoretical coupled vibration model of a maglev train-track-ground girder system with uneven subgrade settlement was proposed and verified.Then,the effect mechanism of the coupled system caused by the uneven subgrade settlement was explored.Finally,settlement types and subgrade support voiding were examined.The analysis showed that the uneven subgrade settlement considerably increased the dynamic responses of the levitation control system and maglev vehicle while having a minor influence on those of the track-ground girder.The influence of a single ground girder settling was the strongest,and adjacent sides’settling of two ground girders was the weakest for the vibration of a maglev train.An extremely large uneven settlement exceeding 6 mm led to active levitation control system instability.The subgrade support voiding enlarged the vehicle-induced vibration of the track ground girder.
基金supported by the National Natural Science Foundation of China(Nos.22475170,52101271,22375166)the Guangdong Basic and Applied Basic Research Foundation(Nos.2020A1515111017,2024A1515011977)the Key Research and Development Program of Shaanxi Province(No.2024GX-YBXM379)。
文摘Molecular catalysts can effectively steer the electrocatalytic acetylene semihydrogenation into ethylene,but realizing high Faradaic efficiency(FE)at industrial current densities remains a challenge.Herein,we report a ligand engineering strategy that utilizes polymeric N–heterocyclic carbene(NHC)as a hydrophobic ligand to modulate the microenvironment of Cu sites.This polymeric NHC imparts appropriate hydrophobic properties for the chelated Cu sites,thereby moderating the H_(2)O transport and enabling easy access of acetylene.Consequently,the polymeric NHC chelated Cu exhibits an FE_(ethylene)of~97%at a current density of 500 m A/cm^(2)in a flow cell.Particularly in a zero-gap reactor,the FE_(ethylene)consistently exceeds 86%across current densities from 100 m A/cm^(2)to 400 m A/cm^(2),reaching an optimal FEethyleneof 98%at 200 m A/cm^(2)and achieving durable operation for 155 h at 100 m A/cm^(2).This work provides a promising paradigm to regulate the microenvironment of molecular catalysts for improving electrocatalytic performances under industrial current densities.
基金financially supported by the Natural Science Foundation of China(52372226,52202300,62288102,62350013,52303325)National Key Research and Development Program of China(2023YFB3608900)+5 种基金the Postdoctoral Fellowship Program ofthe China postdoctoral Science Foundation(CPSF)(Grant GZC20233506)the China Postdoctoral Science Foundation(Grant2024M764252)the Natural Science Foundation of Chongqing China(2023NSCQ-MSX0097)Guangdong Basic and Applied Basic Research Foundation(2024A1515010918)Shenzhen Science and Technology Program(Grant JCYJ20240813150819026)the Fundamental Research Funds for the Central Universities。
文摘Lead-tin(Pb-Sn)perovskites with an ideal bandgap of 1.34-1.40 eV show great promise in perovskite solar cells(PSCs).Recently,to address the environmental pollution and Sn^(2+)oxidation problems of dimethyl sulfoxide,methylammonium acetate(MAAc)ionic liquid has been developed as an alternative to fabricate ideal bandgap MAPb_(0.7)Sn_(0.3)I_(3)(1.36 eV)film via hot-casting in air.However,the spontaneous crystallization of Pb-Sn perovskite initiated by heat-induced supersaturation is fast and random,setting critical challenges in regulating crystal growth during the film-forming process.Herein,a lattice activation strategy is developed to control the crystallization dynamics of MAPb_(0.7)Sn_(0.3)I_(3)in MAAc to produce films with micrometer-sized grains in air.FA is shown to activate the crystal lattice that facilitates the formation of intermediates and balances the crystal growth of MAPb_(0.7)Sn_(0.3)I_(3),producing films with a grain size of 2.78±0.17μm.Furthermore,4-fluoro-phenethylammonium and phenethylammonium are adopted to passivate the defects in the film and promote the energy level alignment at the top interface,respectively.The optimized PSC device achieved an efficiency of 18.24%with a short-circuit current of 29.84 mA/cm^(2),which are both the highest values in 1.36 eV Pb-Sn PSCs to date.Notably,the unencapsulated devices show excellent storage and air stability under various conditions.
