纳米SiO2对环氧树脂浇铸体性能的影响

以纳米SiO2作为增强材料，制备纳米复合材料，研究了不同的纳米SiO2含量对纳米复合材料冲击强度，拉伸模量，玻璃化温度的影响，采用正电子湮没技术研究纳米粒子对自由体积参数的影响。结果表明，当纳米粒子SiO2含量为3％时，纳米复合材料的拉伸模量为3．57GPa，冲击强度为15.94kJ/m^2，玻璃化温度为126．65℃，分别比纯基体提高了12．6％，56．3％，40．4％。     

纳米铜粒子的表面聚合物修饰

为解决纳米铜粒子团聚问题，扩大其应用范围，采用微胶囊技术制备尿素－甲醛纳米铜微胶囊，形成核壳结构来提高铜纳米粒子的分散性，是比较有效的方法.样品的红外、x-射线衍射、SEM、TEM测试、分散性研究结果表明：微胶囊试样的壁材为脲醛树脂，囊芯为纳米铜，试样尺寸在500 nm左右；微胶囊修饰的纳米铜在水中的分散性较在其他溶剂中要好；纳米铜微胶囊在各种溶剂中的分散性要好于纯纳米铜；表面聚合物修饰的纳米铜能分散在极性溶剂中.     

微波烧结氧化铝陶瓷的纳米增韧研究

高纯度氧化铝陶瓷具有极高的机械强度,在航空航天等国防尖端技术领域具有极好的应用前景．针对目前采用普通方法烧结的高纯度氧化铝陶瓷韧性较差的问题,利用圆柱形微波多模烧结腔进行了高纯度氧化铝陶瓷的纳米增韧研究．以氧化铝（质量分数99．9％）、氧化镁（质量分数0．05％）和氧化钇（质量分数0．05％）为基准原料配比,在其中添加不同比例的纳米氧化铝粉末,研究不同比例纳米氧化铝粉末对陶瓷性能的影响．结果表明,当纳米氧化铝粉末添加量达到30％时,高纯度氧化铝陶瓷试样的密度、维氏硬度和断裂韧性分别达到3．92g／cm^3、23．2GPa和4．21Pa·m^1/2;与未添加纳米氧化铝粉末烧结得到的陶瓷试样相比,密度降低0．5％,但其维氏硬度增加了2．2％,断裂韧性甚至增强了33．7％．     

合成水化硅酸钙对水泥基材料微观力学性能的影响

采用水热法合成水化硅酸钙(C-S-H),并将其掺入水泥中,研究其对水泥基材料微纳米力学性能的影响.利用XRD对合成产物进行表征,采用纳米压痕技术对掺有C-S-H的水泥水化产物的弹性模量、硬度等纳米力学性能进行测试,并对纳米压痕试验数据进行分析.结果表明:人工制备的C-S-H能有效地促进水泥水化,填充水泥浆体中的孔隙;随...     

球形金属簇等离子体线宽的研究方法进展

由于量子尺寸效应，金属纳米粒子表现出一些特殊的光学性质，而金属纳米粒子在生物、化学和新型材料等方面的广阔应用前景，使我们对其光学性质的理解和研究变得至关重要．对于中间大小（半径R：0．5-2．5nm）的金属纳米粒子，Landau衰减是其主要的能量耗散方式．作者系统总结了球形金属纳米粒子表面等离子体共振线宽的研究方法，介绍了粒子大小、温度和电介质环境对线宽的影响，并指出了近年来金属纳米粒子光学性质方面的研究热点．     

水泥灰土特性的试验研究

目的为提高灰土的早期强度、增强其水稳定性，扩大工程应用范围．方法将水泥作为一种活性外加剂以不同比例掺入到灰土中对其进行改性．对相同养护条件下的纯二八灰土试样及掺入不同体积分数的水泥灰土试样进行了无侧限抗压强度试验和三轴不固结不排水强度试验研究，并将试验结果进行了整理与比较．结果得到了水泥灰土的强度与龄期、水泥掺入量、含水量、围压、养护条件等因素的关系，浸水后的强度和稳定性与龄期的关系以及相对干同等条件下的纯二八灰土试样的强度增长率等．结论从试验结果分析可知。利用水泥改性后，灰土的早期强度增长能力和水稳定性获得了明显提高．因此，可认为水泥是一种良好的灰土改性外加剂，值得在工程应用中加以推广．     

