The electrical conductivity and piezoresistivity of carbon fiber graphite cement-matrix composites（CFGCC） with carbon fiber content（1% by the weight of cement）,graphite powder contents （0%-50% by the weight of ce...The electrical conductivity and piezoresistivity of carbon fiber graphite cement-matrix composites（CFGCC） with carbon fiber content（1% by the weight of cement）,graphite powder contents （0%-50% by the weight of cement） and CCCW（cementitious capillary crystalline waterproofing materials,4% by the weight of cement） were studied.The experimental results showed that the relationship between the resistivity of CFGCC and the concentration of graphite powders had typical features of percolation phenomena.The percolation threshold was about 20%.A clear piezoresistive effect was observed in CFGCC with 1wt% of carbon fibers,20wt% or 30wt% of graphite powders under uniaxial compressive tests,indicating that this type of smart composites was a promising candidate for strain sensing.The measured gage factor （defined as the fractional change in resistance per unit strain） of CFGCC with graphite content of 20wt% and 30wt% were 37 and 22,respectively.With the addition of CCCW,the mechanical properties of CFGCC were improved,which benefited CFGCC piezoresistivity of stability.展开更多
A kind of piezoresistive response extraction method for smart cement-based composites/sensors was proposed.Two kinds of typical piezoresistive cement-based composites/sensors were fabricated by respectively adding car...A kind of piezoresistive response extraction method for smart cement-based composites/sensors was proposed.Two kinds of typical piezoresistive cement-based composites/sensors were fabricated by respectively adding carbon nanotubes and nickel powders as conductive fillers into cement paste or cement mortar.The variation in measured electrical resistance of such cement-based composites/sensors was explored without loading and under repeated compressive loading and impulsive loading.The experimental results indicate that the measured electrical resistance of piezoresistive cement-based composites/sensors exhibits a two-stage variation trend of fast increase and steady increase with measurement time without loading,and an irreversible increase after loading.This results from polarization caused by ionic conduction in these composites/sensors.After reaching a plateau,the measured electrical resistance can be divided into an electrical resistance part and an electrical capacity part.The piezoresistive responses of electrical resistance part in measured electrical resistance to loading can be extracted by eliminating the linear electrical capacity part in measured electrical resistance.展开更多
Directionally distributed steel fiber cement-based composites(SFCCs)were prepared by magnetic field(MF)induction technology.The orientation factor of steel fibers in the as-obtained SFCCs was determined.Besides,the el...Directionally distributed steel fiber cement-based composites(SFCCs)were prepared by magnetic field(MF)induction technology.The orientation factor of steel fibers in the as-obtained SFCCs was determined.Besides,the electrical resistivity and piezoresistive responses in two directions of aligned steel fiber cement-based composites,i e,parallel and perpendicular to MF,were measured.The effects of several variables,eg,steel fiber content,curing age,humidity,and temperature,on anisotropic electrical property were studied.The cyclic and failure piezoresistive responses in different directions were tested.It is found that the aligned steel fibers in the as-obtained SFCCs have a high orientation factor more than 0.88.Besides,SFCCs with aligned steel fibers exhibit an obvious anisotropic conductivity and piezoelectric sensitivity.The electrical conductivity of SFCCs with aligned steel fibers is less affected by temperature and humidity.At the steel fiber content of 2.5wt%,the piezoelectric sensitivity coefficient of SFCCs in the direction parallel to MF has the highest value of 324.14.In addition,the piezoresistive properties of SFCCs with aligned steel fibers in the direction parallel to MF indicate excellent sensitivity and stability under cyclic loading and monotonic loading.展开更多
In this paper,a split Hopkinson pressure bar(SHPB)was used to investigate the dynamic impact mechanical behavior of sisal fiber-reinforced cement-based composites(SFRCCs),and the microscopic damage evolution of the co...In this paper,a split Hopkinson pressure bar(SHPB)was used to investigate the dynamic impact mechanical behavior of sisal fiber-reinforced cement-based composites(SFRCCs),and the microscopic damage evolution of the composites was analyzed by scanning electron microscopy(SEM)and energy-dispersive X-ray spectrome-try(EDS).The results show that the addition of sisal fibers improves the impact resistance of cement-based composite materials.Compared with ordinary cement-based composites(OCCs),the SFRCCs demonstrate higher post-peak strength,ductility,and energy absorption capacity with higher fiber content.Moreover,the SFRCCs are strain rate sensitive materials,and their peak stress,ultimate strain,and energy integrals all increase with increasing strain rate.From the perspective of fracture failure characteristics,the failure of OCCs is dominated by the brittle failure of crystal cleavage.In contrast,the failure mode of the SFRCCs changes to microscale matrix cracks,multi-scale pull-out interface debonding of fibers(fine filaments and bundles),and mechanical interlock.This research provides an experimental basis for the engineering application of high-performance and green cement-based composites.展开更多
The interfacial transition zone (ITZ) between the aggregates and the bulk paste is the weakest zone of ordinary concrete, which largely determines its mechanical and transporting properties. However, a complete unders...The interfacial transition zone (ITZ) between the aggregates and the bulk paste is the weakest zone of ordinary concrete, which largely determines its mechanical and transporting properties. However, a complete understanding and a quantitative modeling of ITZ are still lacking. Consequently, an integrated modeling and experimental study were conducted. First, the theoretical calculation model of the ITZ volume fraction about the rotary ellipsoidal aggregate particles was established based on the nearest surface function formula. Its calculation programs were written based on Visual Basic 6.0 language and achieved visualization and functionalization. Then, the influencing factors of ITZ volume fraction of the ellipsoidal aggregate particles and the overlapping degree between the ITZ were systematically analyzed. Finally, the calculation models of ITZ volume fraction on actual ellipsoidal aggregate were given, based on cobblestones or pebbles particles with naturally ellipsoidal shape. The results indicate that the calculation model proposed is highly reliable.展开更多
