铁路正交异性桥面加劲肋-横隔板局部疲劳受力特性研究

正交异性钢桥面因整体性好、承载力强等优势在铁路大跨度桁梁及箱梁斜拉桥、拱桥等桥型中应用越来越广泛,其疲劳特性与公路桥面具有显著的差异。针对铁路正交异性钢桥面加劲肋与横隔板连接处的疲劳敏感区,通过弹性支撑梁理论及闭口薄壁杆件理论分析其局部受力特征,提出了加劲肋疲劳敏感部位面内疲劳应力的解析公式,分析了解析公式中各疲劳影响因素的影响程度及作用机理。基于甬江特大桥——大跨度铁路斜拉桥的钢箱梁正交异性桥面设计了包含2个U肋及2个V肋的正交异性桥面疲劳试验模型,并进行了560万次疲劳加载。研究结果表明：解析公式与有限元分析、试验测试结果相符良好;试验模型测试结果能准确反映疲劳敏感点的应力情况,解析理论则能够反映疲劳敏感点应力的影响因素与规律;在铁路荷载下,加劲肋与横隔板的焊缝长度和加劲肋腹板倾角的增大能够有效降低加劲肋的疲劳应力幅;在铁路正交异性钢桥面板中面积相近、抗弯刚度相等的V肋比U肋具有更好的抗疲劳工作性能。     

热电耦合场中压电粘弹性微梁的静力坍塌分析

基于粘弹性理论、欧拉-伯努利梁理论以及压电理论,在考虑微结构蠕变现象的情况下,建立了热电耦合场中压电粘弹性微梁的静力坍塌模型及控制方程,研究了压电粘弹性微梁的静力坍塌临界条件,计算和分析了压电层控制电压和温度等参数对微梁结构静力坍塌的影响。研究结果表明:持久坍塌电压可作为压电粘弹性微梁静力坍塌失稳的临界条件,并且温度和压电层控制电压均会对坍塌失稳的临界值造成影响。该文的研究可为MEMS中梁式微结构的设计与优化提供理论参考。     

基于弹性扭转约束边界的波形钢板整体剪切屈曲分析

波形钢板的整体剪切屈曲对波形钢腹板PC组合箱梁桥的竖向抗剪设计有重要意义。该文在正交各向异性薄板理论的基础上,利用势能驻值原理和瑞利-里兹法,推导了基于弹性扭转约束边界的波形钢板弹性整体剪切屈曲荷载的分析方法,并给出了几种特殊边界条件下的简化计算公式。计算结果表明:对于四边简支板和四边嵌固板,该方法与现有公式计算结果一致;波形钢板强抗弯刚度方向上的约束条件是影响其整体剪切屈曲的决定性因素,随着该方向上约束的增强,屈曲模式将从四边简支情况向四边嵌固情况过渡;弱抗弯刚度方向上约束条件的影响很小,可以忽略。最后给出了将波形钢板在实际梁结构中受到的边界约束等效为弹性扭转弹簧的方法。     

附加集中质量正交各向异性双向连续板结构振动分析

分析了附加集中质量正交各向异性双向连续板结构的振动特性,通过有限傅立叶变换将双向多肋板振动微分方程的解改写为级数形式,通过解附加方程组的方法解出肋梁的约束力和约束力矩与板的相互作用,将其代回原方程得出多肋板的自由振动解,从而可以得到仿真试验模型。     

IN SITU X-RAY PROBES FOR PIEZOELECTRICITY IN EPITAXIAL FERROELECTRIC CAPACITORS

ABSTRACT

Probing the piezoelectricity and ferroelectricity of thin film devices and nanostructures quantitatively has proven to be challenging because the appropriate experimental tools have had a limited range of usefulness. We show here that the piezoelectric and ferroelectric properties of epitaxial thin films can be measured quantitatively using time-resolved synchrotron x-ray microdiffraction. Microdiffraction combines structural specificity with the appropriate spatial resolution and ability to probe structures with electrical contacts. Our measurements of piezoelectric coefficients and coercive electric fields for Pb(Zr,Ti)O₃ capacitors using this approach are in excellent quantitative agreement with results obtained electrically and mechanically. The time and spatial resolution of microdiffraction probes are well-defined and decoupled from electrical and mechanical resonances of the ferroelectric capacitor.     

