This paper presents the results from unidirectional shaking table tests of two reduced scale steel models of a building frame, with one and two floors, respectively. These frames incorporate friction dissipators at ev...This paper presents the results from unidirectional shaking table tests of two reduced scale steel models of a building frame, with one and two floors, respectively. These frames incorporate friction dissipators at every floor. The inputs are sine-dwells and artificial and registered earthquakes. This study is part of a larger research project aiming to assess the seismic efficiency of friction dissipators by means of an integrated numerical and experimental approach. Inside this framework, the main objectives of these experiments are to： （i） collect a wide range of results to calibrate a numerical model derived within the project, （ii） clarify some of the most controversial issues about friction dissipators （including behavior for inputs containing pulses, capacity to reduce resonance peaks, introduction of high frequencies in the response, and self- generated eccentricities）, （iii） better understand their dynamic behavior, （iv） provide insight on the feasibility and reliability of using simple friction dissipators for seismic protection of building structures and （v） characterize the hysteretic behavior of these devices. Most of these objectives are satisfactorily reached and relevant conclusions are stated.展开更多
Cavitation of orifices is one of the main problems of the Xiaolangdi flood discharge tunnels. Along with the decompression experiment, the flow field was calculated by using an axis-symmetrical κ-Ε turbulence model....Cavitation of orifices is one of the main problems of the Xiaolangdi flood discharge tunnels. Along with the decompression experiment, the flow field was calculated by using an axis-symmetrical κ-Ε turbulence model. The calculated pressure distribution was compared with the measured data and in agreement with each other. The calculated results show that few of the cavitation bubbles generating at the orifice edge can reach the wall under the calculation condition, the force applied on the orifice surface and the flow pattern before the orifice may be improved obviously by adding the vortex elimination ring at the upper side of the orifice.展开更多
According to the analysis results of risk,economy and practical experiences for many years,the paper demonstrates that the great economic benifits can be got by reducing the design flood standard of energy dissipators...According to the analysis results of risk,economy and practical experiences for many years,the paper demonstrates that the great economic benifits can be got by reducing the design flood standard of energy dissipators and that the reduction of design flood standard is significant for reducing project investment and speeding project construction.展开更多
To explore the distribution law of the temperature field in the motor pump and the influence of the fanshaped DC channel with spoiler in the pump housing on its heat dissipation performance.This study takes the arc-ge...To explore the distribution law of the temperature field in the motor pump and the influence of the fanshaped DC channel with spoiler in the pump housing on its heat dissipation performance.This study takes the arc-gear type hydraulicmotor pump as the research object.In COMSOL,a coupled heat transfer simulationmodel of themotor pump’s fluid-solid coupling is established,and the internal temperature field characteristics are analyzed.To improve the heat dissipation effect of the motor pump,it is proposed to arrange spoiler in the fan-shaped DC channel of the pump housing to enhance heat dissipation.Three types of spoilers,namely,wing-shaped,inclined rectangle-shaped,and wave-shaped,are designed.The simulation results show that when the motor pump operates under rated conditions,due to the poor heat dissipation environment inside the motor pump,the high-temperature areas of the motor pump are concentrated in the rotor and permanent magnet parts.After arranging the spoiler,the turbulent kinetic energy and vorticity in the fan-shaped DC channel of the pump housing are significantly enhanced.All three spoiler structures can reduce the maximum temperature of each component of the motor.According to the comprehensive performance evaluation criterion(PEC),the inclined rectangle-shaped structure has the best comprehensive heat transfer performance(PEC=1.114),while the wave-shaped structure has higher heat transfer efficiency but greater pressure loss.The wing-shaped structure has relatively limited enhancement effect on heat dissipation.This study systematically quantifies the influence of different spoiler structures on heat dissipation performance and flowresistance characteristics,providing a solution for enhancing the heat dissipation of the motor pump.展开更多
By combining the merits of radiative cooling(RC)and evaporation cooling(EC),radiative coupled evaporative cooling(REC)has attracted considerable attention for sub-ambient cooling purposes.However,for outdoor devices,t...By combining the merits of radiative cooling(RC)and evaporation cooling(EC),radiative coupled evaporative cooling(REC)has attracted considerable attention for sub-ambient cooling purposes.However,for outdoor devices,the interior heating power would increase the working temperature and fire risk,which would suppress their above-ambient heat dissipation capabilities and passive water cycle properties.In this work,we introduced a REC design based on an all-in-one photonic hydrogel for above-ambient heat dissipation and flame retardancy.Unlike conventional design RC film for heat dissipation with limited cooling power and fire risk,REC hydrogel can greatly improve the heat dissipation performance in the daytime with a high workload,indicating a 12.0℃lower temperature than the RC film under the same conditions in the outdoor experiment.In the nighttime with a low workload,RC-assisted adsorption can improve atmospheric water harvesting to ensure EC in the daytime.In addition,our REC hydrogel significantly enhanced flame retardancy by absorbing heat without a corresponding temperature rise,thus mitigating fire risks.Thus,our design shows a promising solution for the thermal management of outdoor devices,delivering outstanding performance in both heat dissipation and flame retardancy.展开更多
Understanding the shakedown behavior of fill material is paramount to estimate the deformation stability of railway subgrade.Especially for red mudstone fill material(RMF),the noticeable overestimation of bearing capa...Understanding the shakedown behavior of fill material is paramount to estimate the deformation stability of railway subgrade.Especially for red mudstone fill material(RMF),the noticeable overestimation of bearing capacity would be encountered if the conventional strength method is used.This paper presents the shakedown analysis on RMF,with a specific emphasis on the effect of water content.A series of cyclic triaxial tests with 50,000 loading cycles was conducted.Two-stage behavior of permanent deformation and dissipated energy responses was clearly characterized,from which an energy-based criterion was proposed to determine the shakedown limits.The proposed energy-based criterion was validated by examining its performance to various geomaterials including cohesive soils and unbound granular materials(UGMs).By applying the proposed method to RMF,the S-shape evolution curve was obtained in terms of shakedown limits with initial suction.Microfabric difference was believed as the main consequence of the S-shape mode.Demonstration was confirmed by the mercury intrusion porosimetry(MIP)and scanning electron microscope(SEM)analyses.By applying the proposed method to different geomaterials,an extensive comparison was made between the shakedown limits and the static shear strength.The ratio of shakedown limits to the static shear strength for saturated RMF specimen fell within the range of soft clays,while that of unsaturated specimen lies within the range of UGMs.展开更多