Mercury intrusion porosimetry was used to measure the pore structure of steel fiber reinforced polymer-cement-based composite. The results indicate that the large pore volume decreases by 57. 8% - 51.2% and by 87. 1% ...Mercury intrusion porosimetry was used to measure the pore structure of steel fiber reinforced polymer-cement-based composite. The results indicate that the large pore volume decreases by 57. 8% - 51.2% and by 87. 1% - 88% with the addition of steel fibers and polymers respectively. When both steel fibers and polymers are simultaneously added, the large pore volume decreases by 88.3% - 90.1% . As a surface active material , polymer has a favorable water-reduced and forming-film effect, which is contributed to the decrease of the thickness of water film and the improvement of the conglutination between the fibers and the matrix. Polymers could form a microstructure network. This network structure and the bone structure of cement hydration products penetrate each other and thus the interpenetrating network with sticky aggregate and steel fiber inside forms.展开更多
The texture of interfacial zone between cement paste and quartz in the cement-based composites containing polyvinyl alcohol (PVA), methylcellulose (MC) and their potyblend in an amount of 10 wt % with respect to cemen...The texture of interfacial zone between cement paste and quartz in the cement-based composites containing polyvinyl alcohol (PVA), methylcellulose (MC) and their potyblend in an amount of 10 wt % with respect to cement, as well as the texture of dehydrated bodies of PVA, MC, and the potyblend solutions, were investigated with SEM. The network texture of the dehydrated polyblend is confirmed by comparing the texture of dehydrated bodies of PVA and MC. The network texture has restrained the movement of polyblend molecules in the cement mortar but is helpful to forming a coherent interface between cement paste and quartz. The key factor of forming the coherent interface is not the neutralization reaction between H + from hydrolysis of quarts: and OH- from hydration of cement, but the electrostatic attraction and the chemical reaction between polar groups on the polyblend molecule and cations and onions from hydrolysis of quartz and hydration of cement, respectively. The model of the coherent interface formation is that excessive [HSiO3]- and [SiO3]2- onions are bonded with the hydrated cations such as Ca2+ and Al3+ , which is confirmed by the gel containing Ca and Si on the quartz surface.展开更多
In view of the disadvantage that the mechanical properties of cement-based composites can be significantly reduced by incorporating waste rubber powder in situ, the surface modification methods of the original rubber ...In view of the disadvantage that the mechanical properties of cement-based composites can be significantly reduced by incorporating waste rubber powder in situ, the surface modification methods of the original rubber powder by coupling agent KH560, sodium hydroxide, polyvinyl alcohol (PVA), methyl hydroxyethyl cellulose ether (MHEC) and tetraethyl orthosilicate (TEOS) as precursors were adopted respectively. The modification of waste rubber powder was studied by Change rate of mortar strength of cement-based composite mortar mixed with waste rubber powder. The results show that the hybrid modification method using tetraethyl orthosilicate as precursor has better ef-fect. When 5 phr ethyl orthosilicate is added, the compressive strength and flexural strength of cement-based composite mortar can be increased by 31.7% and 28%. Scanning electron microscopy (SEM) results show that the surface of waste rubber powder with good modification effect has many pro-trusions and flake-like porous structures which are beneficial to its bonding with cement-based materials.展开更多
Among various architectures of polymers,end-group-free rings have attracted growing interests due to their distinct physicochemical performances over the linear counterparts which are exemplified by reduced hydrodynam...Among various architectures of polymers,end-group-free rings have attracted growing interests due to their distinct physicochemical performances over the linear counterparts which are exemplified by reduced hydrodynamic size and slower degradation.It is key to develop facile methods to large-scale synthesis of polymer rings with tunable compositions and microstructures.Recent progresses in large-scale synthesis of polymer rings against single-chain dynamic nanoparticles,and the example applications in synchronous enhancing toughness and strength of polymer nanocomposites are summarized.Once there is the breakthrough in rational design and effective large-scale synthesis of polymer rings and their functional derivatives,a family of cyclic functional hybrids would be available,thus providing a new paradigm in developing polymer science and engineering.展开更多
Ultrasonic-Assisted Grinding(UAG)is a novel manufacturing technology that shows promising promise for use in processing Ceramic Matrix Composites(CMCs).Nevertheless,analyzing the material removal process of CMCs with ...Ultrasonic-Assisted Grinding(UAG)is a novel manufacturing technology that shows promising promise for use in processing Ceramic Matrix Composites(CMCs).Nevertheless,analyzing the material removal process of CMCs with multidirectional structure during UAG is challenging,impeding the progress and improvement of the UAG process.This work examined the impact of ultrasonic vibration on the dynamic mechanical characteristics during processing.Additionally,we experimentally elucidated the material removal mechanism of CMCs during the scratching process under the influence of vertical vibration.The results indicate that the introduction of ultrasonic vibration causes a strain rate effect,resulting in a modification of the material removal mechanism,subsequently impacting the processing quality.Ultrasonic vibration increases the dynamic strength and brittleness of the fibers in CMCs,leading to more cracks at fracture,which changes from the original bending fracture to shear fracture.In addition,ultrasonic vibration can effectively inhibit the impact of scratching depth and anisotropy on the removal mechanism of CMCs,resulting in a more uniform surface of CMCs after processing.展开更多
A gradient structure was introduced into a metal laminated target plate,and the anti-penetration simulation of the gradient structure was compared with that of a uniform-layer-thickness target plate by finite element ...A gradient structure was introduced into a metal laminated target plate,and the anti-penetration simulation of the gradient structure was compared with that of a uniform-layer-thickness target plate by finite element simulation.The analysis was verified by an impact experiment.Results show that the high-level thickness and appropriate percentage of Ti alloy at the upper side of the gradient structure provide greater impact resistance against the bullet,which increases the warhead breakage and enhances the anti-penetration performance.In addition,during the impact process,the stress is transmitted and reflected in the form of waves in each layer of the target plate,and the interaction between the compression and tension waves causes non-synergistic deformation of the target plate and leads to delamination.The gradient target plate takes penetration resistance a step further through the higher energy absorption rate and more consumption of the bullet kinetic energy.This research provides a theoretical basis for the application of gradient structures in metallic laminated armor.展开更多
