In this paper, a long line-shape dielectric barrier discharge excited by a nanosecond pulse and AC is generated in atmospheric air for the purpose of discussing the uniformity, stability and ability of aramid fiber tr...In this paper, a long line-shape dielectric barrier discharge excited by a nanosecond pulse and AC is generated in atmospheric air for the purpose of discussing the uniformity, stability and ability of aramid fiber treatment. The discharge images, waveforms of current and voltage,optical emission spectra, and gas temperatures of both discharges are compared. It is found that nanosecond pulsed discharge has a more uniform discharge morphology, higher energy efficiency and lower gas temperature, which indicates that nanosecond pulsed discharge is more suitable for surface modification. To reduce the water contact angle from 96° to about 60°, the energy cost is only about 1/7 compared with AC discharge. Scanning electron microscopy,Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy are employed to understand the mechanisms of hydrophilicity improvement.展开更多
Dynamic tensile impact properties of aramid (Technora) and UHMWPE (DC851) fiber bundles were studied at two high strain rates by means of reflecting type Split Hopkinson Bar, and stress-strain curves of fiber yarns ...Dynamic tensile impact properties of aramid (Technora) and UHMWPE (DC851) fiber bundles were studied at two high strain rates by means of reflecting type Split Hopkinson Bar, and stress-strain curves of fiber yarns at different strain rates were obtained. Experimental results show that the initial elastic modulus, failure strength and unstable strain of aramid fiber yarns are strain rate insensitive, whereas the initial elastic modulus and unstable strain of UHMWPE fiber yarns are strain rate sensitive. A fiber-bundle statistical constitutive equation was used to describe the tensile behavior of aramid and UHMWPE fiber bundles at high strain rates. The good consistency between the simulated results and experimental data indicates that the modified double Weibull function can represent the tensile strength distribution of aramid and UHMWPE fibers and the method of extracting Weibull parameters from fiber bundles stress-strain data is valid.展开更多
High-performance ballistic fibers,such as aramid fiber and ultra-high-molecular-weight polyethylene(UHMWPE),are commonly used in anti-ballistic structures due to their low density,high tensile strength and high specif...High-performance ballistic fibers,such as aramid fiber and ultra-high-molecular-weight polyethylene(UHMWPE),are commonly used in anti-ballistic structures due to their low density,high tensile strength and high specific modulus.However,their low modulus in the thickness direction and insufficient shear strength limits their application in certain ballistic structure.In contrast,carbon fiber reinforced epoxy resin matrix composites(CFRP)have the characteristics of high modulus in the thickness direction and high shear resistance.However,carbon fibers are rarely used and applied for protection purposes.A hybridization with aramid fiber reinforced epoxy resin matrix composites(AFRP)and CFRP has the potential to improve the stiffness and the ballistic property of the typical ballistic fiber composites.The hybrid effects on the flexural property and ballistic performance of the hybrid CFRP/AFRP laminates were investigated.Through conducting mechanical property tests and ballistic tests,two sets of reliable simulation parameters for AFRP and CFRP were established using LS-DYNA software,respectively.The experimental results suggested that by increasing the content of CFRP that the flexural properties of hybrid CFRP/AFRP laminates were enhanced.The ballistic tests'results and the simulation illustrated that the specific energy absorption by the perforation method of CFRP achieved 77.7%of AFRP.When CFRP was on the striking face,the shear resistance of the laminates and the resistance force to the projectiles was promoted at the initial penetration stage.The proportion of fiber tensile failures in the AFRP layers was also enhanced with the addition of CFRP during the penetration process.These improvements resulted in the ballistic performance of hybrid CFRP/AFRP laminates was better than AFRP when the CFRP content was 20 wt%and 30 wt%.展开更多