基金support and funding from Guangdong Basic and Applied Basic Research Foundation(2019B1515120093)National Natural Science Foundation of China(51773169 and 51973173)+3 种基金Natural Science Basic Research Plan for Distinguished Young Scholars in Shaanxi Province(2019JC11)Open Fund from Henan University of Science and Technology(2020-RSC02)Foundation for Doctor Dissertation of Northwestern Polytechnical University(CX202055)financially supported by Polymer Electromagnetic Functional Materials Innovation Team of Shaanxi Sanqin Scholars。
文摘Hetero-structured thermally conductive spherical boron nitride and boron nitride nanosheets(BNN-30@BNNS)fillers were prepared via electro static self-assembly method.And the corresponding thermally conductive&electrically insulating BNN-30@BNNS/Si-GFs/E-44 laminated composites were then fabricated via hot compression.BNN-30@BNNS-Ⅲ(fBNN-30/fBNNS,1/2,wt/wt)fillers presented the optimal synergistic improvement effects on the thermal conductivities of epoxy composites.When the mass fraction of BNN-30@BNNS-Ⅲwas 15 wt%,λvalue of the BNN-30@BNNS-Ⅲ/E-44 composites was up to0.61 W m^(-1)K^(-1),increased by 2.8 times compared with pure E-44(λ=0.22 W m^(-1)K^(-1)),also higher than that of the 15 wt%BNN-30/E-44(0.56 W m^(-1)K^(-1)),15 wt%BNNS/E-44(0.42 W m^(-1)K^(-1)),and 15 wt%(BNN-30/BNNS)/E-44(direct blending BNN-30/BNNS hybrid fillers,1/2,wt/wt,0.49 W m^(-1)K^(-1))composites.Theλin-plane(λ//)andλcross-plane(λ_(⊥))of 15 wt%BNN-30@BNNS-Ⅲ/Si-GFs/E-44 laminated composites significantly reached 2.75 W m^(-1)K^(-1)and 1.32 W m^(-1)K^(-1),186.5%and 187.0%higher than those of Si-GFs/E-44 laminated composites(λ//=0.96 W m^(-1)K^(-1)andλ_(⊥)=0.46 W m^(-1)K^(-1)).Established models can well simulate heat transfer efficiency in the BNN-30@BNNS-Ⅲ/Si-GFs/E-44 laminated composites.Under the condition of point heat source,the introduction of BNN-30@BNNS-Ⅲfillers were conducive to accelerating heat flow trans fe r.BNN-30@BNNS-Ⅲ/Si-GFs/E-44 laminated composites also demonstrated outstanding electrical insulating properties(cross-plane withstanding voltage,breakdown strength,surface&volume resistivity of 51.3 kV,23.8 kV mm^(-1),3.7×10^(14)Ω&3.4×10^(14)Ω·cm,favorable mechanical properties(flexural strength of 401.0 MPa and ILSS of 22.3 MPa),excellent dielectric properties(εof 4.92 and tanδof 0.008)and terrific thermal properties(T_(g)of 167.3℃and T_(HRI)of 199.2℃).
基金supported financially by the Science, Technology and Innovation Commission of Shenzhen Municipality (No. JCYJ20180306171121424)the National Key R&D Program of China (Nos. 2018YFB1106600 and 2017YFB1103500)+5 种基金the National Natural Science Foundation of China (Nos. 51822405 and 51472200)the Aeronautics Power Foundation (No. 6141B09050337)the Research Fund of Equipment Development Department (No. 61409230402)the Key R&D Program of ShaanXi Province (No. 2018ZDCXL-GY-0904)the Innovation Fund of the Zhejiang Kechuang New Materials Research Institute (No. ZKN-18-P04)the Research Fund of the State Key Laboratory of Solidification Processing (NPU) (No. 2019QZ-02)。
文摘Distribution control and formation mechanism of gas inclusions formed in directionally solidified Al2O3-Er3Al5O12-ZrO2 eutectic ceramic rods are explored during laser floating zone melting. In atmospheric environment, highly-dense bubble-free eutectic rods are well fabricated at low solidification rate(<25μm/s). Gas inclusions form intermittently when the solidification rate is in the range of 25-50 μm/s,but produce continuously at higher solidification rates(100-200 μm/s). The gas inclusions exhibit an elongated finger-like pattern along the growth direction, which of the maximum value of diameter first increases and then decreases with increasing the solidification rate. Meanwhile, the volume fraction of gas inclusions increased gradually with the solidification rate. Based on the effect of surface tension gradient, heterogeneous nucleation of gas bubbles is evaluated to be the primary formation mechanism of gas inclusions.