KIT-5/Beta composite supports were synthesized using an in situ self-assembly hydrothermal method,and NiW/KIT-5/Beta catalysts were prepared by impregnation.A series of characterization techniques were utilized to eva...KIT-5/Beta composite supports were synthesized using an in situ self-assembly hydrothermal method,and NiW/KIT-5/Beta catalysts were prepared by impregnation.A series of characterization techniques were utilized to evaluate the influence of varying hydrothermal synthesis temperatures on the physicochemical properties of both the KIT-5/Beta supports and the resulting catalysts.The catalytic performances of catalysts were evaluated under reaction conditions of 320℃,4 MPa H_(2)pressure,and a weight hourly space velocity(WHSV)of 4.8 h^(-1)for hydrodenitrogenation(HDN)of quinoline.The results indicated that the specific surface area and pore structure of the materials could be effectively regulated by adjusting the hydrothermal synthesis temperature,which in turn influenced the number of active sites on the catalyst.The NiW/KB-125 catalyst,synthesized at 125℃,presented the highest quinoline HDN efficiency(96.8%),which can be attributed to its favorable pore channel structure,greater Brønsted acid number,higher degree of metal sulfidation(80.12%)and appropriate metal-support interaction(MSI).展开更多
Carbon fiber-reinforced carbon aerogel(C/CA)composites are one of the most promising candidates for applications requiring both thermal insulation and load bearing capabilities.The preparation of anti-oxidation coatin...Carbon fiber-reinforced carbon aerogel(C/CA)composites are one of the most promising candidates for applications requiring both thermal insulation and load bearing capabilities.The preparation of anti-oxidation coatings on C/CA to address its susceptibility to oxidation is a feasible approach to promote its application in oxidative environments.However,the currently reported coatings on C/CA mainly focus on improving the ablation performance and coating preparation process typically necessitating high-temperature heat treatment.This procedure can increase its thermal conductivity and reduce its thermal insulation ability.In this study,a series of ceramic-resin coatings were fabricated on C/CA through a simple slurry brushing-drying approach at room temperature.The effects of phenolic resin content on the coating structure,residual stress,thermal shock,and oxidation behaviors were investigated.Due to the adhesive properties and curing-induced shrinkage,the PR-7.5 coating(containing 7.5%(in mass)phenolic resin in the slurry)exhibits bonding strength close to fracture strength of the substrate and residual compressive stress of 0.853 GPa,which is beneficial for resisting thermal shock cracking.However,excessive resin content(PR-10.0 containing 10.0%(in mass)phenolic resin in the slurry)induces tensile stress due to uneven curing shrinkage,thereby leading to thermal shock cracking.Meanwhile,oxidation tests reveal significantly reduced weight losses for PR-7.5(17.46%at 800℃/100 min,8.15%at 1000℃/120 min,3.15%at 1200℃/120 min)versus uncoated C/CA’s 44.60%loss at 800℃/20 min.This work provides a brand-new and simple approach to improving the anti-oxidation performance of C/CA and expands its application in mild oxidative environments.展开更多
The poor electrical conductivity of metal-organic frameworks(MOFs)limits their electrocatalytic performance in the oxygen evolution reaction(OER).In this study,a Py@Co-MOF composite material based on pyrene(Py)molecul...The poor electrical conductivity of metal-organic frameworks(MOFs)limits their electrocatalytic performance in the oxygen evolution reaction(OER).In this study,a Py@Co-MOF composite material based on pyrene(Py)molecules and{[Co2(BINDI)(DMA)_(2)]·DMA}_(n)(Co-MOF,H4BINDI=N,N'-bis(5-isophthalic acid)naphthalenediimide,DMA=N,N-dimethylacetamide)was synthesized via a one-pot method,leveragingπ-πinteractions between pyrene and Co-MOF to modulate electrical conductivity.Results demonstrate that the Py@Co-MOF catalyst exhibited significantly enhanced OER performance compared to pure Co-MOF or pyrene-based electrodes,achieving an overpotential of 246 mV at a current density of 10 mA·cm^(-2) along with excellent stability.Density functional theory(DFT)calculations reveal that the formation of O*in the second step is the rate-determining step(RDS)during the OER process on Co-MOF,with an energy barrier of 0.85 eV due to the weak adsorption affinity of the OH*intermediate for Co sites.CCDC:2419276.展开更多
A comparative analysis was performed on poly(lactic acid)(PLA),poly(caprolactone)(PCL),basalt fiber(BF)composites produced using two distinct approaches:direct blending and masterbatching.The limitations of PLA-BF com...A comparative analysis was performed on poly(lactic acid)(PLA),poly(caprolactone)(PCL),basalt fiber(BF)composites produced using two distinct approaches:direct blending and masterbatching.The limitations of PLA-BF composites with regard to distribution and adhesion are well-documented,as are chemical treatment methods(addition of compatibilisers,surface treatments,silanization).This work aimed to study an industrially relevant potential solution of utilising a PCL-BF masterbatch,prepared as a 50/50 wt.%blend using planetary roller extrusion(PEX)to both improve the distribution and homogeneity of the fibers as well as provide a secondary adhesion site to facilitate improved mechanical properties of the final PLA-PCL-BF composite.The resultant materials were injection moulded to prepare ISO standard test specimens and tested on the basis of their physical properties via tensile testing,impact strength testing,flexural analysis,Fourier transforminfrared spectroscopy and water absorption capability.The results displayed that the incorporation of PCL and BF led to an increase in ductility of the composite materials,allowing for improvements in the inherent brittleness of virgin PLA.Major increases in the impact strength were achieved with the utilisation of a 25% PCL/BF masterbatch,allowing for a greater than 50%increase.As an overall observation,the use of a masterbatching process,opposed to direct blending of the constituent materials allows for a greater consistency of composite to be achieved at the expense of increased gains.展开更多
