The mismatch in thermal expansion coefficients between the fiber-rich and resin-rich regions of a shape memory polymer composite(SMPC)laminate,along with the residual strain during SMPC fabrication,results in buckling...The mismatch in thermal expansion coefficients between the fiber-rich and resin-rich regions of a shape memory polymer composite(SMPC)laminate,along with the residual strain during SMPC fabrication,results in buckling deformation of the inhomogeneous laminate.This paper presents a macroscopic model for buckling of an inhomogeneous SMPC laminate under initial biaxial prestrains.Both linear and nonlinear buckling analyses are carried out using the energy method.The influences of prestrain biaxiality,temperature,and ply angle on the buckling wavelength,critical buckling prestrain,and buckling amplitude are calculated.The results demonstrate that the critical buckling wavelength of the SMPC laminate is independent of the prestrain,while the amplitude is almost independent of temperature.In addition,the optimal fiber stacking configuration with the maximum critical buckling prestrains of inhomogeneous SMPC laminates is determined by a genetic algorithm.展开更多
Radiative cooling fabric creates a thermally comfortable environment without energy input,providing a sustainable approach to personal thermal management.However,most currently reported fabrics mainly focus on outdoor...Radiative cooling fabric creates a thermally comfortable environment without energy input,providing a sustainable approach to personal thermal management.However,most currently reported fabrics mainly focus on outdoor cooling,ignoring to achieve simultaneous cooling both indoors and outdoors,thereby weakening the overall cooling performance.Herein,a full-scale structure fabric with selective emission properties is constructed for simultaneous indoor and outdoor cooling.The fabric achieves 94%reflectance performance in the sunlight band(0.3–2.5μm)and 6%in the mid-infrared band(2.5–25μm),effectively minimizing heat absorption and radiation release obstruction.It also demonstrates 81%radiative emission performance in the atmospheric window band(8–13μm)and 25%radiative transmission performance in the mid-infrared band(2.5–25μm),providing 60 and 26 W m−2 net cooling power outdoors and indoors.In practical applications,the fabric achieves excellent indoor and outdoor human cooling,with temperatures 1.4–5.5℃ lower than typical polydimethylsiloxane film.This work proposes a novel design for the advanced radiative cooling fabric,offering significant potential to realize sustainable personal thermal management.展开更多
Metamaterials have exotic physical properties that rely on the construction of their underlying architecture.However,the physical properties of conventional mechanical metamaterials are permanently programmed into the...Metamaterials have exotic physical properties that rely on the construction of their underlying architecture.However,the physical properties of conventional mechanical metamaterials are permanently programmed into their periodic interconnect configurations,resulting in their lack of modularity,scalable fabrication,and programmability.Mechanical metamaterials typically exhibit a single extraordinary mechanical property or multiple extraordinary properties coupled together,making it difficult to realize multiple independent extraordinary mechanical properties.Here,the pixel mechanics metamaterials(PMMs)with multifunctional and reprogrammable properties are developed by arraying uncoupled constrained individual modular mechanics pixels(MPs).The MPs enable controlled conversion between two extraordinary mechanical properties(multistability and compression-torsion coupling deformation).Each MP exhibits 32 independent and reversible room temperature programming configurations.In addition,the programmability of metamaterials is further enhanced by shape memory polymer(SMP)and 4D printing,greatly enriching the design freedom.For the PMM consisting of m×n MPs,it has 32(m×n)independent room temperature programming configurations.The application prospects of metamaterials in the vibration isolation device and energy absorption device with programmable performance have been demonstrated.The vibration isolation frequencies of the MP before and after programming were[0 Hz-5.86 Hz],[0 Hz-13.67 Hz and 306.64 Hz-365.23 Hz].The total energy absorption of the developed PMM can be adjusted controllably in the range of 1.01 J-3.91 J.Six standard digital logic gates that do not require sustained external force are designed by controlling the closure between the modules.This design paradigm will facilitate the further development of multifunctional and reprogrammable metamaterials.展开更多
Four-dimensional(4D)printing technology is a revolutionary development that produces structures that can adapt in response to external stimuli.However,the responsiveness and printability of smart materials with shape ...Four-dimensional(4D)printing technology is a revolutionary development that produces structures that can adapt in response to external stimuli.However,the responsiveness and printability of smart materials with shape memory properties,which are necessary for 4D printing,remain limited.Biomass materials derived from nature have offered an effective solution due to their various excellent and unique properties.Biomass materials have been abundant in resources and low in carbon content,contributing to the then-current global green energy-saving goals,including carbon peaking and carbon neutrality.This review focused on different sources of biomass materials used in 4D printing,including plant-based,animal-based,and microbial-based biomass materials.It systematically outlined the responsive deformation mechanisms of printed objects that contained biomass materials and delved into the roles and unique advantages of biomass materials in those printed objects.Leveraging these advantages,the review discussed the potential applications of biomass materials in biomedicine,food printing,and other fields to support ongoing development and application efforts.Additionally,it emphasized the crucial role played by bio-fabrication technologies utilizing biomass materials in the integration of biomass materials with 4D printing.Finally,this paper discussed the then-current challenges and potential future directions of biomass materials in 4D printing,aiming to promote the effective development of biomass materials in 4D printing applications.展开更多
Metamaterials,owing to their exceptional physical characteristics that are absent in natural materials,have emerged as a crucial constituent of intelligent devices and systems.However,there are still significant chall...Metamaterials,owing to their exceptional physical characteristics that are absent in natural materials,have emerged as a crucial constituent of intelligent devices and systems.However,there are still significant challenges that necessitate immediate attention,as they have considerably constrained the applicability of metamaterials,including fixed mechanical properties post-fabrication and restricted design freedom.Here,thermo-responsive,photo-responsive,electro-responsive,and magneto-responsive shape memory polymer nano-composites were developed,and shape memory gradient metamaterials were fabricated using multi-material 4D printing technology.The correlation mechanism between the design parameters and the mechanical properties of multi-responsive gradient metamaterials was systematically analyzed,and the highly designable and programmable configuration and mechanical properties of the gradient metamaterials were realized.More importantly,4D printed multi-responsive shape memory polymer gradient metamaterials can be programmed in situ without additional infrastructure for multi-functional mechanical functions,paving the way for the realization of multiple functions of a single structure.Based on the multi-responsive gradient metamaterials,4D printed digital pixel metamaterial intelligent information carriers were fabricated,featuring customizable encryption and decryption protocols,exceptional scalability,and reusability.Additionally,4D printed gradient metamaterial logic gate electronic devices were developed,which were anticipated to contribute to the development of smart,adaptable robotic systems that combine sensing,actuation,and decision-making capabilities.展开更多