Bolting steel angles at the bottom ends of columns provides a rapid and efficient method for repairing damaged structures,while also offering a viable approach to restore their potential bearing capacity.To validate t...Bolting steel angles at the bottom ends of columns provides a rapid and efficient method for repairing damaged structures,while also offering a viable approach to restore their potential bearing capacity.To validate the suitability of specific strengthening strategies,particularly the utilization of bolted steel angles,three reinforced concrete frame specimens were subjected to hysteresis testing.These specimens all featured RC columns strengthened with steel angle ends.Additionally,one control specimen without steel angle ends was included in the testing.The hysteresis effects of bolting steel angles were discussed in terms of typical failure mode,hysteresis and skeleton curves,stiffness degradation and energy dissipation.The experimental results revealed that the three specimens that had bolted steel angles exhibited ductile failure behavior.Through analysis of hysteresis and skeleton curves,it was observed that the frame demonstrated distinct plasticity,maintaining sufficient load-bearing capacity even after yielding and exhibiting superior displacement ductility performance.Considering equivalent viscous damping,the energy dissipation capacity of the RC frame increased linearly with drift and remained largely unaffected by structural damage.Therefore,bolting steel angles at specified cross-sections proved to be a viable technique for structural repair and restoration.展开更多
There is a need for accurate prediction of heat and mass transfer in aerodynamically designed,non-Newtonian nanofluids across aerodynamically designed,high-flux biomedical micro-devices for thermal management and reac...There is a need for accurate prediction of heat and mass transfer in aerodynamically designed,non-Newtonian nanofluids across aerodynamically designed,high-flux biomedical micro-devices for thermal management and reactive coating processes,but existing work is not uncharacteristically remiss regarding viscoelasticity,radiative heating,viscous dissipation,and homogeneous–heterogeneous reactions within a single scheme that is calibrated.This research investigates the flow of Williamson nanofluid across a dynamically wedged surface under conditions that include viscous dissipation,thermal radiation,and homogeneous-heterogeneous reactions.The paper develops a detailed mathematical approach that utilizes boundary layers to transform partial differential equations into ordinary differential equations using similarity transformations.RK4 is the technique for gaining numerical solutions,but with the addition of ANNs,there is an improvement in prediction accuracy and computational efficiency.The study investigates the influence of wedge angle parameter,along with Weissenberg number,thermal radiation parameter and Brownian motion parameter,and Schmidt number,on velocity distribution,temperature distribution,and concentra-tion distribution.Enhanced Weissenberg numbers enhance viscoelastic responses that modify velocity patterns,but radiation parameters and thermophoresis have key impacts on thermal transfer phenomena.This research develops findings that are of enormous application in aerospace,biomedical(artificial hearts and drug delivery),and industrial cooling technology applications.New findings on non-Newtonian nanofluids under full flow systems are included in this work to enhance heat transfer methods in novel fluid-based systems.展开更多
High ground temperature and unloading disturbance have emerged as critical factors impacting the property of cemented gauge-fly ash backfill(CGFB).The characteristics of energy and damage in CGFB were analyzed under c...High ground temperature and unloading disturbance have emerged as critical factors impacting the property of cemented gauge-fly ash backfill(CGFB).The characteristics of energy and damage in CGFB were analyzed under conditions of high ground temperature and unloading by conducting triaxial unloading tests with different initial confining pressures on CGFB that had been cured at various temperatures.Based on dissipative energy,triaxial unloading confining pressure damage constitutive model of CGFB was constructed.It has been demonstrated that the ratio of elastic strain energy in CGFB decreases and the ratio of dissipated energy increases at the end of unloading increases under higher curing temperature.The change in the elastic energy consumption ratio curve of CGFB,which shifts from a gradual increase to a swift rise at a certain"inflection point",can be utilized as a criterion for evaluating the failure of the unloading strength of CGFB.The triaxial unloading damage constitutive model for CGFB divides the damage progression into three distinct phases:initial damage stage,accelerated damage development stage,and rapid damage growth stage.The research findings offer a theoretical foundation for evaluating the extent of damage to CGFB caused by the combined influences of elevated ground temperature and unloading.展开更多
Polypropylene fibers(PPFs) have been widely used in composite materials due to their sound crack resistance and toughness. In cement-based composites, the incorporation of PPFs can significantly improve their dynamic ...Polypropylene fibers(PPFs) have been widely used in composite materials due to their sound crack resistance and toughness. In cement-based composites, the incorporation of PPFs can significantly improve their dynamic mechanical properties. However, cement-iron ore tailings foam composite(CIFC), a sustainable material utilizing iron ore tailings to partially replace cement, has not been investigated under dynamic loading. This study investigates the dynamic compressive behavior of CIFC with 1%–2.5% PPF content and 3–12 mm PPF lengths under various strain rates. The microstructural characteristics were analyzed prior to dynamic testing. X-ray diffraction(XRD) identified crystalline phases including CaCO_(3)Fe_(2)O_(3), SiO, C-S-H gel, and ettringite. Scanning electron microscopy(SEM) observations demonstrated that appropriate PPF_(2) parameters(e.g., C2L9, a CIFC specimen containing 2% PPF with 9 mm length) enhance fiber-matrix bonding and minimize interconnected pores and microcracks, revealing pronounced fiber bridging effects. Split Hopkinson pressure bar(SHPB) tests were then conducted at strain rates of 120–250 s^(-1), showing that the dynamic properties of CIFC were highly dependent on both strain rates and PPF parameters. Compared to other specimens, C2L9 exhibited a more intact failure pattern with superior compressive strength and energy dissipation capacity, despite showing reduced dynamic increase factor(DIF) and normalized energy dissipation(NED) values. These findings provide practical guidance for applying CIFC with varying PPF parameters in impact-resistant structural designs.展开更多
Electron–hole(e–h)recombination is a fundamental process that governs energy dissipation and device efficiency in semiconductors.In two-dimensional(2D)materials,the formation of tightly bound excitons makes exciton-...Electron–hole(e–h)recombination is a fundamental process that governs energy dissipation and device efficiency in semiconductors.In two-dimensional(2D)materials,the formation of tightly bound excitons makes exciton-mediated e–h recombination the dominant decay pathway.In this work,nonradiative e–h recombination within excitons in monolayer MoS_(2) is investigated using first-principles simulations that combine nonadiabatic molecular dynamics with GW and real-time Bethe–Salpeter equation(BSE)propagation.A two-step process is identified:rapid intervalley redistribution induced by exchange interaction,followed by slower phonon-assisted recombination facilitated by exciton binding.By selectively removing the screened Coulomb and exchange terms from the BSE Hamiltonian,their respective contributions are disentangled—exchange interaction is found to increase the number of accessible recombination pathways,while binding reduces the excitation energy and enhances nonradiative decay.A reduction in recombination lifetime by over an order of magnitude is observed due to the excitonic many-body effects.These findings provide microscopic insights for understanding and tuning exciton lifetimes in 2D transition-metal dichalcogenides.展开更多
