Crack propagation path in two-directionally graded composites was investigated by the finite element method.A graded extended finite element method(XFEM)was employed to calculate displacement and stress fields in crac...Crack propagation path in two-directionally graded composites was investigated by the finite element method.A graded extended finite element method(XFEM)was employed to calculate displacement and stress fields in cracked graded structures.And a post-processing subroutine of interaction energy integral was implemented to extract the mixed-mode stress intensity factors(SIFs).The maximum hoop stress(MHS)criterion was adopted to predict crack growth direction based on the assumption of local homogenization of asymptotic crack-tip fields in graded materials.Effects of material nonhomogeneous parameters on crack propagation paths were also discussed in detail.It is shown that the present method can provide relatively accurate predictions of crack paths in two-directionally graded composites.Crack propagates in the decreasing direction of effective Young′s modulus.The shape and steepness of property gradient perpendicular to the crack surface have great influences on crack paths.Through redesigning material property reasonably,crack growth in graded material can be changed to improve mechanical behaviours of cracked structures.展开更多
Through equilibrium and non-equilibrium molecular dynamics simulations,we have demonstrated the inhibitory effect of composition graded interface on thermal transport behavior in lateral heterostructures.Specifically,...Through equilibrium and non-equilibrium molecular dynamics simulations,we have demonstrated the inhibitory effect of composition graded interface on thermal transport behavior in lateral heterostructures.Specifically,we investigated the influence of composition gradient length and heterogeneous particles at the silicene/germanene(SIL/GER)heterostructure interface on heat conduction.Our results indicate that composition graded interface at the interface diminishes the thermal conductivity of the heterostructure,with a further reduction observed as the length increases,while the effect of the heterogeneous particles can be considered negligible.To unveil the influence of composition graded interface on thermal transport,we conducted phonon analysis and identified the presence of phonon localization within the interface composition graded region.Through these analyses,we have determined that the decrease in thermal conductivity is correlated with phonon localization within the heterostructure,where a stronger degree of phonon localization signifies poorer thermal conductivity in the material.Our research findings not only contribute to understanding the impact of interface gradient-induced phonon localization on thermal transport but also offer insights into the modulation of thermal conductivity in heterostructures.展开更多
The ex-situ incorporation of the secondary SiC reinforcement,along with the in-situ incorporation of the tertiary and quaternary Mg_(3)N_(2) and Si_(3)N_(4) phases,in the primary matrix of Mg_(2)Si is employed in orde...The ex-situ incorporation of the secondary SiC reinforcement,along with the in-situ incorporation of the tertiary and quaternary Mg_(3)N_(2) and Si_(3)N_(4) phases,in the primary matrix of Mg_(2)Si is employed in order to provide ultimate wear resistance based on the laser-irradiation-induced inclusion of N_(2) gas during laser powder bed fusion.This is substantialized based on both the thermal diffusion-and chemical reactionbased metallurgy of the Mg_(2)Si–SiC/nitride hybrid composite.This study also proposes a functional platform for systematically modulating a functionally graded structure and modeling build-direction-dependent architectonics during additive manufacturing.This strategy enables the development of a compositional gradient from the center to the edge of each melt pool of the Mg_(2)Si–SiC/nitride hybrid composite.Consequently,the coefficient of friction of the hybrid composite exhibits a 309.3%decrease to–1.67 compared to–0.54 for the conventional nonreinforced Mg_(2)Si structure,while the tensile strength exhibits a 171.3%increase to 831.5 MPa compared to 485.3 MPa for the conventional structure.This outstanding mechanical behavior is due to the(1)the complementary and synergistic reinforcement effects of the SiC and nitride compounds,each of which possesses an intrinsically high hardness,and(2)the strong adhesion of these compounds to the Mg_(2)Si matrix despite their small sizes and low concentrations.展开更多
Solar-powered interfacial evaporation is an energy-efficient solution for water scarcity.It requires solar absorbers to facilitate upward water transport and limit the heat to the surface for efficient evaporation.Fur...Solar-powered interfacial evaporation is an energy-efficient solution for water scarcity.It requires solar absorbers to facilitate upward water transport and limit the heat to the surface for efficient evaporation.Furthermore,downward salt ion transport is also desired to prevent salt accumulation.However,achieving simultaneously fast water uptake,downward salt transport,and heat localization is challenging due to highly coupled water,mass,and thermal transport.Here,we develop a structurally graded aerogel inspired by tree transport systems to collectively optimize water,salt,and thermal transport.The arched aerogel features root-like,fan-shaped microchannels for rapid water uptake and downward salt diffusion,and horizontally aligned pores near the surface for heat localization through maximizing solar absorption and minimizing conductive heat loss.These structural characteristics gave rise to consistent evaporation rates of 2.09 kg m^(-2) h^(-1) under one-sun illumination in a 3.5 wt%NaCl solution for 7 days without degradation.Even in a high-salinity solution of 20 wt%NaCl,the evaporation rates maintained stable at 1.94 kg m^(-2) h^(-1) for 8 h without salt crystal formation.This work offers a novel microstructural design to address the complex interplay of water,salt,and thermal transport.展开更多