The nonlinear aeroelastic behavior of a folding fin in supersonic flow is investigated in this paper.The finite element model of the fin is established and the deployable hinges are represented by three torsion spring...The nonlinear aeroelastic behavior of a folding fin in supersonic flow is investigated in this paper.The finite element model of the fin is established and the deployable hinges are represented by three torsion springs with the freeplay nonlinearity.The aerodynamic grid point is assumed to be at the center of each aerodynamic box for simplicity.The aerodynamic governing equation is given by using the infinite plate spline method and the modified linear piston theory.An improved fixed-interface modal synthesis method,which can reduce the rigid connections at the interface,is developed to save the problem size and computation time.The uniform temperature field is applied to create the thermal environment.For the linear flutter analyses,the flutter speed increases first and then decreases with the rise of the hinge stiffness due to the change of the flutter coupling mechanism.For the nonlinear analyses,a larger freeplay angle results in a higher vibration divergent speed.Two different types of limit cycle oscillations and a multiperiodic motion are observed in the wide range of airspeed under the linear flutter boundary.The linear flutter speed shows a slight descend in the thermal environment,but the effect of the temperature on the vibration divergent speed is different under different hinge stiffnesses when there exists freeplay.展开更多
Shape-memory polymers(SMPs)and their composite materials are stimuliresponsive materials that have the unique characteristics of lightweight,large deformation,variable stiffness,and biocompatibility.This paper reviews...Shape-memory polymers(SMPs)and their composite materials are stimuliresponsive materials that have the unique characteristics of lightweight,large deformation,variable stiffness,and biocompatibility.This paper reviews the research status of the mechanical models for SMPs,shape-memory nanocomposites and shape-memory polymer composites(SMPCs);it also introduces some spatially deployable structures,such as hinges,beams,and antennae based on SMPCs.In addition,the deformation types of 4D printing structures and the potential applications of this technology in robots and medical devices are also summarized.展开更多
Due to wear and manufacturing tolerance,the freeplay is unavoidable in the hinges of folding fins,which exerts significant effects on the aerodynamic characteristics.This paper proposes a backbone-curve-based framewor...Due to wear and manufacturing tolerance,the freeplay is unavoidable in the hinges of folding fins,which exerts significant effects on the aerodynamic characteristics.This paper proposes a backbone-curve-based framework for the dynamical identification of folding fins containing the freeplay nonlinearity.With no need to measure the input force signal and the response signals of nonlinear related Degrees of Freedom(DOFs),the proposed method is more direct and elegant than most existing nonlinear identification approaches,and it contains three steps:Firstly,the underlying linear model of the folding fin structure is obtained through the modal test on its linear sub-parts,and then,the harmonic approximation solves the analytical expressions of the backbone curves of measurable DOFs.Secondly,response data measured from the sine-sweep test are used to extract the fitting points of backbone curves for these DOFs.Finally,the curve fitting approach is applied to identify the freeplay parameters.A series of numerical experiments verify the effectiveness of the proposed method.A real-life folding fin structure is also employed to illustrate how the method can be applied.These examples demonstrate that the identification framework can give an accurate dynamic model of the folding fin structure.展开更多
Recently,asteroid exploration becomes an important branch of human’s deep space activities.In this paper,a piecewise linear optimal orbital maneuver strategy is designed for a spacecraft soft landing on irregular-sha...Recently,asteroid exploration becomes an important branch of human’s deep space activities.In this paper,a piecewise linear optimal orbital maneuver strategy is designed for a spacecraft soft landing on irregular-shaped asteroids.First,the space around an irregular asteroid is converted into several grid units,and the gravitational field of the asteroid is linearly fitted in each unit.Then,the soft-landing orbital maneuver strategy design problem is formulated as a piecewise linear optimal problem,and further transferred into a family of two-point boundary value problems,which can be solved using collocation method.Finally,a corresponding algorithm is developed to obtain the piecewise linear optimal maneuver strategy,which is proved to be able to achieve the soft-landing mission well.Simulation results show that the error of the model linearization is small enough,while the calculation efficiency is remarkably improved,and the robustness of maneuver strategy is also improved.展开更多
Considering a spherical planet with a liquid core surrounded by a solid shell,we developed a quasi-static model to investigate the deformation of the double-layered planet with self-gravity and obtained the boundary v...Considering a spherical planet with a liquid core surrounded by a solid shell,we developed a quasi-static model to investigate the deformation of the double-layered planet with self-gravity and obtained the boundary value problem about radial equilibrium,which is solved by the numerical methods.The effects of governing parameters about geometry,density and bulk modulus on the deformation of the planet with self-gravity were discussed.In addition,we also developed the incremental equation theory to investigate the stability of the double-layered planet under its own gravity.It is concluded that instability is more likely to occur on the planet with smaller liquid cores when the outer radius and density of the planets are constant.Although we only study special double-layered planets,these methods can be conveniently extended to complex multi-layered planets.展开更多
