碳纤维/碳纳米管增强基体多尺度混杂复合材料的研究现状和趋势

碳纳米管(Carbon Nanotube,CNT)具有非常优异的刚度和强度。CNT增强基体的传统连续纤维多尺度混杂复合材料既具有优良的纤维主导力学性能又有好的基体主导力学性能,具有广泛的应用前景。综述了国内外在碳纳米管增强基体的多尺度混杂复合材料力学性能,制备和数值模拟等方面的最新研究进展。提出了进一步研究需要解决的两个关键问题:(1)量化CNT对传统复合材料的增强效果;(2)阐明CNT对多尺度混杂复合材料的增强机制,并提出了相应的研究手段。

颗粒增强脆性基体复合材料的细观强度模型

用细观力学的方法研究颗粒增强脆性基体复合材料的强度和损伤失效,认为复合材料由随机二相胞元和基体构成,分析基体、颗粒中的局部应力场,根据损伤理论分别得到基体和颗粒的损伤等效应力。在界面脱开成为裂纹源并向基体内扩展的情况下,计算出弧形界面裂纹的能量释放率。最后分别提出基体、颗粒和界面的失效强度准则。结果表明,复合材料的强度与二相胞元的方位角、颗粒体积含量、界面脱粘角、颗粒直径有关。

纤维增强韧性基体界面力学行为

分析了纤维增强韧性基体的界面力学行为及其失效机理 .按剪滞理论和应变硬化规律研究微复合材料的弹塑性变形和应力状态 .讨论了幂硬化和线性硬化基体的弹塑性变形和界面应力分布 ,并给出纤维应力和位移的表达式 .按最大剪应力强度理论建立了纤维 基体界面失效准则 。

气凝胶复合材料的制备及保温隔热应用进展

气凝胶复合材料由于具有密度低、比表面积大、孔隙率高和导热系数低等结构功能特性,成为最主要的新型保温隔热材料之一。本文简述了气凝胶复合材料的发展历程、制备工艺及方法,从气凝胶复合材料的微观形貌结构、热量传递组成、隔热传热表征等方面对其保温隔热性能及机理进行分析,重点介绍了近年来气凝胶复合材料的保温隔热性能应用在军事航空航天、建筑节能环保、能源存储转化、极端环境材料、电动汽车电池、冷藏(冻)运输以及供热锅炉管道等诸多领域中取得的新进展。同时,对其在各个领域应用中遇到的问题进行了详细讨论并给出建议。此外,文末对气凝胶复合材料在未来的研发、生产及应用中的研究方向进行了展望。

基体含量对土体屈服强度影响的试验分析

土体的强度特性与其颗粒的矿物成分、粒度几何尺寸大小及相对含量密切相关,具有尺度效应。为探究基体的含量和增强颗粒对土体剪切屈服强度的影响,以高岭土为基体、以不同粒径的石英砂为增强颗粒,均匀混合,制备不同比例含量的人工土,进行系列直接剪切试验与三轴不固结不排水试验。针对基体含量较小的试样,结合试验分析,提出了能够解释其力学机理的土基体膜-增强颗粒模型,为进一步的理论研究奠定基础。

铝合金活塞材料的研发与应用进展

活塞作为汽车发动机中传递能量的一个非常重要的构件,对其材料具有特殊的要求:密度小、质量轻、热传导性好、热膨胀系数小;并要求具有足够的耐高温、耐磨和耐蚀性能及尺寸稳定性好的特性.在传统的铸造铝硅活塞合金的成分优化和处理工艺的研究还没有大突破的情况下,科研工作者已经在寻求新的途径提高铸造铝合金的极限强度.通过采用基体增强和新型活塞成型工艺,显著提高了活塞的性能.随着汽车发动机向高速化、大功率方向的发展,新型铸造铝合金活塞复合材料及短周期的压力成型技术的开发应用都将成为一个发展趋势.