水泥基粒状复合材料的数值仿真

为研究水泥基粒状复合材料的物理力学性能,采用一种自编的特殊算法生成任意形状的单个复合材料骨料颗粒,利用HADES堆积程序来形成材料结构(HADES是模拟任意形状的颗粒碰撞和堆积的程序).在此基础上加入骨料颗粒与水泥基之间的界面过渡区(ITZ),并采用专门的网格划分工具对粗骨料、水泥浆以及界面过渡区进行网格划分,最后进行有限元计算来得到水泥基复合材料的力学性质.以混凝土作为一种典型的水泥基复合材料进行模拟分析,得到不同骨料颗粒成份下混凝土弹性模量值为14.3GPa到22.9GPa,结果表明上述数值模拟方法可有效的对三相材料(水泥基、界面过渡区、骨料颗粒)构成的混凝土弹性模量进行预测.     

纳米金刚石微粉热浸渗技术对金属材料耐磨性能的影响

分别对两种材料的试样进行渗碳、渗纳米金刚石处理，发现渗纳米金刚石处理的试样比渗碳处理的试样硬度可提高7％和11％．利用T—11摩擦磨损试验机分别对其进行耐磨性能的测试后发现，通过纳米金刚石微粉热浸渗处理的试样比渗碳处理的试样耐磨性能提高得多．对其金相分析，发现钢材经纳米金刚石微粉热浸渗后出现了现在还不知名的新相和新的铁基合金．纳米金刚石微粉热浸渗技术提高了金属材料的硬度和耐磨性能，为易磨损零件的使用寿命的延长提供了一条可靠的途径．     

纳米羟基磷灰石复合陶瓷生物摩擦学行为研究

采用沉淀法合成了纳米羟基磷灰石（HA）粉体，无压烧结工艺制备了HA／PSZ陶瓷复合材料．利用材料试验分析系统（MTS）和纳米硬度分析测试系统（Triboindenter）测定了复合材料的宏观和微观力学性能，用销盘式摩擦磨损试验机考察了血浆润滑条件下复合材料的生物摩擦学性能，探讨了力学性能与摩擦学性能之间的关系．结果表明，无压烧结HA／PSZ复合陶瓷材料断裂韧性比纯HA陶瓷提高近2．7倍，弯曲强度提高近1倍．纳米硬度最高值为10．6GPa，纳米弹性模量为156．OGPa．血浆润滑条件下，HA／PSZ陶瓷和UHMWPE摩擦副的摩擦系数与HA的含量有关，UHMWPE的磨损率与HA／psz复合陶瓷摩擦副的硬度和断裂韧性存在反比关系．     

Ti-B-C-N粉末烧结的微观组织及其性能

以Ti-B-C-N四元相陶瓷粉末为实验材料,采用真空热压烧结和放电等离子烧结(SPS)工艺对其进行烧结,真空热压烧结和放电等离子烧结温度分别为1900℃和1450℃,烧结压力分别为20 MPa和40 MPa,保温时间分别为1h和3min。使用X射线衍射仪分析试样物相组成,扫描电子显微镜观察试样表面微观形貌和断口形貌,并测试了烧结试样的硬度和抗弯强度。结果表明:真空热压烧结和放电等离子烧结块体的主要生成相为TiB2相和TiCN相,相对密度分别为97.40%和93.06%,热压烧结试样致密度高,颗粒尺寸大,放电等离子烧结试样孔隙较多,晶粒尺寸小;抗弯强度分别为259.98 MPa和335.17 MPa;弹性模量分别为89.11GPa和162.92GPa;洛氏硬度分别为78.8和84.9;放电等离子烧结试样表现出较好的力学性能。     

