Imaging of the Elastic Wave Propagation in Concrete Using Scanning Techniques: Application for Impact-Echo and Ultrasonic Echo Methods

Acoustic NDT methods like ultrasonic echo and impact-echo are successfully used for NDT of concrete structures. This paper describes useful techniques for a detailed experimental study of the elastic wave propagation, which is highly relevant for the interpretation of the results obtained from practical measurement applications. By using a scanning laser vibrometer it becomes possible to obtain a 2D visualization of the elastic waves propagating along the surfaces of concrete specimens. Time slices are prepared so that the wave field becomes apparent. In order to visualize especially the surface wave propagation a similar technique using a scanning system with a piezoelectric sensor is applied. The results obtained provide an appropriate basis for the comparison with numerical results from 3-D Elastodynamic finite integration technique (EFIT) calculations, which is demonstrated here. Examples are presented for the application with phased array ultrasonic echo, air-coupled ultrasonic echo and impact-echo.     

碳化混凝土再碱化控制理论研究的探讨

再碱化技术应用于实践必须解决的一个重要问题是再碱化过程的控制.在综合分析国内外相关研究的基础上,首先,对不同研究者所做的研究进行了剖析,分析了其研究的路线方法;然后,从控制理论研究的不同方面分析展示了其研究进展;最后,深入分析了各研究,揭示了其中不足之处,指出了再碱化控制理论的发展现状,为进一步研究提供参考.     

企业新雇员工作态度的结构模型及其验证研究

在对已有研究进行回顾的基础上，提出了一个关于企业新雇员工作态度的结构模型，并利用LISREL8软件采用模型生成方法，通过调查所收集数据对该模型进行验证。经过修正的最后模型表明：组织社会化通过工作适应对新雇员的工作态度产生间接影响，新雇员主观感知到的员工一组织匹配则对其工作态度产生直接影响。     

浸渍及固载法用于混凝土微生物表面处理对比研究

微生物诱导碳酸钙沉积目前已广泛用于各种多孔介质的表面处理,以提高其耐久性和使用寿命。选用了脲解型微生物,分别采用液体浸渍和琼脂固载两种方式对混凝土表面进行处理。沉积一周后,测试混凝土的毛细吸水系数、水渗透系数和氯离子电通量,以及表面接触角和沉积厚度,并综合利用扫描电镜、能谱仪以及X射线衍射仪分析了沉积产物的微观形貌和组成。结果发现,微生物沉积产物膜层厚度约为10 μm。与液体浸渍方式相比,琼脂固载所获得的沉积产物尽管较薄且表面呈亲水性,但固载可为微生物的生长提供良好的微环境,有利于形成致密的碳酸钙层,因此琼脂固载能更有效地提高混凝土的抗渗性,可使水渗透系数降低80%以上。同时,固载方式显然更具备实用价值。     

混凝土低温性能表征技术和研究方法综述

液化天然气(LNG)贸易的繁荣加剧了LNG储罐的需求.以混凝土代替9％镍钢制备"全混凝土"LNG储罐可降低46％的成本和缩短33％的工期并提高结构的耐久性,此技术具有重大经济和科学意义.全混凝土LNG储罐在服役过程中面临的最大风险是温度波动(-40～-165℃)和低温冻融循环(室温至-170℃).目前,低温环境(-40～-197℃)中混凝土的失效机理尚不清楚.低温环境孔隙中的水结冰会引起混凝土孔结构、热导率、热应变、渗透性能和失效过程中能量释放行为的变化.低温环境混凝土性能的演变机制还处于研究初期,采用先进的表征技术和高效的研究方法从多角度探究孔隙中水结冰和混凝土宏观性能演化的内在联系,是明确低温环境混凝土劣化机理的有效策略.本文对低温环境混凝土的表征技术(核磁共振技术(NMR)、X射线计算机断层扫描技术(μ-CT)、差分扫描量热技术(DSC)、低温扫描电子显微技术(LTSEM)、声发射技术(AE)和激光闪光法(LFA))及研究方法(热应变测试和渗透性测试)进行综述,并对超高性能混凝土(UHPC)的低温性能进行总结.在低温环境中,利用NMR技术和DSC技术可原位分析混凝土孔隙中水的结冰行为.其中,NMR技术可研究孔隙中水状态的演化;DSC技术基于热流数据可量化表征孔隙中冰的体积.μ-CT技术可探究冻融前后孔隙和裂缝的三维形态.LTSEM技术可获取孔隙中冰体的微观形貌.热应变测试和AE技术结合使用可明确混凝土热变形与失效过程中能量释放之间的相关性.通过降低孔隙率、含水率和剔除粗骨料,可使UHPC具有优异的耐低温性能.目前,低温环境中混凝土的导热性能和渗透性能仍缺少全面研究,采用LFA技术可测定低温环境混凝土的热导率.本文系统归纳了低温环境混凝土的表征技术和研究方法,有助于深入理解低温环境混凝土的失效机理和研制高耐久性的全混凝土LNG储罐.     