电感耦合等离子发射光谱法测定轻烧镁硼磷硫

建立了使用电感耦合等离子发射光谱法测定轻烧镁中硼、磷、硫的方法。试验发现,硼的测定,有良好精密度、线性和检出限,回收率极好;磷的测定,存在"基体增强效应",通过计算校正,提高了测定结果准确性。检出限硼0.0088mg·L^(-1),磷0.052mg·L^(-1),硫0.068mg·L^(-1);回收率硼99.5%~100.2%,磷100.4%~103.5%,硫91.4%~93.9%;精密度硼14.9%,磷11.0%~15.8%,硫9.7%~13.3%。该法是一种快速简便的测定轻烧镁中硼、磷、硫的适用方法。

二氧化硅气凝胶常压干燥工艺的研究进展

二氧化硅气凝胶因具有低密度、高比表面积、稳定的物理化学性质等特性在吸附分离、隔热保温等领域表现出巨大的应用潜力。但长耗时、高成本的制备工艺限制了它的发展,尤其是湿凝胶向气凝胶转变的干燥工艺。本文介绍了二氧化硅气凝胶在常压干燥的过程中面临的主要难点及解决方法,虽然常压干燥方法工艺简单、过程安全、对设备要求低且可连续制备,成为近年来的研究热点,但也存在制备周期长、体积收缩大、需要消耗大量有机溶剂和改性剂等不足。文中从凝胶基体增强与优化、降低毛细管力与减少不可逆收缩两种角度,介绍了二氧化硅气凝胶常压干燥的改进方法及其发展现状,分析归纳了不同改进方法的优缺点,总结了二氧化硅气凝胶常压干燥目前面临的技术挑战。并且,立足于目前二氧化硅气凝胶基体增强和表面改性技术发展的趋势,对今后二氧化硅气凝胶常压干燥过程中结构可控、成本降低以及产品多功能化的发展路线进行了展望。

指尖密封用炭-炭复合材料摩擦磨损性能

为确定指尖密封用炭-炭(炭纤维增强炭基体)复合材料的摩擦学性能,针对指尖密封的轻载使用条件,应用UMT-2摩擦磨损测试仪进行炭-炭复合材料摩擦磨损性能试验,测量摩擦系数与磨损率,并采用扫描电子显微镜(SEM)分析材料的摩擦磨损机理.结果表明,无纬布层垂直于摩擦平面时,材料的摩擦系数和磨损率较低.载荷增加,较高密度材料的磨损率增加缓慢,摩擦系数减小.与载荷相比,材料磨损率受频率的影响较小,且随频率升高摩擦磨损性能越好.磨损表面的SEM分析表明:低频、低载条件下材料发生磨粒磨损;频率的提高加快磨屑膜的成形,自润滑能力增强;载荷的增加虽使磨屑快速被挤压形成磨屑膜,但磨屑膜被不断挤出剥落,纤维裸露断裂产生严重磨损,这一点在材料密度较低时表现更为显著.选用较高密度的材料以及布置无纬布层垂直于摩擦平面可以有效缓解密封材料的磨损.

铝合金活塞材料的研发与应用进展

活塞作为汽车发动机中传递能量的一个非常重要的构件，对其材料具有特殊的要求：密度小、质量轻、热传导性好、热膨胀系数小；并具有足够的高温强度、耐磨和耐蚀性能、尺寸稳定性好。在传统的铸造铝硅活塞合金的成分优化和处理工艺的的研究还没有大的突破的情况下，科研工作者已经在寻求新的途径提高铸造铝舍金的极限强度。通过采用基体增强和新型活塞成型工艺，显著提高了活塞的性能。随着汽车发动机向高速化、大功率方向的发展，新型铸造铝舍金活塞复合材料的开发应用将成为一个发展趋势。

新型活塞铝基复合材料设计与制备

活塞作为汽车发动机中传递能量的一个非常重要的构件,对其材料具有特殊的要求。本文尝试采用复合材料方法制备活塞用铝基复合材料,研究了铝基复合材料的金相组织及力学性能。

