The monolithic foamed propellants with high densities were prepared by casting and two-step foaming processes.Glycidyl azide polymer(GAP)and isocyanate were used as the binder system and 2,4,6,8,10,12-hexanitro-2,4,6,...The monolithic foamed propellants with high densities were prepared by casting and two-step foaming processes.Glycidyl azide polymer(GAP)and isocyanate were used as the binder system and 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane(HNIW,CL-20)was employed as the energetic component.The newly designed formulation containing 60%CL-20 produced a force constant of 1077 J/g and low flame temperature of 2817 K.Two foamed propellants with densities of 1.32 g/cm^(3)and 1.53 g/cm^(3)were fabricated by a confined foaming process and examined by closed bomb tests.The results revealed that porosity significantly affects burning performance.A size effect on combustion behaviors was observed for the foamed propellant with 5.56%porosity,and a double-hump progressive dynamic vivacity curve was obtained.At last,the 30 mm gun test was carried out to demonstrate the interior ballistic performance,and the muzzle velocity increased by 120 m/s at the same maximum chamber pressure when monolithic propellant was added in the charge.展开更多
In order to solve the issue that the combustible objects for cased telescoped ammunition (CTA) didn't burn completely during the combustion process, the microcellular combustible objects were foamed with numerous ...In order to solve the issue that the combustible objects for cased telescoped ammunition (CTA) didn't burn completely during the combustion process, the microcellular combustible objects were foamed with numerous cells in the micron order to improve the combustion performance by the supercritical carbon dioxide (SCeCO2) foaming technology. As the cell structure determined the combustion properties of microcellular combustible objects, the solubility of SCeCO2 dissolved into the combustible objects was obtained from the gravimetric method, and scanning electron microscope (SEM) was applied to characterize the cell structure under various process conditions of solubility, foaming temperature and foaming time. SEM images indicate that the cell diameter of microcellular combustible objects is in the level of 1 mm and the cell density is about 1011 cell,cm^-3. The microcellular combustible objects fabricated by the SCeCO2 foaming technology are smooth and uniform, and the high specific surface area of cell structure can lead to the significant combustion performance of microcellular combustible object for CTA in the future.展开更多
Sodium cocoyl glycinate(SCG),an environmentally friendly anionic amino acid surfactant,is widely used in daily chemical products as an upgraded alternative to traditional surfactants.In this study,crude Camellia oleif...Sodium cocoyl glycinate(SCG),an environmentally friendly anionic amino acid surfactant,is widely used in daily chemical products as an upgraded alternative to traditional surfactants.In this study,crude Camellia oleifera saponin(COS)was purified using AB-8 macroporous adsorption resin,and its composition and structure were analyzed.The effects of different mole fractions of COS(αCOS)on surface tension(γ),oil-water interfacial tension(IFT),emulsification,and foam properties of COS-SCG binary mixed systems were investigated in mixtures of SCG with purified COS.The stability ofγand foamability under diverse environmental conditions were also discussed.The results indicated that the COS-SCG system exhibited remarkable surface-active synergism.The minimum critical micelle concentration(cmc)of the mixed system was lower than that of SCG,and adding a small mole fraction of COS(1%-2%)induced a synergistic reduction ofγ.Specifically,the cmc andγwere 2.50×10-4 mol/L and 23.1 mN/m forαCOS=1%,respectively.The system exhibited exceptional IFT reduction capacity,achieving a minimum value of 1.42 mN/m atαCOS=10%.The mixed system reached a foaming volume(atαCOS=50%)and foam stability(atαCOS=75%)were 51.0 mL and 97.37%,respectively.Microscopic analysis further confirmed these outstanding foam properties.Moreover,the COS-SCG system displayed reducedγwith enhanced foaming volume under elevated temperatures(35-75℃)and salinity(0-20 g/L).However,acidic conditions and hard water compromised bothγstability and foamability.展开更多