Design and micro mechanical properties of nano-SiO_2 strengthened composite coatings towards remanufacturing

1INTRODUCTION Theapplicationofsurfaceengineeringtech nologieshaspromotedthedevelopmentofremanu facturing,whichplaysanimportantroleinthe sustainabledevelopmentstrategy.Withanewly developednanomaterialsavailable,nanosurfacetechnologies,especiallynanocomposi…     

Dynamic elastic modulus of cement paste at early age based on nondestructive test and multiscale prediction model

This paper introduced a nondestructive testing method to evaluate the dynamic elastic modulus of cement paste. Moreover, the effect of water-cement ratio and conventional admixtures on the dynamic elastic modulus of cement paste was investigated, in which three kinds of admixtures were taken into account including viscosity modifying admixture （VMA）, silica.fume （SF）, and shrinkage-reducing admixture （SRA）. The experimental results indicate that the dynamic elastic modulus of cement paste increases with decreasing water-cement ratio. The addition of SF increases the dynamic elastic modulus, however, the overdosage of VMA causes its reduction. SRA reduces the dynamic elastic modulus at early age without affecting it in later period. Finally, a multiscale micromechanics approach coupled with a hydration model CEMHYD3D and percolation theory is utilized to predict the elastic modulus of cement paste, and the predictive results by the model are in accordance with the experimental data.     

含砖粒再生混凝土基本性能研究

以再生砖粒取代率(0%~30%)和水胶比(0.40~0.50)为主要参数,通过工作性能与弹性模量试验,研究再生砖粒取代率和水胶比对再生混凝土工作性能及弹性模量的影响规律。结果表明:当水胶比相同时,再生混凝土的工作性能和弹性模量均随再生砖粒取代率的增加而降低,且在再生砖粒取代率为30%,水胶比为0.5时,再生混凝土弹性模量的降幅达17.62%;提出适合于含再生砖粒再生混凝土弹性模量估算的预测模型,该预测模型与试验值吻合较好。     

Design and micro mechanical properties of nano-SiO2 strengthened composite coatings towards remanufacturing

Nano-SiO₂ particles strengthened Ni-based composite coating was designed and prepared on steel substrate. The structures and nanoparticle content of the nano-SiO₂/Ni composite coating were determined by SEM, EDS and TEM; and the micro mechanical properties were tested by nano-indentation technique. The results show that 56% of particles in the solution are dispersed in size of less than 100 nm, the content of nanoparticles co-deposited in the coating doubles and structure of the coating is more compact and uniform than that of Ni coating. Nano-SiO₂/Ni coating exhibits excellent micro mechanical properties, and the nanohardness and elastic modulus are 7.81 GPa and 198 GPa, respectively, which are attributed to finer crystal strengthening, dispersion strengthening and high-density dislocation strengthening of nano-SiO₂ particles to the composite coatings. Foundation item: Project (50235030) supported by the National Natural Science Foundation of China; Project (G1999065009) supported by the National Basic Research Program of China     

Ce-Mg合金体系弹性性质与电子结构的第一性原理研究

为了探讨Ce-Mg体系金属间化合物的力学性质与其晶体结构相联系的微观机制,采用基于密度泛函理论的第一性原理计算方法,系统研究了3种立方Ce-Mg体系金属间化合物CeMg、CeMg2和CeMg3的电子结构和弹性性质。计算结果表明,CeMg3有最高的体模量和剪切模量,分别为41.1GPa和30.7GPa,CeMg2的体模量和剪切模量则在3种金属间化合物中最低,分别为35.1GPa和14.0GPa。CeMg、CeMg2和CeMg3均满足立方晶系力学稳定性要求,CeMg3与CeMg为脆性材料,而CeMg2为延性材料。各向异性性质分析表明,CeMg具有很高的弹性各向异性,而CeMg2的体模量、剪切模量以及杨氏模量尽管最低,但其显示出良好的各向同性性能。计算CO-HP及电荷密度分布揭示了Ce-Mg合金体系弹性性质的变化与体系中化学成键差异密切相关,晶体中Mg-Mg键较强的材料比晶体中Ce-Mg键较强的材料有着更好的延展性。     