A new,cost-effective porous polymer composite was developed by reinforcing polypropylene(PP)with cenosphere particles.This study investigates how the composite’s dielectric properties are affected by their porosity.D...A new,cost-effective porous polymer composite was developed by reinforcing polypropylene(PP)with cenosphere particles.This study investigates how the composite’s dielectric properties are affected by their porosity.Dielectric constant(ε′)measurements were taken over a range of frequencies at roomtemperature.A theoreticalmodel was developed to explain the electrical conductivity of the porous PP/cenosphere composites.The study thoroughly examined how the inclusion of cenosphere particles influenced key electrical parameters,including dielectric constant,dissipation factor(tanδ),DC(direct current)conductivity,and AC(alternating current)conductivity.The results revealed that increasing the cenosphere content caused a decrease in the dielectric constant,while the dissipation factor increased.The developed porous PP/cenosphere composite exhibits a unique balance of low dielectric constant,lightweight structure making it suitable for several practical applications.Its low dielectric constant and reduced DC conductivity make it an excellent candidate for electronic packaging,insulating layers,and high-frequency components,where minimal energy loss and signal interference are required.The lightweight nature of the cenosphere-reinforced structure also suggests potential use in aerospace and automotive industries for lightweight insulation panels or structural components.Furthermore,its cost-effectiveness and tunable porosity could enable applications in microwave substrates,radar-absorbing materials,and energy-efficient building materials where dielectric control and weight reduction are critical.Additionally,DC conductivity was found to decline with higher cenosphere concentrations.The theoretical model was in good agreement with the experimental data.展开更多
Biochar and biochar composites are versatile materials that can be used in many applications.In this study,biochar was prepared from sawdust and combined with the yttrium iron garnet(YIG)nanocrystal to investigate the...Biochar and biochar composites are versatile materials that can be used in many applications.In this study,biochar was prepared from sawdust and combined with the yttrium iron garnet(YIG)nanocrystal to investigate the shielding effectiveness of the composite structure.Firstly,the effect of the pyrolysis temperature on the shielding effectiveness of biochar was investigated.Secondly,biochars combined with YIG nanocrystals with different contents and shielding effectiveness of the composites were investigated.The electromagnetic effectiveness of the samples was investigated within the X band(8-12 GHz).The findings indicate that biochar demonstrates enhanced absorption properties with elevated pyrolysis temperatures.Biochars demonstrated an approximate 40 d B shielding effectiveness,while YIG exhibited approximately 7 d B,corresponding to absorption at 8 GHz.However,the combination of biochar and YIG exhibited exceptional absorption,reaching 67.12 d B at 8 GHz.展开更多
To exploit the combined strengthening effects of nanotwins and carbon nanotubes(CNTs)in Cu matrix composites,the nanotwins with a width ranging from 3 to 30 nm were incorporated into the CNTs-reinforced Cu matrix comp...To exploit the combined strengthening effects of nanotwins and carbon nanotubes(CNTs)in Cu matrix composites,the nanotwins with a width ranging from 3 to 30 nm were incorporated into the CNTs-reinforced Cu matrix composites using cryogenic rolling and optimizing the initial particle size of the raw Cu powders.The formation of nanotwins in the Cu matrix composite reinforced by only 0.2 wt.%CNTs is accompanied by the increased dislocation density and refined Cu grain size,resulting in much better strength−ductility synergy than the referenced composite without significant nanotwins formation.The analysis of strengthening and toughening mechanisms demonstrates that the strength increment mainly derives from grain refinement strengthening,dislocation strengthening,and nanotwin strengthening.The strength increment from the contribution of the nanotwins accounts for 19.9%of the overall strength increment for the composite.Meanwhile,the retention of good tensile ductility can be reasonably explained by the increased dislocation accommodation ability due to the formed nanotwins and the decreased induced dislocation proliferation.展开更多
This study evaluates the stabilizing effect of lignin, extracted from Eucalyptus globulus, on an energetic composite of nitrated cellulose carbamate (NCC) plasticized with diethylene glycol dinitrate (DEGDN), compared...This study evaluates the stabilizing effect of lignin, extracted from Eucalyptus globulus, on an energetic composite of nitrated cellulose carbamate (NCC) plasticized with diethylene glycol dinitrate (DEGDN), compared to conventional stabilizers 2-nitrodiphenylamine (2-NDPA) and 1,3-dimethyl-1,3-diphenylurea (C-II). FTIR analysis confirms lignin's capacity to scavenge nitroxyl radicals formed during thermolysis of nitrocarbamate and nitrate ester bonds, thereby inhibiting decomposition. Moreover, the incorporation of C-II, 2-NDPA, and lignin significantly raised the peak temperature of the main thermolysis, as confirmed by DSC and TGA, indicating a progressive stability enhancement in the order: NCC/DEGDN < NCC/DEGDN/C-II < NCC/DEGDN/lignin < NCC/DEGDN/2-NDPA. Additionally, the effect of each stabilizer on the decomposition pathway was characterized by TGA-FTIR. The findings show that stabilizer type significantly affects the intensity of gaseous products released during decomposition without altering their nature. Notably, NH2 groups formed during NCC degradation play a key role in nitrogen conversion, particularly by reducing toxic NO emissions.展开更多
There is an urgent need to develop magnesium-matrix materials that exhibit both high thermal conductivity and low thermal expansion to ensure compatibility with chips.This study aims to develop a Mg-Zn-Cu alloy with h...There is an urgent need to develop magnesium-matrix materials that exhibit both high thermal conductivity and low thermal expansion to ensure compatibility with chips.This study aims to develop a Mg-Zn-Cu alloy with high thermal conductivity.Furthermore,it explores the preparation of AlN_(P)/Mg-Zn-Cu composites featuring low coefficients of thermal expansion.The stir casting method was utilized to fabricate the composites and an investigation was conducted to examine their microstructure and thermal properties.Results indicate that the addition of AlN_(P)reduces the thermal expansion coefficient while maintaining relatively high thermal conductivity.Specifically,the AlN_(P)/Mg-0.5Zn-0.5Cu composite with 30wt.%AlN_(P)achieves a thermal conductivity of 132.7 W·m^(-1)·K^(-1)and a thermal expansion coefficient of 18.5×10^(-6)K^(-1),rendering it suitable for electronic packaging applications where thermal management is critical.展开更多
基金Funded by the National Natural Science Foundation of China(No.50878170 and No. 10672128)
文摘The electrical conductivity and piezoresistivity of carbon fiber graphite cement-matrix composites（CFGCC） with carbon fiber content（1% by the weight of cement）,graphite powder contents （0%-50% by the weight of cement） and CCCW（cementitious capillary crystalline waterproofing materials,4% by the weight of cement） were studied.The experimental results showed that the relationship between the resistivity of CFGCC and the concentration of graphite powders had typical features of percolation phenomena.The percolation threshold was about 20%.A clear piezoresistive effect was observed in CFGCC with 1wt% of carbon fibers,20wt% or 30wt% of graphite powders under uniaxial compressive tests,indicating that this type of smart composites was a promising candidate for strain sensing.The measured gage factor （defined as the fractional change in resistance per unit strain） of CFGCC with graphite content of 20wt% and 30wt% were 37 and 22,respectively.With the addition of CCCW,the mechanical properties of CFGCC were improved,which benefited CFGCC piezoresistivity of stability.