The aramid fiber礥HMWPE (ultrahigh molecular weight polyethylene) fiber hybrid composites (AF礑F) were ma-nufactured. By Charpy impact, the low velocity impact behavior of AF礑F composite was studied. And the high vel...The aramid fiber礥HMWPE (ultrahigh molecular weight polyethylene) fiber hybrid composites (AF礑F) were ma-nufactured. By Charpy impact, the low velocity impact behavior of AF礑F composite was studied. And the high velocity impact behavior under ballistic impact was also investigated. The influence of hybrid ratio on the performances of low and high velocity impact was analyzed, and hybrid structures with good impact properties under low velocity impact and high velocity were optimized. For Charpy impact, the maximal impact load increased with the accretion of the AF layers for AF礑F hybrid composites. The total impact power was reduced with the decrease of DF layers and the delamination can result in the increase of total impact power. For ballistic impact, the DF ballistic performance was better than that of the AF and the hybrid ratio had a crucial influence. The failure morphology of AF礑F hybrid composite under Charpy impact and ballistic impact was analyzed. The AF礑F hybrid composites in suitable hybrid ratio could attain better performance than AF or DF composites.展开更多
Tensile impact tests of aramid (Twaron) fiber bundles were carried out under high strain rates with a wide range of 0. 01/s -1 000/s by using MTS and bar-bar tensile impact apparatus. Based on the statistical constitu...Tensile impact tests of aramid (Twaron) fiber bundles were carried out under high strain rates with a wide range of 0. 01/s -1 000/s by using MTS and bar-bar tensile impact apparatus. Based on the statistical constitutive model of fiber bundles, statistical constitutive equations of aramid fiber bundles are derived from statistical analysis of test data at different strain rates. Comparison between the theoretical predictions and experimental data indicates statistical constitutive equations fit well with the experimental data, and statistical constitutive equations of fiber bundles at different strain rates are valid.展开更多
Residual stresses of the ordinarily cured and pre-stressed unidirectionallaminate are analyzed quantitatively. In order to examine the analyzing formulations,strain gages were embedded in the uni-directional aramid al...Residual stresses of the ordinarily cured and pre-stressed unidirectionallaminate are analyzed quantitatively. In order to examine the analyzing formulations,strain gages were embedded in the uni-directional aramid aluminium laminates (ordi-narily cured and pre-stressed) to determine the residual stresses in the aluminiumlayers. The calculated residual stresses are in good agreement with the experimental val-ues in the longitudinal direction. Therefore, the work in this paper can be used to calcu-late, determine and design the longitudinal residual stresses according to the manufac-ture and application demands.展开更多
The high-strength Basalt Carbon Fiber Reinforced Polymer(BCFRP)composites had been manufactured by guiding Imitating Tree-root Micro/Nano Aramid Short Fiber(ITMNASF)into the interlayer of Basalt Fiber(BF)and Carbon Fi...The high-strength Basalt Carbon Fiber Reinforced Polymer(BCFRP)composites had been manufactured by guiding Imitating Tree-root Micro/Nano Aramid Short Fiber(ITMNASF)into the interlayer of Basalt Fiber(BF)and Carbon Fiber(CF)plies to form thin interleaving,and various mass proportions of IT-MNASF were designed to discuss the reinforcing effect on the BCFRP heterogeneous composites.The results of three points bending tests showed that flexural strength and energy absorption of 4wt%IT-MNASF reinforced BCFRP heterogeneous composites had been improved by 32.4%and 134.4%respectively compared with that of unreinforced specimens.The 4wt%IT-MNASF reinforced BCFRP specimens showed both a greater strength and a lower cost(reduced by 31%around)than that of plain CFRP composites.X-ray micro-computed tomography scanning results exhibited that the delamination-dominated failure of plain BCFRP composites was changed into multi-layer BF and CF fabrics damage.The reinforcing mechanism revealed that the introduced IT-MNASF could construct quasi-vertical fiber bridging,and it was used as"mechanical claws"to grasp adjacent fiber layers for creating a stronger mechanical interlocking,and this effectively improved resin-rich region and interfacial transition region at the interlayers.The simple and effective IT-MNASF interleaving technique was very successful in low-cost and high-strength development of BCFRP heterogeneous composites.展开更多
Heterocyclic aramid fibers,a typical kind of high-performance fibers,have been widely used in aerospace and protection fields because of their excellent mechanical properties.However,the application of heterocyclic ar...Heterocyclic aramid fibers,a typical kind of high-performance fibers,have been widely used in aerospace and protection fields because of their excellent mechanical properties.However,the application of heterocyclic aramid fibers as a reinforcement is hindered by the weak interfacial combination with matrix materials,especially epoxy.Traditional strategies enhancing the interfacial shear strength(IFSS)usually decrease the tensile strength.Therefore,simultaneous enhancement of both mechanical properties remains a challenge.Herein,we report a novel heterocyclic aramid fiber with high interfacial shear strength(49.3 MPa)and tensile strength(6.27 