初凝后水泥浆体的弹性模量研究

在复合材料力学理论与流变学开尔文模型基础上建立了一个用以描述水泥浆体水化早期弹性模量成长的模型.该模型从微观角度出发,在假设水泥颗粒与水化产物为圆球状且水泥浆体形成的孔结构为圆孔形的基础上,应用线弹性理论与有孔介质力学理论研究随着时间的增加、水化度不断增大的情况下,硬化水泥浆体的有效弹性模量.将该有效弹性模量与流变学开尔文模型理论结合起来得出初凝后水泥浆体弹性模量时变方程.研究结果表明:该模型可用于描述水泥浆体初凝后的弹性模量变化,且其变化规律与精度和实验数据符合良好.     

椭圆水泥环厚度和弹性模量对套管受力的影响分析

根据岩石力学和弹塑性力学理论,建立套管-水泥环-地层力学模型,采用有限元方法研究分析不同地应力条件下椭圆水泥环厚度和弹性模量对套管应力的影响,研究结果表明：在均匀地应力条件下,一定厚度的圆形水泥环对减小套管受力有益,在非均匀地应力条件下,采用椭圆水泥环能有效的减小套管应力．     

鲍鱼壳体纳米力学特性及有限元分析

通过纳米压痕技术对鲍鱼壳横切面及纵切面的弹性模量及硬度进行了测试,并建立有限元模型,通过施加载荷进行了模拟分析。结果表明:鲍鱼壳体横切及纵切方向内层到外层弹性模量及硬度值呈上升趋势。     

Nanoindentation analysis of TiN,TiAlN,and TiAlSiN coatings prepared by cathode ion plating

The TiN,TiAlN and TiAlSiN coatings were deposited on H13 hot-worked mold steel by cathodic arc ion plating(CAIP).The morphologies,phase compositions,and nanoindentation parameters,such as creep hardness,elastic modulus and plastic deformation energy of the coatings were analyzed with field emission scanning electron microscopy(FESEM),X-ray diffraction(XRD) and nanoindentation testing,respectively,and the test results were compared with equation describing the indentation model.The results show that the TiN,TiAlN and TiAlSiN coating surfaces were dense and composed of TiN,TiN + TiAlN,TiN + Si3N4 + TiAlN phases,respectively.There was no spalling or cracking on the indentation surface.The creep hardness of the TiN,TiAlN and TiAlSiN coatings was 7.33,13.5,and 15.2 GPa,respectively;the corresponding hardness measured by nanoindentation was 7.09,15.6,and 21.7 GPa,respectively;and the corresponding elastic modulus was 201.93,172.79,and 162.77 GPa,respectively.The contact depth and elastic modulus calculated by the indentation model were close to those of the test results,but the remaining indentation parameters showed discrepancies.The sequence of plastic deformation energy was TiN TiAlNTiAlSiN.     

Quantitative characterization and elastic properties of interfacial transition zone around coarse aggregate in concrete

Backscattered electron images (BSE) obtained by scanning electron microscope was used to quantitatively characterize the microstructure of interfacial transition zone (ITZ) in concrete. Influences of aggregate size (5, 10, 20, and 30 mm), water to cement ratio (0.23, 0.35 and 0.53) and curing time (from 3d to 90d) on the microstructure of interfacial transition zone between coarse aggregate and bulk cement matrix were investigated. The volume percentage of detectable porosity and unhydrated cement in ITZ was quantitatively analyzed and compared with that in the matrix of various concretes. Nanoindentation technology was applied to obtain the elastic properties of ITZ and matrix, and the elastic modulus of concrete was then calculated based on the Lu & Torquato model and self-consistence scheme by using the ITZ thickness and elastic modulus obtained from this investigation. The experimental results demonstrated that the microstructure and thickness of ITZ in concrete vary with a variety of factors, like aggregate size, water to cement ratio and curing time. The relative low elastic properties of ITZ should be paid attention to, especially for early age concrete.