This study employed tri-component continuous monitoring data from 10 measurement points on both sides of a base isolation layer in the basement of a large-span high-rise building in Beijing,as well as from a free-fiel...This study employed tri-component continuous monitoring data from 10 measurement points on both sides of a base isolation layer in the basement of a large-span high-rise building in Beijing,as well as from a free-field station and roof frame,during a Mw 5.5 magnitude earthquake in Pingyuan,Shandong,in 2023.The H/V spectral ratio method was used to evaluate the structural dynamic response characteristics of the building and analyze the regulatory effect of the base-isolation layer on seismic waves.The results indicate that during the earthquake,the peak frequency of the free-field and the measurement points below the base-isolation layer was stable at 0.17 Hz,whereas the main frequency of the measurement points above the base-isolation layer increased to 0.75–1.18 Hz,which is 4–6 times greater than that of the points below.The amplitude was suppressed by more than 70%,confirming that the base isolation layer effectively isolated the low-frequency energy from the ground and increased the response frequency of the building.When the building was excited by an earthquake,a three-tier frequency gradient was formed throughout the building:“base-isolation layer(0.17 Hz)-main body(1.18 Hz)-roof frame(3.83 Hz)”,which can effectively avoid resonance of the entire building.In addition,the composite base-isolation device changed the dynamic characteristics of the structure.The resonance period was extended from 0.74 s(theoretical value without base isolation)to 5.9 s(calculated value),and the resonance frequency was reduced from 1.35 to 0.17 Hz.This finding indicates that the base-isolation layer can enhance seismic performance by increasing flexibility and damping.展开更多
The preparation of carbon-based electromagnetic wave(EMW)absorbers possessing thin matching thickness,wide absorption bandwidth,strong absorption intensity,and low filling ratio remains a huge challenge.Metal-organic ...The preparation of carbon-based electromagnetic wave(EMW)absorbers possessing thin matching thickness,wide absorption bandwidth,strong absorption intensity,and low filling ratio remains a huge challenge.Metal-organic frameworks(MOFs)are ideal self-sacrificing templates for the construction of carbon-based EMW absorbers.In this work,bimetallic FeMn-MOF-derived MnFe_(2)O_(4)/C/graphene composites were fabricated via a two-step route of solvothermal reaction and the following pyrolysis treatment.The results re-veal the evolution of the microscopic morphology of carbon skeletons from loofah-like to octahedral and then to polyhedron and pomegran-ate after the adjustment of the Fe^(3+)to Mn^(2+)molar ratio.Furthermore,at the Fe^(3+)to Mn^(2+)molar ratio of 2:1,the obtained MnFe_(2)O_(4)/C/graphene composite exhibited the highest EMW absorption capacity.Specifically,a minimum reflection loss of-72.7 dB and a max-imum effective absorption bandwidth of 5.1 GHz were achieved at a low filling ratio of 10wt%.In addition,the possible EMW absorp-tion mechanism of MnFe_(2)O_(4)/C/graphene composites was proposed.Therefore,the results of this work will contribute to the construction of broadband and efficient carbon-based EMW absorbers derived from MOFs.展开更多
To examine the effect of bedding angle upon burst proneness in terms of energy,phyllites with seven various bedding angles are selected for conventional uniaxial compression and single-cyclic loading eunloading uniaxi...To examine the effect of bedding angle upon burst proneness in terms of energy,phyllites with seven various bedding angles are selected for conventional uniaxial compression and single-cyclic loading eunloading uniaxial compression tests.The ejection and failure during compression process of phyllites are monitored in real-time by high-speed camera system.The results demonstrate that the phyllites with different bedding angles all consistently follow the linear energy storage and dissipation(LESD)law during compression.The ultimate energy storage of phyllites with varying bedding angles can be calculated precisely via using the LESD law.Based on this,four kinds of energy-based rockburst indices are applied to quantitatively assess the burst proneness for phyllites.Combined with the recorded images of high-speed camera system,ejection distance,and mass of rock fragments and powder,the burst proneness for phyllites with various bedding angles is qualitatively evaluated adopting the far-field ejection mass ratio.Next,burst proneness of anisotropic phyllites is assessed quantitatively and qualitatively.It is found that phyllites with bedding angles of 0°,15°,and 90°have a high burst proneness,and that with bedding angle of 30°has a medium burst proneness,whereas the ones with bedding angles of 45°,60°,and 75°have a low burst proneness.Finally,the published experimental data of shale and sandstone specimens with different bedding angles are extracted,and it is preliminarily verified that the bedding angle does not change the LESD law of rocks.展开更多
Traditional impact protection structures(IPSs)dissipate impact energy according to the plastic dissipation mechanism,which is only effective for single impacts due to the irreversible deformation of structures.To achi...Traditional impact protection structures(IPSs)dissipate impact energy according to the plastic dissipation mechanism,which is only effective for single impacts due to the irreversible deformation of structures.To achieve multi-impact protection,this paper proposes a novel chiral periodic structure with the deformation self-recovery function and the high energy conversion efficiency based on the flexoelectric mechanism.A theoretical model is formulated on the electromechanical responses of a flexoelectric beam under rotational boundaries.The equivalent stiffness and damping characteristics are subsequently derived to construct the electromechanical responses of the structure under constant velocity and mass impacts.Discussions are addressed for the influence of the structural scale effect and resistance on the electromechanical responses.The results show that the energy conversion efficiency increases by 2 to 3 orders of magnitude,reaching as high as 85.3%,which can match well with those of structures reported in the literature based on the plastic energy dissipating mechanism.展开更多
The combination of advanced photoelectric detectors has rendered single-band camouflage materials ineffective,necessitating the development of infrared multispectral camouflage.However,the design and fabrication of ex...The combination of advanced photoelectric detectors has rendered single-band camouflage materials ineffective,necessitating the development of infrared multispectral camouflage.However,the design and fabrication of existing works remain complex as they usually require the integration of multiscale structures.Here,we introduce phase modulation into the infrared camouflage metasurfaces with metal-dielectric-metal configuration,enabling them to achieve camouflage across more bands.Based on this strategy,a simple but effective single-layer cascaded metasurface is demonstrated for the first time to achieve low reflection at multi-wavelength lasers,low infrared radiation in atmospheric windows,and broadband thermal management.As a proof-of-concept,a 4-inch sample with a minimum linewidth of 1.8μm is fabricated using photolithography.The excellent infrared multispectral camouflage performance is verified in experiments,showing low reflectance in 0.9–1.6μm,low infrared emissivity in mid-wavelength infrared(MWIR)and long-wavelength infrared(LWIR)bands,and high absorptance at the wavelength of 10.6μm.Meanwhile,broadband high emissivity in 5–8μm can provide high-performance radiative heat dissipation.When the input power is 1.57 W·cm^(-2),the surface/radiation temperature of the metasurface decreases by 5.3℃/18.7℃ compared to the reference.The proposed metasurface may trigger further innovation in the design and application of compact multispectral optical devices.展开更多