This study focuses on the analysis of the Chinese composition writing performance of fourth,fifth,and sixth grade students in 16 selected schools in Longhua District,Shenzhen during the spring semester of 2023.Using L...This study focuses on the analysis of the Chinese composition writing performance of fourth,fifth,and sixth grade students in 16 selected schools in Longhua District,Shenzhen during the spring semester of 2023.Using LIWC(Linguistic Inquiry and Word Count)as a text analysis tool,the study explores the impact of LIWC categories on writing performance which is scaled by score.The results show that the simple LIWC word categories have a significant positive influence on the composition scores of lower-grade students;while complex LIWC word categories have a significant negative influence on the composition scores of lower-grade students but a significant positive influence on the composition scores of higher-grade students.Process word categories have a positive influence on the composition scores of all three grades,but the impact of complex process word categories increases as the grade level rises.展开更多
Functionally graded Al/B_4C, Al/Si C, Al/Al_2O_3 and Al/TiB_2 composites with constant 12%(mass fraction) of reinforcement were fabricated by centrifugal casting and hollow cylindrical components were obtained. Micros...Functionally graded Al/B_4C, Al/Si C, Al/Al_2O_3 and Al/TiB_2 composites with constant 12%(mass fraction) of reinforcement were fabricated by centrifugal casting and hollow cylindrical components were obtained. Microstructural characteristics were investigated at outer surface of all composites and segregation of reinforcement particles was observed. Graded property of the composites with different reinforcements was investigated through hardness and tensile measurements. Results revealed that the outer peripheries of all composites exhibit higher hardness except in Al/B_4C composite and the outer zones of all composites show higher tensile strength. Abrasive wear test was conducted on the outer peripheries of all composites and Al/TiB_2 composite exhibits less wear rate.展开更多
Al2024/SiC functionally graded materials (FGMs) with different numbers of graded layers and different amounts of SiC were fabricated successfully by powder metallurgy method and hot pressing process. The effects of in...Al2024/SiC functionally graded materials (FGMs) with different numbers of graded layers and different amounts of SiC were fabricated successfully by powder metallurgy method and hot pressing process. The effects of increasing SiC content and number of layers of Al2024/SiC FGMs on the microstructure and mechanical properties of the composite were investigated. X-ray diffraction (XRD) and scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDX) analyses indicated that Al and SiC were dominant components as well as others such as Al4C3, CuAl2, and CuMgAl2展开更多
Al/SiC functionally graded material(FGM) was developed through a novel multi-step friction stir processing(FSP) method. Si C particles with a mean size of 27.5 μm were embedded in the groove on the 6082-Al plate. To ...Al/SiC functionally graded material(FGM) was developed through a novel multi-step friction stir processing(FSP) method. Si C particles with a mean size of 27.5 μm were embedded in the groove on the 6082-Al plate. To create a graded structure over a predefined value, FSP was carried out with three tools with different pin lengths and with varying volume fractions of SiC particles. The structure was formed by passing tools with 1-3 passes with a constant rotational and traveling speeds of 900 r/min and 20 mm/min, respectively. The experiments were conducted at room temperature. Microstructural features of functionally graded(FG) samples were examined by using scanning electron microscopy(SEM) and 3D light microscopy. Mechanical properties in terms of wear resistance and microhardness were thoroughly assessed. The results indicate that the increase in FSP pass number causes more uniform SiC particle dispersion. The microhardness values were impacted by the number of passes and improved by 51.54% for Pass 3 when compared to as-received 6082-Al. Wear resistance of Al/SiC FG samples was found to increase as a result of the addition of SiC particles.展开更多
The perturbation method is used to study the localization of electric field distribution and the effective nonlinear response of graded composites under an external alternating-current（AC） and direct-current（DC） e...The perturbation method is used to study the localization of electric field distribution and the effective nonlinear response of graded composites under an external alternating-current（AC） and direct-current（DC） electric field E app = E 0（1 ＋ sin ωt）.The dielectric profile of the cylindrical inclusions is modeled by function ε i（r） = C k r k（r ≤ a）,where r is the radius of the cylindrical inclusion,and C k,k,a are parameters.In the dilute limit,the local potentials and the effective nonlinear responses at all harmonics are derived.Meanwhile,the general effective nonlinear responses are also derived and compared with the effective nonlinear responses at harmonics under the AC and DC external field.It is found that the effective nonlinear AC and DC responses at harmonics can be calculated by those of the general effective nonlinear of the graded composites under the external DC electric field.Moreover,the obtained local electrical fields show that the electrical field distribution in the cylindrical inclusions is controllable,and the maximum of the electric field inside the cylinder is at its center.展开更多
The effective dielectric response of linear composites containing graded material is investigated under an applied electric field E_0.For the cylindrical inclusion with gradient dielectric function,ει(r)=b+cr,random...The effective dielectric response of linear composites containing graded material is investigated under an applied electric field E_0.For the cylindrical inclusion with gradient dielectric function,ει(r)=b+cr,randomly embedded in a host with dielectric constant εm,we have obtained the exact solution of local electric potential of the composite media regions,which obeys a linear constitutive relation D=εE,using hypergeometric function.In dilute limit,we have derived the effective dielectric response of the linear composite media.Furthermore,for larger volume fraction,the formulas of effective dielectric response of the graded composite media are given.展开更多
The manner by which the particles settle in the laminar flow region is first described and the characteristics of co sedimentation of two species particles are summarized.The subsequent introduction is focused on th...The manner by which the particles settle in the laminar flow region is first described and the characteristics of co sedimentation of two species particles are summarized.The subsequent introduction is focused on the fabrication process of continuously graded composites using co sedimentation technique.Finally,the authors point out the key problem that should be solved immediately,based on their current work.展开更多