GPa),in which 4,4′-diamino-2′-chlorobenzanilide(DABA-Cl)and a small amount of graphene oxide(GO)are introduced through in-situ polymerization.Hydrogen bonds andπ–πinteraction between GO and polymer chains trigger the enhancement in crystallinity,orientation,and lateral interaction of the fibers,thus improving the tensile strength and interfacial shear strength of the fibers.Moreover,the interfacial interaction between fiber and epoxy is enhanced due to the improvement of the surface polarity of the fibers caused by DABA-Cl.Therefore,a method to improve both tensile strength and interfacial shear strength of heterocyclic aramid fibers was found by introducing GO and DABA-Cl,which may provide guidance for the design and preparation of other high-performance fibers.展开更多
Friction between two contacting surfaces is studied extensively.One of the k n o w n friction theories is Amontons,law which states that the friction force is proportional to the normal force.However,Amontons7 law has...Friction between two contacting surfaces is studied extensively.One of the k n o w n friction theories is Amontons,law which states that the friction force is proportional to the normal force.However,Amontons7 law has been found to be invalid for elastomers.In the present study,the validity of Amontons7 law for short-cut aramid fiber reinforced elastomers is studied.Two types of fillers are used to reinforce the elastomers,namely highly dispersible silica and short-cut aramid fibers.Short-cut aramid fibers with two different surface treatments are used,namely non-reactive fibers with standard oily finish(SF-fibers)and fibers treated with an epoxy coating(EF-fibers).A pin-on-disc tribometer is used to investigate the frictional behavior of the composites in sliding contact with a granite counter surface.The results show that,after the run-in phase,Amontons,law is valid for those composites that are reinforced by short-cut aramid fibers(without reinforcing filler,i.e.,silica)if the contact pressure is below a threshold value.However,once the contact pressure exceeds this threshold value,Amontons'law will be invalid.The threshold contact pressure of the composites containing EF-fibers is higher than of the composites containing SF-fibers.The composites that are reinforced by silica and short-cut aramid fibers do not follow Amontons7 law.展开更多
Carbon nanotubes(CNTs)incorporated polymeric composites have been extensively investigated for microwave absorption at target frequencies to meet the requirement of radar cross-section reduction.In this work,a strateg...Carbon nanotubes(CNTs)incorporated polymeric composites have been extensively investigated for microwave absorption at target frequencies to meet the requirement of radar cross-section reduction.In this work,a strategy of efficient utilization of CNT in producing CNT incorporated aramid papers is demonstrated.The layer-by-layer self-assembly technique is used to coat the surfaces of meta-aramid fibers and fibrils with CNT,providing novel raw materials available for the large-scale papermaking.The hierarchical construction of CNT networks resolves the dilemma of increasing CNT content and avoiding the agglomeration of CNT,which is a frequent challenge for CNT incorporated polymeric composites.The composite paper,which contains abundant heterogeneous interfaces and long-range conductive networks,is capable of reaching a high permittivity and dielectric loss tangent at a low CNT loading,its complex permittivity is,so far,adjustable in the range of(1.20−j0.05)to(25.17−j18.89)at 10 GHz.Some papers with optimal matching thicknesses achieve a high-efficiency microwave absorption with a reflection loss lower than−10 dB in the entire X-band.展开更多
Basalt Fiber Reinforced Polymer(BFRP)composites have huge potential application respects for some civil fields due to enough strength/modulus to weight and low cost by replacing carbon fiber composites.Aiming at the i...Basalt Fiber Reinforced Polymer(BFRP)composites have huge potential application respects for some civil fields due to enough strength/modulus to weight and low cost by replacing carbon fiber composites.Aiming at the issues in the Resin-Rich Region(RRR)and Interfacial Transition Region(ITR)of fiber reinforced polymer composites,the characteristic Aramid Pulp(AP)fibers with micro-fiber trunk and nano-fiber branches were manufactured into multiple non-woven ultra-thin interleaving at the interlayers of BFRP composites via compression molding to reinforce the flexural strengths and elastic moduli.AP fibers were introduced into RRR to form interleaving at the interlayer,the brittle epoxy adhesive layer was improved and enabled to avoid cracking under a low external load.Free fiber branches of AP were also embedded into BF layer to construct quasi-vertical fiber bridging behaviors in ITR,stronger mechanical interlocking was created to prevent crack propagation along the bonding interface of BF/epoxy.Three-point bending testing results showed the interleaving film with 4 g/m^(2)AP exhibited the best effect among various areal densities and yielded average 315.75 MPa in flexural strength and 21.38 GPa in elastic modulus,having a 63.4%increment and a 47.1%increment respectively compared with the bases.Overall,the simple and low-cost AP interleaving is confirmed as an effective method in improving interlayer structure and flexural performance of BFRP composites,which may be considered to manufacture high-performance laminated fiber reinforced polymer composites in civil aviation industry.展开更多
