Flexible Polydimethylsiloxane Composite with Multi-Scale Conductive Network for Ultra-Strong Electromagnetic Interference Protection

Highly conductive polymer composites(CPCs) with excellent mechanical flexibility are ideal materials for designing excellent electromagnetic interference(EMI) shielding materials,which can be used for the electromagnetic interference protection of flexible electronic devices.It is extremely urgent to fabricate ultra-strong EMI shielding CPCs with efficient conductive networks.In this paper,a novel silver-plated polylactide short fiber(Ag@PL ASF,AAF) was fabricated and was integrated with carbon nanotubes(CNT) to construct a multi-scale conductive network in polydimethylsiloxane(PDMS) matrix.The multi-scale conductive network endowed the flexible PDMS/AAF/CNT composite with excellent electrical conductivity of 440 S m-1and ultra-strong EMI shielding effectiveness(EMI SE) of up to 113 dB,containing only 5.0 vol% of AAF and 3.0 vol% of CNT(11.1wt% conductive filler content).Due to its excellent flexibility,the composite still showed 94% and 90% retention rates of EMI SE even after subjected to a simulated aging strategy(60℃ for 7 days) and 10,000 bending-releasing cycles.This strategy provides an important guidance for designing excellent EMI shielding materials to protect the workspace,environment and sensitive circuits against radiation for flexible electronic devices.

Fabrication of Short Carbon Fiber Reinforced AZ91D Alloy by Infiltration-Extrusion Integrated Technique

Short carbon fiber reinforced AZ91D alloy (Csf/AZ91D) was fabricated by the infiltration-extrusion method. The short carbon fiber preform was infiltrated with melted AZ91D alloy under the assistant of gas pressure. The extrusion processing was applied following the infiltration processing directly. The tensile property and microstructure of the Csf/AZ91D and that of the die-casting and extruded AZ91D alloy was compared. The results show that the short carbon fiber reinforced AZ91D alloy present excellent tensile property. The tensile strength and modulus of elasticity of Csf/AZ91D is about 50% and 18% higher than that of cast AZ91D alloy, respectively. The elongation to fracture of Csf/AZ91D is about 50% lower than that of AZ91D alloy.

Preparation and microwave dielectric properties of C_(sf)/Si_3N_4 composites

The Csf/Si3N4 composites were prepared by hot-press sintering method using α-Si3N4 power,short carbon fibers and La2O3-Y2O3 sintering additives. The mechanical and microwave dielectric properties of Csf/Si3N4 composites were studied and discussed. The results show that the addition of the short carbon fibers can not destroy the relative density of the sintered samples,but it deteriorates the flexural strength of the sintered samples,so the flexural strength of the silicon nitride matrix is the highest among the samples. The real part(ε′) and the imaginary part(ε″) of the permittivity of Csf/Si3N4 composites greatly increase with increasing volume fraction of the short carbon fibers,achieve the maximum 73.1 and 101.5,respectively. A strong frequency dependence of the imaginary part(ε″) of the permittivity is observed.

Improved multi-orientation dispersion of short carbon fibers in aluminum matrix composites prepared with square crucible by mechanical stirring

In order to improve the strength of short carbon fibers reinforced aluminum matrix(Csf/Al)composite,the dispersion of short carbon fibers with multi-orientation was controlled with a square crucible by mechanical stirring.The three-dimensional flow field models of liquid aluminum melt in the square/round crucibles were established and calculated,and the results were compared.The calculated results show that turbulent flow could be induced both in the square and round crucible,while the non-axisymmetric structure of the square crucible results in higher turbulent kinetic energy in the melt.Therefore,the uniformity and multi-orientation dispersion of the short fibers can be improved by the intensive turbulent flow in the square crucible,which will be increased by increasing the rotational velocity.The distribution of the short carbon fibers in the aluminum matrix prepared under different rotation velocities in square crucible was experimentally investigated.With the increase of stirring velocity,the multi-orientation dispersion of the short fibers in the composites increased gradually.The experimental results are consistent with the calculation results.The tensile testing results show that the strength of the Csf/Al composite can reach 172 MPa when the rotational velocity is 1000 rpm,and it is 48.3%higher than that prepared by the round crucible under the same conditions,which results from the improved multi-orientation dispersion of short carbon fibers in aluminum matrix.