Investigation in Crack Growth of A537 Steel and Its Weld Metal in Artificial Sea Water

The crack growth rates of A537 c1.1 steeland its weld metal have been investigated bothin air and in artificial sea water.The effectsof stress ratio,frequency,residual stressof welds as well as corrosion products on cor-rosion fatigue crack growth rate have been exa-mined.Some electrochemical reactions occurredduring tests and models for describing the cor-rosion fatigue crack growth process in lowstrength of offshore structural steel werediscussed.     

现代混凝土传输行为与其微结构之间关系的研究方法及其进展

开裂是导致结构混凝土过早出现劣化和提前退出服役的主要原因,但其劣化本质上均是侵蚀性介质通过混凝土自身的孔隙、微裂纹或者荷载作用下的裂缝传输所致,因此,要揭示现代混凝土的劣化本质,必须科学地认识并建立其宏观、微观之间的本构关系。过去国内外提出的关于侵蚀性介质在混凝土材料中的传输理论,如Fick定律或者Darcy定律,其本质上属于唯象理论,尽管可以描述离子传输的现象,但关键参数如扩散系数、渗透系数均是通过试验回归,并没有深究现象背后的物理意义。更重要的是,这些理论难以确定混凝土微结构在各尺度层次上对离子传输的影响,进而难以从根源上对混凝土微结构进行调控,难以调节混凝土侵蚀性介质传输的性能。而现代混凝土具有多孔、多相、多层次和多尺度特征,因此需要逐尺度建立侵蚀性介质在混凝土中的传输本构关系。本文以氯离子(诱发钢筋锈蚀导致混凝土劣化最主要的原因之一)在现代混凝土中的扩散为例,介绍了现代混凝土宏观、微观之间传输本构关系建立的理论方法,影响氯离子在现代混凝土中传输行为的主要微结构特征参数(如硬化水泥石的水化产物及其空间分布、界面过渡区孔隙分布、界面过渡区体积分数),混凝土在各尺度上已建立的氯离子扩散与其微结构特征参数之间的本构关系等的国内外研究现状。现有的基于细观力学建立的各尺度传输模型,如常用的自洽模型、广义自洽模型和有效介质理论等均假定夹杂是球形的,夹杂与基体之间保持完好,而对混凝土这种复杂的复合材料需充分考虑夹杂形貌、夹杂体分比以及夹杂与基体之间存在的界面过渡区对传输行为的影响。在混凝土微结构特征参数预测模型中,已初步建立了球形骨料周围界面过渡区体积分数预测模型并充分考虑了界面之间的重叠程度,界面过渡区孔结构分布模型,硅酸盐水泥水化过程的模拟以及水化产物体积分数计算模型。这些模型为混凝土宏观、微观之间的传输本构关系的建立奠定了基础。本文还系统地介绍了从影响离子传输的最小尺度即纳米尺度逐步过渡到宏观尺度的建模过程。最后指出各尺度理论预测模型和微结构特征参数定量表征方面目前存在的不足和今后研究的重点,以期为结构混凝土微结构的调控和服役寿命的预测研究提供参考。     

Cyclic and Linear Structures of C13: A Computational Study

Abstract

Recently, a linear structure of C₁₃ was observed and its infrared spectrum recorded. Computations of the linear and cyclic structures of C₁₃ are thus presented. The computations are performed at ab initio level using the standard 6-31G? basis set. Electron correlation is treated by density functional theory (Becke3LYP) and perturbation treatment (MP2=FC). With the density-functional approach the standard 6-311G? and 6-311G(2d,p) basis sets are applied, too. In all the treatments the cyclic structure (C _2v symmetry) is located about 90 kJ/mol below the linear form (D _∞h symmetry), while a tricyclic structure is considerably higher in energy (about 280 kJ/mol above the monocyclic species). Even at high temperatures the linear form represents less than 10% of the equilibrium isomeric mixture. Computed IR spectra are also reported. The stability evaluation corresponds to the findings of ion chromatography.     