Oriented graphene aerogels have limited applica-tions because the flexibility of their graphene sheets and mi-crostructure give them a low skeleton strength,insufficient compression resilience,and poor flexibility.We ...Oriented graphene aerogels have limited applica-tions because the flexibility of their graphene sheets and mi-crostructure give them a low skeleton strength,insufficient compression resilience,and poor flexibility.We report the preparation of novel aerogel materials with a much better per-formance.Using the driving force of graphene oxide(GO)self-assembly andπ-πinteractions,carbon nanotubes(CNTs)were attached to the GO sheets,and an oriented composite carbon skeleton was constructed using“hydro-plastic foam-ing”.The introduction of CNTs significantly increased the strength of the skeleton and gave the aerogel an excellent re-versible compressibility.The innovative use of cold pressing greatly improved the thermal conductivity and flexibility of the aerogel,providing new ideas for the development of high-performance aerogels.Tests show that the obtained graphene composite aerogel has a reversible compressive strain of over 90%and can withstand 500 compression cycles along the direc-tion of pore accumulation.It can endure more than 10000 bending cycles perpendicular to the direction of composite carbon layer stacking,and its in-plane thermal conductivity reaches 64.5 W·m^(-1)·K^(-1).When filled with phase change materials,the high porosity of the carbon skeleton enables the material to have a high phase change filling rate,and its phase change enthalpy is greater than 150 J/g.Thanks to the exceptional flexibility of the carbon skeleton,the macrostructure of phase change materials can be bent as needed to adapt to thermal management scenarios and conform to device shapes.This significantly enhances practical application compatibility,providing flexible support for temperature control and thermal management across diverse device forms.展开更多
The paper investigates the foaming and mildness properties of trehalolipids surfactant in rinse-off formulations,comparing it with the traditional nonionic surfactant alkyl-polyglycolide(APG).Both single surfactant an...The paper investigates the foaming and mildness properties of trehalolipids surfactant in rinse-off formulations,comparing it with the traditional nonionic surfactant alkyl-polyglycolide(APG).Both single surfactant and their surfactant complexes are evaluated.And the results show that trehalolipids have significant advantages in reducing surface tension,improving foam performance,and enhancing mildness.For mildness evaluation,multiple methods are employed in the study,including in vitro cell toxicity,inflammatory markers,colorimetric index of mildness CIM,and in vivo method of human skin patch test.The results show that the addition of trehalolipids increases IC50 and reduces the release of inflammatory markers of the binary surfactant system.However,the incorporation of trehalolipids has some negative effects on the skin’s lipid barrier function.Skin patch test results indicate that the addition of trehalolipids improves the mildness of surfactant system,particularly in sulfate-free system.Overall,trehalolipids,as nonionic surfactants,presents great potential to replace traditional surfactants in rinse off formulations with enhanced mildness and foam performance.展开更多
The compression and energy absorption properties of foam geopolymers increase stress wave attenuation under explosion impacts,reducing the vibration effect on the structure.Explosion tests were conducted using several...The compression and energy absorption properties of foam geopolymers increase stress wave attenuation under explosion impacts,reducing the vibration effect on the structure.Explosion tests were conducted using several composite structure models,including a concrete lining structure(CLS)without foam geopolymer and six foam geopolymer composite structures(FGCS)with different backfill parameters,to study the dynamic response and wave dissipation mechanisms of FGCS under explosive loading.Pressure,strain,and vibration responses at different locations were synchronously tested.The damage modes and dynamic responses of different models were compared,and how wave elimination and energy absorption efficiencies were affected by foam geopolymer backfill parameters was analyzed.The results showed that the foam geopolymer absorbed and dissipated the impact energy through continuous compressive deformation under high strain rates and dynamic loading,reducing the strain in the liner structure by 52%and increasing the pressure attenuation rate by 28%.Additionally,the foam geopolymer backfill reduced structural vibration and