An efficient method was proposed to prepare high-performance conductive AramidCarbon Blend Fabrics(ACBF)with cobalt-nickel(Co-Ni)alloy coatings,which is conducive to industrial production.The grid-like substrate compo...An efficient method was proposed to prepare high-performance conductive AramidCarbon Blend Fabrics(ACBF)with cobalt-nickel(Co-Ni)alloy coatings,which is conducive to industrial production.The grid-like substrate composed of aramid and carbon fibers was innovatively used in flexible Electromagnetic Interference(EMI)shielding materials.The natural network structure is advantageous to the uniform deposition of metal particles to the establishment of conductive pathways subsequently in order to improve conductivity.The induction of a synergistic effect from Electromagnetic(EM)wave-reflection and EM wave-absorption through the whole carbonCo-Ni-ternary system notably enhanced the EMI Shielding Effectiveness(SE)value to an average of 42.57 d B in the range of 30-6000 MHz.On the other hand,together with the inherent toughness of the alloy coatings,the tensile strength of the aramid fibers used for bulletproof made a significant contribution to the desired mechanical properties.The light weight of the resultant composite made it applicable to aerospace vehicles simultaneously.X-ray Photoelectron Spectroscopy(XPS)was conducted to investigate the variations of elements and groups on the sample surface in pretreating process.The elemental components and surface morphologies of fabric samples during different stages of the process were investigated by Scanning Electron Microscope(SEM)and Energy Dispersive spectrometer(EDX)measurements.X-Ray Diffraction(XRD)results indicated that the obtained Co-Ni alloy coating had a combined Hexagonal Closed-Packed(HCP)and FacedCentered Cubic(FCC)crystalline phase.The relatively high corrosion resistance demonstrated in different acid and alkaline conditions was instrumental in more complex environments as well.展开更多
In this paper,an aramid chopped fiber,so-called(ACF)/polyphenylene sulfide(PPS)composite,containing multi-walled carbon nanotubes(MWCNT),and in situ polymerized polypyrrole(PPy)was designed and fabricated,to be applie...In this paper,an aramid chopped fiber,so-called(ACF)/polyphenylene sulfide(PPS)composite,containing multi-walled carbon nanotubes(MWCNT),and in situ polymerized polypyrrole(PPy)was designed and fabricated,to be applied as a paper based electrode.The ACF/PPS/MWCNT-PPy electrode features highly porous paper-like structure with excel-lent electrochemical activity,rendering it a high areal capacitance of~3205 mF cm^(-2) at a current density of 5 mA cm^(-2).After 5000 charge-discharge cycles,the areal capacitance still maintains 93%and 70%at high current densities of 20 and 80 mA cm^(-2),respectively.Moreover,the ACF/PPS/MWCNT-PPy electrode displays over 50%the areal capacitance and maintains it's mechanical stability after annealing at 300℃.The UL-94 test reveals that the highest V-0 flame-retardant performance can be achieved.All these results suggest that the ACF/PPS/MWCNT-PPy composite is a promising material to be used as electrode for supercapacitor with high energy-storage capability and noninflammability.展开更多
A silane containing isocynate groups(3-(trimethoxysilyl) propyl cyanic acid ester,NCO) associated with hexamethyldisilazane(HDMS) is used to modify the surface of poly-(p-phenylene terephthalamide)(PPTA) pul...A silane containing isocynate groups(3-(trimethoxysilyl) propyl cyanic acid ester,NCO) associated with hexamethyldisilazane(HDMS) is used to modify the surface of poly-(p-phenylene terephthalamide)(PPTA) pulps. As concerns surface chemistry,Attenuated Total Reflection Flourier Transformed Infrared Spectroscopy(ATR FT-IR) and X-ray photoelectron spectroscopy(XPS) confirm that NCO associated with HDMS silylated PPTA pulp surface successfully. While the modified PPTA pulps are used as reinforcing fillers for silicone composites,the dispersibility and storage stability of the composites are improved as Mooney testing indicated. The silicone composites filled with modified PPTA pulps present a higher tensile strength and much higher broken elongation(3.30 MPa and 166.54%) than that with unmodified pulps(3.08 MPa and 68.47%),respectively.展开更多