Tribological properties of short carbon fibers reinforced epoxy composites

Short carbon fiber(SCF)reinforced epoxy composites with different SCF contents were developed to investigate their tribological properties.The friction coefficient and wear of the epoxy composites slid in a circular path against a steel pin inclined at 45°to a vertical axis and a steel ball significantly decreased with increased SCF content due to the solid lubricating effect of SCFs along with the improved mechanical strength of the composites.The scanning electron microscope(SEM)observation showed that the epoxy composites had less sensitive to surface fatigue caused by the repeated sliding of the counterparts than the epoxy.The tribological results clearly showed that the incorporation of SCFs was an effective way to improve the tribological properties of the epoxy composites.

Tribological behaviour of fused deposition modelling printed short carbon fibre reinforced nylon composites with surface textures under dry and water lubricated conditions

Fused deposition modelling(FDM)printed short carbon fibre reinforced nylon(SCFRN)composites were fabricated.The friction and wear behaviour of printed materials were systematically investigated under both dry sliding and water lubricated conditions.The results showed that with short fibre enhancements,the printed SCFRN achieved a lower friction coefficient and higher wear resistance than nylon under all tested conditions.Further,under water lubricated conditions,the printed SCFRN exhibited a low,stable friction coefficient due to the cooling and lubricating effects of water.However,the specific wear rate of the printed specimens could be higher than that obtained under dry sliding conditions,especially when the load was relatively low.The square textured surface was designed and created in the printing process to improve materials’tribological performance.It was found that with the textured surface,the wear resistance of the printed SCFRN was improved under dry sliding conditions,which could be explained by the debris collection or cleaning effect of surface texture.However,such a cleaning effect was less noticeable under lubricated conditions,as the liquid could clean the surface effectively.On the other hand,surface textures could increase the surface area exposed to water,causing surface softening due to the higher water absorption rate.As a result,the samples having surface textures showed higher wear rates under lubricated conditions.The work has provided new insights into designing wear resistant polymer materials using three-dimensional(3D)printing technologies,subjected to different sliding conditions.

短切碳纤维增强MC尼龙复合材料的制备与性能

MC尼龙是一种已得到广泛应用的重要的工程塑料,但存在尺寸稳定性较差、热稳定性不高和重载下强度欠佳等缺点。本研究采用短切碳纤维(SCF)作为改性剂,探索研究了SCF/MC尼龙复合材料的制备工艺,研究了不同的SCF含量对复合材料密度、转化率、机械性能、摩擦性能及结晶度的影响。结果表明:在0~20%SCF含量范围内,复合材料的密度及拉伸强度表现为先增大后减少;转化率和冲击强度为20%SCF复合材料最为突出;而摩擦系数、磨损量在加入SCF后呈现先减少后增加的趋势。在10%SCF含量时,材料表现出较好的摩擦性能,同时结晶温度增大到182.95℃,结晶度为35.57%。研究结果证实通过添加适当比例的SCF改性剂可以有效改善MC尼龙的性能,这为进一步开发满足某些特殊螺旋传动下的新型复合材料做了有益尝试。

A novel approach for manufacturing of layered,ultra-refractory composites using pliable,short fibre-reinforced ceramic sheets

A new additive technique for manufacturing of short fibre-reinforced ultra-refractory ceramics is presented.This technique allows the fabrication of solvent-free,thin(~100µm),flexible,and easy-to-handle sheets suitable for fabricating homogeneous or layered structures.A large range of compositions,in terms of matrix and fibre volumetric contents,from 0%to 100%is possible.The amount of short carbon fibres incorporated in the sheets ranged from 20 to 50 vol%,whereas the fibre length ranged from 3 to 5 mm.The matrix composition investigated with this technique consisted of ZrB_(2)/SiC/Y_(2)O_(3).By increasing the fibre amount from 35 to 50 vol%,an improvement of mechanical properties was observed.Four-point flexural strength(σ)ranged from 107 to 140 MPa,depending on the amount of carbon fibres(Cf).The same holds true for the work of fracture,ranging from 108 to 253 J/m^(2).Functionally graded composites were fabricated by overlapping sheets with a fibre gradient(0%-50%).