基金Funded by the National Natural Science Foundation of China(Nos. 51178148,50808055)the Natural Scientific Research Innovation Foundation in Harbin Institute of Technology(No.HIT.NSRIF.2009096)the Program for New Century Excellent Talents University of China(No.NCET-0798)
文摘A kind of piezoresistive response extraction method for smart cement-based composites/sensors was proposed.Two kinds of typical piezoresistive cement-based composites/sensors were fabricated by respectively adding carbon nanotubes and nickel powders as conductive fillers into cement paste or cement mortar.The variation in measured electrical resistance of such cement-based composites/sensors was explored without loading and under repeated compressive loading and impulsive loading.The experimental results indicate that the measured electrical resistance of piezoresistive cement-based composites/sensors exhibits a two-stage variation trend of fast increase and steady increase with measurement time without loading,and an irreversible increase after loading.This results from polarization caused by ionic conduction in these composites/sensors.After reaching a plateau,the measured electrical resistance can be divided into an electrical resistance part and an electrical capacity part.The piezoresistive responses of electrical resistance part in measured electrical resistance to loading can be extracted by eliminating the linear electrical capacity part in measured electrical resistance.
基金Funded by the National Natural Science Foundation of China(Nos.51478164 and 52079048)the Key Research&Development Plan of Jiangsu Province,China(No.BE2021704)。
文摘Directionally distributed steel fiber cement-based composites(SFCCs)were prepared by magnetic field(MF)induction technology.The orientation factor of steel fibers in the as-obtained SFCCs was determined.Besides,the electrical resistivity and piezoresistive responses in two directions of aligned steel fiber cement-based composites,i e,parallel and perpendicular to MF,were measured.The effects of several variables,eg,steel fiber content,curing age,humidity,and temperature,on anisotropic electrical property were studied.The cyclic and failure piezoresistive responses in different directions were tested.It is found that the aligned steel fibers in the as-obtained SFCCs have a high orientation factor more than 0.88.Besides,SFCCs with aligned steel fibers exhibit an obvious anisotropic conductivity and piezoelectric sensitivity.The electrical conductivity of SFCCs with aligned steel fibers is less affected by temperature and humidity.At the steel fiber content of 2.5wt%,the piezoelectric sensitivity coefficient of SFCCs in the direction parallel to MF has the highest value of 324.14.In addition,the piezoresistive properties of SFCCs with aligned steel fibers in the direction parallel to MF indicate excellent sensitivity and stability under cyclic loading and monotonic loading.
基金supported within the framework of the Basic Research Project of the Yunnan Province-Young Program(No.2019FD097)Agricultural Joint Special Project of the Yunnan Province-General Program(No.202101BD070001-118).
文摘In this paper,a split Hopkinson pressure bar(SHPB)was used to investigate the dynamic impact mechanical behavior of sisal fiber-reinforced cement-based composites(SFRCCs),and the microscopic damage evolution of the composites was analyzed by scanning electron microscopy(SEM)and energy-dispersive X-ray spectrome-try(EDS).The results show that the addition of sisal fibers improves the impact resistance of cement-based composite materials.Compared with ordinary cement-based composites(OCCs),the SFRCCs demonstrate higher post-peak strength,ductility,and energy absorption capacity with higher fiber content.Moreover,the SFRCCs are strain rate sensitive materials,and their peak stress,ultimate strain,and energy integrals all increase with increasing strain rate.From the perspective of fracture failure characteristics,the failure of OCCs is dominated by the brittle failure of crystal cleavage.In contrast,the failure mode of the SFRCCs changes to microscale matrix cracks,multi-scale pull-out interface debonding of fibers(fine filaments and bundles),and mechanical interlock.This research provides an experimental basis for the engineering application of high-performance and green cement-based composites.
基金Funded by the National Natural Science Foundations of China(Nos.51478278 and 51408380)the Natural Science Foundation of Hebei Province(No.E2014210149)Higher Education Science and Technology Research Project of Hebei Province(No.ZD2016065)
文摘The interfacial transition zone (ITZ) between the aggregates and the bulk paste is the weakest zone of ordinary concrete, which largely determines its mechanical and transporting properties. However, a complete understanding and a quantitative modeling of ITZ are still lacking. Consequently, an integrated modeling and experimental study were conducted. First, the theoretical calculation model of the ITZ volume fraction about the rotary ellipsoidal aggregate particles was established based on the nearest surface function formula. Its calculation programs were written based on Visual Basic 6.0 language and achieved visualization and functionalization. Then, the influencing factors of ITZ volume fraction of the ellipsoidal aggregate particles and the overlapping degree between the ITZ were systematically analyzed. Finally, the calculation models of ITZ volume fraction on actual ellipsoidal aggregate were given, based on cobblestones or pebbles particles with naturally ellipsoidal shape. The results indicate that the calculation model proposed is highly reliable.