基金supported by National Natural Science Foundation of China(Grant Nos.51377014,51407022 and 51677019)the National Key Research and Development program of China(2016YFC0207200)
文摘In this paper, a long line-shape dielectric barrier discharge excited by a nanosecond pulse and AC is generated in atmospheric air for the purpose of discussing the uniformity, stability and ability of aramid fiber treatment. The discharge images, waveforms of current and voltage,optical emission spectra, and gas temperatures of both discharges are compared. It is found that nanosecond pulsed discharge has a more uniform discharge morphology, higher energy efficiency and lower gas temperature, which indicates that nanosecond pulsed discharge is more suitable for surface modification. To reduce the water contact angle from 96° to about 60°, the energy cost is only about 1/7 compared with AC discharge. Scanning electron microscopy,Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy are employed to understand the mechanisms of hydrophilicity improvement.
文摘Dynamic tensile impact properties of aramid (Technora) and UHMWPE (DC851) fiber bundles were studied at two high strain rates by means of reflecting type Split Hopkinson Bar, and stress-strain curves of fiber yarns at different strain rates were obtained. Experimental results show that the initial elastic modulus, failure strength and unstable strain of aramid fiber yarns are strain rate insensitive, whereas the initial elastic modulus and unstable strain of UHMWPE fiber yarns are strain rate sensitive. A fiber-bundle statistical constitutive equation was used to describe the tensile behavior of aramid and UHMWPE fiber bundles at high strain rates. The good consistency between the simulated results and experimental data indicates that the modified double Weibull function can represent the tensile strength distribution of aramid and UHMWPE fibers and the method of extracting Weibull parameters from fiber bundles stress-strain data is valid.
文摘High-performance ballistic fibers,such as aramid fiber and ultra-high-molecular-weight polyethylene(UHMWPE),are commonly used in anti-ballistic structures due to their low density,high tensile strength and high specific modulus.However,their low modulus in the thickness direction and insufficient shear strength limits their application in certain ballistic structure.In contrast,carbon fiber reinforced epoxy resin matrix composites(CFRP)have the characteristics of high modulus in the thickness direction and high shear resistance.However,carbon fibers are rarely used and applied for protection purposes.A hybridization with aramid fiber reinforced epoxy resin matrix composites(AFRP)and CFRP has the potential to improve the stiffness and the ballistic property of the typical ballistic fiber composites.The hybrid effects on the flexural property and ballistic performance of the hybrid CFRP/AFRP laminates were investigated.Through conducting mechanical property tests and ballistic tests,two sets of reliable simulation parameters for AFRP and CFRP were established using LS-DYNA software,respectively.The experimental results suggested that by increasing the content of CFRP that the flexural properties of hybrid CFRP/AFRP laminates were enhanced.The ballistic tests'results and the simulation illustrated that the specific energy absorption by the perforation method of CFRP achieved 77.7%of AFRP.When CFRP was on the striking face,the shear resistance of the laminates and the resistance force to the projectiles was promoted at the initial penetration stage.The proportion of fiber tensile failures in the AFRP layers was also enhanced with the addition of CFRP during the penetration process.These improvements resulted in the ballistic performance of hybrid CFRP/AFRP laminates was better than AFRP when the CFRP content was 20 wt%and 30 wt%.
文摘The aramid fiber礥HMWPE (ultrahigh molecular weight polyethylene) fiber hybrid composites (AF礑F) were ma-nufactured. By Charpy impact, the low velocity impact behavior of AF礑F composite was studied. And the high velocity impact behavior under ballistic impact was also investigated. The influence of hybrid ratio on the performances of low and high velocity impact was analyzed, and hybrid structures with good impact properties under low velocity impact and high velocity were optimized. For Charpy impact, the maximal impact load increased with the accretion of the AF layers for AF礑F hybrid composites. The total impact power was reduced with the decrease of DF layers and the delamination can result in the increase of total impact power. For ballistic impact, the DF ballistic performance was better than that of the AF and the hybrid ratio had a crucial influence. The failure morphology of AF礑F hybrid composite under Charpy impact and ballistic impact was analyzed. The AF礑F hybrid composites in suitable hybrid ratio could attain better performance than AF or DF composites.
