Modeling the Response of Ultrasonic Reference Reflectors

Reference reflectors characterized as flat-bottom hole (FBH), side-drilled hole (SDH), and spherical void (SPH) are commonly used in ultrasonic nondestructive evaluation (NDE) for calibration purposes. Here the measurement models currently available to simulate the A-scan response from those types of reference reflectors are examined. Measurement models suitable for both large and small reflectors are described and used to study the effect of beam variations over the surface of the reflector. The adequacy of the Kirchhoff approximation for predicting the waves scattered by these reference reflectors is also studied by comparing the results of that approximation to those obtained from more exact scattering solutions. The waveforms predicted by these various models are compared with experimentally determined responses in a pulse-echo immersion setup, and the accuracy of the models is discussed.     

Grain Size Measurement of Copper Spot Welding Caps Via Ultrasonic Attenuation and Scattering Experiments

During ultrasonic testing of resistance spot welds in real time, the probe sends the sound waves through the thickness of the copper electrode cap into the materials being welded. Characteristics of the reflected waves from the weld interfaces allow a reliable decision to be made on the quality of the joint. Transmission of high frequency sound waves through the relatively thick copper welding cap cause the signal to be greatly attenuated due to grain scattering. For this reason, close monitoring of the copper cap properties prior to installation is essential for adequate performance. Finding copper alloys with a small average grain size is essential in order to minimize the attenuating effects. The conducted backscatter and attenuation experiments indicate correlation between the ultrasonically measured parameters and the optically found copper grain size. This correlation suggests that the attenuation or backscatter technique could be used alone in order to validate the proper copper alloy to be used in spot weld probes. Using nondestructive testing techniques for this purpose greatly reduces the time and cost involved compared to optical techniques.     

激光位移传感器实时测量超声波振幅和频率的试验研究

超声波振动技术已经广泛应用于各类生产加工行业.但是,目前为止有关超声波振动实时监测方面的研究鲜有报道.本文提出了一种可行的实验方法对超声振动进行实时监测.超声波的振动由超声波发生器及其传递装置产生;通过使用世界领先的超高速、高精度电容耦合装置激光位移传感器对超声波振动进行实时跟踪和测量;所测振动数据由计算机存储并且开发了一系列Matlab程序进而从原始数据中滤除噪声对超声波振动数据的干扰.结果显示:通过这一实验方法能够对超声波振动频率和周期进行精确评估,尤其是能够对超声波振幅进行精确测量,其测量精度可达到±0.1μm.超声波功率对超声波振幅的影响也可以通过这一实验方法显著呈现.     

超声波散射式颗粒测量及其测量结果单值性的分析

提出了一种超声波散射式颗粒测量方法,论述了该技术应用的理论基础,并在详细分析其测量原理基础上,指出了在单频率换能器和单散射角下进行颗粒测量时存在着测量结果多值性的可能。给出了解决这一关键技术问题所采取的可能方案和措施。     

Measurement of Dynamically Changing Thermal Diffusivity by the Forced Rayleigh Scattering Method (Measurement of Gelation Process)

A measuring method of the thermal diffusivity with high temporal and spatial resolutions has been studied. The forced Rayleigh scattering method is an optical technique to measure the thermal diffusivity of solids and liquids. Based on its characteristics, this method has the applicability to become a thermal diffusivity real-time monitoring system. The maximum repetition rate of thermal diffusivity measurement is determined by the attenuation of an excited temperature distribution by laser heating, and a mathematical model of three-dimensional heat conduction is constructed. The temporal resolution of continuous measurements was improved to about 1 s, and the sol-gel transition of a gellan gum aqueous solution was studied to check the validity of the dynamic measurement of thermal diffusivity. Through the gelation process, the dynamical change of the thermal diffusivity was measured, and the gelation point of the solution was identified from a series of thermal diffusivity data. The results indicate the capability of the forced Rayleigh scattering method to be a real-time thermal diffusivity measurement technique for monitoring the rapidly changing process of a material.     

单声道超声水表测量特性分段校正方法的研究

当管道内流体处于不同雷诺数测量条件时,超声水表的线平均流速v_L与面平均流速v_S之间存在着显著的非线性。根据管道内被测流体介质流动分布状态不同,提出了一种分段流量测量特性校正新方法,在其临界处设立校正分界点,当层流时,采用常系数校正;湍流与过渡流时,分别采用拟合直线方程校正。经实验验证,该方法是可行的。     

同时测量粒子尺寸和速度的激光散射系统

提出了同时测量粒子尺寸和速度的三光束激光散射系统，叙述了系统的组成、测量原理、以及信号采集和数据处理。并给出了应用本系统对电动喷枪喷雾水滴的尺寸和速度分布的同时测量结果。     

应用声波测试技术分析开挖爆破对边坡的影响

随着高陡边坡开挖在铁路、公路、水电站等国家基础建设中的大量运用,如何最大限度地减小爆破振动对边坡的影响,提高边坡的稳定性,已成为一个不容忽视的难题.探讨了声波测试技术在边坡开挖中的作用;将声波测试应用于某水电站边坡开挖过程分析,在炮前、炮后和再炮后分别对测区进行了测试,由测试数据绘出爆破前后声速 VP(m/s) 与孔深 h(m) 关系曲线图,并通过分析得出了一系列结论,用以指导爆破施工.     

3种典型面心立方金属的超声物态方程比较研究

旨在通过对各种解析物态方程的对比研究,试图寻找一种可以利用较低压力下的超声测量数据建立在较宽广的压力范围内适用于简单面心立方金属的等温物态方程模型。对于Al、Cu、Ag3种面心立方金属,结合实测DAC实验数据对比研究了基于较低压力下的超声测量数据计算的各种解析状态方程适用的压力范围,发现目前尚不存在一种完全适用于材料从低压段到极高压力区的物态方程模型,而从较低压力下得到的超声测量数据出发,选取Vinet等温物态方程模型,可以在相当高的压力范围内(对铝约200GPa,对于铜和银约100GPa)很好地描述几种面心立方金属的压缩性。     

基于收缩流动的气体超声流量计声道稀疏化及测量方法

为了提高低声道数超声流量计的准确度水平,在传统超声流量计的基础上设计了一种具有收缩流动结构的低声道数超声流量计。采用数值模拟研究了渐缩管中收缩流动的流场特征,确定了渐缩管的几何参数及超声探头的安装方式。通过空气实流实验,研究了单声道及双声道在收缩流动条件下流量计量的基本特性。在流量范围27~432m3/h,管径范围100~150mm进行了实验验证。结果表明:收缩流动的数值模拟结果与理论模型相吻合,当渐缩管的收缩比由2增大为6,被测流场均匀区占比显著增大;当收缩比固定不变时,随着流量的增大,边界层厚度显著降低。通过实流实验比较不同结构和配置超声流量计的测量结果,发现单声道收缩管超声流量计的准确度水平显著优于传统单声道气体超声流量计,与传统双声道气体超声流量计的准确度水平相当。