文摘Mercury intrusion porosimetry was used to measure the pore structure of steel fiber reinforced polymer-cement-based composite. The results indicate that the large pore volume decreases by 57. 8% - 51.2% and by 87. 1% - 88% with the addition of steel fibers and polymers respectively. When both steel fibers and polymers are simultaneously added, the large pore volume decreases by 88.3% - 90.1% . As a surface active material , polymer has a favorable water-reduced and forming-film effect, which is contributed to the decrease of the thickness of water film and the improvement of the conglutination between the fibers and the matrix. Polymers could form a microstructure network. This network structure and the bone structure of cement hydration products penetrate each other and thus the interpenetrating network with sticky aggregate and steel fiber inside forms.
基金Funded by Natural Science Foundation of China (No. 49802004)
文摘The texture of interfacial zone between cement paste and quartz in the cement-based composites containing polyvinyl alcohol (PVA), methylcellulose (MC) and their potyblend in an amount of 10 wt % with respect to cement, as well as the texture of dehydrated bodies of PVA, MC, and the potyblend solutions, were investigated with SEM. The network texture of the dehydrated polyblend is confirmed by comparing the texture of dehydrated bodies of PVA and MC. The network texture has restrained the movement of polyblend molecules in the cement mortar but is helpful to forming a coherent interface between cement paste and quartz. The key factor of forming the coherent interface is not the neutralization reaction between H + from hydrolysis of quarts: and OH- from hydration of cement, but the electrostatic attraction and the chemical reaction between polar groups on the polyblend molecule and cations and onions from hydrolysis of quartz and hydration of cement, respectively. The model of the coherent interface formation is that excessive [HSiO3]- and [SiO3]2- onions are bonded with the hydrated cations such as Ca2+ and Al3+ , which is confirmed by the gel containing Ca and Si on the quartz surface.
文摘In view of the disadvantage that the mechanical properties of cement-based composites can be significantly reduced by incorporating waste rubber powder in situ, the surface modification methods of the original rubber powder by coupling agent KH560, sodium hydroxide, polyvinyl alcohol (PVA), methyl hydroxyethyl cellulose ether (MHEC) and tetraethyl orthosilicate (TEOS) as precursors were adopted respectively. The modification of waste rubber powder was studied by Change rate of mortar strength of cement-based composite mortar mixed with waste rubber powder. The results show that the hybrid modification method using tetraethyl orthosilicate as precursor has better ef-fect. When 5 phr ethyl orthosilicate is added, the compressive strength and flexural strength of cement-based composite mortar can be increased by 31.7% and 28%. Scanning electron microscopy (SEM) results show that the surface of waste rubber powder with good modification effect has many pro-trusions and flake-like porous structures which are beneficial to its bonding with cement-based materials.
基金Supported by the National Natural Science Foundation of China(Nos.52293472,22473096 and 22471164)。
文摘Among various architectures of polymers,end-group-free rings have attracted growing interests due to their distinct physicochemical performances over the linear counterparts which are exemplified by reduced hydrodynamic size and slower degradation.It is key to develop facile methods to large-scale synthesis of polymer rings with tunable compositions and microstructures.Recent progresses in large-scale synthesis of polymer rings against single-chain dynamic nanoparticles,and the example applications in synchronous enhancing toughness and strength of polymer nanocomposites are summarized.Once there is the breakthrough in rational design and effective large-scale synthesis of polymer rings and their functional derivatives,a family of cyclic functional hybrids would be available,thus providing a new paradigm in developing polymer science and engineering.
基金supported by the National Science Foundation for Distinguished Young Scholars of China(No.52325506)the Fundamental Research Funds for the Central Universities(No.DUT22LAB501)。
文摘Ultrasonic-Assisted Grinding(UAG)is a novel manufacturing technology that shows promising promise for use in processing Ceramic Matrix Composites(CMCs).Nevertheless,analyzing the material removal process of CMCs with multidirectional structure during UAG is challenging,impeding the progress and improvement of the UAG process.This work examined the impact of ultrasonic vibration on the dynamic mechanical characteristics during processing.Additionally,we experimentally elucidated the material removal mechanism of CMCs during the scratching process under the influence of vertical vibration.The results indicate that the introduction of ultrasonic vibration causes a strain rate effect,resulting in a modification of the material removal mechanism,subsequently impacting the processing quality.Ultrasonic vibration increases the dynamic strength and brittleness of the fibers in CMCs,leading to more cracks at fracture,which changes from the original bending fracture to shear fracture.In addition,ultrasonic vibration can effectively inhibit the impact of scratching depth and anisotropy on the removal mechanism of CMCs,resulting in a more uniform surface of CMCs after processing.
基金National Defense Basic Scientific Research Program of China(JCKY2020408B002,WDZC2022-12)Key Research and Development Program of Shanxi Province(202102050201011,202202050201014)Fundamental Research Program of Shanxi Province(20210302124178,20210302123061,202103021224183)。
文摘A gradient structure was introduced into a metal laminated target plate,and the anti-penetration simulation of the gradient structure was compared with that of a uniform-layer-thickness target plate by finite element simulation.The analysis was verified by an impact experiment.Results show that the high-level thickness and appropriate percentage of Ti alloy at the upper side of the gradient structure provide greater impact resistance against the bullet,which increases the warhead breakage and enhances the anti-penetration performance.In addition,during the impact process,the stress is transmitted and reflected in the form of waves in each layer of the target plate,and the interaction between the compression and tension waves causes non-synergistic deformation of the target plate and leads to delamination.The gradient target plate takes penetration resistance a step further through the higher energy absorption rate and more consumption of the bullet kinetic energy.This research provides a theoretical basis for the application of gradient structures in metallic laminated armor.