A multi-inclusion cell model is used to investigate the effect of deformation temperature and whisker rotation on the hot compressive behavior of metal matrix composites with misaligned whiskers. Numerical results sho...A multi-inclusion cell model is used to investigate the effect of deformation temperature and whisker rotation on the hot compressive behavior of metal matrix composites with misaligned whiskers. Numerical results show that deformation temperature influences the work-hardening behavior of the matrix and the rotation behavior of the whiskers. With increasing temperature, the work hardening rate of the matrix decreases, but the whisker rotation angle increases. Both whisker rotation and the increase of deformation temperature can induce reductions in the load supported by whisker and the load transferred from matrix to whisker. Additionally, it is found that during large strain deformation at higher temperatures, the enhancing of deformation temperature can reduce the effect of whisker rotation. Meanwhile, the stress-strain behavior of the composite is rather sensitive to deformation temperature. At a relatively lower temperature （150℃）, the composite exhibits work hardening due to the matrix work hardening, but at relatively higher temperatures （300℃ and above）, the composite shows strain softening due to whisker rotation. It is also found that during hot compression at higher temperatures, the softening rate of the composite decreases with increasing temperature. The predicted stress-strain behavior of the composite is approximately in agreement with the experimental results.展开更多
When the electric field caused by voltage reaches a certain level,the charge on the compliant electrodes will not increase owing to the polarization saturation,which would limit the deformation of the dielectric elast...When the electric field caused by voltage reaches a certain level,the charge on the compliant electrodes will not increase owing to the polarization saturation,which would limit the deformation of the dielectric elastomer.Some experiments show that temperature also has a significant effect on the deformation of dielectric elastomer.In this work,a free energy model coupling temperature and polarization saturation is developed to characterize the thermoelectromechanical instability of dielectric elastomer.The results reveal that both the polarization saturation parameters and electric field have a significant influence on the actuation ability of the dielectric elastomer,and the increase of temperature enhances thermoelectromechanical stability.It is hoped that this work could guide the development of dielectric elastomer materials and application devices operating in variable temperatures.展开更多
Kirigami arts have provided a more promising method for building multiscale structures,which can shape two-dimensional(2D)sheets into three-dimensional(3D)configurations by cutting and folding.Here,we first carried ou...Kirigami arts have provided a more promising method for building multiscale structures,which can shape two-dimensional(2D)sheets into three-dimensional(3D)configurations by cutting and folding.Here,we first carried out a theoretical analysis of the mechanical properties of 2D honeycomb lattice structures and experimental verification combined with finite element(FE)simulation.Furthermore,a series of thick-walled 3D kirigami-inspired honeycomb(TW3KH)structures with different mechanical properties were designed and fabricated on the exploration and optimization of geometric parameters of 2D honeycomb structures.The investigations of folding feasibility,self-expansion,and self-folding performance experimentally showed that our designed four-dimensional(4D)printing structure had good programmability and shape memory capability and a large volume change ratio during shape change.Meanwhile,research on its compression deformation behavior found that the TW3KH structures can recover load-bearing capacity very well when the angle is positive.Therefore,these TW3KH structures have great advantages in space-saving smart load-bearing equipment.展开更多
An anomalous phenomenon was observed in the retarding potential analyzer （RPA） measurements of the energy of the ion beam from an 8 cm argon ion source. The current-voltage （Ⅰ- Ⅴ） curve, which should theoretical...An anomalous phenomenon was observed in the retarding potential analyzer （RPA） measurements of the energy of the ion beam from an 8 cm argon ion source. The current-voltage （Ⅰ- Ⅴ） curve, which should theoretically descend, went up as the ion retarding potential was increased. Various explanations, such as the Townsend discharge theory and secondary electron emission etc. were proposed but denied by the theory application condition or the experiment results. An angle of about -10° was found between the axes of the ion beam and the RPA according to the contours of the ion beam density and direction. The particle simulation and experiment of the sum of the collector and wall current were conducted at different incident ion angles. The trends of the Ⅰ- Ⅴ curve in simulation results conformed with the experimental results in most cases. The ion trajectories were simulated at different retarding potentials with an incident angle of -10°. According ：to these results, the reason for the anomalous phenomenon is that when there is a specific angle between the axes of the ion beam and the RPA, more ions are repelled from the vicinity of the ion retarding grid to avoid striking on the grid as the ion retarding potential increases. These redundant ions reach the plate and thus lead to the formation of an ascending Ⅰ- Ⅴ curve.展开更多
Molecular dynamics(MD) simulations are performed to study the composition-dependent elastic modulus and thermal conductivity for carbon/silicon core/shell nanowires(NWs).For each concerned carbon/silicon core/shell NW...Molecular dynamics(MD) simulations are performed to study the composition-dependent elastic modulus and thermal conductivity for carbon/silicon core/shell nanowires(NWs).For each concerned carbon/silicon core/shell NW with a specified diameter,it is found that elastic modulus is reduced with a linear dependence on cross-sectional area ratio.The fact matches well with the results of theoretical model.Analysis based on the cross-sectional stress distribution indicates that the core region of core/shell NW is capable of functioning as a mechanical support.On the other hand,thermal conductivity also relies on the cross-sectional area ratio of amorphous silicon shell.The core/shell interface plays a considerable influence on the thermal transport property. The decreasing rate of thermal conductivity is gradually decreased as the composition of amorphous silicon shell increases.In addition,by calculating the phonon density of state,we demonstrate that the reduction in thermal conductivity of the core/shell NW stems from the increase of the low frequency modes and the depression of high-frequency nonpropagating diffusion modes.These results provide an effective way to modify the properties of core/shell NWs for related application.展开更多
The main aim of this paper is to present an easy to use methodology for assessing the potential amount of electricity or thermal energy production in urban areas located in natural protected sites. The methodology is ...The main aim of this paper is to present an easy to use methodology for assessing the potential amount of electricity or thermal energy production in urban areas located in natural protected sites. The methodology is based on two different steps: a territorial analysis for the evaluation of solar radiation and usable surfaces for photovoltaic or solar thermal plant, and a plant analysis for highlighting those photovoltaic and solar thermal technologies which installation will not generate significant impacts in areas characterized by high environmental and landscaping value. The methodology was successfully applied in two case studies inside two different Italian natural protected areas. The obtained results were provided to local administrations and communities as a useful tool for sustainable energy planning.展开更多