Under an external uniform electric field, the dielectric response of graded cylindrical composites having generalized dielectric profile inclusions is investigated. The generalized dielectric profile of graded cylindr...Under an external uniform electric field, the dielectric response of graded cylindrical composites having generalized dielectric profile inclusions is investigated. The generalized dielectric profile of graded cylindrical inclusion is expressed in the form, εi（r） = c（b ＋ r）^keβr where r is the radial variable of the cylindrical inclusions and c, b, k and β are parameters. The local potential solution of generalized dielectric profile graded composites is derived by means of the power series method and the effective dielectric response is predicted in the dilute limit. Moreover, from the result of generalized profile, the analytical solutions of local potentials and the effective responses of graded composites having three cases of dielectric profiles, i.e., the exponential profile εi（r） = ce^βr, the general power law profile εi（r） = c（b ＋ r）^k and the profile εi（r） = cr^keβr, are sorted out, respectively. In the dilute limit, our exact results are used to test the validity of differential effective dipole approximation （DEDA） for estimating the effective response of graded cylindrical composites, and it is shown that the DEDA is in excellent agreement with the exact result.展开更多
A novel unselective regrowth buried heterostructure long-wavelength superluminescent diode （SLD） with a graded composition bulk InGaAs active region is developed by metalorganic vapor phase epitaxy （MOVPE）. At a 1...A novel unselective regrowth buried heterostructure long-wavelength superluminescent diode （SLD） with a graded composition bulk InGaAs active region is developed by metalorganic vapor phase epitaxy （MOVPE）. At a 150mA injection current, the full width at half maximum of the emission spectrum of the SLD is about 72nm, ranging from 1602 to 1674nm. The emission spectrum is smooth and flat. The ripple of the spectrum is less than 0.3dB at any wavelength from 1550 to 1700nm. An output power of 4.3mW is obtained at a 200mA injection current under continuous-wave operation at room temperature. This device is suitable for the applications of light sources for gas detectors and L-band optical fiber communications.展开更多
In this study,the first-order shear deformation theory(FSDT)is used to establish a nonlinear dynamic model for a conical shell truncated by a functionally graded graphene platelet-reinforced composite(FG-GPLRC).The vi...In this study,the first-order shear deformation theory(FSDT)is used to establish a nonlinear dynamic model for a conical shell truncated by a functionally graded graphene platelet-reinforced composite(FG-GPLRC).The vibration analyses of the FG-GPLRC truncated conical shell are presented.Considering the graphene platelets(GPLs)of the FG-GPLRC truncated conical shell with three different distribution patterns,the modified Halpin-Tsai model is used to calculate the effective Young’s modulus.Hamilton’s principle,the FSDT,and the von-Karman type nonlinear geometric relationships are used to derive a system of partial differential governing equations of the FG-GPLRC truncated conical shell.The Galerkin method is used to obtain the ordinary differential equations of the truncated conical shell.Then,the analytical nonlinear frequencies of the FG-GPLRC truncated conical shell are solved by the harmonic balance method.The effects of the weight fraction and distribution pattern of the GPLs,the ratio of the length to the radius as well as the ratio of the radius to the thickness of the FG-GPLRC truncated conical shell on the nonlinear natural frequency characteristics are discussed.This study culminates in the discovery of the periodic motion and chaotic motion of the FG-GPLRC truncated conical shell.展开更多
Theoretical analysis and numerical calculations of Love wave propagation in layered graded composites with imperfectly bonded interface are described in this paper. On the basis of WKB method, the approximate analytic...Theoretical analysis and numerical calculations of Love wave propagation in layered graded composites with imperfectly bonded interface are described in this paper. On the basis of WKB method, the approximate analytic solutions for Love waves are obtained. By the interface shear spring model, the dispersion relations for Love waves in layered graded composite structures with rigid, slip, and imperfectly bonded interfaces are given, and the effects of the interface conditions on the phase velocities of Love waves in SiC/Al layered graded composites are discussed. Numerical analysis shows that the phase velocity decreases when the defined flexibility parameter is greater. For the general imperfectly bonded interface, the phase velocity changes in the range of the velocities for the rigid and slip interface conditions.展开更多
By means of an inherent elevated-temperature of poured liquid steel,a Ti-C-30wt%Fe preform,which was pre-placed in a mould cavity,was directly ignited and a combustion synthesis reaction took place.As a result,a TiC-F...By means of an inherent elevated-temperature of poured liquid steel,a Ti-C-30wt%Fe preform,which was pre-placed in a mould cavity,was directly ignited and a combustion synthesis reaction took place.As a result,a TiC-Fe cermet coating with a thickness of about 10mm was simultaneously synthesized on the solidified steel matrix.The synthesized coating exhibits a feature of graded composite structure,in which both the amount and size of TiC particles decrease gradually with an increasing distance from the furface of the coating.Moreover,by a proper casting technique,the pores formed during the combustion synthesis of the preform could be centrally distributed in 2-3mm in outer layer of the coating.When this outer porous layer was worn off,the rest coating with a thickness of about 8mm possesses a dense structure and a high abrasive wear resistance.展开更多