liner deformation,with the FGCS structure showing 35%less displacement and 70%less acceleration compared to the CLS.The FGCS model with thicker,less dense foam geopolymer backfill,having more pores and higher porosity,demonstrated better compression and energy absorption under dynamic impact,increasing stress wave attenuation efficiency.By analyzing the stress wave propagation and the compression characteristics of the porous medium,it was concluded that the stress transfer ratio of FGCS-ρ-579 was 77%lower than that of CLS,and the transmitted wave energy was 90%lower.The results of this study provide a scientific basis for optimizing underground composite structure interlayer parameters.展开更多
Bauxite tailing(BT)slurry has been generated and accumulated in large quantities,posing a threat to the green and sustainable development of the alumina industry.The regression equation between the actual water conten...Bauxite tailing(BT)slurry has been generated and accumulated in large quantities,posing a threat to the green and sustainable development of the alumina industry.The regression equation between the actual water content and mud water separation rate was established to achieve efficient resource utilization,and the feasibility of foam lightweight soil(FLS)prepared from BT was investigated.The effects of industrial waste residues(fly ash and slag powder)on the properties of FLS were studied.Meanwhile,the micro-mechanisms were revealed by XRD,SEM-EDS,and TG-DSC.The results revealed that fly ash reduced the workability and compressive strength of FLS.Slag powder can significantly enhance the compressive strength of FLS,which increased by 18.60%-23.26%,17.07%-58.54% and 12.12%-52.12%,respectively.Besides,slag powder can improve the long-term water stability performance and enhance carbonation resistance.XRD and thermal analyses showed that adding fly ash decreased the hydration degree of FLS,leading to a decrease in the hydration products.Slag powder improved the pore structure and compacted the skeleton structure of FLS.This study would provide an effective way to realize the resource utilization of BT,fly ash,and slag powder,with certain socio-economic and environmental benefits.展开更多
Carbonized melamine foam has been recognized as a promising material for microwave absorption due to its exceptional thermal stability,lightweight,and remarkable dielectric properties.In this study,we investigated the...Carbonized melamine foam has been recognized as a promising material for microwave absorption due to its exceptional thermal stability,lightweight,and remarkable dielectric properties.In this study,we investigated the impact of nitric acid oxidation on the surface of carbonized melamine foam and its microwave absorption properties.The treated foam exhibits optimal reflection loss of−21.51 dB at 13.20 GHz,with an effective absorption bandwidth of 7.04 GHz.The enhanced absorption properties are primarily attributed to the strengthened dielectric loss,improved impedance matching,and increased polarization losses resulting from the oxidized surfaces.This research demonstrates a promising new approach for research into surface treatments to improve the performances of microwave absorbers.展开更多
Polymethacrylimide(PMI)foam has the highest specific stiffness and strength among polymer foams,with excellent radar-absorbing capabilities,which provide it with broad prospects in underwater ap-plications.To evaluate...Polymethacrylimide(PMI)foam has the highest specific stiffness and strength among polymer foams,with excellent radar-absorbing capabilities,which provide it with broad prospects in underwater ap-plications.To evaluate the impact resistance of PMI foam sandwich structures,the dynamic response and energy absorption characteristics of PMI foam sandwich structures with different core layers under various water impact loads were investigated using combined experimental and numerical methods.A fluid-structure interaction device with a diffusion angle was used for water impact testing of the PMI foam sandwich structures.The 3D-DIC technique was employed to process the deformation images of the sandwich-structure back panel captured by the high-speed cameras.Numerical simulations were performed to analyze the dynamic deformation process of the PMI foam core.The results indicated that the maximum deformation of the back panel exhibited a nonlinear relationship with the impulse.Below the critical impulse,the maximum deformation of the back panel plateaued,which was determined by the core density.Beyond the critical impulse,the rate of deformation increased with the impulse was governed by the core thickness.Compared with different sandwich panels,PMI foam sandwich struc-tures demonstrate significant advantages in terms of impact resistance under high-impulse conditions.展开更多