Cyclic and Linear Structures of C13: A Computational Study

Recently, a linear structure of C₁₃ was observed and its infrared spectrum recorded. Computations of the linear and cyclic structures of C₁₃ are thus presented. The computations are performed at ab initio level using the standard 6-31G* basis set. Electron correlation is treated by density functional theory (Becke3LYP) and perturbation treatment (MP2=FC). With the density-functional approach the standard 6-311G* and 6-311G(2d,p) basis sets are applied, too. In all the treatments the cyclic structure (C_2v symmetry) is located about 90 kJ/mol below the linear form (D_∞h symmetry), while a tricyclic structure is considerably higher in energy (about 280 kJ/mol above the monocyclic species). Even at high temperatures the linear form represents less than 10% of the equilibrium isomeric mixture. Computed IR spectra are also reported. The stability evaluation corresponds to the findings of ion chromatography.     

小径管超声导波检测有效检测距离研究

针对CFETR装置中真空管道的在役检测及维护方法,指出现有氦质谱检测技术的局限性。在此基础上,提出超声导波检测技术应用于真空管道检测,并且对应用中关键问题进行讨论。应用有限元法,分析了已确定结构及材料的管道检测的超声模态及波结构。在此基础上进行对检测距离进行数值模拟仿真,结果表明:对直径32 mm壁厚3 mm不锈钢管道,可单次检测出1 mm×4 mm×0.5 mm的表面裂纹,有较好的检测特性。最后,通过现场试验分析,得到检测信号反射系数与距离的关系(信噪比关系),对仿真进行了验证。     

NanoPaint: A Tool for Rapid and Dynamic Imaging of Membrane Structural Plasticity at the Nanoscale

Single‐particle tracking with quantum dots (QDs) constitutes a powerful tool to track the nanoscopic dynamics of individual cell membrane components unveiling their membrane diffusion characteristics. Here, the nano‐resolved population dynamics of QDs is exploited to reconstruct the topography and structural changes of the cell membrane surface with high temporal and spatial resolution. For this proof‐of‐concept study, bright, small, and stable biofunctional QD nanoconstructs are utilized recognizing the endogenous neuronal cannabinoid receptor 1, a highly expressed and fast‐diffusing membrane protein, together with a commercial point‐localization microscope. Rapid QD diffusion on the axonal plasma membrane of cultured hippocampal neurons allows precise reconstruction of the membrane surface in less than 1 min with a spatial resolution of tens of nanometers. Access of the QD nanoconstructs to the synaptic cleft enables rapid 3D topological reconstruction of the entire presynaptic component. Successful reconstruction of membrane nano‐topology and deformation at the second time‐scale is also demonstrated for HEK293 cell filopodia and axons. Named “nanoPaint,” this super‐resolution imaging technique amenable to any endogenous transmembrane target represents a versatile platform to rapidly and accurately reconstruct the cell membrane nano‐topography, thereby enabling the study of the rapid dynamic phenomena involved in neuronal membrane plasticity.     

基于全站仪测距的超声波液位计检校方法的提出和研究

通过全站仪的精确测距功能,对量程较大的超声波液位计进行检较,既能保证使用标准器的使用准确度,又能提高工作效率.     

Comparative Study of Laser Doppler Vibrometer and Capacitive Air‐coupled Transducer for Ultrasonic Propagation Imager and the New Development of an Efficient Ultrasonic Wavenumber Imaging Algorithm

Damage detection techniques using guided waves have been studied for decades with very few successful real‐world applications. The recent development with the full wavefield technique using the Ultrasonic Propagation Imager (UPI) is one of those few exceptions. In this paper, we study two non‐contact sensors: the laser Doppler vibrometer and the capacitive air‐coupled transducer in the context as the sensing modules for the UPI. The aim of this paper is to provide a comprehensive study for optimisation of the two sensors, as well as a comparison between them for use in the UPI. First, the parameters for laser ultrasonic measurement of each sensor were studied: surface treatment, measurement angle and stand‐off distance in the case of the laser Doppler vibrometer and measurement angle, lift‐off distance and bias voltage in the case of the capacitive air‐coupled transducer. Two optimised sensors were then compared in terms of their ability to detect damages using the UPI. Also, in this paper, we presented the ultrasonic wavenumber imaging (UWI) algorithm with the new development towards an efficient implementation. The uniqueness of the UWI algorithm with the capability of damage size estimation makes this algorithm very attractive for the future study with full wavefield signal processing.     

