超声波声速测量技术及其在材料评价中的应用

介绍两种测量声速的方法，阐述这两种方法的原理和区别，并列举了利用声速评价材料性能的实例。     

声振动无损检测材料强度的方法及其检测机理

本文简介了几种声振动无损检测材料强度的方法,阐明它们所检测的物理量实际上都是材料的弹性模量,并引用硅橡胶实验予以验证,进而推论:对于σ_b和E之间呈“正比”或“单调”关系的材料都可用声振动法(或其他测E方法)来无损检测其强度。     

在线声速测量中阵发性气泡影响的消除方法

我们利用气泡比重轻的重点，采用机械装置先使绝大部分的气泡不通过超声测试区。然后对进入测试区的气泡，利用有气泡时衰减会增加和声时会突变的原理，通过计算机软件判断接收波的幅度是否过小，和声时有无突变，有效地排除了阵发性气泡对声速测量的影响。     

提高测量声时精度的“过零检测数字平均法”

本文介绍了一种新颖的脉冲回波技术，它是用过零点测回波间的声时间隔，并 将时间间隔内的时标计数值作多次平均，这样得到的声时测量精度可达毫微秒水平 ，甚至更高。而且这种方法非常适合于测量连续变化的声时，具有很强的抗干扰能 力，在工业量超声检测方面有广阔的应用前景。     

非线性声参量B/A和声速与物质结构的关系研究

本文用我们改进的热力学方法，在温度２０℃和５ＭＨＺ的频率下，测量了三类有机液的同分异构体──正丙醇、异丙醇；正丁醇、异丁醇、叔丁醇；正戊醇、异戊醇、仲戊醇、叔戊醇的非线性声参量Ｂ／Ａ。旨在直接探讨物质结构的变化与非线性声参量的关系。实验结果表明：物质结构对Ｂ／Ａ的影响确实存在的。这对于医学超声的临床应具有重要实际意义。     

声激励共振法测量微机械材料的杨氏模量

微机械材料的杨氏模量测量是随着微机械构件的产生而提出的一项新技术。文章综述了已有的测量微机械材料杨氏模量的方法。提出了用声激励共振法来测量微机械材料的杨氏模量。这种方法具有测试装置简单、测量容易、精度高等特点。     

高静水压下障板样品声特性的计算与测量

为研制一种在声呐水下声系统中起到屏蔽噪声、提高声基阵空间增益作用的耐压、低频、宽带声障板,设计了声管样品,根据分层介质中的声传播理论,利用多层均匀结构的传递矩阵法计算了它在空气和水介质背衬下的声压反射系数和透射系数,在不同的背衬情况下具有明显不同的声学特性。制备了直径206mm的样品,利用杭州应用声学研究所水声驻波管和行波管测量系统测量了频率范围100Hz～4kHz、静水压范围从常压到2MPa的声学性能,测量结果和理论计算值基本吻合,声障板样品在静水压状态下具有一定的低频、宽带反声特性。     

自由场中采用短时信号分析法的声脉冲叠加法测量反射系数

本文叙述了在自由场有限尺寸平板样品的反射系数测量中降低测试频率的新方法。在声脉冲叠加法基础上引入了短时信号分析法和发射器瞬态抑制法,使平板有效测试频段比经典的声脉冲响应法向低频延伸一个倍频程。本文给出了在铝板反射系数测量中用短时信号分析的结果,在有效测试频段内与理论值相比,误差小于10％。     

Model-based phase velocity and attenuation estimation in wideband ultrasonic measurement systems

A parametric method to estimate frequency-dependent phase velocity and attenuation is presented in this paper. The parametric method is compared with standard nonparametric Fourier analysis techniques using numerical simulations as well as real pulse-echo experiments. Approximate standard deviations are derived for both methods and validated with numerical simulations. Compared to standard Fourier analysis, the parametric model gives considerably lower variance when estimating attenuation and phase velocity. In contrast to nonparametric techniques, the proposed estimator avoids the phase unwrapping problem because analytical expressions for the continuous phase velocity and attenuation can be derived.     

Errors and uncertainties in the measurement of ultrasonic wave attenuation and phase velocity

This paper presents an analysis of the error generation mechanisms that affect the accuracy of measurements of ultrasonic wave attenuation coefficient and phase velocity as functions of frequency. In the first stage of the analysis we show that electronic system noise, expressed in the frequency domain, maps into errors in the attenuation and the phase velocity spectra in a highly nonlinear way; the condition for minimum error is when the total measured attenuation is around 1 Neper. The maximum measurable total attenuation has a practical limit of around 6 Nepers and the minimum measurable value is around 0.1 Neper. In the second part of the paper we consider electronic noise as the primary source of measurement error; errors in attenuation result from additive noise whereas errors in phase velocity result from both additive noise and system timing jitter. Quantization noise can be neglected if the amplitude of the additive noise is comparable with the quantization step, and coherent averaging is employed. Experimental results are presented which confirm the relationship between electronic noise and measurement errors. The analytical technique is applicable to the design of ultrasonic spectrometers, formal assessment of the accuracy of ultrasonic measurements, and the optimization of signal processing procedures to achieve a specified accuracy.     