To prepare the porous NC-based(nitrocellulose-based) gun propellants,the batch foaming process of using supercritical CO_2 as the physical blowing agent is used.The solubilities of CO_2 in the single-base propellants ...To prepare the porous NC-based(nitrocellulose-based) gun propellants,the batch foaming process of using supercritical CO_2 as the physical blowing agent is used.The solubilities of CO_2 in the single-base propellants and TEGDN(trimethyleneglycol dinitrate) propellants are measured by the gravimetric method,and SEM(scanning electron microscope) is used to observe the morphology of foamed propellants.The result shows that a large amount of CO_2 could be dissolved in NC-based propellants.The experimental results also reveal that the energetic plasticizer TEGDN exerts an important influence on the pore structure.The triaxial tensile failure mechanism for solid-state nucleation is used to explain the nucleation of NC-based propellants in the sol id state.Since some specific foaming behaviors of NC-based propellants can not be explained by the failure mechanism,a solid-state nucleation mechanism which revises the triaxial tensile failure mechanism is proposed and discussed.展开更多
为了检验北京大学街区尺度模式BSMPKU(Block Scale Model of Peking University)在城市大气环境研究中的适用性,首先利用Thompson风洞试验的数据集对BSMPKU模式进行了验证,并将其模拟结果与Open FOAM(Open Source Field Operation and M...为了检验北京大学街区尺度模式BSMPKU(Block Scale Model of Peking University)在城市大气环境研究中的适用性,首先利用Thompson风洞试验的数据集对BSMPKU模式进行了验证,并将其模拟结果与Open FOAM(Open Source Field Operation and Manipulation)的模拟结果进行比较,然后将BSMPKU模式应用在复杂的实际建筑物群中,进行了3种不同交通线源排放的理想数值模拟研究。结果表明:1)对于单个建筑物,随建筑物宽度增加,建筑物迎风面回流区和建筑物背风面的尾流涡区范围增大;2)BSMPKU和Open FOAM对单个建筑物周围的流场及浓度场有较好的模拟能力;3)与基于高斯扩散理论的AERMOD相比,BSMPKU和Open FOAM能更好地模拟出建筑物周围的浓度场,但两个模式的模拟结果都与实测值存在一定误差;4)在实际小区中,受建筑物群影响,建筑物群内的流场分布比较复杂,大部分地区风速大幅下降,建筑物群内污染物浓度场的分布受排放源位置和走向的影响很大;5)BSMPKU能较好地模拟出实际城区的流场和浓度场分布,具有一定模拟和预报复杂城区污染物扩散过程的能力。展开更多
The long-term stability of large-span soft rock tunnel is influenced greatly by the creep effect of surrounding rock.The development of a new type of foam concrete which has the property of high compressibility and lo...The long-term stability of large-span soft rock tunnel is influenced greatly by the creep effect of surrounding rock.The development of a new type of foam concrete which has the property of high compressibility and low ductility was introduced.And it was made as filling material of reserved deformation layer between the first lining and the second lining used in large-span soft rock tunnel.The effect of the new type of foam concrete was simulated as filling material of reserved deformation layer using numerical simulation.Through the comparison with the common large-span soft rock tunnel,the vault settlement and surrounding convergence are reduced by about 61% and 45%,respectively,after creep of 100 a.And in the second lining,the plastic zone reduces apparently and the maximum equivalent plastic strain decreases relatively.So,it can be found that the application of the new type of foam concrete as the filling material of reserved deformation layer can relieve the excessive force in second lining induced by rock creep,reduce its deformation and improve the stability of tunnel.展开更多
文摘The monolithic foamed propellants with high densities were prepared by casting and two-step foaming processes.Glycidyl azide polymer(GAP)and isocyanate were used as the binder system and 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane(HNIW,CL-20)was employed as the energetic component.The newly designed formulation containing 60%CL-20 produced a force constant of 1077 J/g and low flame temperature of 2817 K.Two foamed propellants with densities of 1.32 g/cm^(3)and 1.53 g/cm^(3)were fabricated by a confined foaming process and examined by closed bomb tests.The results revealed that porosity significantly affects burning performance.A size effect on combustion behaviors was observed for the foamed propellant with 5.56%porosity,and a double-hump progressive dynamic vivacity curve was obtained.At last,the 30 mm gun test was carried out to demonstrate the interior ballistic performance,and the muzzle velocity increased by 120 m/s at the same maximum chamber pressure when monolithic propellant was added in the charge.