Mechanical properties of 3D carbon/carbon composites by nanoindentation technique

Nanoindentation tests were conducted to investigate the near-surface mechanical properties of the individual components(fiber and matrix) for three-dimensional reinforced carbon/carbon composites(3D C/C).Optical microscope and polarizing light microscope were used to characterize the microstructure of 3D C/C.The microscopy results show that large number of pores and cracks exist at both bundle/matrix interface and pitch carbon matrix.These defects have important effect on the mechanical behavior of 3D C/C.The in situ properties for components of 3D C/C were acquired by nanoindentation technique.Relative to the matrix sample,the fiber samples have more larger values for modulus,stiffness and hardness.However,there is no significant difference of modulus and stiffness among fiber samples with different directions.

Optimization of process parameters for in situ casting of Al/TiB_2 composites through response surface methodology

The mathematical models were developed to predict the ultimate tensile strength （UTS） and hardness of Al/TiB2 MMCs fabricated by in situ reaction process. The process parameters include temperature, reaction time and mass fraction of TiB2. The in-situ casting was carried out based on three-factor five-level central composite rotatable design using response surface methodology （RSM）. The validation of the model was carried out using ANOVA. The mathematical models developed for the mechanical properties were predicted at 95% confidence limit.

Dry sliding wear behavior of stir cast AA6061-T6/AlN_p composite

The dry sliding wear behavior of AA6061 matrix composite reinforced with aluminium nitride particles（AlN） produced by stir casting process was investigated. A regression model was developed to predict the wear rate of the prepared composite. A four-factor, five-level central composite rotatable design matrix was used to minimize the number of experimental runs. The factors considered in this study were sliding velocity, sliding distance, normal load and mass fraction of AlN reinforcement in the matrix. The developed regression model was validated by statistical software SYSTAT 12 and statistical tools such as analysis of variance（ANOVA） and student＇s t test. It was found that the developed regression model could be effectively used to predict the wear rate at 95% confidence level. The influence of these factors on wear rate of AA6061/AlNp composite was analyzed using the developed regression model and predicted trends were discussed with the aid of worn surface morphologies. The regression model indicated that the wear rate of cast AA6061/AlNp composite decreased with an increase in the mass fraction of AlN and increased with an increase of the sliding velocity, sliding distance and normal load acting on the composite specimen.

Magnesium composites with hybrid nano-reinforcements:3D simulation of dynamic tensile response at elevated temperatures

3D numerical simulations of dynamical tensile response of hybrid carbon nanotube(CNT)and SiC nanoparticle reinforced AZ91D magnesium(Mg)based composites considering interface cohesion over a temperature range from 25 to 300℃ were carried out using a 3D representative volume element(RVE)approach.The simulation predictions were compared with the experimental results.It is clearly shown that the overall dynamic tensile properties of the nanocomposites at different temperatures are improved when the total volume fraction and volume fraction ratio of hybrid CNTs to SiC nanoparticles increase.The overall maximum hybrid effect is achieved when the hybrid volume fraction ratio of CNTs to SiC nanoparticles is in the range from 7:3 to 8:2 under the condition of total volume fraction of 1.0%.The composites present positive strain rate hardening and temperature softening effects under dynamic loading at high temperatures.The simulation results are in good agreement with the experimental data.

Fabrication characteristics and tensile strength of novel Al2024/SiC/red mud composites processed via stir casting route

The stir casting technique was used to fabricate aluminum2024matrix hybrid composites reinforced with SiC(5%,mass fraction)and red mud(5%-20%,mass fraction)particles.The developed composites were characterized by using scanning electron microscopy(SEM)and electron dispersive spectrum(EDS)techniques.Further,Taguchi’s approach of experimental design was used to examine the tensile strength of the hybrid composites(with minimum number of experiments).It was found that the reinforcing particles were well dispersed and adequately bonded in the hybrid composites.The density and porosity of the hybrid composites were reduced with the increase in reinforcement content.The tensile strength of the composites increased with the increase in the red mud content and the ageing time.The developed model indicated that the red mud content had the highest influence on the tensile strength response followed by the ageing time.Overall,it was found that Al2024/SiC/red mud composites exhibited superior tensile strength(about34%higher)in comparison to the Al2024alloy under optimized conditions.