In this paper</span><span style="font-family:Verdana;">,</span><span style="font-family:Verdana;"> the performance and overall efficiency optimization process for a full-ele...In this paper</span><span style="font-family:Verdana;">,</span><span style="font-family:Verdana;"> the performance and overall efficiency optimization process for a full-electric Formula Student car are reported. The Formula Student Electric is a scientific-educational competition of high technological value that requires the development and construction of a fully electric open-wheel prototype car;the cars rival both in terms of absolute performance and in terms of total energy efficiency, especially in the most important test, the endurance event. The optimization of the performance and efficiency of the cars affects various aspects of both the powertrain and the car body and, as macro areas, three crucial themes can be identified for the development of the cars: the power maps with which the inverter manages the electric motor, the aerodynamic kit installed onboard and the overall weight of the car. In this regard, in fact, it is not obvious, for example, that it is convenient to use the maximum power allowed by the rules for the powertrain (80 kW);in the same way, it is not inevitable that it is advantageous to install all the components of the aerodynamic kit (front wing, rear wing and undertray with diffusers) and, finally, the best configuration may not be the one with the lightest car. This is also in consideration of the fact that some choices must necessarily be a compromise, such as completeness of the aerodynamic kit and vehicle weight. Hence the search for an optimum point is necessary. The work proposed here aims to describe the experimental search for the optimal configuration for the car of the Sapienza Fast Charge team. To achieve the goal, the analysis has been conducted with several experimental tests on a simple test ring with a dynamic configuration comparable to that of a typical endurance track. The tests have been fulfilled with different combinations of aero-kit configurations, with the aero devices available on the car, rear wing, front wing and undertray, and with different energy management strategies, implemented in the power map of the inverter. The best result has been achieved considering the official ranking calculation of the Formula Student rules 2020, with a combination of best track time and lower energy consumption. The work described here will start with the description of the prototype vehicle, reporting the details of the powertrain and storage system installed onboard. Then, the aerodynamic devices designed and built will be described, and the CFD analysis of their performances will also be reported. In the following, the description of the test track will be discussed and a comparison of a typical track of an Endurance test in Formula Student will be fulfilled. Finally, the parameters measured experimentally will be described and all the tests carried out will be discussed, in order to determine the optimal configuration of the car.展开更多
Designing a good energy storage system represents the most important chall</span><span style="font-family:Verdana;">enge for spreading over a large scale of electric mobility. Proper thermal</...Designing a good energy storage system represents the most important chall</span><span style="font-family:Verdana;">enge for spreading over a large scale of electric mobility. Proper thermal</span> <span style="font-family:Verdana;">management is critical and guarantees optimum working temperature in a</span><span style="font-family:Verdana;"> battery pack. In the various battery thermal management technologies, air cooling is one of the most used solutions. The following work analyzes the cooling performance of the air-cooling thermal management system by choosing appropriate system parameters and analyzes using CFD simulations for accurate thermal modeling. These parameters include the influence of airflow rate </span><span style="font-family:Verdana;">and cell spacing on the configuration. The outcome of the simulations is</span><span style="font-family:Verdana;"> compared using parameters like maximum temperature, and temperature distribution in the battery module to obtain optimum results for further applications. Finally, the simulations of the optimal solution will be compared to experimental results for validation.展开更多
The aim of this paper is to present the preliminary experimental analysis results carried out on the commercial internal combustion engine set in a CHP （combined heat and power） mode, fueled by renewable hydrogen an...The aim of this paper is to present the preliminary experimental analysis results carried out on the commercial internal combustion engine set in a CHP （combined heat and power） mode, fueled by renewable hydrogen and methane mixtures. The hydrogen is produced by an alkaline electrolyser fed by a 5.8 kWp grid connected PV （photovoltaic） plant. The acceptance test conducted with hydrogen percentages ranging from 0%-10% has been carried out at partial load： 45 kW^l instead of the full power of 60 kWe~. In order to evaluate the CHP energy consumption and environmental performance （NOx and CO）, the analysis was conducted for 240 h, using a portable flue gas analyser and two mass flow meters for hydrogen and methane. Without engine parameters optimization--relative equivalence ratio （2） and spark advance--increasing hydrogen addition rate, a slight enhancement in electrical efficiency occurs. Furthermore, due to the engine control system and lower blends LHV （lower heating value）, the methane consumption decreases disproportionately to the hydrogen amount in the mixture. Finally, referring to standard operating condition, the environmental results show that using enrichment of 10%, running the engine with 18 degrees spark advance and 2 of 1.4, CO and NOx emissions are reduced by 6.3% and 27% respectively.展开更多
There is a growing interest in the electrical energy storage system, especially for matching intermittent sources of renewable energy with customers＇ demand. Furthermore, it is possible, with these system, to level t...There is a growing interest in the electrical energy storage system, especially for matching intermittent sources of renewable energy with customers＇ demand. Furthermore, it is possible, with these system, to level the absorption peak of the electric network （peak shaving） and the advantage of separating the production phase from the exertion phase （time shift）. CAES （compressed air energy storage systems） are one of the most promising technologies of this field, because they are characterized by a high reliability, low environmental impact and a remarkable energy density. The main disadvantage of big systems is that they depend on geological formations which are necessary to the storage. The micro-CAES system, with a rigid storage vessel, guarantees a high portability of the system and a higher adaptability even with distributed or stand-alone energy productions. This article carries out a thermodynamical and energy analysis of the micro-CAES system, as a result of the mathematical model created in a Matlab/Simulink environment. New ideas will be discussed, as the one concerning the quasi-isothermal compression/expansion, through the exertion of a biphasic mixture, that will increase the total system efficiency and enable a combined production of electric, thermal and refrigeration energies. The exergy analysis of the results provided by the simulation of the model reports that more than one third of the exergy input to the system is lost. This is something promising for the development of an experimental device.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.12102107 and 12272113)China National Postdoctoral Program for Innovative Talents(No.BX2021090).