文摘In order to solve the issue that the combustible objects for cased telescoped ammunition (CTA) didn't burn completely during the combustion process, the microcellular combustible objects were foamed with numerous cells in the micron order to improve the combustion performance by the supercritical carbon dioxide (SCeCO2) foaming technology. As the cell structure determined the combustion properties of microcellular combustible objects, the solubility of SCeCO2 dissolved into the combustible objects was obtained from the gravimetric method, and scanning electron microscope (SEM) was applied to characterize the cell structure under various process conditions of solubility, foaming temperature and foaming time. SEM images indicate that the cell diameter of microcellular combustible objects is in the level of 1 mm and the cell density is about 1011 cell,cm^-3. The microcellular combustible objects fabricated by the SCeCO2 foaming technology are smooth and uniform, and the high specific surface area of cell structure can lead to the significant combustion performance of microcellular combustible object for CTA in the future.
文摘Sodium cocoyl glycinate(SCG),an environmentally friendly anionic amino acid surfactant,is widely used in daily chemical products as an upgraded alternative to traditional surfactants.In this study,crude Camellia oleifera saponin(COS)was purified using AB-8 macroporous adsorption resin,and its composition and structure were analyzed.The effects of different mole fractions of COS(αCOS)on surface tension(γ),oil-water interfacial tension(IFT),emulsification,and foam properties of COS-SCG binary mixed systems were investigated in mixtures of SCG with purified COS.The stability ofγand foamability under diverse environmental conditions were also discussed.The results indicated that the COS-SCG system exhibited remarkable surface-active synergism.The minimum critical micelle concentration(cmc)of the mixed system was lower than that of SCG,and adding a small mole fraction of COS(1%-2%)induced a synergistic reduction ofγ.Specifically,the cmc andγwere 2.50×10-4 mol/L and 23.1 mN/m forαCOS=1%,respectively.The system exhibited exceptional IFT reduction capacity,achieving a minimum value of 1.42 mN/m atαCOS=10%.The mixed system reached a foaming volume(atαCOS=50%)and foam stability(atαCOS=75%)were 51.0 mL and 97.37%,respectively.Microscopic analysis further confirmed these outstanding foam properties.Moreover,the COS-SCG system displayed reducedγwith enhanced foaming volume under elevated temperatures(35-75℃)and salinity(0-20 g/L).However,acidic conditions and hard water compromised bothγstability and foamability.
文摘Oriented graphene aerogels have limited applica-tions because the flexibility of their graphene sheets and mi-crostructure give them a low skeleton strength,insufficient compression resilience,and poor flexibility.We report the preparation of novel aerogel materials with a much better per-formance.Using the driving force of graphene oxide(GO)self-assembly andπ-πinteractions,carbon nanotubes(CNTs)were attached to the GO sheets,and an oriented composite carbon skeleton was constructed using“hydro-plastic foam-ing”.The introduction of CNTs significantly increased the strength of the skeleton and gave the aerogel an excellent re-versible compressibility.The innovative use of cold pressing greatly improved the thermal conductivity and flexibility of the aerogel,providing new ideas for the development of high-performance aerogels.Tests show that the obtained graphene composite aerogel has a reversible compressive strain of over 90%and can withstand 500 compression cycles along the direc-tion of pore accumulation.It can endure more than 10000 bending cycles perpendicular to the direction of composite carbon layer stacking,and its in-plane thermal conductivity reaches 64.5 W·m^(-1)·K^(-1).When filled with phase change materials,the high porosity of the carbon skeleton enables the material to have a high phase change filling rate,and its phase change enthalpy is greater than 150 J/g.Thanks to the exceptional flexibility of the carbon skeleton,the macrostructure of phase change materials can be bent as needed to adapt to thermal management scenarios and conform to device shapes.This significantly enhances practical application compatibility,providing flexible support for temperature control and thermal management across diverse device forms.