Traditionally reduced graphene oxide(RGO)-based electromagnetic wave(EMW)absorbing materials have poor absorption effectiveness due to impedance mismatch caused by skin effect.The introduction of structural defects an...Traditionally reduced graphene oxide(RGO)-based electromagnetic wave(EMW)absorbing materials have poor absorption effectiveness due to impedance mismatch caused by skin effect.The introduction of structural defects and the design of heterogeneous interfaces play a crucial role in enhancing the polarization effect of EMW absorbers.In this study,nitrogen-doped reduced graphene oxide/zinc ferrite@nitrogen-doped carbon(NRGO/ZnFe_(2)O_(4)@NC)ternary composite with rich heterogeneous interfaces is constructed by combining solvothermal reaction,in-situ polymerization,annealing treatment with subsequent hydrothermal reaction.The research results have shown that the obtained NRGO/ZnFe_(2)O_(4)@NC ternary composite exhibits a unique core-shell structure and excellent EMW absorption performance.At a thickness of 2.61 mm,the maximum effective absorption bandwidth can reach 7.2 GHz,spanning the entire Ku-band and a portion of the X-band,and the minimum reflection loss is-61.1 dB,which is superior to most reported RGO-based EMW absorbers.The excellent EMW absorbing ability is mainly ascribed to the optimized impedance matching and the enhanced polarization loss caused by the abundant heterogeneous interfaces and structural defects derived from heteroatomic nitrogen doping.Furthermore,the radar cross section in the far field is simulated by a computer simulation technique.This study provides a novel way to prepare core-shell magnetic carbon composites as highly efficient and broadband EMW absorbers.展开更多
Permeable roads generally exhibit inferior mechanical properties and shorter service life than traditional dense-graded/impermeable roads.Furthermore,the incorporation of recycled aggregates in their construction may ...Permeable roads generally exhibit inferior mechanical properties and shorter service life than traditional dense-graded/impermeable roads.Furthermore,the incorporation of recycled aggregates in their construction may exacerbate these limitations.To address these issues,this study introduced a novel cement-stabilized permeable recycled aggregate material.A total of 162 beam specimens prepared with nine different levels of cement-aggregate ratio were tested to evaluate their permeability,bending load,and bending fatigue life.The experimental results indicate that increasing the content of recycled aggregates led to a reduction in both permeability and bending load.Additionally,the inclusion of recycled aggregates diminished the energy dissipation capacity of the specimens.These findings were used to establish a robust relationship between the initial damage in cement-stabilized permeable recycled aggregate material specimens and their fatigue life,and to propose a predictive model for their fatigue performance.Further,a method for assessing fatigue damage based on the evolution of fatigue-induced strain and energy dissipation was developed.The findings of this study provide valuable insights into the mechanical behavior and fatigue performance of cement-stabilized permeable recycled aggregate materials,offering guidance for the design of low-carbon-emission,permeable,and durable roadways incorporating recycled aggregates.展开更多
With the urgent need to resolve complex behaviors in nonlinear evolution equations,this study makes a contribution by establishing the local existence of solutions for Cauchy problems associated with equations of mixe...With the urgent need to resolve complex behaviors in nonlinear evolution equations,this study makes a contribution by establishing the local existence of solutions for Cauchy problems associated with equations of mixed types.Our primary contribution is the establishment of solution existence,illuminating the dynamics of these complex equations.To tackle this challenging problem,we construct an approximate solution sequence and apply the contraction mapping principle to rigorously prove local solution existence.Our results significantly advance the understanding of nonlinear evolution equations of mixed types.Furthermore,they provide a versatile,powerful approach for tackling analogous challenges across physics,engineering,and applied mathematics,making this work a valuable reference for researchers in these fields.展开更多
Filler-reinforced polymer composites demonstrate pervasive applications due to their strengthened performances,multi-degree tunability,and ease of manufacturing.In thermal management field,polymer composites reinforce...Filler-reinforced polymer composites demonstrate pervasive applications due to their strengthened performances,multi-degree tunability,and ease of manufacturing.In thermal management field,polymer composites reinforced with thermally conductive fillers are widely adopted as thermal interface materials(TIMs).However,the three dimensional(3D)-stacked heterogenous integration of electronic devices has posed the problem that high-density heat sources are spatially distributed in the package.This situation puts forward new requirements for TIMs,where efficient heat dissipation channels must be established according to the specific distribution of discrete heat sources.To address this challenge,a 3D printing-assisted streamline orientation(3D-PSO)method was proposed to fabricate composite thermal materials with 3D programmable microstructures and orientations of fillers,which combines the shape-design capability of 3D printing and oriented control ability of fluid.The mechanism of fluid-based filler orientation control along streamlines was revealed by mechanical analysis of fillers in matrix.Thanks to the designed heat dissipation channels,composites showed better thermal and mechanical properties in comparison to random composites.Specifically,the thermal conductivity of 3D mesh-shape polydimethylsiloxane/liquid metal(PDMS/LM)composite was5.8 times that of random PDMS/LM composite under filler loading of 34.8 vol%.The thermal conductivity enhancement efficiency of 3D mesh-shape PDMS/carbon fibers composite reached101.05%under filler loading of 5.2 vol%.In the heat dissipation application of 3D-stacked chips,the highest chip temperature with 3D-PSO composite was 42.14℃lower than that with random composites.This is mainly attributed to the locally aggregated and oriented fillers'microstructure in fluid channels,which contributes to thermal percolation phenomena.The3D-PSO method exhibits excellent programmable design capabilities to adopt versatile distributions of heat sources,paving a new way to solve the complicated heat dissipation issue in 3D-stacked chips integration application.展开更多
基金Supported by Spanish Government,Grant CGL2008-00869/BTE
文摘This paper presents the results from unidirectional shaking table tests of two reduced scale steel models of a building frame, with one and two floors, respectively. These frames incorporate friction dissipators at every floor. The inputs are sine-dwells and artificial and registered earthquakes. This study is part of a larger research project aiming to assess the seismic efficiency of friction dissipators by means of an integrated numerical and experimental approach. Inside this framework, the main objectives of these experiments are to： （i） collect a wide range of results to calibrate a numerical model derived within the project, （ii） clarify some of the most controversial issues about friction dissipators （including behavior for inputs containing pulses, capacity to reduce resonance peaks, introduction of high frequencies in the response, and self- generated eccentricities）, （iii） better understand their dynamic behavior, （iv） provide insight on the feasibility and reliability of using simple friction dissipators for seismic protection of building structures and （v） characterize the hysteretic behavior of these devices. Most of these objectives are satisfactorily reached and relevant conclusions are stated.