Buckling and postbuckling characteristics of laminated graphene-enhanced composite(GEC)truncated conical shells exposed to torsion under temperature conditions using finite element method(FEM)simulation are presented ...Buckling and postbuckling characteristics of laminated graphene-enhanced composite(GEC)truncated conical shells exposed to torsion under temperature conditions using finite element method(FEM)simulation are presented in this study.In the thickness direction,the GEC layers of the conical shell are ordered in a piece-wise arrangement of functionally graded(FG)distribution,with each layer containing a variable volume fraction for graphene reinforcement.To calculate the properties of temperaturedependent material of GEC layers,the extended Halpin-Tsai micromechanical framework is used.The FEM model is verified via comparing the current results obtained with the theoretical estimates for homogeneous,laminated cylindrical,and conical shells,the FEM model is validated.The computational results show that a piece-wise FG graphene volume fraction distribution can improve the torque of critical buckling and torsional postbuckling strength.Also,the geometric parameters have a critical impact on the stability of the conical shell.However,a temperature rise can reduce the crucial torsional buckling torque as well as the GEC laminated truncated conical shell’s postbuckling strength.展开更多
p-i-n Al_(x)Ga_(1−x)As/GaAs detectors with graded compositions and graded doping were grown and prepared.From the current-voltage and capacitance-voltage measurement results,the devices had good p-n junction diode cha...p-i-n Al_(x)Ga_(1−x)As/GaAs detectors with graded compositions and graded doping were grown and prepared.From the current-voltage and capacitance-voltage measurement results,the devices had good p-n junction diode characteristics,and the electric field strength under an unbiased voltage was 1.7×10^(5) Vcm^(-1).The full width at half maximum and charge collection efficiency of the detectors obtained from energy spectrum measurements of 5.48-MeV alpha particles were 3.04 and approximately 93%,respectively.In this study,we created the most advanced and promising state-of-the-art unbiased detector reported to date.展开更多
The nonlinear stability of sandwich cylindrical shells comprising porous functionally graded material(FGM) and carbon nanotube reinforced composite(CNTRC)layers subjected to uniform temperature rise is investigated. T...The nonlinear stability of sandwich cylindrical shells comprising porous functionally graded material(FGM) and carbon nanotube reinforced composite(CNTRC)layers subjected to uniform temperature rise is investigated. Two sandwich models corresponding to CNTRC and FGM face sheets are proposed. Carbon nanotubes(CNTs) in the CNTRC layer are embedded into a matrix according to functionally graded distributions. The effects of porosity in the FGM and the temperature dependence of properties of all constituent materials are considered. The effective properties of the porous FGM and CNTRC are determined by using the modified and extended versions of a linear mixture rule, respectively. The basic equations governing the stability problem of thin sandwich cylindrical shells are established within the framework of the Donnell shell theory including the von K’arm’an-Donnell nonlinearity. These equations are solved by using the multi-term analytical solutions and the Galerkin method for simply supported shells.The critical buckling temperatures and postbuckling paths are determined through an iteration procedure. The study reveals that the sandwich shell model with a CNTRC core layer and relatively thin porous FGM face sheets can have the best capacity of thermal load carrying. In addition, unlike the cases of mechanical loads, porosities have beneficial effects on the nonlinear stability of sandwich shells under the thermal load. It is suggested that an appropriate combination of advantages of FGM and CNTRC can result in optimal efficiency for advanced sandwich structures.展开更多
In INs study, the fabrication of multilayer AI（Zn）-A1203 with different volume fractions of A1203 was investigated. A1 and ZnO powders were milled by a plaaetaxy ball mill, after which five-layer functionally graded...In INs study, the fabrication of multilayer AI（Zn）-A1203 with different volume fractions of A1203 was investigated. A1 and ZnO powders were milled by a plaaetaxy ball mill, after which five-layer functionally graded samples were produced flarough hot pressing at 580~C and 90 MPa pressure for 30 min. Formation of reinforcing A1203 particles occurred in the aluminum matrix via the aluminolkermic reaction. Determination of the ignition temperature of the aluminolkennic reaction was accomplished using differential lkermal and lkermo- gravimelric amlyses. Scaaming electron microscopy, energy dispersive spectroscopy, and X-ray diffractometery amlyses were utilized to characterize the specimens. The lkermal amlysis results showed that the ignition temperatures for the aluminolkennic reaction of layers with the highest and lowest ZnO contents were 667 and 670~C, respectively. Microslxuctural observation and chemical amlysis confirmed the fa- brication of AI（Zn）-A1203 functionally graded materials composites with precipitation of additional Zn in the matrix. Moreover, nearly dense functionally graded samples demonstrated minimum and maximum hacdness values of HV 75 and HV 130, respectively.展开更多
基金supported by the Fundamental Research Funds for the Central Universities(No.NS2016003)
文摘Crack propagation path in two-directionally graded composites was investigated by the finite element method.A graded extended finite element method(XFEM)was employed to calculate displacement and stress fields in cracked graded structures.And a post-processing subroutine of interaction energy integral was implemented to extract the mixed-mode stress intensity factors(SIFs).The maximum hoop stress(MHS)criterion was adopted to predict crack growth direction based on the assumption of local homogenization of asymptotic crack-tip fields in graded materials.Effects of material nonhomogeneous parameters on crack propagation paths were also discussed in detail.It is shown that the present method can provide relatively accurate predictions of crack paths in two-directionally graded composites.Crack propagates in the decreasing direction of effective Young′s modulus.The shape and steepness of property gradient perpendicular to the crack surface have great influences on crack paths.Through redesigning material property reasonably,crack growth in graded material can be changed to improve mechanical behaviours of cracked structures.