文摘The paper investigates the foaming and mildness properties of trehalolipids surfactant in rinse-off formulations,comparing it with the traditional nonionic surfactant alkyl-polyglycolide(APG).Both single surfactant and their surfactant complexes are evaluated.And the results show that trehalolipids have significant advantages in reducing surface tension,improving foam performance,and enhancing mildness.For mildness evaluation,multiple methods are employed in the study,including in vitro cell toxicity,inflammatory markers,colorimetric index of mildness CIM,and in vivo method of human skin patch test.The results show that the addition of trehalolipids increases IC50 and reduces the release of inflammatory markers of the binary surfactant system.However,the incorporation of trehalolipids has some negative effects on the skin’s lipid barrier function.Skin patch test results indicate that the addition of trehalolipids improves the mildness of surfactant system,particularly in sulfate-free system.Overall,trehalolipids,as nonionic surfactants,presents great potential to replace traditional surfactants in rinse off formulations with enhanced mildness and foam performance.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.52378401,12202494)the Fundamental Research Funds for the Central Universities(Grant No.30922010918)。
文摘The compression and energy absorption properties of foam geopolymers increase stress wave attenuation under explosion impacts,reducing the vibration effect on the structure.Explosion tests were conducted using several composite structure models,including a concrete lining structure(CLS)without foam geopolymer and six foam geopolymer composite structures(FGCS)with different backfill parameters,to study the dynamic response and wave dissipation mechanisms of FGCS under explosive loading.Pressure,strain,and vibration responses at different locations were synchronously tested.The damage modes and dynamic responses of different models were compared,and how wave elimination and energy absorption efficiencies were affected by foam geopolymer backfill parameters was analyzed.The results showed that the foam geopolymer absorbed and dissipated the impact energy through continuous compressive deformation under high strain rates and dynamic loading,reducing the strain in the liner structure by 52%and increasing the pressure attenuation rate by 28%.Additionally,the foam geopolymer backfill reduced structural vibration and liner deformation,with the FGCS structure showing 35%less displacement and 70%less acceleration compared to the CLS.The FGCS model with thicker,less dense foam geopolymer backfill,having more pores and higher porosity,demonstrated better compression and energy absorption under dynamic impact,increasing stress wave attenuation efficiency.By analyzing the stress wave propagation and the compression characteristics of the porous medium,it was concluded that the stress transfer ratio of FGCS-ρ-579 was 77%lower than that of CLS,and the transmitted wave energy was 90%lower.The results of this study provide a scientific basis for optimizing underground composite structure interlayer parameters.
基金Project(5206800)supported by the National Natural Science Foundation of ChinaProject(2024JJA160096)supported by the Natural Science Foundation of Guangxi Province,China。
文摘Bauxite tailing(BT)slurry has been generated and accumulated in large quantities,posing a threat to the green and sustainable development of the alumina industry.The regression equation between the actual water content and mud water separation rate was established to achieve efficient resource utilization,and the feasibility of foam lightweight soil(FLS)prepared from BT was investigated.The effects of industrial waste residues(fly ash and slag powder)on the properties of FLS were studied.Meanwhile,the micro-mechanisms were revealed by XRD,SEM-EDS,and TG-DSC.The results revealed that fly ash reduced the workability and compressive strength of FLS.Slag powder can significantly enhance the compressive strength of FLS,which increased by 18.60%-23.26%,17.07%-58.54% and 12.12%-52.12%,respectively.Besides,slag powder can improve the long-term water stability performance and enhance carbonation resistance.XRD and thermal analyses showed that adding fly ash decreased the hydration degree of FLS,leading to a decrease in the hydration products.Slag powder improved the pore structure and compacted the skeleton structure of FLS.This study would provide an effective way to realize the resource utilization of BT,fly ash,and slag powder,with certain socio-economic and environmental benefits.
基金Project(2023RC3066)supported by the Science and Technology Innovation Program of Hunan Province,ChinaProject(2023JJ50079)supported by the Hunan Provincial Natural Science Foundation,China。
文摘Carbonized melamine foam has been recognized as a promising material for microwave absorption due to its exceptional thermal stability,lightweight,and remarkable dielectric properties.In this study,we investigated the impact of nitric acid oxidation on the surface of carbonized melamine foam and its microwave absorption properties.The treated foam exhibits optimal reflection loss of−21.51 dB at 13.20 GHz,with an effective absorption bandwidth of 7.04 GHz.The enhanced absorption properties are primarily attributed to the strengthened dielectric loss,improved impedance matching,and increased polarization losses resulting from the oxidized surfaces.This research demonstrates a promising new approach for research into surface treatments to improve the performances of microwave absorbers.