基金The project is supported by Zhejiang Provincial Natural Science Foundaion of China(599113)Science and Technology Foundation of Ministy of Educationd of China(DF 02064)
文摘Tensile impact tests of aramid (Twaron) fiber bundles were carried out under high strain rates with a wide range of 0. 01/s -1 000/s by using MTS and bar-bar tensile impact apparatus. Based on the statistical constitutive model of fiber bundles, statistical constitutive equations of aramid fiber bundles are derived from statistical analysis of test data at different strain rates. Comparison between the theoretical predictions and experimental data indicates statistical constitutive equations fit well with the experimental data, and statistical constitutive equations of fiber bundles at different strain rates are valid.
文摘Residual stresses of the ordinarily cured and pre-stressed unidirectionallaminate are analyzed quantitatively. In order to examine the analyzing formulations,strain gages were embedded in the uni-directional aramid aluminium laminates (ordi-narily cured and pre-stressed) to determine the residual stresses in the aluminiumlayers. The calculated residual stresses are in good agreement with the experimental val-ues in the longitudinal direction. Therefore, the work in this paper can be used to calcu-late, determine and design the longitudinal residual stresses according to the manufac-ture and application demands.
基金Supported financially by the National Natural Science Foundation of China(No.52102115)the High-end Foreign Expert Recruitment Plan of China(No.G2023036002L)+2 种基金the Natural Science Foundation of Sichuan Province,China(No.2023NSFSC0961)Shock and Vibration of Engineering Materials and Structures Key Lab of Sichuan Province,China(No.23kfgk06)the Postgraduate Innovation Fund Project by Southwest University of Science and Technology,China(No.24ycx2027).
文摘The high-strength Basalt Carbon Fiber Reinforced Polymer(BCFRP)composites had been manufactured by guiding Imitating Tree-root Micro/Nano Aramid Short Fiber(ITMNASF)into the interlayer of Basalt Fiber(BF)and Carbon Fiber(CF)plies to form thin interleaving,and various mass proportions of IT-MNASF were designed to discuss the reinforcing effect on the BCFRP heterogeneous composites.The results of three points bending tests showed that flexural strength and energy absorption of 4wt%IT-MNASF reinforced BCFRP heterogeneous composites had been improved by 32.4%and 134.4%respectively compared with that of unreinforced specimens.The 4wt%IT-MNASF reinforced BCFRP specimens showed both a greater strength and a lower cost(reduced by 31%around)than that of plain CFRP composites.X-ray micro-computed tomography scanning results exhibited that the delamination-dominated failure of plain BCFRP composites was changed into multi-layer BF and CF fabrics damage.The reinforcing mechanism revealed that the introduced IT-MNASF could construct quasi-vertical fiber bridging,and it was used as"mechanical claws"to grasp adjacent fiber layers for creating a stronger mechanical interlocking,and this effectively improved resin-rich region and interfacial transition region at the interlayers.The simple and effective IT-MNASF interleaving technique was very successful in low-cost and high-strength development of BCFRP heterogeneous composites.
基金the Ministry of Science and Technology of China(No.2016YFA0200100)the Beijing National Laboratory for Molecular Sciences(No.BNLMS-CXTD-202001)+1 种基金the National Natural Science Foundation of China(Nos.52102035,52021006,T2188101,51720105003,and 21790052)the Strategic Priority Research Program of CAS(No.XDB36030100).
