加载频率对多壁碳纳米管/天然橡胶复合材料压阻传感行为的影响

为考察多壁碳纳米管/天然橡胶(MWCNT/NR)复合材料压阻传感特性与加载频率的相关性，对不同加载频率下MWCNT/NR复合材料的压敏传感行为进行了系统研究。分析了加载频率对MWCNT/NR复合材料循环应力分布、电阻-应变响应特征和肩峰强度的影响，探讨了电阻变化幅值衰减行为、恢复能力及灵敏度与加载频率间的关系。结果表明，加载频率越大，MWCNT/NR复合材料应力强度越高；其电阻-应变响应行为随着加载循环的进行逐渐独立于加载频率，电阻变化幅值衰减随着加载频率的增大逐渐减小并趋于稳定；而在整个循环加载过程中肩峰强度发展趋势与加载频率呈正相关性。传感特性恢复能力随循环次数的增加而增强，而随加载频率的增加呈下降趋势。     

多壁碳纳米管水泥基复合材料的压敏性能研究

采用聚羧酸系减水剂分散多壁碳纳米管（ MWCNTs ）,利用四电极法研究了 MWCNTs 掺量对28 d 龄期MWCNTs水泥基复合材料导电特性和在循环荷载作用下压敏性能的影响以及不同最大加载力和加载速率下材料压敏性能的变化。研究表明：随 MWCNTs 掺量的增加,复合材料的电阻率逐渐降低,极化时间逐渐减少。当MWCNTs的掺量在0．06wt％～0．3wt％范围时,复合材料电阻率的变化最大,在循环荷载作用下也表现出良好的压敏性。当加载至试块破坏的情况下,最大电阻变化率可达到70％。随着加载力和加载速率的增加,电阻率的变化率均逐渐变大。本项研究对于实现混凝土材料的智能化以及工程结构检测的实时化具有重要意义。     

循环荷载下钢渣砂浆的压敏特性研究

为研究钢渣掺量对钢渣砂浆强度特性的影响及钢渣砂浆压敏性在循环荷载下的变化规律,对不同钢渣掺量、不同龄期的钢渣砂浆进行无侧限抗压强度测试,分析了循环荷载下抗压强度范围内电阻率变化率随应力变化的规律.结果表明:钢渣砂浆无侧限抗压强度随钢渣掺量的增加而降低,随龄期的增加而增加;此外,在电阻率测试及压敏性分析时,由于电阻率受电流频率影响较大,建议选用50 kHz作为取值频率;当应力变化在无侧限抗压强度范围内时,电阻率变化率幅度随养护龄期的增加逐渐减小,其变化率可由养护7 d时的-4.83％降至28 d时-3.16％,同时变化幅度随钢渣掺量的增加逐渐增大.     

聚丙烯/石墨烯片纳米复合材料阻燃及导热性能

采用熔融共混法制备了聚丙烯(PP)/石墨烯片(GNPs)纳米复合材料。讨论了添加不同质量分数的GNPs对PP/GNPs纳米复合材料的阻燃性能以及导热性能的影响。结果表明,随着GNPs用量的增加,PP/GNPs纳米复合材料的极限氧指数升高,水平燃烧速率下降,烟密度等级虽有波动但总体呈升高趋势;与比表面积大的GNPs相比,比表面积小的对减缓水平燃烧速率作用较好;不同厚度的试样对水平燃烧速率的影响差异很大;随着GNPs质量分数的增加,复合材料的比热容有所降低,热扩散系数明显增加;与比表面积小的GNPs相比,比表面积大的对复合材料散热能力影响更显著。     

石墨烯/聚丙烯复合材料制备及性能研究

以石墨烯(GNPs)为填料对聚丙烯(PP)进行改性,通过球磨和熔融挤出共混的方法制备了一系列不同GNPs含量的GNPs/PP复合材料。用X射线衍射、扫描电子显微镜、电导率测试及拉伸测试等手段对复合材料的结构和性能进行表征分析,研究GNPs含量对复合材料性能的影响。结果表明:随着GNPs含量的增加,复合材料的电导率逐渐增大;当GNPs质量分数为15%时,复合材料的电导率达到0. 127 S/cm;复合材料的电阻逾渗阈值在GNPs质量分数为5%～8%之间。在力学性能方面,随着GNPs含量的增加,复合材料的拉伸强度呈现出先增加后降低的趋势;当GNPs质量分数为3%时,复合材料的拉伸强度达到最大,为35. 658 MPa,比纯PP提高了21. 04%;复合材料的弹性模量随着GNPs含量的增加而增加,在GNPs质量分数为15%时,复合材料的弹性模量比纯PP提高了89. 6%,达到2 068. 54 MPa。本文对制备高导电和高强度的导电聚合物或者导电纤维母粒可以提供一定的参考价值。     