文摘Cavitation of orifices is one of the main problems of the Xiaolangdi flood discharge tunnels. Along with the decompression experiment, the flow field was calculated by using an axis-symmetrical κ-Ε turbulence model. The calculated pressure distribution was compared with the measured data and in agreement with each other. The calculated results show that few of the cavitation bubbles generating at the orifice edge can reach the wall under the calculation condition, the force applied on the orifice surface and the flow pattern before the orifice may be improved obviously by adding the vortex elimination ring at the upper side of the orifice.
文摘According to the analysis results of risk,economy and practical experiences for many years,the paper demonstrates that the great economic benifits can be got by reducing the design flood standard of energy dissipators and that the reduction of design flood standard is significant for reducing project investment and speeding project construction.
基金supported by the Henan Provincial Key Research and Development Special Project(251111220200)Natural Science Foundation of Henan Province Project(252300420446).
文摘To explore the distribution law of the temperature field in the motor pump and the influence of the fanshaped DC channel with spoiler in the pump housing on its heat dissipation performance.This study takes the arc-gear type hydraulicmotor pump as the research object.In COMSOL,a coupled heat transfer simulationmodel of themotor pump’s fluid-solid coupling is established,and the internal temperature field characteristics are analyzed.To improve the heat dissipation effect of the motor pump,it is proposed to arrange spoiler in the fan-shaped DC channel of the pump housing to enhance heat dissipation.Three types of spoilers,namely,wing-shaped,inclined rectangle-shaped,and wave-shaped,are designed.The simulation results show that when the motor pump operates under rated conditions,due to the poor heat dissipation environment inside the motor pump,the high-temperature areas of the motor pump are concentrated in the rotor and permanent magnet parts.After arranging the spoiler,the turbulent kinetic energy and vorticity in the fan-shaped DC channel of the pump housing are significantly enhanced.All three spoiler structures can reduce the maximum temperature of each component of the motor.According to the comprehensive performance evaluation criterion(PEC),the inclined rectangle-shaped structure has the best comprehensive heat transfer performance(PEC=1.114),while the wave-shaped structure has higher heat transfer efficiency but greater pressure loss.The wing-shaped structure has relatively limited enhancement effect on heat dissipation.This study systematically quantifies the influence of different spoiler structures on heat dissipation performance and flowresistance characteristics,providing a solution for enhancing the heat dissipation of the motor pump.
基金financially supported by the Science and Technology Innovation Program of Hunan Province(2024RC3003)the Central South University Innovation-Driven Research Programme(2023CXQD012)the Initiative for Sustainable Energy for its financial support。
文摘By combining the merits of radiative cooling(RC)and evaporation cooling(EC),radiative coupled evaporative cooling(REC)has attracted considerable attention for sub-ambient cooling purposes.However,for outdoor devices,the interior heating power would increase the working temperature and fire risk,which would suppress their above-ambient heat dissipation capabilities and passive water cycle properties.In this work,we introduced a REC design based on an all-in-one photonic hydrogel for above-ambient heat dissipation and flame retardancy.Unlike conventional design RC film for heat dissipation with limited cooling power and fire risk,REC hydrogel can greatly improve the heat dissipation performance in the daytime with a high workload,indicating a 12.0℃lower temperature than the RC film under the same conditions in the outdoor experiment.In the nighttime with a low workload,RC-assisted adsorption can improve atmospheric water harvesting to ensure EC in the daytime.In addition,our REC hydrogel significantly enhanced flame retardancy by absorbing heat without a corresponding temperature rise,thus mitigating fire risks.Thus,our design shows a promising solution for the thermal management of outdoor devices,delivering outstanding performance in both heat dissipation and flame retardancy.
基金support from the National Natural Science Foundation of China(Grant Nos.52278432 and 52478475)the Science and Technology Research and Development Plan of China National Railway Group Co.,Ltd.(Grant No.K2023G033)were greatly appreciated.
文摘Understanding the shakedown behavior of fill material is paramount to estimate the deformation stability of railway subgrade.Especially for red mudstone fill material(RMF),the noticeable overestimation of bearing capacity would be encountered if the conventional strength method is used.This paper presents the shakedown analysis on RMF,with a specific emphasis on the effect of water content.A series of cyclic triaxial tests with 50,000 loading cycles was conducted.Two-stage behavior of permanent deformation and dissipated energy responses was clearly characterized,from which an energy-based criterion was proposed to determine the shakedown limits.The proposed energy-based criterion was validated by examining its performance to various geomaterials including cohesive soils and unbound granular materials(UGMs).By applying the proposed method to RMF,the S-shape evolution curve was obtained in terms of shakedown limits with initial suction.Microfabric difference was believed as the main consequence of the S-shape mode.Demonstration was confirmed by the mercury intrusion porosimetry(MIP)and scanning electron microscope(SEM)analyses.By applying the proposed method to different geomaterials,an extensive comparison was made between the shakedown limits and the static shear strength.The ratio of shakedown limits to the static shear strength for saturated RMF specimen fell within the range of soft clays,while that of unsaturated specimen lies within the range of UGMs.
基金National Key R&D Program of China under Grant No.2023YFC3805100Technologies R&D Project of China Construction First Group Corporation Limited under Grant No.PT-2022-09National Natural Science Foundation of China under Grant No.52178126。
文摘Bolting steel angles at the bottom ends of columns provides a rapid and efficient method for repairing damaged structures,while also offering a viable approach to restore their potential bearing capacity.To validate the suitability of specific strengthening strategies,particularly the utilization of bolted steel angles,three reinforced concrete frame specimens were subjected to hysteresis testing.These specimens all featured RC columns strengthened with steel angle ends.Additionally,one control specimen without steel angle ends was included in the testing.The hysteresis effects of bolting steel angles were discussed in terms of typical failure mode,hysteresis and skeleton curves,stiffness degradation and energy dissipation.The experimental results revealed that the three specimens that had bolted steel angles exhibited ductile failure behavior.Through analysis of hysteresis and skeleton curves,it was observed that the frame demonstrated distinct plasticity,maintaining sufficient load-bearing capacity even after yielding and exhibiting superior displacement ductility performance.Considering equivalent viscous damping,the energy dissipation capacity of the RC frame increased linearly with drift and remained largely unaffected by structural damage.Therefore,bolting steel angles at specified cross-sections proved to be a viable technique for structural repair and restoration.