基金Supported by the Autonomous Research Project of SKLCC(2024BWZ003)Strategic Priority Research Program of the Chinese Academy of Sciences(XDA0390401)the Doctoral Research Start-up Funding of Shanxi Institute of Technology(026012).
文摘KIT-5/Beta composite supports were synthesized using an in situ self-assembly hydrothermal method,and NiW/KIT-5/Beta catalysts were prepared by impregnation.A series of characterization techniques were utilized to evaluate the influence of varying hydrothermal synthesis temperatures on the physicochemical properties of both the KIT-5/Beta supports and the resulting catalysts.The catalytic performances of catalysts were evaluated under reaction conditions of 320℃,4 MPa H_(2)pressure,and a weight hourly space velocity(WHSV)of 4.8 h^(-1)for hydrodenitrogenation(HDN)of quinoline.The results indicated that the specific surface area and pore structure of the materials could be effectively regulated by adjusting the hydrothermal synthesis temperature,which in turn influenced the number of active sites on the catalyst.The NiW/KB-125 catalyst,synthesized at 125℃,presented the highest quinoline HDN efficiency(96.8%),which can be attributed to its favorable pore channel structure,greater Brønsted acid number,higher degree of metal sulfidation(80.12%)and appropriate metal-support interaction(MSI).
基金National Natural Science Foundation of China(52272075,52472053)Research Fund of Youth Innovation Promotion Association of CAS,China(2021190)Defense Industrial Technology Development Program(JCKY2021130B007)。
文摘Carbon fiber-reinforced carbon aerogel(C/CA)composites are one of the most promising candidates for applications requiring both thermal insulation and load bearing capabilities.The preparation of anti-oxidation coatings on C/CA to address its susceptibility to oxidation is a feasible approach to promote its application in oxidative environments.However,the currently reported coatings on C/CA mainly focus on improving the ablation performance and coating preparation process typically necessitating high-temperature heat treatment.This procedure can increase its thermal conductivity and reduce its thermal insulation ability.In this study,a series of ceramic-resin coatings were fabricated on C/CA through a simple slurry brushing-drying approach at room temperature.The effects of phenolic resin content on the coating structure,residual stress,thermal shock,and oxidation behaviors were investigated.Due to the adhesive properties and curing-induced shrinkage,the PR-7.5 coating(containing 7.5%(in mass)phenolic resin in the slurry)exhibits bonding strength close to fracture strength of the substrate and residual compressive stress of 0.853 GPa,which is beneficial for resisting thermal shock cracking.However,excessive resin content(PR-10.0 containing 10.0%(in mass)phenolic resin in the slurry)induces tensile stress due to uneven curing shrinkage,thereby leading to thermal shock cracking.Meanwhile,oxidation tests reveal significantly reduced weight losses for PR-7.5(17.46%at 800℃/100 min,8.15%at 1000℃/120 min,3.15%at 1200℃/120 min)versus uncoated C/CA’s 44.60%loss at 800℃/20 min.This work provides a brand-new and simple approach to improving the anti-oxidation performance of C/CA and expands its application in mild oxidative environments.
文摘The poor electrical conductivity of metal-organic frameworks(MOFs)limits their electrocatalytic performance in the oxygen evolution reaction(OER).In this study,a Py@Co-MOF composite material based on pyrene(Py)molecules and{[Co2(BINDI)(DMA)_(2)]·DMA}_(n)(Co-MOF,H4BINDI=N,N'-bis(5-isophthalic acid)naphthalenediimide,DMA=N,N-dimethylacetamide)was synthesized via a one-pot method,leveragingπ-πinteractions between pyrene and Co-MOF to modulate electrical conductivity.Results demonstrate that the Py@Co-MOF catalyst exhibited significantly enhanced OER performance compared to pure Co-MOF or pyrene-based electrodes,achieving an overpotential of 246 mV at a current density of 10 mA·cm^(-2) along with excellent stability.Density functional theory(DFT)calculations reveal that the formation of O*in the second step is the rate-determining step(RDS)during the OER process on Co-MOF,with an energy barrier of 0.85 eV due to the weak adsorption affinity of the OH*intermediate for Co sites.CCDC:2419276.
文摘A comparative analysis was performed on poly(lactic acid)(PLA),poly(caprolactone)(PCL),basalt fiber(BF)composites produced using two distinct approaches:direct blending and masterbatching.The limitations of PLA-BF composites with regard to distribution and adhesion are well-documented,as are chemical treatment methods(addition of compatibilisers,surface treatments,silanization).This work aimed to study an industrially relevant potential solution of utilising a PCL-BF masterbatch,prepared as a 50/50 wt.%blend using planetary roller extrusion(PEX)to both improve the distribution and homogeneity of the fibers as well as provide a secondary adhesion site to facilitate improved mechanical properties of the final PLA-PCL-BF composite.The resultant materials were injection moulded to prepare ISO standard test specimens and tested on the basis of their physical properties via tensile testing,impact strength testing,flexural analysis,Fourier transforminfrared spectroscopy and water absorption capability.The results displayed that the incorporation of PCL and BF led to an increase in ductility of the composite materials,allowing for improvements in the inherent brittleness of virgin PLA.Major increases in the impact strength were achieved with the utilisation of a 25% PCL/BF masterbatch,allowing for a greater than 50%increase.As an overall observation,the use of a masterbatching process,opposed to direct blending of the constituent materials allows for a greater consistency of composite to be achieved at the expense of increased gains.
