推进剂界面脱黏的有限元分析

采用黏结界面单元对推进剂的界面脱黏过程进行模拟,通过分析发现,由于推进剂内各组分的材料属性不同,受载条件下推进剂的应力应变分布很不均匀,基体变形大,颗粒变形小。推进剂黏结界面颗粒大小、取向以及相互之间的靠近程度对应力应变分布的影响较大,粒径越大,对应力应变分布的影响越大。应力集中首先出现在大颗粒周围,随着载荷的增加,大颗粒对应力应变分布的影响增大;并且界面脱黏位置受颗粒之间的影响较大,颗粒之间的相互作用影响了推进剂中微观损伤的演化,大颗粒之间的相互影响较大。     

残余应力对碳纤维填充聚合物注塑制品电阻率的影响

为了研究残余应力对注塑导电高分子复合材料导电性能的影响,以碳纤维填充聚合物注塑成型为试验对象,采用剥层法计算制品的残余应力,测量退火前后制品各层的电阻率变化,得到注塑工艺、残余应力和制品电阻率之间的关系。为了提高计算结果的可靠性,采用连续追踪截面形貌测量各层的纤维取向,并将结果集成于制品残余应力计算中。研究结果表明,残余应力对制品电阻率的影响主要集中在表层,芯部影响较小。在退火处理过程中,受残余应力释放和高分子链动态回复运动的双重影响,碳纤维在基体中分布状态更加均匀,提高了导电网络结构的连续性,从而使制品电阻率下降。残余压应力越高,退火过程中高分子链动态回复越快,制品表层电阻率下降越多,制品导电性能越好。     

波形碳纳米管增强复合材料的有效刚度和局部应力的宏微观均质化数值模拟

采用分子动力学方法简化的碳纳米管等效纤维模型,利用具有精确周期性边界条件的均质化理论和宏微观均质化法分析正弦波形非连续碳纳米管的有效刚度和局部应力分布规律.结果表明,纳米增强复合材料的有效刚度和局部应力对碳纳米管的波形非常敏感,碳纳米管稍有弯曲就会导致复合材料有效刚度降低和应力传递能力的下降,为揭示复合材料中碳纳米管的增强机制和改善增强效果提供理论依据.     

溶剂对碳纳米管/环氧树脂复合材料力热性能的影响

制备了碳纳米管／环氧树脂复合材料，分析了分散碳纳米管的溶剂对复合材料热学，力学行为的影响。溶剂效应由大到小依次为DMF，乙醇和丙酮，与三种溶剂的沸点顺序一致。溶剂效应被认为是未挥发完全的残留溶剂对环氧树脂固化反应的影响，从而导致了固化机理的不同。FTIR通过对比不同溶剂分散的复合材料的分子结构，证明了溶剂效应与复合材料中未反应完的环氧树脂及固化反应的完全程度有关，因而导致了不同的热、力学行为。     

碳纳米管增强铜基复合材料的研究进展

综述了碳纳米管增强铜基复合材料的预处理和制备方法,探讨了复合材料的组织、力学性能与摩擦学性能、电学性能和热学性能;最后指出了碳纳米管增强铜基复合材料今后的研究方向。     

碳纳米管增强铝基复合材料的研究进展

介绍了碳纳米管增强铝基复合材料的研究现状,通过对比不同制备工艺以及碳纳米管增强铝基复合材料的抗拉强度、硬度、伸长率等力学性能,总结了粉末冶金法、高能球磨法、热喷涂法以及其它新技术的优缺点,同时阐述了复合材料制备过程中存在的问题及解决方法;此外还介绍了碳纳米管的强化机制;最后讨论了碳纳米管增强铝基复合材料未来的发展方向和研究重点。     

填充颗粒对聚合物复合材料黏弹性的影响

利用CETRUMT-2试验机及LKDM-2000轮廓摩擦磨损仪考察CuO颗粒填充PA1010复合材料的静态蠕变特性、松弛特性,利用Tribo Indenter测试系统考察复合材料的动态黏弹特性。结果表明:CuO颗粒填充后复合材料仍具备黏弹性质;复合材料的静态蠕变量、残余变形及损失正切tanδ均小于PA1010材料,且CuO颗粒含量越多,复合材料的黏弹性质越不显著。     

界面尺寸对热障涂层残余应力的影响

广泛应用于高温部件的热障涂层,其凹凸不平的界面形貌不仅影响界面的结合强度、应力分布,严重时甚至会导致涂层剥离、层裂和失效.文中针对正弦波形界面形貌的热障涂层,研究了界面尺寸（微坑深度、宽度和间距）对界面残余应力的影响.结果表明,界面几何形貌突变越严重,应力突变也随之加剧;不同的微结构尺寸影响因素对残余应力影响各不相同,其中微坑深度对残余应力的影响最为显著.     

