Structural characteristics of oxide nanosphere supported metal nanoparticles

Structural characterization by transmission electron microscopy of metal nanoparticle coatings on oxide nanospheres has been employed to point out the potential of such materials for use as porous support model catalysts. On silica and titania nanospheres of various origins surface-mediated metal deposition at mild temperature conditions has been utilized to fabricate Pt, Pd, Ag, and Au nanoparticle coatings on the oxide supports. Promising coating characteristics have been achieved for Ag and Au nanoparticles by direct reduction on terminating hydroxyl-rich St?ber silica. A high-resolution electron microscopy analysis directed to surface stress, lattice contraction and planar lattice defects of the latter particles revealed no strong metal-support interaction.     

Contraction stress build‐up of anisotropic conductive films (ACFs) for flip‐chip interconnection: Effect of thermal and mechanical properties of ACFs

The important mechanical mechanism for the electrical conduction of anisotropic conductive films (ACFs) is the joint clamping force after the curing and cooling processes of ACFs. In this study, the mechanism of shrinkage and contraction stress and the relationship between these mechanisms and the thermomechanical properties of ACFs were investigated in detail. Both thickness shrinkages and modulus changes of four kinds of ACFs with different thermomechanical properties were experimentally investigated with thermomechanical and dynamic mechanical analysis. Based on the incremental approach to linear elasticity, contraction stresses of ACFs developed along the thickness direction were estimated. Contraction stresses in ACFs were found to be significantly developed by the cooling process from the glass‐transition temperature to room temperature. Moreover, electrical characteristics of ACF contact during the cooling process indicate that the electrical conduction of ACF joint is robustly maintained by substantial contraction stress below T_g. The increasing rate of contraction stresses below T_g was strongly dependent on both thermal expansion coefficient (CTE) and elastic modulus (E) of ACFs. A linear relationship between the experimental increasing rate and E × CTE reveals that the build‐up behavior of contraction stress is closely correlated with the ACF material properties: thermal expansion coefficient, glassy modulus, and T_g. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2634–2641, 2004     

HDPE耐环境应力开裂性能的研究及改进

对HDPE的耐环境应力开裂性能进行了研究。试验表明:采用共混及化学改性的方法,HDPE的耐环境应力开裂性能有了很大提高,为解决HDPE树脂在制作管材时出现的短时间内应力开裂问题提供了依据。     

表面处理对氮化硅陶瓷力学性能的影响

采用X射线衍射应力分析的sin2ψ法计算了Si3N4陶瓷试样的残余应力，并分别测量了表面处理前后Si3N4试样的力学性能。结果表明，经平面磨削后的Si3N4试样表面残余应力为拉应力，而抛光处理可适当降低残余应力。两种方法都使试样抗弯强度降低。     

单向Cf/SiC复合材料的弯曲疲劳性能

对单向Cf/SiC复合材料进行了三点弯曲疲劳性能测试,得到了复合材料的应力－寿命曲线（S－N曲线）,并对其进行线性拟合,得到疲劳最大应力与复合材料疲劳寿命的关系;考察了疲劳过程中刚度下降和疲劳裂纹产生情况。结果表明在疲劳过程中复合材料的弯曲模量有3个变化阶段：首先在疲劳加载初期,弯曲模量的下降速度及幅度都较大;其次在弯曲模量下降到原始弯曲模量的85％（133GPa)后,其变化方式没有明显的规律可循,有时甚至可能上升;最后复合材料发生疲劳断裂时,模量将发生突变。显微结构分析表明：基体横向裂纹群的产生是疲劳断裂的独有特征。它的产生是由于基体SiC的断裂应变小于碳纤维的断裂应变,基体首先开裂并导致应力重新分布的结果。     

基于敲击声振法的风机叶片脱层检测系统设计

脱层是风机叶片的主要损伤形式,根据风电叶片的材料特性及外形特点,分析和研究了敲击声振检测原理和现场检测的可行性。叶片出现脱层时,缺陷处刚度下降,敲击应力持续时间增大。依据此检测原理,计算出合理的等效锤头质量,利用压电薄膜作为动态冲击力传感器进行了力锤的结构设计;利用FPGA设计了便携式检测仪,对敲击信号进行信息提取和处理,计算敲击力脉冲信号的宽度,具有结果图形显示和串行通信的功能。经过实验,验证了脉冲宽度与损伤深度的关系。     

应力型微悬臂梁生化传感器响应机理研究进展

针对静态微悬臂梁表面特异性结合产生表面应力信号的响应机制问题,介绍了微悬臂梁生化传感器的工作原理,阐述了应力响应机制的简化模型,从纵向界面上和横向分子间2个方面对特异性吸附引起的悬臂梁表面应力的变化进行了剖析,讨论了界面能变化、位阻作用、静电力、氢键作用等与表面应力大小及方向之间的关系,总结了应力型微悬臂梁生化传感器的响应机理的研究。     

冷却器盘管失效分析及防范措施

本文介绍了冷却器盘管破裂泄漏的情况，分析了失效破坏的原因，并提出防止冷却器盘管破裂泄漏的措施。     

残余应力对TiC_p－AIN复合材料的影响

本工作采用热压工艺，以Ｙ＿２Ｏ＿３为烧结添加剂，在１８５０℃下制备ＴｉＣ＿ｐ－ＡＩＮ复合材料。结果表明：复合材料的密度、抗折强度、断裂韧性受第二相ＴｉＣ＿ｐ的影响，通过合理工艺因素选择，可以使复合材料的抗折强度和断裂韧性比基体ＡＩＮ材料分别提高４０％，８０％，达到４３８ＭＰａ，５．５９ＭＰａ·ｍ￣（１／２）。由ＸＲＤ内应力分析和ＴＥＭ显微结构测试结果可知，复合材料性能改善原因在于高弹性用量的ＴｉＣ引入以及ＡＩＮ和ＴｉＣ热膨胀系数不匹配导致的残余内应力。     

MgO／Ni系梯度功能材料的设计与制备

对ＭｇＯ／Ｎｉ系梯度功能材料（ＦＧＭ），分别用实验和微观力学模型测定和计算了用于热应力缓和设计的各物性参数。讨论了两种结果之间存在差异的原因。用有限元方法模拟了制备过程中ＦＧＭ的热应力，得到ＭｇＯ／Ｎｉ系ＦＧＭ的综合设计准则。按设计结果进一步调整粉末工艺性质，成功地烧制出ＭｇＯ／Ｎｉ系ＦＧＭ。