Novel C_(sf)/SiBCN composites prepared by densifying C_(sf)/MA-SiBCN with the PIP process:Oxidation behavior and damage mechanism

To improve the oxidation resistance of short carbon fiber(C_(sf))-reinforced mechanically alloyed SiBCN(MA-SiBCN)(C_(sf)/MA-SiBCN)composites,dense amorphous C_(sf)/SiBCN composites containing both MA-SiBCN and polymer-derived ceramics SiBCN(PDCs-SiBCN)were prepared by repeated polymer infiltration and pyrolysis(PIP)of layered C_(sf)/MA-SiBCN composites at 1100℃,and the oxidation behavior and damage mechanism of the as-prepared C_(sf)/SiBCN at 1300–1600℃ were compared and discussed with those of C_(sf)/MA-SiBCN.The C_(sf)/MA-SiBCN composites resist oxidation attack up to 1400℃ but fail at 1500℃ due to the collapse of the porous framework,while the PIP-densified C_(sf)/SiBCN composites are resistant to static air up to 1600℃.During oxidation,oxygen diffuses through preexisting pores and the pores left by oxidation of carbon fibers and pyrolytic carbon(PyC)to the interior of the matrix.Owing to the oxidative coupling effect of the MA-SiBCN and PDCs-SiBCN matrices,a relatively continuous and dense oxide layer is formed on the sample surface,and the interfacial region between the oxide layer and the matrix of the as-prepared composite contains an amorphous glassy structure mainly consisting of Si and O and an incompletely oxidized but partially crystallized matrix,which is primarily responsible for improving the oxidation resistance.

短切碳纤维对泵用SiC复合陶瓷强度与耐冲蚀性影响研究

将0.5 mm、1 mm和3 mm的短切碳纤维分别加入SiC树脂复合陶瓷中,研究不同短切碳纤维长度对SiC复合陶瓷抗折强度和耐冲蚀性能的影响。研究结果表明,添加短切碳纤维后,试样的体积密度从2.45降低至2.32 g/cm^(3),而显气孔率变化不大,维持在4%。随着添加短切碳纤维长度的增加,试样的抗折强度显著提升,从61.57 MPa增加至71.67 MPa。添加3 mm的短切碳纤维后,试样的抗折强度更加稳定,多个试样间的差距显著降低。添加不同长度短切碳纤维后,试样的常温耐冲蚀性无明显变化,一次和二次冲蚀损失体积分别维持在0.033 cm^(3)和0.045 cm^(3)左右。SiC树脂复合陶瓷浇注料的制备过程中,添加3 mm的短切碳纤维可以有效提升抗折强度,同时保持复合陶瓷优秀的耐冲蚀性能。

短碳纤维增强铜基复合材料的摩擦磨损性能研究

采用冷压烧结工艺制备了短碳纤维增强铜基复合材料,考察了该复合材料的干摩擦磨损性能。讨论了短碳纤维含量、载荷、转速等对复合材料摩擦性能的影响。结果表明:复合材料的耐磨性能明显优于基体材料;随着碳纤维含量的增加复合材料的耐磨性能进一步提高;随载荷和转速的提高,摩擦系数和磨损量也随之增加;复合材料由纯铜的粘着磨损转变为剥层磨损,并均伴有一定的氧化磨损。