基金Project supported by the National Natural Science Foundation of China (Grant No.12104291)。
文摘Through equilibrium and non-equilibrium molecular dynamics simulations,we have demonstrated the inhibitory effect of composition graded interface on thermal transport behavior in lateral heterostructures.Specifically,we investigated the influence of composition gradient length and heterogeneous particles at the silicene/germanene(SIL/GER)heterostructure interface on heat conduction.Our results indicate that composition graded interface at the interface diminishes the thermal conductivity of the heterostructure,with a further reduction observed as the length increases,while the effect of the heterogeneous particles can be considered negligible.To unveil the influence of composition graded interface on thermal transport,we conducted phonon analysis and identified the presence of phonon localization within the interface composition graded region.Through these analyses,we have determined that the decrease in thermal conductivity is correlated with phonon localization within the heterostructure,where a stronger degree of phonon localization signifies poorer thermal conductivity in the material.Our research findings not only contribute to understanding the impact of interface gradient-induced phonon localization on thermal transport but also offer insights into the modulation of thermal conductivity in heterostructures.
基金supported by the Learning & Academic Research Institution for Master’s and Ph.D. Students and Postdocs (LAMP) Program of the National Research Foundation of Korea (NRF) grant funded by the Ministry of Education (No. RS-2023-00285353)supported by the National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIP) (NRF-2021R1A2C3006662, NRF-2022R1A5A1030054, and 2021R1A2C1091301)+3 种基金the support from Natural Sciences and Engineering Research Council of Canada (NSERC)Canada Foundation for Innovation (CFI)Atlantic Canada Opportunities Agency (ACOA)the New Brunswick Innovation Foundation (NBIF)
文摘The ex-situ incorporation of the secondary SiC reinforcement,along with the in-situ incorporation of the tertiary and quaternary Mg_(3)N_(2) and Si_(3)N_(4) phases,in the primary matrix of Mg_(2)Si is employed in order to provide ultimate wear resistance based on the laser-irradiation-induced inclusion of N_(2) gas during laser powder bed fusion.This is substantialized based on both the thermal diffusion-and chemical reactionbased metallurgy of the Mg_(2)Si–SiC/nitride hybrid composite.This study also proposes a functional platform for systematically modulating a functionally graded structure and modeling build-direction-dependent architectonics during additive manufacturing.This strategy enables the development of a compositional gradient from the center to the edge of each melt pool of the Mg_(2)Si–SiC/nitride hybrid composite.Consequently,the coefficient of friction of the hybrid composite exhibits a 309.3%decrease to–1.67 compared to–0.54 for the conventional nonreinforced Mg_(2)Si structure,while the tensile strength exhibits a 171.3%increase to 831.5 MPa compared to 485.3 MPa for the conventional structure.This outstanding mechanical behavior is due to the(1)the complementary and synergistic reinforcement effects of the SiC and nitride compounds,each of which possesses an intrinsically high hardness,and(2)the strong adhesion of these compounds to the Mg_(2)Si matrix despite their small sizes and low concentrations.