Ultrasonic velocity and attenuation in glass

Ultrasonic velocity and attenuation in glasses exhibit anomalous properties and the current theory most successful in explaining these anomalous properties in the high temperature range has been presented. The model considers that the disorder inherent in amorphous network results in a double well potential corresponding to two equilibrium configurations and a particle is ascribed to move in the double-well potential. Acoustic behaviours in glasses have been interpreted in terms of a thermally activated relaxation process. Improvement of this basic model has also been discussed. Mention has also been made of some behaviours at high temperature that need further research for convincing explanation.     

Application of ultrasonic velocity measurement for flow stress determination of TWIP steel

Abstract

In the present work, the ultrasonic velocity measurement was used as a non-destructive technique for flow stress determination of a twinning induced plasticity steel. For this purpose, first, a relationship between mechanical twinning and ultrasonic velocity was found out and then, it was used in the flow stress model previously suggested by the authors. Comparison of the obtained results with the experimental values revealed a good agreement.     

Ultrasonic velocity and attenuation determination by laser-ultrasonics

Materials are often characterized by measuring the velocity and attenuation of ultrasonic waves. Laser-ultrasonics, which uses lasers for generation and detection of ultrasound, has several advantages compared to the classical piezoelectric techniques, but the use of lasers is often associated with ill-defined source and receiver characteristics making diffraction effects hard to evaluate. We have identified two regimes which, in practice, allow the measurement of velocity and attenuation: the point source/point receiver and the large uniform source/large uniform receiver regimes. These approaches are discussed and illustrated with several examples of application. Limitations caused by misalignment between the generating and detecting laser spots are also analyzed.     

Ultrasonic attenuation and sound velocity of the excitonic state

Ultrasonic attenuation and sound velocity of a metal in the excitonic state are investigated theoretically in the limitq1 1 and/T _c 1, whereq is the sound-wave vector,1 is the electron mean-free path, is the phonon energy, andT _c is the transition temperature of the excitonic state. The attenuation coefficient of the longitudinal wave increases drastically upon entrance into the excitonic state, then passes a maximum and decreases exponentially as temperature tends to 0 K. The attenuation coefficient of the transverse wave, on the other hand, is described in terms of the electric conductivity in the limitq1 1 and generally increases in the excitonic state. Furthermore, we find that the sound velocity of the longitudinal wave increases rapidly in the excitonic state, which is a simple manifestation of the anomaly of the dielectric function in the excitonic state.     

未胶结砂的声波速度测量

1　引　言在利用声波进行海底勘探和地面勘探以及桩基评价中 ,不可避免的遇到未胶结细砂这种声学介质。因此研究这种介质的声传播特性是很有意义的。本文介绍了用声波透射法测量未胶结细砂的群速度和相速度的方法和测量结果。图 1　测量装置示意图( a)潮湿砂( b)水饱和砂2　发射和接收探头之间的距离为不同数值时测得的波形3mm。盛放砂子的容器为带夹层的保温桶 ,其内径为2 4 1.3mm,深度约为 50 0 mm。3　实验结果及分析在实验中 ,使发收探头之间的距离的变化范围为 4 5mm - 345mm ,每隔 50 mm进行一次测量 .得到一道波形。图 2 (a)和图 2 (…     

Experimental determination of contraction coefficient and velocity coefficient for radial gates with elliptical lips

Radial gates are widely used to control the flow in irrigation channels and spillways. Radial gates require lower hoisting force and have better discharge characteristics in partial gate openings. The accurate discharge measurement through a radial gate is a challenging problem especially in submerged flow conditions. The coefficient of contraction \( C_{c} \) is an important parameter for accurate discharge measurement in open channels. In this study, an attempt has been made to determine the coefficient of contraction\( C_{c} \) and velocity coefficient \( C_{v} \) for radial gates both for free flow and submerged flow conditions. The flow emanating from a gate is similar to the wall jet emerging from a nozzle. The \( C_{c} \) and \( C_{v} \) values under free and submerged flow conditions are obtained from the measured jet velocity and the discharge. The coefficient of discharge values under submerged flow conditions show large variations with submergence and hence discharge characteristics needs to be improved for better control of flow. Hence, experiments are conducted so as to improve the discharge characteristics by modifying the exit geometry of the radial gate by attaching a quarter of an elliptical lip. Three different geometries of elliptical lips were attempted and the results show reasonable increase in the contraction coefficient.