基金supported by the Korea Institute of Energy Technology Evaluation and Planning(KETEP)and the Ministry of Trade,Industry&Energy(MOTIE)of the Republic of Korea(No.RS-2025-02315209).
文摘There is a need for accurate prediction of heat and mass transfer in aerodynamically designed,non-Newtonian nanofluids across aerodynamically designed,high-flux biomedical micro-devices for thermal management and reactive coating processes,but existing work is not uncharacteristically remiss regarding viscoelasticity,radiative heating,viscous dissipation,and homogeneous–heterogeneous reactions within a single scheme that is calibrated.This research investigates the flow of Williamson nanofluid across a dynamically wedged surface under conditions that include viscous dissipation,thermal radiation,and homogeneous-heterogeneous reactions.The paper develops a detailed mathematical approach that utilizes boundary layers to transform partial differential equations into ordinary differential equations using similarity transformations.RK4 is the technique for gaining numerical solutions,but with the addition of ANNs,there is an improvement in prediction accuracy and computational efficiency.The study investigates the influence of wedge angle parameter,along with Weissenberg number,thermal radiation parameter and Brownian motion parameter,and Schmidt number,on velocity distribution,temperature distribution,and concentra-tion distribution.Enhanced Weissenberg numbers enhance viscoelastic responses that modify velocity patterns,but radiation parameters and thermophoresis have key impacts on thermal transfer phenomena.This research develops findings that are of enormous application in aerospace,biomedical(artificial hearts and drug delivery),and industrial cooling technology applications.New findings on non-Newtonian nanofluids under full flow systems are included in this work to enhance heat transfer methods in novel fluid-based systems.
基金Project(2024YFC2911000)supported by the National Key Research and Development Program Young Scientist Project,ChinaProject(2022HWYQ-078)supported by the Natural Science Foundation of Shandong Province of China+1 种基金Project(tsqn202103074)supported by the"Taishan Scholars Young Expert Program"of Shandong Province,ChinaProject(2023GX051)supported by the Tai'an Science and Technology Innovation Development Project(Policy Guidance),China。
文摘High ground temperature and unloading disturbance have emerged as critical factors impacting the property of cemented gauge-fly ash backfill(CGFB).The characteristics of energy and damage in CGFB were analyzed under conditions of high ground temperature and unloading by conducting triaxial unloading tests with different initial confining pressures on CGFB that had been cured at various temperatures.Based on dissipative energy,triaxial unloading confining pressure damage constitutive model of CGFB was constructed.It has been demonstrated that the ratio of elastic strain energy in CGFB decreases and the ratio of dissipated energy increases at the end of unloading increases under higher curing temperature.The change in the elastic energy consumption ratio curve of CGFB,which shifts from a gradual increase to a swift rise at a certain"inflection point",can be utilized as a criterion for evaluating the failure of the unloading strength of CGFB.The triaxial unloading damage constitutive model for CGFB divides the damage progression into three distinct phases:initial damage stage,accelerated damage development stage,and rapid damage growth stage.The research findings offer a theoretical foundation for evaluating the extent of damage to CGFB caused by the combined influences of elevated ground temperature and unloading.
基金supported by the National Science Foundation for Excellent Young Scholars of China (Grant No.52422809)the National Natural Science Foundation of China (Grant No.52208491)。
文摘Polypropylene fibers(PPFs) have been widely used in composite materials due to their sound crack resistance and toughness. In cement-based composites, the incorporation of PPFs can significantly improve their dynamic mechanical properties. However, cement-iron ore tailings foam composite(CIFC), a sustainable material utilizing iron ore tailings to partially replace cement, has not been investigated under dynamic loading. This study investigates the dynamic compressive behavior of CIFC with 1%–2.5% PPF content and 3–12 mm PPF lengths under various strain rates. The microstructural characteristics were analyzed prior to dynamic testing. X-ray diffraction(XRD) identified crystalline phases including CaCO_(3)Fe_(2)O_(3), SiO, C-S-H gel, and ettringite. Scanning electron microscopy(SEM) observations demonstrated that appropriate PPF_(2) parameters(e.g., C2L9, a CIFC specimen containing 2% PPF with 9 mm length) enhance fiber-matrix bonding and minimize interconnected pores and microcracks, revealing pronounced fiber bridging effects. Split Hopkinson pressure bar(SHPB) tests were then conducted at strain rates of 120–250 s^(-1), showing that the dynamic properties of CIFC were highly dependent on both strain rates and PPF parameters. Compared to other specimens, C2L9 exhibited a more intact failure pattern with superior compressive strength and energy dissipation capacity, despite showing reduced dynamic increase factor(DIF) and normalized energy dissipation(NED) values. These findings provide practical guidance for applying CIFC with varying PPF parameters in impact-resistant structural designs.
基金supported by the National Key Research and Development Program of China (Grant Nos.2024YFA1409800 for J.Z.and2024YFA1408603 for Q.Z.)the National Natural Science Foundation of China (Grant Nos.12125408,12334004for J.Z.,and 12174363 for Q.Z.)+1 种基金the Innovation Program for Quantum Science and Technology (Grant No.2021ZD0303306 for J.Z.)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB0450101 for J.Z.)。
文摘Electron–hole(e–h)recombination is a fundamental process that governs energy dissipation and device efficiency in semiconductors.In two-dimensional(2D)materials,the formation of tightly bound excitons makes exciton-mediated e–h recombination the dominant decay pathway.In this work,nonradiative e–h recombination within excitons in monolayer MoS_(2) is investigated using first-principles simulations that combine nonadiabatic molecular dynamics with GW and real-time Bethe–Salpeter equation(BSE)propagation.A two-step process is identified:rapid intervalley redistribution induced by exchange interaction,followed by slower phonon-assisted recombination facilitated by exciton binding.By selectively removing the screened Coulomb and exchange terms from the BSE Hamiltonian,their respective contributions are disentangled—exchange interaction is found to increase the number of accessible recombination pathways,while binding reduces the excitation energy and enhances nonradiative decay.A reduction in recombination lifetime by over an order of magnitude is observed due to the excitonic many-body effects.These findings provide microscopic insights for understanding and tuning exciton lifetimes in 2D transition-metal dichalcogenides.