基金financially supported by the Research Grants Council of Hong Kong SAR(16200720)Environment and Conservation Fund of Hong Kong SAR(Project No.21/2022)+2 种基金Young Scientists Fund of National Natural Science Foundation of China(Grant No.52303106)Research Institute for Advanced Manufucturing(Project No.CD8R)the startup fund for new recruits of PolyU(Project Nos.P0038855 and P0038858)。
文摘Solar-powered interfacial evaporation is an energy-efficient solution for water scarcity.It requires solar absorbers to facilitate upward water transport and limit the heat to the surface for efficient evaporation.Furthermore,downward salt ion transport is also desired to prevent salt accumulation.However,achieving simultaneously fast water uptake,downward salt transport,and heat localization is challenging due to highly coupled water,mass,and thermal transport.Here,we develop a structurally graded aerogel inspired by tree transport systems to collectively optimize water,salt,and thermal transport.The arched aerogel features root-like,fan-shaped microchannels for rapid water uptake and downward salt diffusion,and horizontally aligned pores near the surface for heat localization through maximizing solar absorption and minimizing conductive heat loss.These structural characteristics gave rise to consistent evaporation rates of 2.09 kg m^(-2) h^(-1) under one-sun illumination in a 3.5 wt%NaCl solution for 7 days without degradation.Even in a high-salinity solution of 20 wt%NaCl,the evaporation rates maintained stable at 1.94 kg m^(-2) h^(-1) for 8 h without salt crystal formation.This work offers a novel microstructural design to address the complex interplay of water,salt,and thermal transport.
文摘This study focuses on the analysis of the Chinese composition writing performance of fourth,fifth,and sixth grade students in 16 selected schools in Longhua District,Shenzhen during the spring semester of 2023.Using LIWC(Linguistic Inquiry and Word Count)as a text analysis tool,the study explores the impact of LIWC categories on writing performance which is scaled by score.The results show that the simple LIWC word categories have a significant positive influence on the composition scores of lower-grade students;while complex LIWC word categories have a significant negative influence on the composition scores of lower-grade students but a significant positive influence on the composition scores of higher-grade students.Process word categories have a positive influence on the composition scores of all three grades,but the impact of complex process word categories increases as the grade level rises.
基金Department of Science and Technology (India) for the financial support (Grant No.SR/S3/MERC/0116/2012)
文摘Functionally graded Al/B_4C, Al/Si C, Al/Al_2O_3 and Al/TiB_2 composites with constant 12%(mass fraction) of reinforcement were fabricated by centrifugal casting and hollow cylindrical components were obtained. Microstructural characteristics were investigated at outer surface of all composites and segregation of reinforcement particles was observed. Graded property of the composites with different reinforcements was investigated through hardness and tensile measurements. Results revealed that the outer peripheries of all composites exhibit higher hardness except in Al/B_4C composite and the outer zones of all composites show higher tensile strength. Abrasive wear test was conducted on the outer peripheries of all composites and Al/TiB_2 composite exhibits less wear rate.
文摘Al2024/SiC functionally graded materials (FGMs) with different numbers of graded layers and different amounts of SiC were fabricated successfully by powder metallurgy method and hot pressing process. The effects of increasing SiC content and number of layers of Al2024/SiC FGMs on the microstructure and mechanical properties of the composite were investigated. X-ray diffraction (XRD) and scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDX) analyses indicated that Al and SiC were dominant components as well as others such as Al4C3, CuAl2, and CuMgAl2
文摘Al/SiC functionally graded material(FGM) was developed through a novel multi-step friction stir processing(FSP) method. Si C particles with a mean size of 27.5 μm were embedded in the groove on the 6082-Al plate. To create a graded structure over a predefined value, FSP was carried out with three tools with different pin lengths and with varying volume fractions of SiC particles. The structure was formed by passing tools with 1-3 passes with a constant rotational and traveling speeds of 900 r/min and 20 mm/min, respectively. The experiments were conducted at room temperature. Microstructural features of functionally graded(FG) samples were examined by using scanning electron microscopy(SEM) and 3D light microscopy. Mechanical properties in terms of wear resistance and microhardness were thoroughly assessed. The results indicate that the increase in FSP pass number causes more uniform SiC particle dispersion. The microhardness values were impacted by the number of passes and improved by 51.54% for Pass 3 when compared to as-received 6082-Al. Wear resistance of Al/SiC FG samples was found to increase as a result of the addition of SiC particles.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.40876094 and JQ10974106)the National High Technology Research and Development Program of China(Grant Nos.2009AA09Z102 and 2008AA09A403)+1 种基金the Excellent Youth Fundation of Shandong Scientific Committee,China(Grant No.JQ201018)the Natural Science Foundation of Shandong Province,China(Grant No.ZR2009AZ002)
文摘The perturbation method is used to study the localization of electric field distribution and the effective nonlinear response of graded composites under an external alternating-current（AC） and direct-current（DC） electric field E app = E 0（1 ＋ sin ωt）.The dielectric profile of the cylindrical inclusions is modeled by function ε i（r） = C k r k（r ≤ a）,where r is the radius of the cylindrical inclusion,and C k,k,a are parameters.In the dilute limit,the local potentials and the effective nonlinear responses at all harmonics are derived.Meanwhile,the general effective nonlinear responses are also derived and compared with the effective nonlinear responses at harmonics under the AC and DC external field.It is found that the effective nonlinear AC and DC responses at harmonics can be calculated by those of the general effective nonlinear of the graded composites under the external DC electric field.Moreover,the obtained local electrical fields show that the electrical field distribution in the cylindrical inclusions is controllable,and the maximum of the electric field inside the cylinder is at its center.
