INVESTIGATION OF BEHAVIOR OF MODE-I INTERFACE CRACK IN PIEZOELECTRIC MATERIALS BY USING SCHMIDT METHOD

The behavior of a Mode-Ⅰinterface crack in piezoelectric materials was investigated under the assumptions that the effect of the crack surface overlapping very near the crack tips was negligible. By use of the Fourier transform, the problem can be solved with the help of two pairs of dual integral equations. To solve the dual integral equations, the jumps of the displacements across the crack surfaces were expanded in a series of Jacobi polynomials. It is found that the stress and the electric displacement singularities of the present interface crack solution are the same as ones of the ordinary crack in homogenous materials. The solution of the present paper can be returned to the exact solution when the upper half plane material is the same as the lower half plane material.     

INVESTIGATION OF BEHAVIOR OF MODE-Ⅰ INTERFACE CRACK IN PIEZOELECTRIC MATERIALS BY USING SCHMIDT METHOD

The behavior of a Mode-Ⅰ interface crack in piezoelectric materials was investigated under the assumptions that the effect of the crack surface overlapping very near the crack tips was negligible. By use of the Fourier transform, the problem can be solved with the help of two pairs of dual integral equations. To solve the dual integral equations, the jumps of the displacements across the crack surfaces were expanded in a series of Jacobi polynomials. It is found that the stress and the electric displacement singularities of the present interface crack solution are the same as ones of the ordinary crack in homogenous materials. The solution of the present paper can be returned to the exact solution when the upper half plane material is the same as the lower half plane material.     

SYNTHESIS OF MESOPOROUS TiO_2 MATERIALS WITH HIGH SPECIFIC AREA USING INORGANIC ACIDS AS CATALYSTS

This paper presents a synthesis process for preparing mesoporous titanium dioxide materials in the absence of any templates and using inorganic acids as catalysts. Tetrabutyl titanate was used as the precursor at ambient temperature, and four different inorganic acids, i.e., hydrochloric, nitric, sulfuric and phosphoric, were used as catalysts. The as-prepared mesoporous TiO2 materials were characterized by SEM, XRD and nitrogen adsorption/desorption measurements. The influences of different inorganic acids on the properties of TiO2 were discussed and compared in details. Experiments showed that the inorganic acids have significant effects on the surface area, pore volume, pore size, and pore size distribution of the products. The mesoporous TiO2 materials catalyzed by phosphoric acid exhibited the largest specific surface area and largest pore volume with narrow pore size distribution. Vacuum and infrared drying methods tested in the process were found to have subtle impact on the structure of the TiO2 materials prepared.     

SYNTHESIS OF MESOPOROUS TiOz MATERIALS WITH HIGH SPECIFIC AREA USING INORGANIC ACIDS AS CATALYSTS

This paper presents a synthesis process for preparing mesoporous titanium dioxide materials in the absence of any templates and using inorganic acids as catalysts. Tetrabutyl titanate was used as the precursor at ambient temperature, and four different inorganic acids, i.e., hydrochloric, nitric, sulfuric and phosphoric, were used as catalysts.The as-prepared mesoporous TiO2 materials were characterized by SEM, XRD and nitrogen adsorption/desorption measurements, The influences of different inorganic acids on the properties of TiO2 were discussed and compared in details. Experiments showed that the inorganic acids have significant effects on the surface area, pore volume, pore size,and pore size distribution of the products. The mesoporous TiO2 materials catalyzed by phosphoric acid exhibited the largest specific surface area and largest pore volume with narrow pore size distribution. Vacuum and infrared drying methods tested in the process were found to have subtle impact on the structure of the TiO2 materials prepared,     