应变率对氧化石墨烯水泥基复合材料微观力学性能的影响

研究不同氧化石墨烯掺量的水泥净浆在不同应变率作用下的硬度和弹性模量。结果表明:在氧化石墨烯掺量为0 ～ 0.06%的范围内,水泥净浆的弹性模量随氧化石墨烯掺量的增加而增大,掺量为0.06%时的弹性模量增强效果最佳,相比未掺时提高了39%,此时试件微观结构更加紧密,孔隙变小。应变率的改变对氧化石墨烯水泥净浆硬度的变化影响不大;在0.01s~(-1 )～ 0.5s~(-1)应变率变化范围内,同一掺量氧化石墨烯水泥净浆的弹性模量随应变率的增加而增大,应变率为0.5s~(-1)时的弹性模量比应变率为0.01s~(-1)时提高了46%。     

高填充石墨烯纳米片/硅橡胶复合材料的结构与性能

通过机械共混法将石墨烯纳米片分散至30 000 m Pa·s乙烯基封端的聚二甲基硅氧烷中,并制备了石墨烯纳米片/硅橡胶复合材料。对其微观形貌进行了表征,并考察了复合材料的性能。结果发现,随石墨烯纳米片用量的增加,复合材料的熔点逐渐下降,结晶度呈现先升后降的趋势。当石墨烯纳米片填充量达30份时,复合材料的导热和导电性能明显提升,当填充80份时,石墨烯纳米片/硅橡胶复合材料的热导率和体积电阻率分别达到2. 648 W/(m·K)和0. 156Ω·cm。     

石墨烯改性水泥砂浆导电性能和压敏性能研究

采用Hummers法制备氧化石墨烯(GO),并经过800℃高温还原制备石墨烯(RGO)。采用TEM、FTIR微观手段对其结构进行表征。并将其应用在水泥砂浆中,研究不同掺量石墨烯改性水泥砂浆的导电性能和压敏性能的影响。研究结果表明,在水化早期,石墨烯对水泥砂浆的导电增强作用不明显,但在水化后期,石墨烯能大大增加水泥砂浆的导电性。水泥砂浆的导电性随着薄层石墨掺量的增加呈现先增加后减小的趋势,增加水泥基材料导电性的较佳掺量为0.9%;并且,石墨烯改性水泥砂浆具有明显的压力依赖性,在受到压应力时,表现出明显的压敏特性。     

不同含水率下赤泥改良土的动弹模及阻尼比研究

为研究不同初始含水状态下赤泥改良土的动力学参数,利用GDS动三轴仪对不同含水率下改良土进行了不同频率下的循环加载试验,研究分析了振次、含水率、加载频率对改良土动弹性模量和阻尼比的影响.试验结果表明:动应力幅值一定时,动弹模随振次增加基本无变化,阻尼比随振次增加呈波动变化,且提出并证明了可用第10振次下的动弹模阻尼比值代表各级荷载下的动弹模阻尼比值;动弹模随动应变幅值的增加先增大后减小,并用二次函数对其进行了拟合,阻尼比随动应变的增加先减小后增大;改良土动弹模在其最优含水率处达到最大,较高的含水率使改良土动弹模明显下降;较小应变幅下动弹模随频率增加而减小,较大应变幅时动弹模随频率增加而增大,阻尼比在加载频率较高时较大.     

PP/多层石墨烯纳米复合材料性能研究

利用双螺杆挤出机制备了聚丙烯/多层石墨烯(GNPs)纳米复合材料并研究了其性能。结果表明,GNPs具有明显的异相成核作用,使PP的结晶过程可在较高温度下进行。GNPs对PP具有增强增韧作用,在GNPs质量分数为1.5%时,拉伸强度增加了15%,弹性模量增加了33%。GNPs能有效地提高聚丙烯的耐热性能,在GNPs质量分数为2%时,维卡软化点提高了10℃以上。     

Mechanical and thermal properties of hybrid carbon fibre–phenolic matrix composites containing graphene nanoplatelets and graphite powder

Carbon fibre–phenolic matrix (CF–P) composites containing graphene nanoplatelets (GNPs) were manufactured for improved mechanical and thermal properties. For comparison, micrometer-size pyrolytic graphite powder (GP) was also incorporated in CF–P composites. The loading of carbon fibres was kept constant at 60?wt-% while the quantity of GNPs was varied from 0.1?wt-% to 0.3?wt-% and GP from 1.0?wt-% to 3.0?wt-%. Only GNPs were functionalised by ultraviolet-ozone treatment to improve their dispersion in the matrix while all the composites were manufactured by hand layup method and characterised by scanning electron microscopy, impact, flexural, thermogravimetry and ablation tests. The composite containing 0.3?wt-% GNPs showed considerable improvement in ablation, flexural and impact testing as compared to CF-P composites containing GP. Finally, the ablation mechanisms of post-ablated composites were discussed in the light of available data in the literature.     