基金the Science,Technology and Innovation Commission of Shenzhen Municipality of China(Nos.JCYJ20170306160003433 and JCYJ20180306171058717)111 Project of China(No.B08040)for the support given to this research。
文摘The bent double-ridged rectangular tube(DRRT)with high forming quality is helpful to improve the microwave transmission accuracy.For reducing the cross-sectional deformation in the H-typed bending process,in addition to using rigid mandrel to support the inside of tube,ridge groove fillers are also added to restrict the deformation of ridge grooves.Because of the change of stress and strain state of bent tube in bending,rigid mandrel retracting and specially twicespringback stages,and the springback of fillers,the cross-sectional deformation of tube in each stage may be different.Therefore,based on the ABAQUS platform,the finite element models(FEM)for H-typed bending,mandrel retracting and twice-springback stages of H96 DRRT with fillers were established and validated.It is found that,for the height and width deformation of tube and spacing deformation of ridge grooves,retraction of mandrel can make the distribution of these deformations more uniform along the bending direction.The first springback can reduce these deformations significantly,which should be emphasized.But the second springback only increases them by less amount,which can be ignored.The smaller height deformation of ridge groove and filler can be neglected.
基金supported by the National Natural Science Foundation of China (No. 11872314)the Key R&D Program in Shaanxi Province of China (No. 2020GY-154)
文摘The force-generation mechanism of a dovelike flapping-wing micro air vehicle was studied by numerical simulation and experiment.To obtain the real deformation pattern of the flapping wing,the digital image correlation technology was used to measure the dynamic deformation of the wing.The dynamic deformation data were subsequently interpolated and embedded into the CFD solver to account for the aeroelastic effects.The dynamic deformation data were further used to calculate the inertial forces by regarding the wing as a system of particles to take into account the wing flexibility.The temporal variation of the forces produced by the flapping wing was measured by a miniature load cell.The numerical results provide more flow details of the unsteady aerodynamics of the flapping wing in terms of vortex formation and evolution.The calculated results of the inertial forces are analyzed and compared with the CFD results which represent the aerodynamic forces.In addition,the total forces,i.e.,the sum of the CFD result and inertial result,are compared with the experimental results,and an overall good agreement is obtained.
基金supported by the National Natural Science Foundation of China(No.11872314 and U1613227)the China Scholarship Council,Key R&D Program in Shaanxi Province of China(No.2020GY-154)Natural Science Basic Research Plan in Shaanxi Province of China(No.2019JQ-394)。
文摘Natural flyers have extraordinary flight skills and their prominent aerodynamic performance has attracted a lot of attention.However,the aerodynamic mechanism of birds’flapping wing kinematics still lacks in-depth understanding.In this paper,the aerodynamic performance of owl-like airfoil undergoing bio-inspired flapping kinematics extracted from a free-flying owl wing has been numerically investigated.The overset mesh technique is used to deal with the large range movements of flapping airfoils.The bio-inspired kinematics consist of plunging and pitching movement.A pure sinusoidal motion and a defined motion composed of plunging of sinusoidal motion and pitching of the bio-inspired kinematics are selected for comparison.The other two NACA airfoils are also selected to figure out the advantages of the owl-like airfoil.It is found that the cambered owl-like airfoil can enhance lift during the downstroke.The bio-inspired kinematics have an obvious advantage in lift generation with a presence of higher peak lift and positive lift over a wider proportion of the flapping cycle.Meanwhile,the bio-inspired motion is more economical for a lower power consumption compared with the sinusoidal motion.The sinusoidal flapping motion is better for thrust generation for a higher peak thrust value in both upstroke and downstroke,while the bio-inspired kinematics mainly generate thrust during the downstroke but produce more drag during the upstroke.The defined motion has similar lift performance with the bio-inspired kinematics,while it consumes more energy and generates less thrust.The unsteady flow field around airfoils is also analyzed to explain the corresponding phenomenon.The research in this paper is helpful to understand the flight mechanism of birds and to design a micro air vehicle with higher performance.
基金financial support of the projects from National Key Research and Development Program of China(No.2017YFB1300102)National Natural Science Foundation of China(Nos.11872314 and U1613227)Youth Program of Natural Science Basic Research Plan in Shaanxi Province of China(No.2019JQ-394)。
文摘This paper establishes and analyzes a high-fidelity nonlinear time-periodic dynamic model and the corresponding state observer for flapping vibration suppression of a novel tailless Flapping Wing Micro Air Vehicle(FWMAV),named NPU-Tinybird.Firstly,a complete modeling of NPU-Tinybird is determined,including the aerodynamic model based on the quasi-steady method,the kinematic and dynamic model about the mechanism of flapping and attitude control,combined with the single rigid body dynamic model.Based on this,a linearized longitudinal pitch dynamic cycle-averaged model is obtained and analyzed through the methods of neural network fitting and system identification,preparing for the design of flapping vibration suppression observer.Flapping vibration is an inherent property of the tailless FWMAV,which arises from the influence of time-periodic aerodynamic forces and moments.It can be captured by attitude and position sensors on the plane,which impairs the flight performance and efficiency of flight controller and actuators.To deal with this problem,a novel state observer for flapping vibration suppression is designed.A robust optimal controller based on the linear quadratic theory is also designed to stabilize the closed-loop system.Simulation results are given to verify the performance of the observer,including the closed loop responses combined with robust optimal controller,the comparison of different parameters of observer and the comparison with several classic methods,such as Kalman filter,H-infinity filter and low-pass filter,which prove that the novel observer owns a fairly good suppression effect on flapping vibration and benefits for the improvement of flight performance and control efficiency.