Comparative performance of different urea coating materials for slow release

Approximately 70%of the applied urea fertilizer may be lost into the environment.This loss is due to leaching,decomposition and ammonium volatilization in soil,water and air.Through coating,the slow release technology can be used to reduce losses and to increase the fertilizer efficiency.Sulfur has been used as a coating material,but the coating cracks easily because of its friability,sometimes being peeled off from the urea surface.In this study,four types of materials,namely,gypsum,cement,sulfur and zeolite,were mixed and used as coating materials to search for the most effective and cheap coating materials.The primary reasons for selecting these materials were improving fruit quality and preventing plant diseases,providing a plant nutrient,increasing soil fertility and water retention.The materials were also selected based on their availability,processiblity and price.The effects of the coating materials,thickness,drying time,sieving and sealant on the crushing strength and dissolution rate of urea were investigated.Coated urea with the same proportion of gypsum-sulfur exhibited high crushing strength and lower dissolution rate.However,the performance was further enhanced by applying molten paraffin wax on the hot urea surface.SEM images demonstrated that the micro-structure of gypsum-sulfur coated urea after sieving resulted in a smoother coated layer.The efficiency of the coated urea was improved by26%using gypsum-sulfur（20%total coating）,3%paraffin wax and sieving the coating materials before application.     

Vibration analysis of hard-coated composite beam considering the strain dependent characteristic of coating material

The strain dependent characteristics of hard coat-ings make the vibration analysis of hard-coated composite structure become a challenging task. In this study, the mod-eling and the analysis method of a hard-coated composite beam was developed considering the strain dependent char-acteristics of coating material. Firstly, based on analyzing the properties of hard-coating material, a high order polynomial was adopted to characterize the strain dependent character-istics of coating materials. Then, the analytical model of a hard-coated composite beam was created by the energy method. Next, using the numerical method to solve the vibra-tion response and the resonance frequencies of the composite beam, a specific calculation flow was also proposed. Finally, a cantilever beam coated with MgO+Al2 O3 hard coating was chosen as the study case;under different excitation levels, the resonance region responses and the resonance frequencies of the composite beam were calculated using the proposed method. The calculation results were compared with the experiment and the linear calculation, and the correctness of the created model was verified. The study shows that compared with the general linear calculation, the proposed method can still maintain an acceptable precision when the excitation level is larger.     

Dry modification of electrode materials by roller vibration milling at room temperature

For the first time dry roller vibration milling at room temperature was used to prepare active carbon （AC） nano-particles and to modify MnO2 powder as electrode materials. In 30 min AC was milled to a mean particle size of 30-50 nm with increased crystallinity and higher specific surface area, predominantly mesoporous and with improved pore diameter distribution. Then, AC nano-particles were incorporated with MnO2 or bismuth-doped MnO2 nano-particles synthesized by sol-gel methods to prepare nano-composite electrode materials for studying their electrochemical performance. The AC nano-particles combined with 10 wt.% bismuth-doped MnO2 nano-particles were found to possess excellent electrochemical property with specific capacitance up to 308 F/g and without obvious attenuation with increasing current. Our method seems to ooen a new way to imorove AC based electrode materials used for clean energy such as suner capacitors.     

Mesoporous composite of LiFePO4 and carbon microspheres as positive-electrode materials for lithium-ion batteries

Mesoporous LiFePO4/C microspheres consisting of LiFePO4 nanoparticles are successfully fabricated by an eco-friendly hydrothermal approach combined with high-temperature calcinations using cost-effective LiOH and Fe3＋ salts as raw materials.In this strategy,pure mesoporous LiFePO4 microspheres,which are composed of LiFePO4 nanoparticles,were uniformly coated with carbon（1.5nm）.Benefiting from this unique architecture,these mesoporous LiFePO4/C microspheres can be closely packed,having high tap density.The initial discharge capacity of LiFePO4/C microspheres as positive-electrode materials for lithium-ion batteries could reach 165.3 mAh/g at 0.1 C rate,which is notably close to the theoretical capacity of LiFePO4 due to the large BET surface area,which provides for a large electrochemically available surface for the active material and electrolyte.The material also exhibits high rate capability（100 mAh/g at 8 C） and good cycling stability（capacity retention of 92.2%after 400 cycles at 8 C rate）.     