Physicochemical characteristics of bio-based thermoplastic polyurethane/graphene nanocomposite for piezoresistive strain sensor

Herein, we report the physicochemical characteristics and piezoresistive strain sensing performance of flexible thin film comprising graphene and bio-based thermoplastic polyurethane (TPU) prepared by solution cast method. A detailed analysis was carried to study the influence of graphene nanoplatelets on the morphological, thermal, mechanical, and electrical properties of TPU nanocomposite. Upon increasing the graphene nanoplatelets loading, the thermal stability and tensile properties improved remarkably, while glass transition temperature decreased slightly. Owing to better dispersion of graphene, the electrical conductivity was significantly increased, which broaden the utilization of the nanocomposite for various applications. The piezoresistive sensor was able to respond to various stress modes such as tapping, bending, and finger touch. The piezoresistive sensor was sensitive and achieved a gauge factor of 11. Sensor attached to finger, showed distinctive response upon bending at different angles and showed high stability and reproducibility even after >10,000 cycles under repetitive constant load. Also, the nanocomposite was able to detect any breakage or fracture in the form of change in electrical resistance. A combination of bio-based TPU and graphene offered improved physical properties and high sensing performance, which could be a potential material in flexible electronics and structural health monitoring systems.     

The effects of surface-modified graphene nanoplatelets on the sliding wear properties of basalt fibers-reinforced epoxy composites

Possessing unique designs and properties absent in conventional materials, nanocomposites have made a remarkable imprint in science and technology. This is particularly true regarding the polymer matrix composites when they are further reinforced with nanoparticles. In this study, the effects of different weight percentages (0, 0.1, 0.2, 0.3, 0.4, and 0.5) of surface-modified graphene nanoplatelets (GNPs) on the microhardness and wear properties of basalt fibers/epoxy composites were investigated. The GNPs were surface modified by silane, and the composites were made by the hand lay-up method. The wear tests were conducted under two different loads of 20 and 40 N. The best wear properties were achieved at 0.3 wt % GNPs as a result of the GNPs' self-lubrication property and the formation of a stable transfer/lubricating film at the pin and disk interface. Moreover, the friction coefficient was lower at the higher normal load of 40 N. The microscopic studies by FESEM and SEM showed that the presence of GNPs up to 0.3 wt % led to the stability of the transfer/lubricating film by enhancing the adhesion of the basalt fibers to the epoxy resin. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47986.     

Piezoresistive behavior of graphene nanoplatelets/carbon black/silicone rubber nanocomposite

Silicon rubber (SR) filled with carbon black (CB) and carbon black (CB)/graphene nanoplatelets (GNPs) hybrid fillers are synthesized via a liquid mixing method. The effects of filler type on the electrical properties and piezoresistive properties (near the region of the percolation) of the conductive SR composites are studied. It is suggested that the conductivity of the composite filled with CB/GNPs hybrid fillers in the mass ratio of 2 : 4 is much higher than that in other ratio. Percolation threshold for CB/GNPs/SR is found to be 0.18 volume fractions lower than CB/SR. Moreover, force rang and linearity of GNPs/CB/SR is higher than CB alone filling system. And the repeatability of the GNPs/CB/SR composites is better than CB/SR. Not repetitive index () of them is 0.1 and 0.18, respectively. The results suggest that the GNPs/CB/SR composites provide a new route toward fabrication of flexible piezoresistive sensors with high performance. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39778.     

Contact damage resistant SiC/graphene nanofiller composites

The short-crack domain and contact damage resistances of silicon carbide (SiC) ceramics containing graphene fillers (graphene nanoplatelets -GNPs- or reduced graphene oxide sheets -rGOs) are investigated by performing Hertzian contact tests. A progressive deviation from the linear Hertzian elastic response with increasing graphene content takes place, the composite containing 20 vol.% GNPs being the most deformable material. When adding increasing amounts of GNPs, the damage beneath the contact zone turns from well-defined cone cracks of monolithic SiC to a widespread subsurface damage where microcracks are generated due to the matrix/graphene interface debonding by a shear faulting process. This mechanism enhances the contact damage resistance of the composites, redistributing the stresses at the contact and limiting the long-crack formation. The composite containing 5 vol.% rGOs fully precludes the cone cracks development and enlarges the quasi-plastic damage zone, extraordinarily enhancing the contact damage resistance that approaches to that of a ductile material.     