文摘The mismatch in thermal expansion coefficients between the fiber-rich and resin-rich regions of a shape memory polymer composite(SMPC)laminate,along with the residual strain during SMPC fabrication,results in buckling deformation of the inhomogeneous laminate.This paper presents a macroscopic model for buckling of an inhomogeneous SMPC laminate under initial biaxial prestrains.Both linear and nonlinear buckling analyses are carried out using the energy method.The influences of prestrain biaxiality,temperature,and ply angle on the buckling wavelength,critical buckling prestrain,and buckling amplitude are calculated.The results demonstrate that the critical buckling wavelength of the SMPC laminate is independent of the prestrain,while the amplitude is almost independent of temperature.In addition,the optimal fiber stacking configuration with the maximum critical buckling prestrains of inhomogeneous SMPC laminates is determined by a genetic algorithm.
基金financially supported by Heilongjiang Postdoctoral Fund(Grant No.LBH-Z24057)Outstanding Master’s and Doctoral Thesis of Longjiang in the New Era(Grant No.LJYXL2023-076).
文摘Radiative cooling fabric creates a thermally comfortable environment without energy input,providing a sustainable approach to personal thermal management.However,most currently reported fabrics mainly focus on outdoor cooling,ignoring to achieve simultaneous cooling both indoors and outdoors,thereby weakening the overall cooling performance.Herein,a full-scale structure fabric with selective emission properties is constructed for simultaneous indoor and outdoor cooling.The fabric achieves 94%reflectance performance in the sunlight band(0.3–2.5μm)and 6%in the mid-infrared band(2.5–25μm),effectively minimizing heat absorption and radiation release obstruction.It also demonstrates 81%radiative emission performance in the atmospheric window band(8–13μm)and 25%radiative transmission performance in the mid-infrared band(2.5–25μm),providing 60 and 26 W m−2 net cooling power outdoors and indoors.In practical applications,the fabric achieves excellent indoor and outdoor human cooling,with temperatures 1.4–5.5℃ lower than typical polydimethylsiloxane film.This work proposes a novel design for the advanced radiative cooling fabric,offering significant potential to realize sustainable personal thermal management.
基金the financial support provided by the National Key R&D Program of China(2022YFB3805700)the National Natural Science Foundation of China(Grant Nos.12072094 and 12172106)+2 种基金the China Postdoctoral Science Foundation(Grant No.2023M730869)the Heilongjiang Natural Science Foundation Joint Guidance Project(Grant No.LH2023A004)the Postdoctoral Fellowship Program of CPSF(Grant No.GZB20230959)。
文摘Metamaterials have exotic physical properties that rely on the construction of their underlying architecture.However,the physical properties of conventional mechanical metamaterials are permanently programmed into their periodic interconnect configurations,resulting in their lack of modularity,scalable fabrication,and programmability.Mechanical metamaterials typically exhibit a single extraordinary mechanical property or multiple extraordinary properties coupled together,making it difficult to realize multiple independent extraordinary mechanical properties.Here,the pixel mechanics metamaterials(PMMs)with multifunctional and reprogrammable properties are developed by arraying uncoupled constrained individual modular mechanics pixels(MPs).The MPs enable controlled conversion between two extraordinary mechanical properties(multistability and compression-torsion coupling deformation).Each MP exhibits 32 independent and reversible room temperature programming configurations.In addition,the programmability of metamaterials is further enhanced by shape memory polymer(SMP)and 4D printing,greatly enriching the design freedom.For the PMM consisting of m×n MPs,it has 32(m×n)independent room temperature programming configurations.The application prospects of metamaterials in the vibration isolation device and energy absorption device with programmable performance have been demonstrated.The vibration isolation frequencies of the MP before and after programming were[0 Hz-5.86 Hz],[0 Hz-13.67 Hz and 306.64 Hz-365.23 Hz].The total energy absorption of the developed PMM can be adjusted controllably in the range of 1.01 J-3.91 J.Six standard digital logic gates that do not require sustained external force are designed by controlling the closure between the modules.This design paradigm will facilitate the further development of multifunctional and reprogrammable metamaterials.
基金the support by National Natural Science Foundation of China(No.52375314,12472147,U23A20412)the National Key R&D Program of China(No.2024YFB4710205,2024YFD2200700)Heilongjiang Provincial Natural Science Foundation of China(No.2022ZX02C25).
文摘Four-dimensional(4D)printing technology is a revolutionary development that produces structures that can adapt in response to external stimuli.However,the responsiveness and printability of smart materials with shape memory properties,which are necessary for 4D printing,remain limited.Biomass materials derived from nature have offered an effective solution due to their various excellent and unique properties.Biomass materials have been abundant in resources and low in carbon content,contributing to the then-current global green energy-saving goals,including carbon peaking and carbon neutrality.This review focused on different sources of biomass materials used in 4D printing,including plant-based,animal-based,and microbial-based biomass materials.It systematically outlined the responsive deformation mechanisms of printed objects that contained biomass materials and delved into the roles and unique advantages of biomass materials in those printed objects.Leveraging these advantages,the review discussed the potential applications of biomass materials in biomedicine,food printing,and other fields to support ongoing development and application efforts.Additionally,it emphasized the crucial role played by bio-fabrication technologies utilizing biomass materials in the integration of biomass materials with 4D printing.Finally,this paper discussed the then-current challenges and potential future directions of biomass materials in 4D printing,aiming to promote the effective development of biomass materials in 4D printing applications.