文摘Heterocyclic aramid fibers,a typical kind of high-performance fibers,have been widely used in aerospace and protection fields because of their excellent mechanical properties.However,the application of heterocyclic aramid fibers as a reinforcement is hindered by the weak interfacial combination with matrix materials,especially epoxy.Traditional strategies enhancing the interfacial shear strength(IFSS)usually decrease the tensile strength.Therefore,simultaneous enhancement of both mechanical properties remains a challenge.Herein,we report a novel heterocyclic aramid fiber with high interfacial shear strength(49.3 MPa)and tensile strength(6.27 GPa),in which 4,4′-diamino-2′-chlorobenzanilide(DABA-Cl)and a small amount of graphene oxide(GO)are introduced through in-situ polymerization.Hydrogen bonds andπ–πinteraction between GO and polymer chains trigger the enhancement in crystallinity,orientation,and lateral interaction of the fibers,thus improving the tensile strength and interfacial shear strength of the fibers.Moreover,the interfacial interaction between fiber and epoxy is enhanced due to the improvement of the surface polarity of the fibers caused by DABA-Cl.Therefore,a method to improve both tensile strength and interfacial shear strength of heterocyclic aramid fibers was found by introducing GO and DABA-Cl,which may provide guidance for the design and preparation of other high-performance fibers.
基金This work is part of the Research Program of the Dutch Polymer Institute DPI,The Netherlands(Project No.#782).
文摘Friction between two contacting surfaces is studied extensively.One of the k n o w n friction theories is Amontons,law which states that the friction force is proportional to the normal force.However,Amontons7 law has been found to be invalid for elastomers.In the present study,the validity of Amontons7 law for short-cut aramid fiber reinforced elastomers is studied.Two types of fillers are used to reinforce the elastomers,namely highly dispersible silica and short-cut aramid fibers.Short-cut aramid fibers with two different surface treatments are used,namely non-reactive fibers with standard oily finish(SF-fibers)and fibers treated with an epoxy coating(EF-fibers).A pin-on-disc tribometer is used to investigate the frictional behavior of the composites in sliding contact with a granite counter surface.The results show that,after the run-in phase,Amontons,law is valid for those composites that are reinforced by short-cut aramid fibers(without reinforcing filler,i.e.,silica)if the contact pressure is below a threshold value.However,once the contact pressure exceeds this threshold value,Amontons'law will be invalid.The threshold contact pressure of the composites containing EF-fibers is higher than of the composites containing SF-fibers.The composites that are reinforced by silica and short-cut aramid fibers do not follow Amontons7 law.
基金the National Natural Science Foundation of China(No.U21A2093).
文摘Carbon nanotubes(CNTs)incorporated polymeric composites have been extensively investigated for microwave absorption at target frequencies to meet the requirement of radar cross-section reduction.In this work,a strategy of efficient utilization of CNT in producing CNT incorporated aramid papers is demonstrated.The layer-by-layer self-assembly technique is used to coat the surfaces of meta-aramid fibers and fibrils with CNT,providing novel raw materials available for the large-scale papermaking.The hierarchical construction of CNT networks resolves the dilemma of increasing CNT content and avoiding the agglomeration of CNT,which is a frequent challenge for CNT incorporated polymeric composites.The composite paper,which contains abundant heterogeneous interfaces and long-range conductive networks,is capable of reaching a high permittivity and dielectric loss tangent at a low CNT loading,its complex permittivity is,so far,adjustable in the range of(1.20−j0.05)to(25.17−j18.89)at 10 GHz.Some papers with optimal matching thicknesses achieve a high-efficiency microwave absorption with a reflection loss lower than−10 dB in the entire X-band.
基金supported financially by the National Natural Science Foundations of China(No.52102115)the Overseas High-End Talent Introduction Project of Sichuan Province,China(No.2023JDGD0013)the Natural Science Foundations of Sichuan Province,China(No.2023NSFSC0961)。
文摘Basalt Fiber Reinforced Polymer(BFRP)composites have huge potential application respects for some civil fields due to enough strength/modulus to weight and low cost by replacing carbon fiber composites.Aiming at the issues in the Resin-Rich Region(RRR)and Interfacial Transition Region(ITR)of fiber reinforced polymer composites,the characteristic Aramid Pulp(AP)fibers with micro-fiber trunk and nano-fiber branches were manufactured into multiple non-woven ultra-thin interleaving at the interlayers of BFRP composites via compression molding to reinforce the flexural strengths and elastic moduli.AP fibers were introduced into RRR to form interleaving at the interlayer,the brittle epoxy adhesive layer was improved and enabled to avoid cracking under a low external load.Free fiber branches of AP were also embedded into BF layer to construct quasi-vertical fiber bridging behaviors in ITR,stronger mechanical interlocking was created to prevent crack propagation along the bonding interface of BF/epoxy.Three-point bending testing results showed the interleaving film with 4 g/m^(2)AP exhibited the best effect among various areal densities and yielded average 315.75 MPa in flexural strength and 21.38 GPa in elastic modulus,having a 63.4%increment and a 47.1%increment respectively compared with the bases.Overall,the simple and low-cost AP interleaving is confirmed as an effective method in improving interlayer structure and flexural performance of BFRP composites,which may be considered to manufacture high-performance laminated fiber reinforced polymer composites in civil aviation industry.