Efficient production of transgenic chickens using self-inactive HIV-based lentiviral vectors

We demonstrated the simple and effective production of transgenic chickens, in which the enhanced green fluorescence protein （EGFP） was expressed by using third-generation self-inactive HIV-based lentiviral vectors. In our experiments, lentiviruses were injected into 204 fertilized eggs, from which 30 （15%） chickens were hatched. The exogenous gene was detected in the genomes of 16 out of 30 （53%） chickens. The green fluorescence signal was observed directly in various body parts, and was particularly significant in the testes. The transgenes were also found in the offspring of these chickens. The results indicate that HIV-based lentiviral vectors can be used to generate transgenic birds economically and effectively [ Current Zoology 55 （5）： 383 - 387,2009].

Experimental study on bearing capacity of shell strip footings near geotextile-reinforced earth slopes

From a financial point of view,urbanization frequently enforces the clients to construct superstructures near the slopes,giving rise to increasing the risk of building instability.By conducting a series of small-scale plate load tests,this work aims to investigate the effects of installing geotextile reinforcement layers in sandy slope and reducing the apex angle of triangular shell strip footings.The results show considerable effect of using geotextile-reinforced layers and decreasing the apex angle on the ultimate bearing capacity of shell foundations.With increasing foundation distance from the slope,the adverse effect of the slope is reduced.However,as the distance decreases,the effect of reinforcement and apex angle is increased.For practical applications,empirical equations are also presented for determining the ultimate bearing capacity of the footings and scale effect as well.Finally,3D numerical simulations are executed and compared with the experimental results.

Study on Stability of Ion-exchange Resin Catalysts:Ⅱ. Desulfonation during Isobutylene Dimerization

The performance of ion-exchange resin catalysts during isobutene (IB) dimerization was investigated under different IB contents,temperatures and liquid-volume hourly space velocity (LHSV) using a plug flow reactor in the absence of any selectivity enhancing component.High IB content and temperature resulted in a high conversion and C12 selectivity bu low C8 selectivity.The influence of LHSV was related with the IB content:LHSV had great effect at high IB content,while the performance of ion-exchange resin changed little with LHSV if IB content was low.The effect of water on the stability of resins was also studied.Desulfonation was observed during the C4 dimerization reaction when water was added to the feed.Chlorinated resin was more stable than conventional polystyrene-based resins during the test.

Construction,Stable Expression of Survivin shRNA Vector

Objective： To construct sarvivin shRNA expression vector carting enhanced green fluorescent protein gene, transfect it into GBC-SDH cells via electroporation, and get GBC-SD cells which are stable expressing survivin shRNA. Methods： The siRNA sequence targeting survivin mRNA was synthesized and cloned into pEGFP-H1. The constructed plasmid and pEGFP-H1 were transfected into GBC-SI） cells respectively via liposome, and the transfecting effect was detected with Flow Cytometry. Then the transfected cells were selected with G418. Results： The recombinant plasmid was successfully constructed, named pEGFP-survivin. The gene transfection efficiencies in pEGFP-H1-transfected group and pEGFP-survivin- transfected group were the 80.29% ± 2.71% and 83.85% ±2.34%（P〉0.05）, which was successful to get the cells that are stable expressing shRNA, named GBC-SD/EGFP and GBC-SD/survivin. Conclusion： Survivin shRNA successfully and got GBC-SD cells which are stable expression vector was constructed expression shRNA.