基金the Guangdong Basic and Applied Basic Research Foundation(grant No.2021B1515120028)National Natural Science Foundation of China(grant Nos.52130204,52174376,51822405,and 52202070)+5 种基金Science and Technology Innovation Team Plan of Shann Xi Province(grant No.2021TD-17)Youth Innovation Team of Shaanxi UniversitiesThousands Person Plan of Jiangxi Province(grant No.JXSQ2020102131)Xi’an Science and Technology Program(grant No.21ZCZZHXJS-QCY6-0005)Fundamental Research Funds for the Central Universities(grant Nos.D5000210902 and D5000220057)Innovation Foundation for Doctor Dissertation of Northwestern Polytechnical University(grant No.CX2022033).
文摘A novel AlCoCrFeNi2.1 eutectic high entropy alloy(EHEA)composite doped with SiC particles was designed and fabricated by laser powder bed fusion(LPBF).Its microstructure characteristic,tensile properties,and metallurgical defects,with an emphasis on cracking behavior,have been investigated.The results showed that the addition of SiC particles into the AlCoCrFeNi_(2.1)matrix enabled the development of a{100}texture and highly elongated columnar grains,which were the main contributors to mechanical behavior anisotropy.The ultimate tensile strength of 1466±26 MPa and elongation of 9%±3%achieved in the as-deposited EHEA composite surpassed those of advanced metal alloys subjected to additive manufacturing processes.Unfortunately,severe horizontal and longitudinal cracks,as well as a few micro-cracks were observed in the as-deposited bulk samples.Micro-cracks were verified to be associated with the aggregation of carbon and oxide particles.They formed in the final stage of solidification owing to insufficient liquid feeding ability and solidification contraction.The formation of macroscopic cracking was induced by the tensile stress accumulations at sample edges,and the stress concentration areas where microcracks and pores were located were the predominant propagation location.This work provides guidelines for defect control in SiC-reinforced EHEA,assisting in the high-performance design and integrated manufacturing of EHEA composite components.
基金financially supported by the Guangdong Basic and Applied Basic Research Foundation(No.2021B1515120028)the National Natural Science Foundation of China(Nos.52130204,52174376,51822405)+4 种基金the Science and Technology Innovation Team Plan of Shann Xi Province(No.2021TD-17)the Youth Innovation Team of Shaanxi Universities,Joint Research Funds of the Department of Science&Technology of Shaanxi Province and NPU(No.2020GXLH-Z-024)the Key R&D Program of ShaanXi Province(No.2019ZDLGY 04-04)the Fundamental Research Funds for the Central Universities(No.D5000210902)the Innovation Foundation for Doctor Dissertation of Northwestern Polytechnical University(Nos.CX2021056 and CX2021066)。
文摘Al–Co–Cr–Fe–Ni high entropy alloy(HEA) system is a newly developed category of metallic materials possessing unique microstructure, mechanical and functional properties, which presents many promising industrial applications. In recent years, additive manufacturing technology has given rise to a great potential for fabricating HEA parts of ultra-fine grains and geometrical complexity, thereby attracting great interest of researchers. Herein, a comprehensive review emphasizes on the recent developments in high-energy beam additive manufacturing of Al–Co–Cr–Fe–Ni HEA, in the aspects of their printing processes, microstructures, properties, defects, and post treatments. The technical characteristics of three typical high-energy beam additive manufacturing technologies for printing HEA, namely, selective laser melting(SLM), selective electron beam melting(SEBM), and directed energy deposition(DED) are systematically summarized. Typical crystal structure, grain, microstructure, as well as corresponding properties of Al–Co–Cr–Fe–Ni HEA manufactured by those technologies are primarily presented and discussed. It also elaborates the formation mechanisms of harmful defects related to the rapid solidification and complex thermal cycle during high-energy beam additive manufacturing. Furthermore, several kinds of post treatments with an aim to improve performance of HEA are illustrated. Finally, future research directions for HEA by additive manufacturing are outlined to tackle current challenges and accelerate their applications in industrial fields.