The axisymmetric torsional contact problem of a functionally graded piezoelectric coated half-space

In this article, we study the axisymmetric tor-sional contact problem of a half-space coated with func-tionally graded piezoelectric material (FGPM) and subjected to a rigid circular punch. It is found that, along the thick-ness direction, the electromechanical properties of FGPMs change exponentially. We apply the Hankel integral trans-form technique and reduce the problem to a singular integral equation, and then numerically determine the unknown con-tact stress and electric displacement at the contact surface. The results show that the surface contact stress, surface azimuthal displacement, surface electric displacement, and inner electromechanical field are obviously dependent on the gradient index of the FGPM coating. It is found that we can adjust the gradient index of the FGPM coating to modify the distributions of the electric displacement and contact stress.     

CHARACTERISTICS OF FATIGUE SURFACE MICROCRACK GROWTH IN VICINAL INCLUSION FOR POWDER METALLURGY ALLOYS

Inclusion flaw is one of the worst flaws of powder metallurgy. The inclusion flaw plays an important role in the failure of high temperature turbine materials in aircraft components and automotive parts, especially fatigue failure. In this paper, an experimental investigation of fatigue microcrack propagation in the vicinal inclusion were carried out by the servo-hydraulic fatigue test system with scanning electron microscope (SEM). It has been found from the SEM images that the fatigue surface microcrack occurs in the matrix and inclusion. According to the SEM images, the characteristics of fatigue crack initiation and growth in vicinal inclusion for powder metallurgy alloys are analyzed in detail. The effect of the geometrical shape and material type of surface inclusions on the cracking is also discussed with the finite element method (FEM).     

Material cloud method—its mathematical investigation and numerical application for 3D engineering design

Recently, material cloud method (MCM) has been developed as a new approach for topology optimization. In MCM, an optimal structure can be obtained by manipulating the sizes and positions of material clouds, which are material patches with finite sizes and constant material densities, and the numerical analysis can be done using fixed background finite element mesh. During the optimization procedure, only active elements, where more than one material cloud is contained, are treated. With MCM, an expansion–reduction procedure of the design domain can be naturally realized through movements of material clouds, so that a true optimal solution can be found without any significant increase of computational costs. In this paper, we summarize the concept of MCM and prove the existence of optimal solution(s) in the formulation of MCM to show the mathematical rigorousness of this new method. We show the design examples for 3D engineering design problems to show the generality of this method.     

干燥环境下表面黏附性能调控研究进展

实现黏附可控是解决微/纳机械产品黏附失效问题和发展先进黏附材料及新型微操作/微装配技术等的有效途径. 基于该研究背景,针对干燥不带电系统,对近年来发展的几类黏附调控方法进行了综述,从表面改形、材料改性及外场控制三方面介绍了织构、涂层/薄膜和复合材料、速度、温度、外力和磁场在黏附调控方面的研究进展,分析和总结了各类方法的黏附调控机理、关键影响因素和特点,并指出了应用领域,介绍了多手段复合调控黏附方法的最新研究成果. 最后,探讨了当前黏附调控方面存在的问题和未来可能的发展方向.      

钴基合金刷丝与碳化铬涂层高线速度磨损行为研究

在超高速磨损试验器上开展刷式密封磨损试验,摩擦副为GH5605钴基高温合金刷丝束和喷涂碳化铬耐磨涂层的跑道试样,最高摩擦线速度达到400 m/s. 利用扫描电镜和能谱分析研究了摩擦表面的磨损形貌及材料成分,发现试验后的碳化铬涂层存在材料剥落和刷丝材料附着,刷丝尖端出现以犁沟和涂抹为主要特征的磨损,且摩擦线速度达到400 m/s时出现刷丝尖端粘连和严重氧化现象. 通过分析刷丝尖端磨损形貌的形成机制及摩擦表面的材料转移机理,认为刷丝尖端的主要磨损机制为二体磨粒磨损,而涂层的材料剥落现象会加剧其对刷丝的磨粒磨损作用. 使用共聚焦显微镜测量了磨痕深度,并与转子离心涨大变形量进行对比分析,分析结果表明超高线速度条件下转子的离心涨大增加了刷丝束和跑道涂层间的干涉,显著加剧了摩擦副的磨损.      