基金supported by the National Key R&D Program of China(2022YFB3805700)the National Natural Science Foundation of China(Grant No.12302198)+2 种基金China Postdoctoral Science Foundation(2022M720042)Heilongjiang Postdoctoral Science Foundation(LBH-Z22016)Key Project of Heilongjiang Provincial Department of Science and Technology(2022ZX02C25).
文摘Metamaterials,owing to their exceptional physical characteristics that are absent in natural materials,have emerged as a crucial constituent of intelligent devices and systems.However,there are still significant challenges that necessitate immediate attention,as they have considerably constrained the applicability of metamaterials,including fixed mechanical properties post-fabrication and restricted design freedom.Here,thermo-responsive,photo-responsive,electro-responsive,and magneto-responsive shape memory polymer nano-composites were developed,and shape memory gradient metamaterials were fabricated using multi-material 4D printing technology.The correlation mechanism between the design parameters and the mechanical properties of multi-responsive gradient metamaterials was systematically analyzed,and the highly designable and programmable configuration and mechanical properties of the gradient metamaterials were realized.More importantly,4D printed multi-responsive shape memory polymer gradient metamaterials can be programmed in situ without additional infrastructure for multi-functional mechanical functions,paving the way for the realization of multiple functions of a single structure.Based on the multi-responsive gradient metamaterials,4D printed digital pixel metamaterial intelligent information carriers were fabricated,featuring customizable encryption and decryption protocols,exceptional scalability,and reusability.Additionally,4D printed gradient metamaterial logic gate electronic devices were developed,which were anticipated to contribute to the development of smart,adaptable robotic systems that combine sensing,actuation,and decision-making capabilities.
文摘The nonlinear aeroelastic behavior of a folding fin in supersonic flow is investigated in this paper.The finite element model of the fin is established and the deployable hinges are represented by three torsion springs with the freeplay nonlinearity.The aerodynamic grid point is assumed to be at the center of each aerodynamic box for simplicity.The aerodynamic governing equation is given by using the infinite plate spline method and the modified linear piston theory.An improved fixed-interface modal synthesis method,which can reduce the rigid connections at the interface,is developed to save the problem size and computation time.The uniform temperature field is applied to create the thermal environment.For the linear flutter analyses,the flutter speed increases first and then decreases with the rise of the hinge stiffness due to the change of the flutter coupling mechanism.For the nonlinear analyses,a larger freeplay angle results in a higher vibration divergent speed.Two different types of limit cycle oscillations and a multiperiodic motion are observed in the wide range of airspeed under the linear flutter boundary.The linear flutter speed shows a slight descend in the thermal environment,but the effect of the temperature on the vibration divergent speed is different under different hinge stiffnesses when there exists freeplay.
基金This work is supported by the National Natural Science Foundation of China(Grant Nos.11772109,11632005 and 11672086)the Foundation for Innovative Research Groups of the National Natural Science Foundation of China(Grant No.11421091).
文摘Shape-memory polymers(SMPs)and their composite materials are stimuliresponsive materials that have the unique characteristics of lightweight,large deformation,variable stiffness,and biocompatibility.This paper reviews the research status of the mechanical models for SMPs,shape-memory nanocomposites and shape-memory polymer composites(SMPCs);it also introduces some spatially deployable structures,such as hinges,beams,and antennae based on SMPCs.In addition,the deformation types of 4D printing structures and the potential applications of this technology in robots and medical devices are also summarized.
基金financial supports from the Fundamental Research Funds for the Central Universities, China (No. HIT. NSRIF. 2020014)the National Natural Science Foundation of China (No. 12102103)
文摘Due to wear and manufacturing tolerance,the freeplay is unavoidable in the hinges of folding fins,which exerts significant effects on the aerodynamic characteristics.This paper proposes a backbone-curve-based framework for the dynamical identification of folding fins containing the freeplay nonlinearity.With no need to measure the input force signal and the response signals of nonlinear related Degrees of Freedom(DOFs),the proposed method is more direct and elegant than most existing nonlinear identification approaches,and it contains three steps:Firstly,the underlying linear model of the folding fin structure is obtained through the modal test on its linear sub-parts,and then,the harmonic approximation solves the analytical expressions of the backbone curves of measurable DOFs.Secondly,response data measured from the sine-sweep test are used to extract the fitting points of backbone curves for these DOFs.Finally,the curve fitting approach is applied to identify the freeplay parameters.A series of numerical experiments verify the effectiveness of the proposed method.A real-life folding fin structure is also employed to illustrate how the method can be applied.These examples demonstrate that the identification framework can give an accurate dynamic model of the folding fin structure.
基金the Fundamental Research Funds for the Central Universities,China(No.HIT.NSRIF.201620)supported by the NASA Planetary System。
文摘Recently,asteroid exploration becomes an important branch of human’s deep space activities.In this paper,a piecewise linear optimal orbital maneuver strategy is designed for a spacecraft soft landing on irregular-shaped asteroids.First,the space around an irregular asteroid is converted into several grid units,and the gravitational field of the asteroid is linearly fitted in each unit.Then,the soft-landing orbital maneuver strategy design problem is formulated as a piecewise linear optimal problem,and further transferred into a family of two-point boundary value problems,which can be solved using collocation method.Finally,a corresponding algorithm is developed to obtain the piecewise linear optimal maneuver strategy,which is proved to be able to achieve the soft-landing mission well.Simulation results show that the error of the model linearization is small enough,while the calculation efficiency is remarkably improved,and the robustness of maneuver strategy is also improved.
基金supported by the Science Foundation of National Key Laboratory of Science and Technology on advanced composites in special environments,and Heilongjiang Touyan Innovation Team Program.