基金supported by the National Natural Science Foundation of China(No.U1830108)the Shanghai Natural Science Foundation,China(No.20ZR1405000)+1 种基金the Innovation Foundation of Shanghai Aerospace Science and Technology,China(No.SAST2018-061)the Exploratory Research Project of“Yanchang Petroleum(Group)-Fudan University”,China。
文摘An efficient method was proposed to prepare high-performance conductive AramidCarbon Blend Fabrics(ACBF)with cobalt-nickel(Co-Ni)alloy coatings,which is conducive to industrial production.The grid-like substrate composed of aramid and carbon fibers was innovatively used in flexible Electromagnetic Interference(EMI)shielding materials.The natural network structure is advantageous to the uniform deposition of metal particles to the establishment of conductive pathways subsequently in order to improve conductivity.The induction of a synergistic effect from Electromagnetic(EM)wave-reflection and EM wave-absorption through the whole carbonCo-Ni-ternary system notably enhanced the EMI Shielding Effectiveness(SE)value to an average of 42.57 d B in the range of 30-6000 MHz.On the other hand,together with the inherent toughness of the alloy coatings,the tensile strength of the aramid fibers used for bulletproof made a significant contribution to the desired mechanical properties.The light weight of the resultant composite made it applicable to aerospace vehicles simultaneously.X-ray Photoelectron Spectroscopy(XPS)was conducted to investigate the variations of elements and groups on the sample surface in pretreating process.The elemental components and surface morphologies of fabric samples during different stages of the process were investigated by Scanning Electron Microscope(SEM)and Energy Dispersive spectrometer(EDX)measurements.X-Ray Diffraction(XRD)results indicated that the obtained Co-Ni alloy coating had a combined Hexagonal Closed-Packed(HCP)and FacedCentered Cubic(FCC)crystalline phase.The relatively high corrosion resistance demonstrated in different acid and alkaline conditions was instrumental in more complex environments as well.
基金The authors thank the financial support from Key Research and Development Plan of Hubei Province(2020BCB068).
文摘In this paper,an aramid chopped fiber,so-called(ACF)/polyphenylene sulfide(PPS)composite,containing multi-walled carbon nanotubes(MWCNT),and in situ polymerized polypyrrole(PPy)was designed and fabricated,to be applied as a paper based electrode.The ACF/PPS/MWCNT-PPy electrode features highly porous paper-like structure with excel-lent electrochemical activity,rendering it a high areal capacitance of~3205 mF cm^(-2) at a current density of 5 mA cm^(-2).After 5000 charge-discharge cycles,the areal capacitance still maintains 93%and 70%at high current densities of 20 and 80 mA cm^(-2),respectively.Moreover,the ACF/PPS/MWCNT-PPy electrode displays over 50%the areal capacitance and maintains it's mechanical stability after annealing at 300℃.The UL-94 test reveals that the highest V-0 flame-retardant performance can be achieved.All these results suggest that the ACF/PPS/MWCNT-PPy composite is a promising material to be used as electrode for supercapacitor with high energy-storage capability and noninflammability.
文摘A silane containing isocynate groups(3-(trimethoxysilyl) propyl cyanic acid ester,NCO) associated with hexamethyldisilazane(HDMS) is used to modify the surface of poly-(p-phenylene terephthalamide)(PPTA) pulps. As concerns surface chemistry,Attenuated Total Reflection Flourier Transformed Infrared Spectroscopy(ATR FT-IR) and X-ray photoelectron spectroscopy(XPS) confirm that NCO associated with HDMS silylated PPTA pulp surface successfully. While the modified PPTA pulps are used as reinforcing fillers for silicone composites,the dispersibility and storage stability of the composites are improved as Mooney testing indicated. The silicone composites filled with modified PPTA pulps present a higher tensile strength and much higher broken elongation(3.30 MPa and 166.54%) than that with unmodified pulps(3.08 MPa and 68.47%),respectively.