超声技术真空管道检测模拟分析与研究

在核聚变领域、加速器领域、航天等领域中,根据装置或设备运行要求,很多大型真空容器里需布置着许多冷却管道。在运行过程中,若有冷却管道发生泄漏,将直接影响整个系统的稳定性和安全性,则需对管道进行泄漏检测并快速定位漏点位置对其修复。基于此要求,本文在不破真空的条件下提出超声检测方法对管道泄漏点进行检测定位分析研究。借助有限元分析模拟方法,在真空环境下,以不锈钢材质管道为研究对象,对管道泄漏检测的进行数值仿真,以管道一端通过加载中心频率100 kHz瞬态位移载荷,选定一截面进行信号接收方式,进行仿真模拟,获得截面的位移时程变化。结果表明:对1.5 m长管道可有效检测出2 mm当量孔径漏点;通过信号处理方法对检测信号分析,显示管道定位精度在2 cm以内。分析研究结果和方法为后续更长管道泄漏检测定位研究提供借鉴,也为未来管道泄漏检测定位应用研究奠定理论和技术基础。     

真空泵微小抽速测试方法研究进展与分析

基于真空泵发展的实际需求,本文对真空泵微小抽速测试方法的研究现状与进展进行全面论述。首先,从三种常用的测试方法(流量计法、定容法和动态流导法)具体展开。通过回顾国内外学者的典型应用案例,分别介绍其测试原理与特点;接下来,讨论微小抽速的测试方法的难点及其应对策略,并对这几种测试方法进行对比分析,最后,就不同压力条件与测试方法的选用关系给出建议。同时,本文也提出未来可在真空泵极小抽速(<10^-5 m³/s)的精确测试和拓展测试气体的种类两方面开展进一步研究,以推动真空计量基础科研的跨越式发展。     

X射线束点尺寸对X射线相位衬度成像的影响

X射线相位衬度成像利用X射线穿过样品后的相位变化, 通过衍射信息来获得样品的结构特征。X射线相位衬度成像在生物影像、显微成像以及材料科学研究中有重要的应用。如果X射线成像样品物质密度比较低, 它对X射线的吸收很小, 所以常规的吸收衬度成像质量较差, 不易分辨样品的结构细节。理论分析和实验研究都表明当X射线束点尺寸减小到一定尺度后, X射线源的空间相干性增强, 采用相位衬度成像可以提高低密度样品的成像质量。X射线相位衬度成像质量与X射线束点尺寸, 样品到影像记录平面之间距离直接相关。本文研究了X射线束点尺寸与低密度样品影像边沿轮廓宽度和对比度之间的影响关系。研究结果表明, 根据低密度样品的介电常数、X射线源到样品距离, 以及样品到影像记录平面距离, 存在最优化的X射线束点尺寸。在该最优化配置条件下, 低密度样品的X射线成像可以获得最好的图像质量。     

金属及合金熔点热物性动态测试新方法研究

利用物质熔化与凝固过程中导热逆(或反)问题原理，在建立了相界面移动与两相热物理性质关系的基础上，提出了一种新颖的热物性动态测试方法，即由相变速率动态测试热物性参数。由于是对熔点高的金属进行测试，故不能采用解析求解，而是运用数值求解；并用铅、锌、铝等已知热物性的金属对此方法进行了评定，测试结果与参照值误差不超过3％；还对相变导热系数未知的铅锑、铅锡、铋锡、铝硅、铝铜5种共晶合金进行了测试，其结果具有较高的参考价值。该方法的优点在于测试过程中所求热物性参数与相界面位置是由精确的传热方程所约束，故测量较简便，结果准确、可靠、误差小，并可测得多个热物性数据。