基金support from the National Natural Science Foundation of China(51903207 and 51773169)Guangdong Basic and Applied Basic Research Foundation(2019B1515120093)+3 种基金Natural Science Basic Research Plan for Distinguished Young Scholars in Shaanxi Province(2019JC-11)Priority Research and Development Foundations of Shaanxi Provincial Government(2018GY-174)Fundamental Research Funds for the Central Universities(No.310201911py010)Open Fund from Henan University of Science and Technology(2020-RSC02)。
文摘Polymer-dispersed liquid crystal(PDLC)films comprising polyvinyl alcohol(PVA)and liquid crystal monomer(LCM)were successfully obtained by the method of solution casting&thermal compressing.LCM was distributed orderly in PVA matrix by hydrogen bond interaction,to form PVA-LCM interpe net rating-layered networks.When the mass fraction of LCM was up to 35 wt%,the corresponding in-plane thermal conductivity coefficient(λ//)of PDLC film was significantly increased to 1.41 W m^(-1)K^(-1),about 10.8 times that of neat PVA(0.13 W m^(-1)K^(-1)).High intrinsicλ//values of PDLC films were mainly attributed to the formed microscopic-ordered structures from ordered stacking of LCM,ordered arrangement of PVA chains,and their hydrogen bond interaction.This work would offer a new way to design and prepare novel intrinsic high thermal conductive polymers.
基金supported by the National Natural Science Foundation of China(Nos.52130204,52174376 and 51822405)the Guangdong Basic and Applied Basic Research Foundation(No.21201910250000848)+4 种基金the Science and Technology Innovation Team Plan of Shaan Xi Province(No.2021TD-17)the Joint Research Funds of the Department of Science&Technology of Shaanxi Province and NPU(No.2020GXLH-Z-024)The Youth Innovation Team of Shaanxi Universities,the Key R&D Program of Shaanxi Province(No.2019ZDLGY 04-04)the Fundamental Research Funds for the Central Universities(No.D5000210902)the Innovation Foundation for Doctor Dissertation of Northwestern Polytechnical University(Nos.CX2021056,CX2021066 and CX2022033),China.
文摘Crystallographic texture control is a major challenge in directionally solidified multiphase eutectic ceramics with complex faceted growth characteristics.In this study,the Czochralski(CZ)technique is proposed to prepare eutectic single crystal ceramic with large size(30 mm×125 mm).A highly oriented and unique texture of Al_(2)O_(3)/Y_(3)Al_(5)O_(12)(YAG)eutectic ceramic is formed via the 112¯0Al_(2)O_(3) single crystal seed induction based on crystallographic orientation tailoring.The orientations of Al_(2)O_(3)/YAG eutectic are more strictly constrained by single crystal seed induction on the basis of the minimum interface energy principle,resulting in a defined single orientation relationship along the solidification direction.In particular,the single crystallographic orientation can be obtained in a short competitive solidification distance under the influence of epitaxial solidification from single crystal seed.Therefore,it has been confirmed that the orientations of 112¯0Al_(2)O_(3) and 111YAG are preferentially stabilized with the minimum under-cooling during directional solidification.Crystallographic orientation disturbances and instabilities due to polycrystalline crystal seed are avoided.Finally,the successful texture control inducted by 112¯0Al_(2)O_(3) single crystal seed can provide a promising orientation design pathway for faced oxide eutectic solidification.
基金supported by Guangdong Basic and Applied Basic Research Foundation,China(No.2019A1515111146)the Fundamental Research Funds for the Central Universities,China(No.3102020HHZY030005)+2 种基金the Natural Science Basic Research Plan in Shaanxi Province of China(No.2021JQ-104)the National Natural Science Foundation of China(No.51676163)the National 111 Project,China(No.B18041)。
文摘This paper presents the results of a numerical study of the effects of swirling flow in coolant jets on film cooling performance.Some combined-hole designs with swirling coolant flow entering the delivery hole are proposed and analyzed.Adiabatic film cooling effectiveness values for cases with various blowing ratios are compared.Detailed flow structures and underlying mechanisms are discussed.The results show that film cooling effectiveness is improved with jet swirl at high blowing ratios,and that swirl strength has significant influence on film cooling performance.Combined-hole designs can further improve film cooling performance using swirling jets due to mixing of coolant flows and interaction of vortices.The largest improvements of area-averaged film cooling effectiveness for a single-hole swirl case and a combined-hole swirl case over corresponding non-swirling case results are 157%and 173%,respectively.