Carbon nanotubes and graphene into thermosetting composites: Synergy and combined effect

This work analyzes the morphology and behavior of hybrid composites reinforced with carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs). In order to avoid the weak interface of laminar nanofillers, GNPs were functionalized with amine groups. Different tendencies were observed as a function of the measured property. Storage modulus showed a synergic trend, being the stiffness of hybrid CNT/GNP/epoxy composites higher than the corresponding ones measured in neat epoxy composites reinforced with CNTs or GNPs. In contrast, the thermal and electrical conductivity increased with the nanofiller addition, the final value of the mentioned properties in the hybrid composites was strongly influenced by specific graphitic nanofiller. Neat GNP/epoxy composites showed the highest thermal conductivity, while neat CNT/epoxy composites presented the highest electrical conductivity. This behavior is explained by the observed morphology. All composites exhibited a suitable nanofiller dispersion. However, on hybrid GNP/CNT/epoxy composites, CNTs tend to be placed between nanoplatelets, forming bridges between nanoplatelets. This morphology implies a less effective electrical network, limiting the synergic effect in the properties, which requires percolation. In spite of this, the hybrid GNP/CNT/epoxy composites showed a better combination of properties than the neat composites. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46475.     

Friction and wear behaviour of silicon carbide/graphene composites under isooctane lubrication

The tribological performance of silicon carbide (SiC)/graphene nanoplatelets (GNPs) composites is analysed under oscillating sliding tests lubricated with isooctane, looking to explore their potential as components for gasoline direct injection (GDI) engines. High graphene filler contents (20?vol.% of GNPs) are required to substantially reduce the friction coefficient of SiC ceramics, attaining decreases on friction up to 30% independently of the applied load. For all materials and testing conditions a mild wear regime is evidenced. SiC/20?vol.% GNPs composite also enhances the wear resistance up to 35% at low load, but the addition of GNPs produces a deleterious effect as the load augments. The tribological behaviour depends on the formation and destabilization of a solid lubricant carbon-based tribofilm and strongly correlates with the mechanical properties of the tested materials.     

石墨烯/聚乙烯复合改性沥青胶结料的流变性能研究

为提高沥青胶结料的综合路用性能,尤其是高温性能,本文采用高速剪切机将质优价廉的聚乙烯(PE)与石墨烯纳米片(GNPs)复合制备新型沥青胶结料,同时使用温度扫描(TeS)、多重应力蠕变恢复(MSCR)、线性振幅扫描(LAS)和傅里叶变换红外光谱(FTIR)研究了石墨烯/聚乙烯复合改性沥青胶结料的流变性能和作用机理。结果表明:GNPs和PE能够协同改善沥青胶结料的高温性能,提高路面的高温车辙抗性;预混的PE/GNPs母粒具有良好的中温疲劳和低温开裂抗性。同时复合改性沥青的FTIR光谱中未出现新的吸收峰,表明石墨烯和聚乙烯在沥青基体中以物理改性为主。     

Microstructure and anisotropic mechanical properties of graphene nanoplatelet toughened biphasic calcium phosphate composite

Graphene nanoplatelets (GNPs) reinforced biphasic calcium phosphate (BCP) composites were prepared by hot pressing (HP). Based on in-depth mechanical test and observation of microstructure, the influence of GNPs on BCP matrix was investigated. A preferred orientation of GNPs occurred during sintering, leading to anisotropic mechanical properties. The mechanical properties of GNPs/BCP composite measured along the direction parallel to the HP direction are higher than those measured along the perpendicular direction. Parallel to the HP direction, the composite containing 1.5 wt% GNPs exhibited the maximun bending strength and fracture toughness of 151.82 MPa and 1.74 MPa m^1/2, about 55% and 76% higher than those of monolithic BCP, respectively. The improvement in mechanical properties was mainly attributable to crack deflection, crack branching, bridging, pullout and fracture of GNPs. Especially GNPs can force crack to propagate not only in two but also in three dimensions.     

The beneficial effect of graphene nanofillers on the tribological performance of ceramics

The tribological properties of graphene nanoplatelets (GNPs)/Si₃N₄ composites are investigated for the first time using a reciprocating ball-on-plate configuration under isooctane lubrication. The role of these carbon nanostructures is studied through the analysis of the debris and wear tracks by micro-Raman spectroscopy. GNPs are excellent nanofillers for enhancing the tribological performance of ceramics. Under high contact pressures, GNPs are able to reduce friction and, especially, to increase the wear resistance up to 56% due to the exfoliation of the nanoplatelets that creates an adhered protective tribofilm. These composites are promising for their use in gasoline direct injection systems.