Heat and mass transfer characteristics of organic sorbent coated on heat transfer surface of a heat exchanger

This paper describes heat and mass transfer characteristics of organic sorbent coated on heat transfer surface of a fin-tube heat exchanger. The experiments in which the moist air was passed into the heat exchanger coated with sorption material were conducted under various conditions of air flow rate (0.5–1.0 m/s) and the temperature of brine (14–20°C) that was the heat transfer fluid to cool the air flow in the dehumidifying process. It is found that the sorption rate of vapor is affected by the air flow rate and the brine temperature. Meanwhile, the attempt of clarifying the sorption mechanism is also conducted. Finally the average mass transfer coefficient of the organic sorbent coated on heat transfer surface of a fin-tube heat exchanger is non-dimensionalzed as a function of Reynolds number and non-dimensional temperature, and it is found that the effect of non-dimensional temperature on them is larger than Reynolds number .     

基于Monte Carlo方法的磁驱动准等熵压缩实验不确定度量化评估

磁驱动准等熵压缩实验是研究材料偏离Hugoniot状态高压物性和动力学行为的重要实验技术之一，开展不确定量化评估具有重要意义和价值。基于Monte Carlo原理，结合磁驱动准等熵压缩实验过程分析、Lagrange分析和特征线正向数据处理方法建立了适用于此类实验的Monte Carlo不确定度量化评估方法，实现利用磁驱动准等熵压缩实验获取材料声速、应力、应变等物理量以及状态方程和本构关系等物理模型的不确定度量化评估。利用建立的不确定度评估方法，对文献中已开展的钽、铜和NiTi合金的磁驱动准等熵压缩实验结果进行不确定度量化评估与分析。结果表明，基于本文中方法的评估结果与国外文献以相同原理得到的评估结果一致。对基于CQ-4装置开展的NiTi合金磁驱动准等熵压缩实验的评估结果表明，设计的磁驱动准等熵压缩实验是一种可靠的精密物理实验。在此基础上，深入讨论了磁驱动准等熵压缩实验的误差相关性和敏感性。结果表明：台阶样品厚度和粒子速度的测量是影响实验精度的主要因素。     

A Normal Force on the Free Surface of a Coated Material

The three-dimensional theoretical solution of a concentrated normal force acting on the free surface of a coated material has been deduced by applying the reflection method. It is found that all stress functions defined in the local coordinate systems with their origins placed at each mirror point can be deduced from the fundamental solution of a concentrated normal force acting on the free surface of a semi-infinite homogeneous medium. The structure of the elastic solution has been illustrated by numerical analysis. It is found that only the stress functions corresponding to the first few mirror points are influential. It is also found that the effect of material combination on the stress field shall be described by three parameters, the two Dundurs' parameters and one additional parameter.     

Comparative performance of different urea coating materials for slow release

Approximately 70% of the applied urea fertilizer may be lost into the environment. This loss is due to leaching, decomposition and ammonium volatilization in soil, water and air. Through coating, the slow release technology can be used to reduce losses and to increase the fertilizer efficiency. Sulfur has been used as a coating material, but the coating cracks easily because of its friability, sometimes being peeled off from the urea surface. In this study, four types of materials, namely, gypsum, cement, sulfur and zeolite, were mixed and used as coating materials to search for the most effective and cheap coating materials. The primary reasons for selecting these materials were improving fruit quality and preventing plant diseases, providing a plant nutrient, increasing soil fertility and water retention. The materials were also selected based on their availability, processiblity and price. The effects of the coating materials, thickness, drying time, sieving and sealant on the crushing strength and dissolution rate of urea were investigated. Coated urea with the same proportion of gypsum–sulfur exhibited high crushing strength and lower dissolution rate. However, the performance was further enhanced by applying molten paraffin wax on the hot urea surface. SEM images demonstrated that the micro-structure of gypsum–sulfur coated urea after sieving resulted in a smoother coated layer. The efficiency of the coated urea was improved by 26% using gypsum–sulfur (20% total coating), 3% paraffin wax and sieving the coating materials before application.