基金supported by the Deep Earth Probe and Mineral Resources Exploration-National Science and Technology Major Project(Grant No.2025ZD005100)by Beijing Geolight Technology Co.,Ltd.under the project“The Impact of Strong Ground Motion on Buildings”(YF-202520).
文摘This study employed tri-component continuous monitoring data from 10 measurement points on both sides of a base isolation layer in the basement of a large-span high-rise building in Beijing,as well as from a free-field station and roof frame,during a Mw 5.5 magnitude earthquake in Pingyuan,Shandong,in 2023.The H/V spectral ratio method was used to evaluate the structural dynamic response characteristics of the building and analyze the regulatory effect of the base-isolation layer on seismic waves.The results indicate that during the earthquake,the peak frequency of the free-field and the measurement points below the base-isolation layer was stable at 0.17 Hz,whereas the main frequency of the measurement points above the base-isolation layer increased to 0.75–1.18 Hz,which is 4–6 times greater than that of the points below.The amplitude was suppressed by more than 70%,confirming that the base isolation layer effectively isolated the low-frequency energy from the ground and increased the response frequency of the building.When the building was excited by an earthquake,a three-tier frequency gradient was formed throughout the building:“base-isolation layer(0.17 Hz)-main body(1.18 Hz)-roof frame(3.83 Hz)”,which can effectively avoid resonance of the entire building.In addition,the composite base-isolation device changed the dynamic characteristics of the structure.The resonance period was extended from 0.74 s(theoretical value without base isolation)to 5.9 s(calculated value),and the resonance frequency was reduced from 1.35 to 0.17 Hz.This finding indicates that the base-isolation layer can enhance seismic performance by increasing flexibility and damping.
基金supported by the Natural Science Research Project of the Anhui Educational Committee,China(No.2022AH050827)the Open Research Fund Program of Anhui Province Key Laboratory of Specialty Polymers,Anhui University of Science and Technology,China(No.AHKLSP23-12)the Joint National-Local Engineering Research Center for Safe and Precise Coal Mining Fund,China(No.EC2022020)。
文摘The preparation of carbon-based electromagnetic wave(EMW)absorbers possessing thin matching thickness,wide absorption bandwidth,strong absorption intensity,and low filling ratio remains a huge challenge.Metal-organic frameworks(MOFs)are ideal self-sacrificing templates for the construction of carbon-based EMW absorbers.In this work,bimetallic FeMn-MOF-derived MnFe_(2)O_(4)/C/graphene composites were fabricated via a two-step route of solvothermal reaction and the following pyrolysis treatment.The results re-veal the evolution of the microscopic morphology of carbon skeletons from loofah-like to octahedral and then to polyhedron and pomegran-ate after the adjustment of the Fe^(3+)to Mn^(2+)molar ratio.Furthermore,at the Fe^(3+)to Mn^(2+)molar ratio of 2:1,the obtained MnFe_(2)O_(4)/C/graphene composite exhibited the highest EMW absorption capacity.Specifically,a minimum reflection loss of-72.7 dB and a max-imum effective absorption bandwidth of 5.1 GHz were achieved at a low filling ratio of 10wt%.In addition,the possible EMW absorp-tion mechanism of MnFe_(2)O_(4)/C/graphene composites was proposed.Therefore,the results of this work will contribute to the construction of broadband and efficient carbon-based EMW absorbers derived from MOFs.
基金supported by the National Natural Science Foundation of China(Grant No.42077244).
文摘To examine the effect of bedding angle upon burst proneness in terms of energy,phyllites with seven various bedding angles are selected for conventional uniaxial compression and single-cyclic loading eunloading uniaxial compression tests.The ejection and failure during compression process of phyllites are monitored in real-time by high-speed camera system.The results demonstrate that the phyllites with different bedding angles all consistently follow the linear energy storage and dissipation(LESD)law during compression.The ultimate energy storage of phyllites with varying bedding angles can be calculated precisely via using the LESD law.Based on this,four kinds of energy-based rockburst indices are applied to quantitatively assess the burst proneness for phyllites.Combined with the recorded images of high-speed camera system,ejection distance,and mass of rock fragments and powder,the burst proneness for phyllites with various bedding angles is qualitatively evaluated adopting the far-field ejection mass ratio.Next,burst proneness of anisotropic phyllites is assessed quantitatively and qualitatively.It is found that phyllites with bedding angles of 0°,15°,and 90°have a high burst proneness,and that with bedding angle of 30°has a medium burst proneness,whereas the ones with bedding angles of 45°,60°,and 75°have a low burst proneness.Finally,the published experimental data of shale and sandstone specimens with different bedding angles are extracted,and it is preliminarily verified that the bedding angle does not change the LESD law of rocks.
基金Project supported by the National Natural Science Foundation of China(No.12272138)。
文摘Traditional impact protection structures(IPSs)dissipate impact energy according to the plastic dissipation mechanism,which is only effective for single impacts due to the irreversible deformation of structures.To achieve multi-impact protection,this paper proposes a novel chiral periodic structure with the deformation self-recovery function and the high energy conversion efficiency based on the flexoelectric mechanism.A theoretical model is formulated on the electromechanical responses of a flexoelectric beam under rotational boundaries.The equivalent stiffness and damping characteristics are subsequently derived to construct the electromechanical responses of the structure under constant velocity and mass impacts.Discussions are addressed for the influence of the structural scale effect and resistance on the electromechanical responses.The results show that the energy conversion efficiency increases by 2 to 3 orders of magnitude,reaching as high as 85.3%,which can match well with those of structures reported in the literature based on the plastic energy dissipating mechanism.
基金financial supports from the National Natural Science Foundation of China(Grant Nos.51925503&52105575)the Fundamental Research Funds for the Central Universities(Grant No.QTZX23063)+2 种基金the Aeronautical Science Foundation of China(Grant No.2022Z073081001)the Postdoctoral Fellowship Program of CPSF(Grant No.GZC20232028)the Open Research Funds of State Key Laboratory of Intelligent Manufacturing Equipment and Technology(Grant No.IMETKF2024008).
文摘The combination of advanced photoelectric detectors has rendered single-band camouflage materials ineffective,necessitating the development of infrared multispectral camouflage.However,the design and fabrication of existing works remain complex as they usually require the integration of multiscale structures.Here,we introduce phase modulation into the infrared camouflage metasurfaces with metal-dielectric-metal configuration,enabling them to achieve camouflage across more bands.Based on this strategy,a simple but effective single-layer cascaded metasurface is demonstrated for the first time to achieve low reflection at multi-wavelength lasers,low infrared radiation in atmospheric windows,and broadband thermal management.As a proof-of-concept,a 4-inch sample with a minimum linewidth of 1.8μm is fabricated using photolithography.The excellent infrared multispectral camouflage performance is verified in experiments,showing low reflectance in 0.9–1.6μm,low infrared emissivity in mid-wavelength infrared(MWIR)and long-wavelength infrared(LWIR)bands,and high absorptance at the wavelength of 10.6μm.Meanwhile,broadband high emissivity in 5–8μm can provide high-performance radiative heat dissipation.When the input power is 1.57 W·cm^(-2),the surface/radiation temperature of the metasurface decreases by 5.3℃/18.7℃ compared to the reference.The proposed metasurface may trigger further innovation in the design and application of compact multispectral optical devices.