短碳纤维增强PPEK复合材料的性能研究

采用熔融共混的方式制备了不同短碳纤维含量增强含二氮杂萘酮聚芳醚酮(PPEK)基复合材料,对复合材料的加工性能、力学性能、摩擦性能、耐热性进行了研究。结果表明:短碳纤维增强复合材料均可以注塑成型;短碳纤维对PPEK的增强作用明显,拉伸强度和弯曲强度均有大幅提高;复合材料中短碳纤维起到了明显的自润滑作用,复合材料的摩擦系数和磨损率均随碳纤维含量的增加而明显降低;短碳纤维的加入进一步提高了复合材料的耐热性。

短切炭纤维增强沥青基C/C复合材料的力学性能

利用模压半炭化成型工艺在大气环境下制备出了短切炭纤维增强沥青基C/C复合材料(简称SCFRC)。研究了短切炭纤维的体积分数对SCFRC材料的体积密度和力学性能的影响规律。借助光学显微镜和扫描电镜对其微观组织和断口形貌进行了观察,分析了短切炭纤维对SCFRC材料的增强机制。结果表明,当短切炭纤维的体积分数由0%增大到11.8%时,SCFRC材料的力学性能随之呈线性增加;短切炭纤维增强SCFRC材料的机制主要有裂纹偏转效应、桥联效应以及脱粘和拔出效应。

粉末冶金法炭纤维/Mg复合材料的界面对其力学性能的影响

采用表面化学镀镍前后的短炭纤维(Cf)做为增强体,纯镁粉为基体金属,通过粉末冶金法和热挤压制备镁基复合材料。采用SEM-EDS、TEM、XRD和拉伸等测试手段表征短炭纤维增强镁基复合材料的微观形貌、元素组成、物相组成及其力学性能。结果表明:炭纤维在复合材料中分布均匀且沿挤压方向定向排列;采用经过表面化学镀镍处理的短炭纤维与金属镁复合后界面结合状态优良,M g2N i物相的存在表明润湿性的改善是通过金属镁与涂层发生反应而实现;对比屈服强度测试值和理论计算值的大小,表明涂层炭纤维增强镁基复合材料的增强机理主要是界面载荷传递效应。

铁氧体和碳纤维双层复合材料吸波性能研究

使用溶胶凝胶法制备了M型六角铁氧体,测量了铁氧体和短切碳纤维复合材料在Ku波段的电磁参数,并根据电磁参数设计了双层吸波材料.结果表明:M型铁氧体复合材料的介电损耗和磁损耗都比较小,而短切碳纤维复合材料具有较高的介电损耗;内外层材料相同但厚度不同的双层复合材料表现出不同的微波吸收特性,其中,内层为M型铁氧体复合材料、外层为碳纤维复合材料、层厚分别为1.5 mm和0.5 mm的双层复合材料,表现出优良的微波吸收性能,反射率在-10 dB以下的有效带宽覆盖了整个Ku波段,最大吸收位于15.3 GHz处,反射率约为23.0 dB.

短碳纤维增强铜基复合材料制备新工艺

开发了一种对短碳纤维直接电镀铜的新方法,并将得到的镀铜短碳纤维直接进行冷压烧结制备铜基复合材料,对镀铜碳纤维和复合材料的组织和性能进行了研究。结果表明:电镀得到的电沉积物呈疏松多孔状,且镀层均匀可控;在铜基复合材料中,碳纤维分布均匀,界面结合良好;随着碳纤维含量的增加,复合材料的抗弯强度、硬度也随之增加,但电导率、热导率有所降低;复压复烧工艺能显著提高复合材料的强度;在电镀工艺为3．0 A／dm2、60 min时,制得的复合材料中碳纤维体积分数为17．9％,综合性能较佳,抗弯强度为282．1MFa,硬度为96．5 HV,电导率为24．5 m／(Ωmm2),热导率为193．2 W／(mK),经复压复烧后抗弯强度、硬度分别达到327．6 MPa,119 HV。