混凝土正交各向异性损伤模型的研究

混凝土的基本破坏机理是微开裂。基于不可逆过程热力学,用连续介质力学的方法建立了一个混凝土正交各向异性损伤模型。在模型中用一个二阶对称张量Ｄ来描述损伤,利用能量等效假设来考虑损伤对弹性张量的影响,并直接假设了损伤增量与不可逆应变增量之间的关系式,而不是用经典塑性理论来处理不可逆应变。模型只需一个加载函数。模型与Ｋｕｐｆｅｒ,Ｔａｓｕｊｉ等的试验结果吻合较好。     

The effects of point defects on transmission coefficients in two-dimensional piezoelectric phononic crystals

Based on finite-difference time-domain(FDTD) method,the wave propagation and localization in two-dimensional defect-containing piezoelectric phononic crystals are investigated when the mechanical-electrical coupling is taken into account.The characteristics of localized defect modes are studied,and the effects of the number and direction of defects on the defect modes and transmission coefficients are discussed.Numerical results of defect modes and transmission coefficients are presented for BaTiO3/polymer piezocomposite,and from which we can see that the number and direction of defects have pronounced effects on the defect modes and transmission coefficients.The results also show the existence of elastic wave localization in piezoelectric phononic crystals containing defects.     

高灵敏度Si基纤毛式MEMS湍流传感器

为了满足湍流探测高灵敏度、高分辨率的要求,提出了一种新型纤毛微电子机械系统(MEMS)湍流传感器。基于MEMS技术制作了硅十字梁敏感受力结构,通过橡胶探头的受力振动传递水中的湍流信号,凭借传感器头部的导流罩来保证传感器的高分辨率探测。对MEMS湍流传感器进行理论和仿真分析,其一阶共振频率达到481.04 Hz。经过海洋环境模拟机测试实验,结果显示其在50 MPa压力下保持了完好的结构和良好的性能,验证了其水下的可靠性。在湍流实验平台进行测试,通过比较标定法得出其灵敏度为1.92×10^-4 V·m·s^2/kg,满足海洋湍流测试要求。     

Renewable energy harvesting from water flow

The hydrokinetic energy of flowing water is plentiful, environment-friendly, renewable and can be harvested. This paper reports a new energy harvesting system using vortex-induced vibration (VIV). The proposed convertor harvests vibrations of a bluff body resulting from interaction of the alternating vortices created by the unsteady separation. These vortices are shed from the sides of the bluff body and form a pattern in the wake known as the von Kármán vortex street. The vortices create unsteady loading and induce vibrations with a predictable frequency and amplitude. Assisted by the bluff body with specific geometry and piezoelectric generators, the kinetic energy of the water flow can be converted into mechanical vibrations and electrical energy. In order to maximise the output energy of the harvester, the natural frequency of the mechanical system needs to lock into the frequency of the VIVs. Thus, the geometry of the bluff body has to be optimised to match the natural frequency of the convertor. This study examines the conceptual design of the physical model. The fluid–structure interaction model is applied to study the preliminary design. The maximum energy density that can be extracted by the proposed convertor from the water flow with velocities from 0.2 to 1 m/s is also estimated.Abbreviations: 1.CFD Computational Fluid Dynamics; 2.DC Direct Current (electricity); 3.FIM Fluid Induced Motion; 4.ODE Ordinary Differential Equation; 5.PTC Passive Turbulence Control; 6.VIV Vortex Induced Vibration; 7.VIVACE Vortex Induced Vibration Aquatic Clean Energy; 8.2D Two Dimensional     

Performance Analysis of the Mesh‐Free Random Grid Method for Full‐Field Synthetic Strain Measurements

Abstract: In responding to the needs of the material characterization community, the recently developed mesh‐free random grid method (MFRGM) has been exhibiting very promising characteristics of accuracy, adaptability, implementation flexibility and efficiency. To address the design specification of the method according to an intended application, we are presenting a sensitivity analysis that aids into determining the effects of the experimental and computational parameters characterizing the MFRGM in terms of its performance. The performance characteristics of the MFRGM are mainly its accuracy, sensitivity, smoothing properties and efficiency. In this paper, we are presenting a classification of a set of parameters associated with the characteristics of the experimental set‐up and the random grid applied on the specimen under measurement. The applied sensitivity analysis is based on synthetic images produced from analytic solutions of specific isotropic and orthotropic elasticity boundary value problems. This analysis establishes the trends in the performance characteristics of the MFRGM that will enable the selection of the user controlled variables for a desired performance specification.