基金supported by the Open Research Fund Program of Engineering Technology Research Center of Coal Resources Comprehensive Utilization,Anhui Province,Anhui University of Science and Technology(Grant No.MTYJZX202301)the Anhui Provincial Natural Science Foundation(Grant No.2008085J27).
文摘Traditionally reduced graphene oxide(RGO)-based electromagnetic wave(EMW)absorbing materials have poor absorption effectiveness due to impedance mismatch caused by skin effect.The introduction of structural defects and the design of heterogeneous interfaces play a crucial role in enhancing the polarization effect of EMW absorbers.In this study,nitrogen-doped reduced graphene oxide/zinc ferrite@nitrogen-doped carbon(NRGO/ZnFe_(2)O_(4)@NC)ternary composite with rich heterogeneous interfaces is constructed by combining solvothermal reaction,in-situ polymerization,annealing treatment with subsequent hydrothermal reaction.The research results have shown that the obtained NRGO/ZnFe_(2)O_(4)@NC ternary composite exhibits a unique core-shell structure and excellent EMW absorption performance.At a thickness of 2.61 mm,the maximum effective absorption bandwidth can reach 7.2 GHz,spanning the entire Ku-band and a portion of the X-band,and the minimum reflection loss is-61.1 dB,which is superior to most reported RGO-based EMW absorbers.The excellent EMW absorbing ability is mainly ascribed to the optimized impedance matching and the enhanced polarization loss caused by the abundant heterogeneous interfaces and structural defects derived from heteroatomic nitrogen doping.Furthermore,the radar cross section in the far field is simulated by a computer simulation technique.This study provides a novel way to prepare core-shell magnetic carbon composites as highly efficient and broadband EMW absorbers.
基金Project(2024JJ2073)supported by the Science Fund for Distinguished Young Scholars of Hunan Province,ChinaProjects(2023YFC3807205,2019YFC1904704)+4 种基金supported by the National Key R&D Program of ChinaProject(52178443)supported by the National Natural Science Foundation of ChinaProject(2024ZZTS0109)supported by Fundamental Research Funds for the Central Universities of Central South University,China。
文摘Permeable roads generally exhibit inferior mechanical properties and shorter service life than traditional dense-graded/impermeable roads.Furthermore,the incorporation of recycled aggregates in their construction may exacerbate these limitations.To address these issues,this study introduced a novel cement-stabilized permeable recycled aggregate material.A total of 162 beam specimens prepared with nine different levels of cement-aggregate ratio were tested to evaluate their permeability,bending load,and bending fatigue life.The experimental results indicate that increasing the content of recycled aggregates led to a reduction in both permeability and bending load.Additionally,the inclusion of recycled aggregates diminished the energy dissipation capacity of the specimens.These findings were used to establish a robust relationship between the initial damage in cement-stabilized permeable recycled aggregate material specimens and their fatigue life,and to propose a predictive model for their fatigue performance.Further,a method for assessing fatigue damage based on the evolution of fatigue-induced strain and energy dissipation was developed.The findings of this study provide valuable insights into the mechanical behavior and fatigue performance of cement-stabilized permeable recycled aggregate materials,offering guidance for the design of low-carbon-emission,permeable,and durable roadways incorporating recycled aggregates.
基金Supported by the National Natural Science Foundation of China(12201368,62376252)Key Project of Natural Science Foundation of Zhejiang Province(LZ22F030003)Zhejiang Province Leading Geese Plan(2024C02G1123882,2024C01SA100795).
文摘With the urgent need to resolve complex behaviors in nonlinear evolution equations,this study makes a contribution by establishing the local existence of solutions for Cauchy problems associated with equations of mixed types.Our primary contribution is the establishment of solution existence,illuminating the dynamics of these complex equations.To tackle this challenging problem,we construct an approximate solution sequence and apply the contraction mapping principle to rigorously prove local solution existence.Our results significantly advance the understanding of nonlinear evolution equations of mixed types.Furthermore,they provide a versatile,powerful approach for tackling analogous challenges across physics,engineering,and applied mathematics,making this work a valuable reference for researchers in these fields.
基金supported by the National Natural Science Foundation of China(Grant No.52106089)the National Key R&D Project from Ministry of Science and Technology of China(Grant No.2022YFA1203100)。
文摘Filler-reinforced polymer composites demonstrate pervasive applications due to their strengthened performances,multi-degree tunability,and ease of manufacturing.In thermal management field,polymer composites reinforced with thermally conductive fillers are widely adopted as thermal interface materials(TIMs).However,the three dimensional(3D)-stacked heterogenous integration of electronic devices has posed the problem that high-density heat sources are spatially distributed in the package.This situation puts forward new requirements for TIMs,where efficient heat dissipation channels must be established according to the specific distribution of discrete heat sources.To address this challenge,a 3D printing-assisted streamline orientation(3D-PSO)method was proposed to fabricate composite thermal materials with 3D programmable microstructures and orientations of fillers,which combines the shape-design capability of 3D printing and oriented control ability of fluid.The mechanism of fluid-based filler orientation control along streamlines was revealed by mechanical analysis of fillers in matrix.Thanks to the designed heat dissipation channels,composites showed better thermal and mechanical properties in comparison to random composites.Specifically,the thermal conductivity of 3D mesh-shape polydimethylsiloxane/liquid metal(PDMS/LM)composite was5.8 times that of random PDMS/LM composite under filler loading of 34.8 vol%.The thermal conductivity enhancement efficiency of 3D mesh-shape PDMS/carbon fibers composite reached101.05%under filler loading of 5.2 vol%.In the heat dissipation application of 3D-stacked chips,the highest chip temperature with 3D-PSO composite was 42.14℃lower than that with random composites.This is mainly attributed to the locally aggregated and oriented fillers'microstructure in fluid channels,which contributes to thermal percolation phenomena.The3D-PSO method exhibits excellent programmable design capabilities to adopt versatile distributions of heat sources,paving a new way to solve the complicated heat dissipation issue in 3D-stacked chips integration application.