文摘Considering a spherical planet with a liquid core surrounded by a solid shell,we developed a quasi-static model to investigate the deformation of the double-layered planet with self-gravity and obtained the boundary value problem about radial equilibrium,which is solved by the numerical methods.The effects of governing parameters about geometry,density and bulk modulus on the deformation of the planet with self-gravity were discussed.In addition,we also developed the incremental equation theory to investigate the stability of the double-layered planet under its own gravity.It is concluded that instability is more likely to occur on the planet with smaller liquid cores when the outer radius and density of the planets are constant.Although we only study special double-layered planets,these methods can be conveniently extended to complex multi-layered planets.
基金This study was financially supported by the National Natural Science Foundation of China (No. 50071008).
文摘A multi-inclusion cell model is used to investigate the effect of deformation temperature and whisker rotation on the hot compressive behavior of metal matrix composites with misaligned whiskers. Numerical results show that deformation temperature influences the work-hardening behavior of the matrix and the rotation behavior of the whiskers. With increasing temperature, the work hardening rate of the matrix decreases, but the whisker rotation angle increases. Both whisker rotation and the increase of deformation temperature can induce reductions in the load supported by whisker and the load transferred from matrix to whisker. Additionally, it is found that during large strain deformation at higher temperatures, the enhancing of deformation temperature can reduce the effect of whisker rotation. Meanwhile, the stress-strain behavior of the composite is rather sensitive to deformation temperature. At a relatively lower temperature （150℃）, the composite exhibits work hardening due to the matrix work hardening, but at relatively higher temperatures （300℃ and above）, the composite shows strain softening due to whisker rotation. It is also found that during hot compression at higher temperatures, the softening rate of the composite decreases with increasing temperature. The predicted stress-strain behavior of the composite is approximately in agreement with the experimental results.
基金This work was supported by the National Natural Science Foundation of China(Grant 11772109).
文摘When the electric field caused by voltage reaches a certain level,the charge on the compliant electrodes will not increase owing to the polarization saturation,which would limit the deformation of the dielectric elastomer.Some experiments show that temperature also has a significant effect on the deformation of dielectric elastomer.In this work,a free energy model coupling temperature and polarization saturation is developed to characterize the thermoelectromechanical instability of dielectric elastomer.The results reveal that both the polarization saturation parameters and electric field have a significant influence on the actuation ability of the dielectric elastomer,and the increase of temperature enhances thermoelectromechanical stability.It is hoped that this work could guide the development of dielectric elastomer materials and application devices operating in variable temperatures.
基金This work was supported by the National Natural Science Foundation of China(Nos.12072094 and 12172106).
文摘Kirigami arts have provided a more promising method for building multiscale structures,which can shape two-dimensional(2D)sheets into three-dimensional(3D)configurations by cutting and folding.Here,we first carried out a theoretical analysis of the mechanical properties of 2D honeycomb lattice structures and experimental verification combined with finite element(FE)simulation.Furthermore,a series of thick-walled 3D kirigami-inspired honeycomb(TW3KH)structures with different mechanical properties were designed and fabricated on the exploration and optimization of geometric parameters of 2D honeycomb structures.The investigations of folding feasibility,self-expansion,and self-folding performance experimentally showed that our designed four-dimensional(4D)printing structure had good programmability and shape memory capability and a large volume change ratio during shape change.Meanwhile,research on its compression deformation behavior found that the TW3KH structures can recover load-bearing capacity very well when the angle is positive.Therefore,these TW3KH structures have great advantages in space-saving smart load-bearing equipment.
基金supported by National Natural Science Foundation of China(No.10805004)the Fundamental Research Funds for the Central Universities of China(No.YWF-13-D2-HT-12)
文摘An anomalous phenomenon was observed in the retarding potential analyzer （RPA） measurements of the energy of the ion beam from an 8 cm argon ion source. The current-voltage （Ⅰ- Ⅴ） curve, which should theoretically descend, went up as the ion retarding potential was increased. Various explanations, such as the Townsend discharge theory and secondary electron emission etc. were proposed but denied by the theory application condition or the experiment results. An angle of about -10° was found between the axes of the ion beam and the RPA according to the contours of the ion beam density and direction. The particle simulation and experiment of the sum of the collector and wall current were conducted at different incident ion angles. The trends of the Ⅰ- Ⅴ curve in simulation results conformed with the experimental results in most cases. The ion trajectories were simulated at different retarding potentials with an incident angle of -10°. According ：to these results, the reason for the anomalous phenomenon is that when there is a specific angle between the axes of the ion beam and the RPA, more ions are repelled from the vicinity of the ion retarding grid to avoid striking on the grid as the ion retarding potential increases. These redundant ions reach the plate and thus lead to the formation of an ascending Ⅰ- Ⅴ curve.
基金the China Postdoctoral Science Foundation and Fundamental Research Funds for the Central Universities(No.HIT NSRIF 2013031)
文摘Molecular dynamics(MD) simulations are performed to study the composition-dependent elastic modulus and thermal conductivity for carbon/silicon core/shell nanowires(NWs).For each concerned carbon/silicon core/shell NW with a specified diameter,it is found that elastic modulus is reduced with a linear dependence on cross-sectional area ratio.The fact matches well with the results of theoretical model.Analysis based on the cross-sectional stress distribution indicates that the core region of core/shell NW is capable of functioning as a mechanical support.On the other hand,thermal conductivity also relies on the cross-sectional area ratio of amorphous silicon shell.The core/shell interface plays a considerable influence on the thermal transport property. The decreasing rate of thermal conductivity is gradually decreased as the composition of amorphous silicon shell increases.In addition,by calculating the phonon density of state,we demonstrate that the reduction in thermal conductivity of the core/shell NW stems from the increase of the low frequency modes and the depression of high-frequency nonpropagating diffusion modes.These results provide an effective way to modify the properties of core/shell NWs for related application.
