Exact 2D Solution and Assessment of a 1D Zigzag Theory for Vibration of Thermally Stressed Hybrid Beams

ABSTRACT

A benchmark two-dimensional (2D) piezothermoelasticity solution is presented for buckling and free vibration of simply supported symmetrically laminated hybrid piezoelectric beams under initial stresses due to thermoelectric load. The solution, based second Piola stress tensor and nonlinear Lagrangian strains, accounts for the effect of initial transverse normal strain and the two-way piezoelectric coupling. Benchmark results are presented for the buckling temperature, natural frequencies under initial thermal stresses and modal distributions of displacements and stresses across the thickness, against which the accuracy of 1D beam theories for hybrid beams can be assessed. A recently developed coupled 1D zigzag theory for hybrid beams is extended for vibration under initial thermal stresses. The theory uses a piecewise linear approximation for the thermal and potential fields across sublayers, an approximation for the deflection, which explicitly accounts for the transverse normal strain due to thermal and electric fields and a layerwise (zigzag) variation for the axial displacement. The transverse shear continuity conditions at the layer interfaces and the shear traction-free conditions at the top and bottom are enforced to reduce the number of primary displacement variables to three. The new 1D theory is assessed in comparison with the exact 2D solution for the natural frequencies and mode shapes of beams and panels under initial thermoelectric load. The zigzag theory results show excellent agreement with the 2D results when the initial transverse normal strain is neglected.     

A Thermo-Mechanical Analysis of Isotropic and Composite Beams via Collocation with Radial Basis Functions

In this article, the mechanical behavior of beams subjected to thermal loads is investigated. The temperature field is obtained by exactly solving Fourier's heat conduction equation and it is considered as an external load within the mechanical analysis. Several higher-order beam models as well as Timoshenko's classical theory are derived thanks to a compact notation for the a priori approximation of the displacement field upon the cross-section. The governing differential equations and boundary conditions are obtained in a compact nucleal form that does not depend upon the displacements’ expansion order. The latter can be regarded as a free parameter of the formulation. A meshless strong-form solution based upon collocation with Wendland's radial basis functions is adopted. Isotropic and laminated orthotropic beams are investigated. Results are validated toward an analytical Navier-type solution and three-dimensional FEM results. It is shown that good accuracy can be obtained.     

Enhanced-sensitivity version of the Baryscan technique

A promising alternative to the widespread Z-scan technique has been recently proposed. This technique, named Baryscan, is based upon the use of a Position Sensitive Detector (PSD) and is about 170 times more sensitive than the Z-scan technique while preserving its simple theoretical scheme and ease of implementation. In this paper, we demonstrate both numerically and experimentally that inserting a phase plate before the PSD and setting an opaque disk as close as possible to its active area results in a substantial sensitivity enhancement of the Baryscan technique.     

Microstructural Change of Ni–GDC Cermet Anode in the Electrolyte‐supported Disk‐type SOFC upon Daily Start‐up and Shout‐down Operations

The daily start‐up and shut‐down operations were carried out for the 1 kW‐class solid oxide fuel cell stack composed of 46 electrolyte‐supported disk‐type planar cells made by Mitsubishi Materials Corporation and Kansai Electric Power Company. The representative Ni–gadolinia doped ceria cermet anodes in the deteriorated cells were analyzed by the dual‐beam focused ion beam‐scanning electron microscope. The anode microstructures were reconstructed and the microstructural parameters such as triple phase boundary (TPB) length were quantified. The surface area of nickel phase decreased with an increase in the deterioration rate, leading to a reduction in the TPB length. Furthermore, the TPB length had a strong correlation with the voltage deterioration rate.     

氯盐腐蚀下钢管混凝土方柱的承载力试验研究

对氯盐腐蚀下钢管混凝土方柱的承载性能进行试验研究。试验包含28个试件(17根短柱和11根梁),主要参数为腐蚀情况下的荷载比(0～0.75)及腐蚀状况(无腐蚀、完全腐蚀及部分腐蚀)。根据试验结果,对荷载及腐蚀对钢管混凝土和钢管性能的影响进行分析,并将按现有规范DBJ/T13-51-2010及EC4-2004计算的极限承载力与试验进行对比分析。     

角钢梁在静态和突发性动态荷载下的非线性不稳定性

介绍了纯弯曲载荷作用下角钢梁的扁屈性能。使用能量法对角钢梁弱轴在纯弯曲载荷下静态与动态的不稳定性推导出一种解析解。结果显示,角钢在受瞬间压力的作用时,其弯矩达到静态临界弯矩的71%时,即发生失稳;但是其在动力状态下纵向弯曲和屈曲的变形临界值是静力状态下的2倍。     

薄壁框架节点中的翘曲扭转传递:运动、建模及结构响应

在梁的有限元分析中,采用简化运动模型模拟翘曲扭转约束及其在框架节点中的传递。简要说明薄壁杆件的扭转性能,建立运动模型,模拟翘曲扭转在2个以上U型或I型杆件交汇的框架节点中的传递。为了说明本模型的应用及有效性,列出数值结果,并进行讨论。将梁元与壳元的有限元结果进行对比,验证了本模型可考虑节点的翘曲扭转性能。     

PGNAA方法学的发展与现状

瞬发伽马中子活化分析(PGNAA)为非破坏性、在线测量的核分析方法。目前国际上有30多座研究堆建立了PGNAA实验室。本文介绍了三种定量瞬发伽马活化分析方法:相对法、校准曲线法、k0因子法,阐述了基本原理及其应用领域,以及针对短寿命核素高精度测量的束流斩波器技术,针对大样品测量带来的中子自吸收和伽马自屏蔽效应的内标法。此外还简介了基于CARR堆的热中子瞬发伽马活化分析装置进展情况,对国内的PGNAA问题进行了探讨。     

不同扩束镜对激光切割质量的影响研究

光束质量的好坏直接影响激光切割的水平,扩束镜是激光器光束整形中常用的光学元器件,然而扩束镜的质量对切割质量的影响鲜有报道。本文从理论和实验上分析两款不同扩束镜对切割质量的影响。研究表明:扩束镜1使激光光束发散角更小,真圆度更好,能量分布更集中,明显的改善了光束质量,因此明显的减轻了炭化,切缝更窄,满足了实际切割的要求。     

基于方位Deramp处理的宽覆盖DBS全孔径成像方法

为了获得大幅宽多普勒波束锐化(DBS)图像,现有的DBS成像算法往往需要进行复杂图像拼接.此外,现有成像方法为了保证DBS图像的锐化比恒定,除了要实时调整波束扫描速度外,还需要实时调整脉冲重复频率或积累脉冲个数,使得系统复杂度显著增加.文中在深入研究DBS成像机理的基础上,提出了一种基于方位Deramp处理的宽覆盖DBS全孔径成像方法.该方法利用方位Deramp消除了全场景回波的多普勒频谱混叠,无需进行图像拼接,通过一次全孔径FFT就能获得宽覆盖DBS图像.同时,只需实时调整波束指向,该方法就能实现恒定锐化比成像.实测数据处理结果证明文中方法的有效性.