文摘A new,cost-effective porous polymer composite was developed by reinforcing polypropylene(PP)with cenosphere particles.This study investigates how the composite’s dielectric properties are affected by their porosity.Dielectric constant(ε′)measurements were taken over a range of frequencies at roomtemperature.A theoreticalmodel was developed to explain the electrical conductivity of the porous PP/cenosphere composites.The study thoroughly examined how the inclusion of cenosphere particles influenced key electrical parameters,including dielectric constant,dissipation factor(tanδ),DC(direct current)conductivity,and AC(alternating current)conductivity.The results revealed that increasing the cenosphere content caused a decrease in the dielectric constant,while the dissipation factor increased.The developed porous PP/cenosphere composite exhibits a unique balance of low dielectric constant,lightweight structure making it suitable for several practical applications.Its low dielectric constant and reduced DC conductivity make it an excellent candidate for electronic packaging,insulating layers,and high-frequency components,where minimal energy loss and signal interference are required.The lightweight nature of the cenosphere-reinforced structure also suggests potential use in aerospace and automotive industries for lightweight insulation panels or structural components.Furthermore,its cost-effectiveness and tunable porosity could enable applications in microwave substrates,radar-absorbing materials,and energy-efficient building materials where dielectric control and weight reduction are critical.Additionally,DC conductivity was found to decline with higher cenosphere concentrations.The theoretical model was in good agreement with the experimental data.
基金support provided by the Center for Fabrication and Application of Electronic Materials at Dokuz Eylül University,Türkiye。
文摘Biochar and biochar composites are versatile materials that can be used in many applications.In this study,biochar was prepared from sawdust and combined with the yttrium iron garnet(YIG)nanocrystal to investigate the shielding effectiveness of the composite structure.Firstly,the effect of the pyrolysis temperature on the shielding effectiveness of biochar was investigated.Secondly,biochars combined with YIG nanocrystals with different contents and shielding effectiveness of the composites were investigated.The electromagnetic effectiveness of the samples was investigated within the X band(8-12 GHz).The findings indicate that biochar demonstrates enhanced absorption properties with elevated pyrolysis temperatures.Biochars demonstrated an approximate 40 d B shielding effectiveness,while YIG exhibited approximately 7 d B,corresponding to absorption at 8 GHz.However,the combination of biochar and YIG exhibited exceptional absorption,reaching 67.12 d B at 8 GHz.
基金financially supported by the Fundamental Research Funds for the Central Universities,China(No.21624408)the Guangdong Basic and Applied Basic Research Foundation,China(Nos.2023A1515012850,2024A1515010416)+2 种基金Guangzhou Science and Technology Planning Project,China(No.2024A04J9966)the National Natural Science Foundation of China(Nos.52271132,52004101)the Key Laboratory of Advanced Materials of Yunnan Province,China(No.2024KF02)。
文摘To exploit the combined strengthening effects of nanotwins and carbon nanotubes(CNTs)in Cu matrix composites,the nanotwins with a width ranging from 3 to 30 nm were incorporated into the CNTs-reinforced Cu matrix composites using cryogenic rolling and optimizing the initial particle size of the raw Cu powders.The formation of nanotwins in the Cu matrix composite reinforced by only 0.2 wt.%CNTs is accompanied by the increased dislocation density and refined Cu grain size,resulting in much better strength−ductility synergy than the referenced composite without significant nanotwins formation.The analysis of strengthening and toughening mechanisms demonstrates that the strength increment mainly derives from grain refinement strengthening,dislocation strengthening,and nanotwin strengthening.The strength increment from the contribution of the nanotwins accounts for 19.9%of the overall strength increment for the composite.Meanwhile,the retention of good tensile ductility can be reasonably explained by the increased dislocation accommodation ability due to the formed nanotwins and the decreased induced dislocation proliferation.
文摘This study evaluates the stabilizing effect of lignin, extracted from Eucalyptus globulus, on an energetic composite of nitrated cellulose carbamate (NCC) plasticized with diethylene glycol dinitrate (DEGDN), compared to conventional stabilizers 2-nitrodiphenylamine (2-NDPA) and 1,3-dimethyl-1,3-diphenylurea (C-II). FTIR analysis confirms lignin's capacity to scavenge nitroxyl radicals formed during thermolysis of nitrocarbamate and nitrate ester bonds, thereby inhibiting decomposition. Moreover, the incorporation of C-II, 2-NDPA, and lignin significantly raised the peak temperature of the main thermolysis, as confirmed by DSC and TGA, indicating a progressive stability enhancement in the order: NCC/DEGDN < NCC/DEGDN/C-II < NCC/DEGDN/lignin < NCC/DEGDN/2-NDPA. Additionally, the effect of each stabilizer on the decomposition pathway was characterized by TGA-FTIR. The findings show that stabilizer type significantly affects the intensity of gaseous products released during decomposition without altering their nature. Notably, NH2 groups formed during NCC degradation play a key role in nitrogen conversion, particularly by reducing toxic NO emissions.
基金financially supported by National Natural Science Foundation of China(No.52175321)the Fund of Key Laboratory of High Temperature Electromagnetic Materials and Structure of MOE(No.KB202505)。
文摘There is an urgent need to develop magnesium-matrix materials that exhibit both high thermal conductivity and low thermal expansion to ensure compatibility with chips.This study aims to develop a Mg-Zn-Cu alloy with high thermal conductivity.Furthermore,it explores the preparation of AlN_(P)/Mg-Zn-Cu composites featuring low coefficients of thermal expansion.The stir casting method was utilized to fabricate the composites and an investigation was conducted to examine their microstructure and thermal properties.Results indicate that the addition of AlN_(P)reduces the thermal expansion coefficient while maintaining relatively high thermal conductivity.Specifically,the AlN_(P)/Mg-0.5Zn-0.5Cu composite with 30wt.%AlN_(P)achieves a thermal conductivity of 132.7 W·m^(-1)·K^(-1)and a thermal expansion coefficient of 18.5×10^(-6)K^(-1),rendering it suitable for electronic packaging applications where thermal management is critical.
