Mechanism behind the Size Effect Phenomenon

Size effect (SE) on quasi-brittle fracture of concrete and concretelike heterogeneous materials has been commonly demonstrated by the influence of specimen size D on the transition from strength-dominant fracture to toughness-dominant fracture for geometrically similar specimens with a common initial-crack/specimen-size ratio, i.e., a0/D = constant. Under such a condition, size D appears to be the single controlling parameter for SE. In this study, we clarify that the primary source of quasi-brittle fracture, the presence of a large fracture process zone (FPZ) in front of a crack-tip, does not follow the condition of geometry similarity even for geometrically similar specimens. This suggests that the role of FPZ is not clearly explained for SE. Therefore, this study emphasizes the interaction between FPZ and the nearest specimen/structure boundary, and the consequent SE phenomenon. The deficiencies associated with the common SE models developed by Bazant and his coworkers are discussed through comparisons with the analysis on the boundary and FPZ interaction, or the boundary effect. It is shown that quasi-brittle fracture and the transition from strength-dominant fracture to toughness-dominant fracture can occur even if specimen/structure size D is constant, i.e., size D is not the dominant factor for SE.     

Development of ceramic fiber reinforced glass ceramic sealants for microtubular solid oxide fuel cells

Ceramic fibers in various forms with different fiber sizes are tested to improve the sealing performance of glass ceramic seals for microtubular solid oxide fuel cell applications. In this regard, several sealing pastes are prepared by mixing each ceramic fibers type with glass ceramics at 1.25 wt %. Five layered microtubular anode supported cells are also fabricated by extrusion and dip coating methods to evaluate the sealing performance of the composite sealants. The pastes are applied between the cells and gas manifolds made of Crofer22 APU. The electrochemical and sealing performances at an operating temperature of 800 °C under hydrogen are investigated after the glass forming process. Microstructures of the sealants are also examined by a scanning electron microscope. Experimental investigations reveal that the cells sealed by the pastes with ceramic bulk fiber and ceramic fiber rope gasket show acceptable open circuit potentials close to the theoretical one. These cells can be also pressurized up to around 150 kPa back pressure in the sealing performance tests. On the other hand, the pastes without any filler, with ceramic rope and with ceramic blanket exhibit poor sealing performance due to gas leakage originated from flowing of the main glass ceramic matrix from the joints. Therefore, ceramic bulk fiber and ceramic fiber rope gasket are found to behave as a stopper and can be used to prevent glass ceramics from flowing for microtubular solid oxide fuel cells or similar applications.     

新型材料的现状与未来

对新型材料和传统材料体系作了此较。分析几种新型金属材料(防振、减振、超导、非晶态、超塑性、记忆、贮氢用材料等)、高分子材料、精细陶瓷以及复合材料的应用现状。展望了新材料的应用前景。     

基于TL081的电荷信号适调电路的研究

讨论了压电加速度传感器信号适调电路的原理，并对电路的各种干扰因素进行了深入的分析，为了使电荷放大器能更方便地在实际当中应用，提出用高阻运放TL081芯片取代大量分立元件，并进一步设计和制作了这种传感器的信号适调电路。实验表明，这个电路具有可靠性、可行性、集成度高、设计成本低等优点。     

体视学及其在古陶瓷中的应用

本文以古陶瓷复相显微结构图像为研究对象,利用体视学方法分析古陶瓷中釉的各相参数,并对其进行定量表征,为古陶瓷的研究与应用提供数据依据.     

电子商务环境下建筑陶瓷行业CRM解决方案

本文讨论了电子商务环境下建筑陶瓷行业CRM的功能目标,在此基础上提出了一种包括客户信息管理与分析、营销管理与分析、数据整合分析与决策支持的建筑陶瓷行业CRM解决方案。     

超声波电动机技术创新点的设定

文章简明阐述了当前超声波电动机研究工作中在理论研究、设计编程、材料研究、试验测试及产业化开发中应如何确定和选择超声波电动机研究的技术创新点。     

电子商务环境下建筑陶瓷行业CRM解决方案

本文讨论了电子商务环境下建筑陶瓷行业CRM的功能目标，在此基础上提出了一种包括客户信息管理与分析、营销管理与分析、数据整合分析与决策支持的建筑陶瓷行业CRM解决方案。     

A piezoelectric transducer‐tuned microstrip‐ring resonator oscillator operating at the second resonant mode of the ring resonator

A microstrip open‐loop resonator oscillator operating at even modes is proposed. The even mode of the ring circuit can be predicted by using a simple transmission‐line model. The new oscillator has a characteristic similar to that of a push‐push oscillator. In addition, in comparison with the push‐push oscillator, the new oscillator with one active device can minimize the size and lower the cost. A voltage‐controlled piezoelectric transducer (PET) is used to vary the resonant frequencies of the ring resonator, which in turn tunes the oscillator with a good tuning range of 4.9% at around 12.1 GHz. This tuned oscillator should have many applications in wireless systems. © 2005 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2005.