文摘The effective dielectric response of linear composites containing graded material is investigated under an applied electric field E_0.For the cylindrical inclusion with gradient dielectric function,ει(r)=b+cr,randomly embedded in a host with dielectric constant εm,we have obtained the exact solution of local electric potential of the composite media regions,which obeys a linear constitutive relation D=εE,using hypergeometric function.In dilute limit,we have derived the effective dielectric response of the linear composite media.Furthermore,for larger volume fraction,the formulas of effective dielectric response of the graded composite media are given.
基金FundedbytheNationalNaturalScienceFoundationofChi na (GrantNo.5 0 1710 4 9)
文摘The manner by which the particles settle in the laminar flow region is first described and the characteristics of co sedimentation of two species particles are summarized.The subsequent introduction is focused on the fabrication process of continuously graded composites using co sedimentation technique.Finally,the authors point out the key problem that should be solved immediately,based on their current work.
基金Project supported by National Natural Science Foundation of China （Grant Nos 40476062 and 10374026）. Yu Kin-Wah acknowledges the support from RGC Earmarked Grant of the Hong Kong SAR Government.
文摘Under an external uniform electric field, the dielectric response of graded cylindrical composites having generalized dielectric profile inclusions is investigated. The generalized dielectric profile of graded cylindrical inclusion is expressed in the form, εi（r） = c（b ＋ r）^keβr where r is the radial variable of the cylindrical inclusions and c, b, k and β are parameters. The local potential solution of generalized dielectric profile graded composites is derived by means of the power series method and the effective dielectric response is predicted in the dilute limit. Moreover, from the result of generalized profile, the analytical solutions of local potentials and the effective responses of graded composites having three cases of dielectric profiles, i.e., the exponential profile εi（r） = ce^βr, the general power law profile εi（r） = c（b ＋ r）^k and the profile εi（r） = cr^keβr, are sorted out, respectively. In the dilute limit, our exact results are used to test the validity of differential effective dipole approximation （DEDA） for estimating the effective response of graded cylindrical composites, and it is shown that the DEDA is in excellent agreement with the exact result.
文摘A novel unselective regrowth buried heterostructure long-wavelength superluminescent diode （SLD） with a graded composition bulk InGaAs active region is developed by metalorganic vapor phase epitaxy （MOVPE）. At a 150mA injection current, the full width at half maximum of the emission spectrum of the SLD is about 72nm, ranging from 1602 to 1674nm. The emission spectrum is smooth and flat. The ripple of the spectrum is less than 0.3dB at any wavelength from 1550 to 1700nm. An output power of 4.3mW is obtained at a 200mA injection current under continuous-wave operation at room temperature. This device is suitable for the applications of light sources for gas detectors and L-band optical fiber communications.
基金Project supported by the National Natural Science Foundation of China(Nos.12002057,11872127,11832002)the Scientific Research Project of Beijing Educational Committee(No.KM202111232023)the Qin Xin Talents Cultivation Program,Beijing Information Science&Technology University(Nos.QXTCP C202102,A201901)。
文摘In this study,the first-order shear deformation theory(FSDT)is used to establish a nonlinear dynamic model for a conical shell truncated by a functionally graded graphene platelet-reinforced composite(FG-GPLRC).The vibration analyses of the FG-GPLRC truncated conical shell are presented.Considering the graphene platelets(GPLs)of the FG-GPLRC truncated conical shell with three different distribution patterns,the modified Halpin-Tsai model is used to calculate the effective Young’s modulus.Hamilton’s principle,the FSDT,and the von-Karman type nonlinear geometric relationships are used to derive a system of partial differential governing equations of the FG-GPLRC truncated conical shell.The Galerkin method is used to obtain the ordinary differential equations of the truncated conical shell.Then,the analytical nonlinear frequencies of the FG-GPLRC truncated conical shell are solved by the harmonic balance method.The effects of the weight fraction and distribution pattern of the GPLs,the ratio of the length to the radius as well as the ratio of the radius to the thickness of the FG-GPLRC truncated conical shell on the nonlinear natural frequency characteristics are discussed.This study culminates in the discovery of the periodic motion and chaotic motion of the FG-GPLRC truncated conical shell.
基金Engineering Research Institute of Peking University (ERIPKU) Joint Building Project of Beijing Education Committee
文摘Theoretical analysis and numerical calculations of Love wave propagation in layered graded composites with imperfectly bonded interface are described in this paper. On the basis of WKB method, the approximate analytic solutions for Love waves are obtained. By the interface shear spring model, the dispersion relations for Love waves in layered graded composite structures with rigid, slip, and imperfectly bonded interfaces are given, and the effects of the interface conditions on the phase velocities of Love waves in SiC/Al layered graded composites are discussed. Numerical analysis shows that the phase velocity decreases when the defined flexibility parameter is greater. For the general imperfectly bonded interface, the phase velocity changes in the range of the velocities for the rigid and slip interface conditions.