碳纤维含量对C_f/SiO_2复合材料组织与性能的影响

采用真空热压烧结工艺制备了碳纤维体积分数分别为 2 0 %、4 0 %和 6 0 %的高致密Cf/SiO2 复合材料 ,研究了碳纤维含量对其组织结构、力学性能、热膨胀特性和抗氧化性能的影响规律。结果表明 :SiO2基体及 2 0 %Cf/SiO2 复合材料中 ,SiO2 仍保持非晶态 ,碳纤维含量为 4 0 %和 6 0 %时 ,SiO2 发生部分析晶 ;Cf/SiO2 复合材料的抗弯强度、断裂韧性和断裂应变 ,随碳纤维含量增加均呈现先降低后又增加的趋势 ,而弹性模量则先增后降 ;6 0 %Cf/SiO2 表现出明显伪塑性 ;碳纤维含量增大 ,使复合材料的热膨胀系数成倍增加 。

短切碳纤维增强B_4C/环氧树脂基中子屏蔽材料的力学性能优化研究

为满足工程应用领域对中子屏蔽材料力学性能的要求,采用短切碳纤维增强方法对传统的含B4C中子屏蔽材料进行了改良,研制出的新型B4C/环氧树脂基中子屏蔽材料具有良好的力学性能和屏蔽性能。重点研究了短切碳纤维含量、长度及表面处理工艺对碳纤维增强环氧树脂屏蔽材料力学性能的影响,结果表明,含10wt%B4C的碳纤维增强环氧树脂材料中树脂与纤维质量之比为5:1时,材料的拉伸强度最佳;当纤维长度为3–10 mm时,对材料拉伸性能影响较小;选用硅烷偶联剂KH-550进行纤维表面处理,能有效提高材料20%的拉伸性能。利用镅-铍中子源对含10wt%B4C碳纤维增强环氧树脂材料与含硼聚丙烯材料进行中子屏蔽比较实验,实验结果证明,该新型中子屏蔽材料能够满足中子屏蔽要求,具有良好的力学性能和广阔的应用前景。

碳纤维含量对Al_2O_3+C/ZL109混杂复合材料摩擦磨损性能的影响

利用挤压铸造法制备了Al2 O3 +C/ZL10 9短纤维混杂金属基复合材料 ,并探讨了Al2 O3 纤维体积分数为 12 %时 ,C纤维含量对该混杂复合材料摩擦磨损性能的影响。结果表明 :随着C纤维体积分数的增加 ,复合材料的摩擦因数和磨损率逐渐降低。12 %Al2 O3 和 4%C短纤维的协同作用使复合材料从轻微磨损到急剧磨损的临界转变载荷比基体合金提高了 1倍。当载荷低于临界载荷时 ,复合材料的主要磨损机制为犁沟磨损和层离 ,C纤维的加入有利于磨损表面裂纹尺寸的减小。但随着载荷的逐渐增加并发生严重磨损时 。

短碳纤维增强羟基磷灰石生物材料的制备与性能

以短碳纤维(C_f)为增强体,采用湿法搅拌均化和自组装合成工艺使短碳纤维均匀分散于反应生成的羟基磷灰石(HA)粉体中,30 MPa下将复合粉体压制成型,并于1250℃氮气保护气氛常压烧结制备了短碳纤维增强羟基磷灰石生物复合材料(C_f/HA)。为提高复合材料的界面结合,低温氧化法对碳纤维进行表面处理。采用IR,SEM技术研究短碳纤维处理前后的表面状态;SEM观察复合粉体的分散效果及复合陶瓷的断口形貌:三点弯曲法测其抗弯强度;单边切口梁法测其断裂韧性。实验结果表明:碳纤维的表面处理对力学性能有很大影响,可大大提高复合材料界面结合强度,C_f添加量为0.5%(质量分数)时,增强效果最为理想,最大抗弯强度为67.70 MPa,断裂韧性达1.18 MPa.m^(1/2),比C_f未氧化处理的复合材料分别提高近20%和18%。研究表明湿法搅拌均化和自组装合成工艺是一种行之有效的均化技术,具有最小的纤维损伤度、高的碳纤维体积分数以及操作便利等优点,常压下烧结制备的短Cf/HA复合材料是一种很有发展前途的骨替代植入材料。