碳纳米管增强PTFE复合材料摩擦磨损性能研究

以不同含量的CNTs(碳纳米管)为填料制备了PTFE基复合材料,测量其硬度,在M-2000型摩擦磨损试验机上研究其摩擦磨损行为。结果表明,CNTs能提高PTFE的硬度,CNTs/PTFE复合材料的耐磨性能明显优于纯PT-FE,当CNTs的质量分数为3%时,复合材料的耐磨性能大幅度提高。其摩擦因数随着CNTs含量的增加而加大,当CNTs的质量分数为1%时,摩擦因数随载荷的增加而减少,CNTs的质量分数为3%和5%时,摩擦因数随载荷的增加而增大。SEM观察发现:纯PTFE的断面上分布着大量的带状结构,而填充CNTs后,摩擦表面较平整光滑,表明CNTs作为填料可有效地抑制PTFE的犁削和粘着磨损。     

SiC/Ti55复合材料残余应力的研究

采用ANSYS有限元法计算了SiC/Ti55复合材料中的残余应力,分析了不同纤维体积分数下纤维中径向、轴向和环向残余应力的大小和分布。结果表明,径向和轴向残余压应力均随纤维体积分数的增大而减小;环向残余应力在纤维内部为压应力,表面附近为拉应力,且纤维体积分数越高,表面环向拉应力越大。     

Wear behaviour of carbon nanotube reinforced epoxy resin composites

This paper deals with the effect of a multi-walled carbon nanotube (MWCNT) reinforcement on the wear behaviour of Epoxy (EP) composites. Firstly, various dispersion methods were compared. Secondly, the optimum CNT amount was evaluated. In a third step, dry lubricants were added to the optimised EP/CNT composite. Finally, the influence of the steel counterpart (martensitic bearing steel 100Cr6 and austenitic stainless steel X5CrNi18-10) was studied. The preparation method was found to have a decisive effect on the wear behaviour of the composite. A pre-treatment of the CNTs in concentrated nitric acid proved beneficial. Even more important was the mixing method. A dual asymmetric centrifuge delivered so good wear results that the pre-treatment could be skipped. The optimum CNT content was at about 1 wt%, regardless of the preparation method. The lowest wear rates were found after addition of 10 wt% graphite. MoS₂ proved to be less effective and Polytetrafluorethylene (PTFE) even increased the wear. The wear rates against the unalloyed martensitic steel were far higher than against austenitic stainless steel.     

In-situ transmission electron microscopy studies of polymer–carbon nanotube composite deformation

This paper demonstrates the viability of in-situ transmission electron microscopy for studying the deformation mechanisms of polymer nano-composites. In-situ straining studies are performed on carbon multiwalled nanotube (MWNT)–polystyrene composite films. The experiments show that load transfer across the nanotube–polystyrene interface is operative well into the plastic deformation regime of the composite film. The MWNTs are observed to bridge cracks propagating through the polystyrene, providing closure stresses across the crack wake. Although some MWNTs fracture by either a sword-in-sheath mechanism or transverse shear fracture, most of the MWNTs eventually debond at the MWNT–polymer interface and subsequently pull out of the matrix.     

Friction and wear of carbon nanohorn-containing polyimide composites

Polyimide (PI)-based composites containing single-wall carbon nanohorn aggregate (NH) were fabricated using the spark plasma sintering (SPS) process. For comparison, composites with carbon nanotube (NT) and traditional graphite (Gr) were also fabricated. The NH was produced using CO₂ laser vaporization and a graphite target and the NT was produced by a chemical synthesis method. We evaluated the friction and wear properties of the PI-based composites with a reciprocating friction tester in air using an AISI 304 mating ball. NH drastically decreased the wear of PI-based composites; the specific wear rate of composite with NH of only 5 wt% was of the order of 10⁻⁸ mm³/Nm, which was two orders of magnitude less than that of PI alone. The wear reduction ability of NT seemed to be slightly inferior to that of NH, although it was considerably better than that of Gr. NH and NT lowered the friction of composites. The friction coefficient of composite with 10 wt% NH was less than 0.25, although it was slightly higher than that of composite with 10 wt% Gr. There was no clear difference in the friction reduction effect of NH and NT. The further addition of Gr to composites with NH or NT rather deteriorated the antiwear property of composites, although the friction coefficient was slightly reduced. The transferred materials existed on the friction surface of the mating ball, sliding against composites with three types of carbon filler. These transferred materials seemed to correlate with the low friction and wear properties of composites.     