文摘The main aim of this paper is to present an easy to use methodology for assessing the potential amount of electricity or thermal energy production in urban areas located in natural protected sites. The methodology is based on two different steps: a territorial analysis for the evaluation of solar radiation and usable surfaces for photovoltaic or solar thermal plant, and a plant analysis for highlighting those photovoltaic and solar thermal technologies which installation will not generate significant impacts in areas characterized by high environmental and landscaping value. The methodology was successfully applied in two case studies inside two different Italian natural protected areas. The obtained results were provided to local administrations and communities as a useful tool for sustainable energy planning.
文摘In this paper</span><span style="font-family:Verdana;">,</span><span style="font-family:Verdana;"> the performance and overall efficiency optimization process for a full-electric Formula Student car are reported. The Formula Student Electric is a scientific-educational competition of high technological value that requires the development and construction of a fully electric open-wheel prototype car;the cars rival both in terms of absolute performance and in terms of total energy efficiency, especially in the most important test, the endurance event. The optimization of the performance and efficiency of the cars affects various aspects of both the powertrain and the car body and, as macro areas, three crucial themes can be identified for the development of the cars: the power maps with which the inverter manages the electric motor, the aerodynamic kit installed onboard and the overall weight of the car. In this regard, in fact, it is not obvious, for example, that it is convenient to use the maximum power allowed by the rules for the powertrain (80 kW);in the same way, it is not inevitable that it is advantageous to install all the components of the aerodynamic kit (front wing, rear wing and undertray with diffusers) and, finally, the best configuration may not be the one with the lightest car. This is also in consideration of the fact that some choices must necessarily be a compromise, such as completeness of the aerodynamic kit and vehicle weight. Hence the search for an optimum point is necessary. The work proposed here aims to describe the experimental search for the optimal configuration for the car of the Sapienza Fast Charge team. To achieve the goal, the analysis has been conducted with several experimental tests on a simple test ring with a dynamic configuration comparable to that of a typical endurance track. The tests have been fulfilled with different combinations of aero-kit configurations, with the aero devices available on the car, rear wing, front wing and undertray, and with different energy management strategies, implemented in the power map of the inverter. The best result has been achieved considering the official ranking calculation of the Formula Student rules 2020, with a combination of best track time and lower energy consumption. The work described here will start with the description of the prototype vehicle, reporting the details of the powertrain and storage system installed onboard. Then, the aerodynamic devices designed and built will be described, and the CFD analysis of their performances will also be reported. In the following, the description of the test track will be discussed and a comparison of a typical track of an Endurance test in Formula Student will be fulfilled. Finally, the parameters measured experimentally will be described and all the tests carried out will be discussed, in order to determine the optimal configuration of the car.
文摘Designing a good energy storage system represents the most important chall</span><span style="font-family:Verdana;">enge for spreading over a large scale of electric mobility. Proper thermal</span> <span style="font-family:Verdana;">management is critical and guarantees optimum working temperature in a</span><span style="font-family:Verdana;"> battery pack. In the various battery thermal management technologies, air cooling is one of the most used solutions. The following work analyzes the cooling performance of the air-cooling thermal management system by choosing appropriate system parameters and analyzes using CFD simulations for accurate thermal modeling. These parameters include the influence of airflow rate </span><span style="font-family:Verdana;">and cell spacing on the configuration. The outcome of the simulations is</span><span style="font-family:Verdana;"> compared using parameters like maximum temperature, and temperature distribution in the battery module to obtain optimum results for further applications. Finally, the simulations of the optimal solution will be compared to experimental results for validation.
文摘The aim of this paper is to present the preliminary experimental analysis results carried out on the commercial internal combustion engine set in a CHP （combined heat and power） mode, fueled by renewable hydrogen and methane mixtures. The hydrogen is produced by an alkaline electrolyser fed by a 5.8 kWp grid connected PV （photovoltaic） plant. The acceptance test conducted with hydrogen percentages ranging from 0%-10% has been carried out at partial load： 45 kW^l instead of the full power of 60 kWe~. In order to evaluate the CHP energy consumption and environmental performance （NOx and CO）, the analysis was conducted for 240 h, using a portable flue gas analyser and two mass flow meters for hydrogen and methane. Without engine parameters optimization--relative equivalence ratio （2） and spark advance--increasing hydrogen addition rate, a slight enhancement in electrical efficiency occurs. Furthermore, due to the engine control system and lower blends LHV （lower heating value）, the methane consumption decreases disproportionately to the hydrogen amount in the mixture. Finally, referring to standard operating condition, the environmental results show that using enrichment of 10%, running the engine with 18 degrees spark advance and 2 of 1.4, CO and NOx emissions are reduced by 6.3% and 27% respectively.
文摘There is a growing interest in the electrical energy storage system, especially for matching intermittent sources of renewable energy with customers＇ demand. Furthermore, it is possible, with these system, to level the absorption peak of the electric network （peak shaving） and the advantage of separating the production phase from the exertion phase （time shift）. CAES （compressed air energy storage systems） are one of the most promising technologies of this field, because they are characterized by a high reliability, low environmental impact and a remarkable energy density. The main disadvantage of big systems is that they depend on geological formations which are necessary to the storage. The micro-CAES system, with a rigid storage vessel, guarantees a high portability of the system and a higher adaptability even with distributed or stand-alone energy productions. This article carries out a thermodynamical and energy analysis of the micro-CAES system, as a result of the mathematical model created in a Matlab/Simulink environment. New ideas will be discussed, as the one concerning the quasi-isothermal compression/expansion, through the exertion of a biphasic mixture, that will increase the total system efficiency and enable a combined production of electric, thermal and refrigeration energies. The exergy analysis of the results provided by the simulation of the model reports that more than one third of the exergy input to the system is lost. This is something promising for the development of an experimental device.