基金FinanciallysupportedbytheNationalNaturalScienceFoundationofChina (No .5 0 2 76 0 2 3)
文摘By means of an inherent elevated-temperature of poured liquid steel,a Ti-C-30wt%Fe preform,which was pre-placed in a mould cavity,was directly ignited and a combustion synthesis reaction took place.As a result,a TiC-Fe cermet coating with a thickness of about 10mm was simultaneously synthesized on the solidified steel matrix.The synthesized coating exhibits a feature of graded composite structure,in which both the amount and size of TiC particles decrease gradually with an increasing distance from the furface of the coating.Moreover,by a proper casting technique,the pores formed during the combustion synthesis of the preform could be centrally distributed in 2-3mm in outer layer of the coating.When this outer porous layer was worn off,the rest coating with a thickness of about 8mm possesses a dense structure and a high abrasive wear resistance.
文摘Buckling and postbuckling characteristics of laminated graphene-enhanced composite(GEC)truncated conical shells exposed to torsion under temperature conditions using finite element method(FEM)simulation are presented in this study.In the thickness direction,the GEC layers of the conical shell are ordered in a piece-wise arrangement of functionally graded(FG)distribution,with each layer containing a variable volume fraction for graphene reinforcement.To calculate the properties of temperaturedependent material of GEC layers,the extended Halpin-Tsai micromechanical framework is used.The FEM model is verified via comparing the current results obtained with the theoretical estimates for homogeneous,laminated cylindrical,and conical shells,the FEM model is validated.The computational results show that a piece-wise FG graphene volume fraction distribution can improve the torque of critical buckling and torsional postbuckling strength.Also,the geometric parameters have a critical impact on the stability of the conical shell.However,a temperature rise can reduce the crucial torsional buckling torque as well as the GEC laminated truncated conical shell’s postbuckling strength.
基金supported by the National Natural Science Foundation of China(No.61964001)General Project of Jiangxi Province Key R&D Program(No.20212BBG73012)+3 种基金Natural Science Foundation of Jiangxi Province(No.20192BAB207033)Key Scientific Research Projects of Henan Higher Education Institutions(No.22A490001)State Key Laboratory of Particle Detection and Electronics(No.SKLPDE-KF-2019)Jiangxi Provincial Postdoctoral Science Foundation(No.2019RC30).
文摘p-i-n Al_(x)Ga_(1−x)As/GaAs detectors with graded compositions and graded doping were grown and prepared.From the current-voltage and capacitance-voltage measurement results,the devices had good p-n junction diode characteristics,and the electric field strength under an unbiased voltage was 1.7×10^(5) Vcm^(-1).The full width at half maximum and charge collection efficiency of the detectors obtained from energy spectrum measurements of 5.48-MeV alpha particles were 3.04 and approximately 93%,respectively.In this study,we created the most advanced and promising state-of-the-art unbiased detector reported to date.
基金the Vietnam National Foundation for Science and Technology Development(NAFOSTED)(No.107.02-2019.318)。
文摘The nonlinear stability of sandwich cylindrical shells comprising porous functionally graded material(FGM) and carbon nanotube reinforced composite(CNTRC)layers subjected to uniform temperature rise is investigated. Two sandwich models corresponding to CNTRC and FGM face sheets are proposed. Carbon nanotubes(CNTs) in the CNTRC layer are embedded into a matrix according to functionally graded distributions. The effects of porosity in the FGM and the temperature dependence of properties of all constituent materials are considered. The effective properties of the porous FGM and CNTRC are determined by using the modified and extended versions of a linear mixture rule, respectively. The basic equations governing the stability problem of thin sandwich cylindrical shells are established within the framework of the Donnell shell theory including the von K’arm’an-Donnell nonlinearity. These equations are solved by using the multi-term analytical solutions and the Galerkin method for simply supported shells.The critical buckling temperatures and postbuckling paths are determined through an iteration procedure. The study reveals that the sandwich shell model with a CNTRC core layer and relatively thin porous FGM face sheets can have the best capacity of thermal load carrying. In addition, unlike the cases of mechanical loads, porosities have beneficial effects on the nonlinear stability of sandwich shells under the thermal load. It is suggested that an appropriate combination of advantages of FGM and CNTRC can result in optimal efficiency for advanced sandwich structures.
文摘In INs study, the fabrication of multilayer AI（Zn）-A1203 with different volume fractions of A1203 was investigated. A1 and ZnO powders were milled by a plaaetaxy ball mill, after which five-layer functionally graded samples were produced flarough hot pressing at 580~C and 90 MPa pressure for 30 min. Formation of reinforcing A1203 particles occurred in the aluminum matrix via the aluminolkermic reaction. Determination of the ignition temperature of the aluminolkennic reaction was accomplished using differential lkermal and lkermo- gravimelric amlyses. Scaaming electron microscopy, energy dispersive spectroscopy, and X-ray diffractometery amlyses were utilized to characterize the specimens. The lkermal amlysis results showed that the ignition temperatures for the aluminolkennic reaction of layers with the highest and lowest ZnO contents were 667 and 670~C, respectively. Microslxuctural observation and chemical amlysis confirmed the fa- brication of AI（Zn）-A1203 functionally graded materials composites with precipitation of additional Zn in the matrix. Moreover, nearly dense functionally graded samples demonstrated minimum and maximum hacdness values of HV 75 and HV 130, respectively.