Influence of the multi-walled carbon nanotube and short carbon fibre composition on tribological properties of epoxy composites

The present research work deals with the development of a novel polymer composite for brake pad applications. The composite that was used consists of epoxy resin, carbon fibre and carbon nanotubes in varying weight percentage. The tribological performance of three different samples was tested using a pin-on-disc under dry contact condition. The results indicated that the sample filled with short carbon fibres (SCF), and multi-walled carbon nanotube (MWCNT) had superior performance. Reduction in wear rate was observed due to synergism between SCF and MWCNT as compared to SCF only. Scanning electron microscopy was subsequently performed on all samples. The micrographs show changes in the structural formation after the incorporation of SCFs and MWCNT. This increased composite structural strength and explains why SCF and MWCNT’s hybrid-filled composite material has better tribological properties.     

The effect of amorphous carbon layer on the field emission characteristics of carbon nanotube film

Carbon nanotube (CNT) has excellent field emission characteristics and could play as a good cold cathode in the application of vacuum electronic devices. However, the practical application faces a big obstacle regarding current fluctuation and deterioration of the CNT cathode. In this research, the formation of amorphous carbon (ac) layer between the CNT film and the substrate, and the effect of the existence of this layer on field emission stability of the CNT film are studied. The formation of the ac layer could be controlled by adjustment of growth temperature and hydrocarbon flow rate. The field emission character and current stability of the CNT film without ac layer are better than those of the CNT film with ac layer. The results attribute to the ac layer a thermal disequilibrium state under high current level. Moreover, adhesion capacity of the CNT film without ac layer is also better than that with the ac layer. It is concluded that the ac layer between the CNT film and substrate is a key factor in the stability of field emission characteristics and should be eliminated before applications.     

Multiscale model of micro curing residual stress evolution in carbon fiber-reinforced thermoset polymer composites

Frontiers of Mechanical Engineering - In this study, the micro curing residual stresses of carbon fiber-reinforced thermoset polymer (CFRP) composites are evaluated using a multiscale modeling...     

Dry friction and wear characteristics of nickel/carbon nanotube electroless composite deposits

Ni/carbon nanotube (Ni/CNTs) composite coatings were deposited on carbon steel plate by electroless deposition. The friction and wear properties were examined under dry sliding conditions using the ball-on-disk configuration. For reference, carbon steel plate was coated with Ni, Ni/SiC and Ni/graphite. The results show that the Ni/CNT coating has a microhardness value of 865 Hv, greater than for SiC reinforced composite deposits. The Ni/CNTs composite coating possesses not only a higher wear resistance but also a lower friction coefficient, resulting from their improved mechanical characteristics and the unique topological structure of the hollow nanotubes.     

基于电活性聚合物薄膜柔性器件的触觉传感特性

针对电活性聚合物(EAP)薄膜制造柔性智能器件的发展要求,分析了电活性聚合物薄膜的正/逆力-电特性及发电机理,采用静电诱导自组装技术在电活性聚合物表面制备了碳纳米管薄膜电极,然后构建了柔性传感器件。实验研究了EAP柔性器件的手指关节弯曲姿态及脚踏运动触觉的传感特性。扫描电子显微(SEM)形貌观察表明:碳纳米管薄膜呈网状结构且质地致密均匀。基于EAP柔性器件的手指弯曲姿态实验结果表明:在手指弯曲度为15~90°时,输出电压峰值为1.2~3.7V,展示了输出电压峰值与手指弯曲度之间的高线性度,线性相关系数为0.9951。此外,采用EAP薄膜器件对踏步触觉进行了实验测试,其输出电压峰值在1V左右,而且具有响应快、可重复性好等优势。本文的研究为电活性聚合物薄膜型电子皮肤及触觉传感器的发展提供了理论基础和实验依据。     

Soundproofing effect of nano particle reinforced polymer composites

In this paper, the effects of soundproofing by polymer and carbon-nanotube (CNT) composites were investigated. The specimens for sound insulation measurement were fabricated with Acrylonitrile Butadiene Styrene (ABS)/CNT composites. Tests showed that sound transmission loss of ABS/CNT 15 vol.% composite was higher by 21.7% (4.1 dB) than that of pure ABS specimen at a frequency of 3400 Hz. It was found that the principal factor influencing the improvement of sound insulations of ABS/CNT composites was increased stiffness by CNT additives. To demonstrate the practical applicability of polymer/CNT composites, tests were conducted for the reduction of operational noise from mechanical relay.     

Effect of rare earth solution on mechanical and tribological properties of carbon fiber reinforced thermoplastic polyimide composite

Rare earth solution (RES) surface modification and air-oxidation methods were used to improve the interfacial adhesion of the carbon fiber reinforced polyimide (CF/PI) composite. The mechanical and tribological properties of the PI composites reinforced by the carbon fibers treated with different surface modification methods were comparatively investigated. Results showed that both the strength parameters (tensile and flexural) of the CF/PI composites improved remarkably due to RES treatment along with enhancement in friction and wear performance.