文摘Polymethacrylimide(PMI)foam has the highest specific stiffness and strength among polymer foams,with excellent radar-absorbing capabilities,which provide it with broad prospects in underwater ap-plications.To evaluate the impact resistance of PMI foam sandwich structures,the dynamic response and energy absorption characteristics of PMI foam sandwich structures with different core layers under various water impact loads were investigated using combined experimental and numerical methods.A fluid-structure interaction device with a diffusion angle was used for water impact testing of the PMI foam sandwich structures.The 3D-DIC technique was employed to process the deformation images of the sandwich-structure back panel captured by the high-speed cameras.Numerical simulations were performed to analyze the dynamic deformation process of the PMI foam core.The results indicated that the maximum deformation of the back panel exhibited a nonlinear relationship with the impulse.Below the critical impulse,the maximum deformation of the back panel plateaued,which was determined by the core density.Beyond the critical impulse,the rate of deformation increased with the impulse was governed by the core thickness.Compared with different sandwich panels,PMI foam sandwich struc-tures demonstrate significant advantages in terms of impact resistance under high-impulse conditions.
基金funded by the priority academic program development of Jiangsu Higher Education Institutions
文摘To prepare the porous NC-based(nitrocellulose-based) gun propellants,the batch foaming process of using supercritical CO_2 as the physical blowing agent is used.The solubilities of CO_2 in the single-base propellants and TEGDN(trimethyleneglycol dinitrate) propellants are measured by the gravimetric method,and SEM(scanning electron microscope) is used to observe the morphology of foamed propellants.The result shows that a large amount of CO_2 could be dissolved in NC-based propellants.The experimental results also reveal that the energetic plasticizer TEGDN exerts an important influence on the pore structure.The triaxial tensile failure mechanism for solid-state nucleation is used to explain the nucleation of NC-based propellants in the sol id state.Since some specific foaming behaviors of NC-based propellants can not be explained by the failure mechanism,a solid-state nucleation mechanism which revises the triaxial tensile failure mechanism is proposed and discussed.
文摘为了检验北京大学街区尺度模式BSMPKU(Block Scale Model of Peking University)在城市大气环境研究中的适用性,首先利用Thompson风洞试验的数据集对BSMPKU模式进行了验证,并将其模拟结果与Open FOAM(Open Source Field Operation and Manipulation)的模拟结果进行比较,然后将BSMPKU模式应用在复杂的实际建筑物群中,进行了3种不同交通线源排放的理想数值模拟研究。结果表明:1)对于单个建筑物,随建筑物宽度增加,建筑物迎风面回流区和建筑物背风面的尾流涡区范围增大;2)BSMPKU和Open FOAM对单个建筑物周围的流场及浓度场有较好的模拟能力;3)与基于高斯扩散理论的AERMOD相比,BSMPKU和Open FOAM能更好地模拟出建筑物周围的浓度场,但两个模式的模拟结果都与实测值存在一定误差;4)在实际小区中,受建筑物群影响,建筑物群内的流场分布比较复杂,大部分地区风速大幅下降,建筑物群内污染物浓度场的分布受排放源位置和走向的影响很大;5)BSMPKU能较好地模拟出实际城区的流场和浓度场分布,具有一定模拟和预报复杂城区污染物扩散过程的能力。
基金Projects(41072238,51009133)supported by the National Natural Science Foundation of China
文摘The long-term stability of large-span soft rock tunnel is influenced greatly by the creep effect of surrounding rock.The development of a new type of foam concrete which has the property of high compressibility and low ductility was introduced.And it was made as filling material of reserved deformation layer between the first lining and the second lining used in large-span soft rock tunnel.The effect of the new type of foam concrete was simulated as filling material of reserved deformation layer using numerical simulation.Through the comparison with the common large-span soft rock tunnel,the vault settlement and surrounding convergence are reduced by about 61% and 45%,respectively,after creep of 100 a.And in the second lining,the plastic zone reduces apparently and the maximum equivalent plastic strain decreases relatively.So,it can be found that the application of the new type of foam concrete as the filling material of reserved deformation layer can relieve the excessive force in second lining induced by rock creep,reduce its deformation and improve the stability of tunnel.
