基于超声谱分析的颗粒粒度测量研究

为验证不同超声谱测量和分析方式对颗粒粒度测试的影响,设计了一种非侵入式超声波透射和多次反射信号同步测量实验装置。采用脉冲回波法、反射比样法和透射法分别对体积分数为1%~4%的聚苯乙烯-水悬浮液进行实验,结合理论模型,分析超声波在颗粒两相体系中的衰减谱、相速度谱和阻抗谱。以ECAH模型为理论基础,结合ORT反演算法,对不同超声谱进行反演获得了聚苯乙烯样品颗粒粒径分布。将上述结果与图像法对比,颗粒中位径结果偏差均在15%之内,3种谱分析的粒径分布也较为吻合。     

生物延迟发光双曲线衰减方程的修正

本文对生物超微弱发光进行了简介,将延迟发光衰减的理论方程与实际得到实验数据进行比较,推导出延迟发光的双曲线衰减方程形式,并对双曲线方程进行修正,得到了延迟发光“1／P”参数随时间变化的结论;并初步探讨了延迟发光衰减与1／P参数之间的关系。     

饮用水中总α、β-样品源存放测量的异常变化

本文介绍对测量水中总α、β-放射性活性度变化的现状。在测量样品源过程中总α放射性的活度(Bq／L),开始测量的数值偏高或超标,后经过存放一段时间再进行测量,发现其数值逐渐下降,甚至不超标,这说明测量样品源与存放时间有关系。     

饮用水中总α、β-样品源存放测量的异常变化

本文介绍对测量水中总α、β-放射性活性度变化的现状.在测量样品源过程中总α放射性的活度(Bq/L),开始测量的数值偏高或超标,后经过存放一段时间再进行测量,发现其数值逐渐下降,甚至不超标,这说明测量样品源与存放时间有关系.     

饮用水中总α、β-样品源存放测量的异常变化

本文介绍对测量水中总α、β-放射性活性度变化的现状。在测量样品源过程中总α放射性的活度(Bq/ L),开始测量的数值偏高或超标,后经过存放一段时间再进行测量,发现其数值逐渐下降,甚至不超标,这说明测量样品源与存放时间有关系。     

现代超声工业测量的若干发展

超声波在工业测量领域中的可用性非常广。目前，由于现代电子技术与微机技术的飞速发展；这种可用性得到愈来愈多的体现。本文简要介绍了超声波技术在若干方面的研究进展，其中包括：高精度声速测量，材料应力测量，化工过程检测及超声谱分析技术。     

超声造影剂衰减系数随时间变化特性研究

为了研究微泡型超声造影剂对声传播衰减的影响,基于气泡动力学理论模型计算微观粒径变化引起的声传播衰减,推导出超声造影剂衰减系数随时间变化的解析表达式,并构建了实验系统,对超声造影剂的衰减系数进行测量。实验结果验证了理论模型的有效性,以及超声造影剂衰减系数随时间变化呈现出指数衰减规律。该研究为减小超声波的传播衰减和畸变提供了依据,使得超声造影剂有效地应用于超声医学领域。     

超声谱法在颗粒两相流测量中的应用进展

颗粒两相流测量技术指对连续相中的颗粒粒度和浓度等参数进行测量,是两相流测量中非常重要的分支。它与化工、能源、动力、材料、食品等诸多行业都有着密切联系,随着近年来工业的高速发展,颗粒两相流测量技术获得越来越多关注。结合近几年超声谱法在颗粒测量中的研究现状,重点回顾超声谱法颗粒两相流测量技术的应用进展状况,并分析其发展前景。     

碳纳米管声学桥的分析

首先阐述了碳纳米管声学桥的这一新概念,即通过共振超声谱方法测量置放在两个微型压电换能器之间的碳纳米管的多个固有频率,确定其物理特性.作为碳纳米管声学桥的理论基础,文中应用解析方法和有限元数值方法分析了碳纳米管声学桥的声波传播特性,重点研究了碳纳米管声学桥结构尺寸与振动模式的品质因数之间的关系.在此基础上,探讨了声学桥的三个潜在应用场合:作为研究碳纳米管材料特性的有力工具;碳纳米管声学桥对微小质量变化具有10-220g/Hz的灵敏度,可作为高精度质量敏感元件;碳纳米管声学桥在周围环境真空压力改变时,谐振频率会变化,通过测量频移来确定真空压力,故碳纳米管声学桥可作为超高真空传感器.     

Al—Cu合金在拉压循环过程中的超声衰减

测量了Ａｌ０．０２１ｗｔ－％Ｃｕ在拉压过程中的超声衰减的变化，结果与其他研究者的不同，并用位错的弓出，缩回与滑移予以解释。     

Nondestructive Porosity Assessment of CFRP Composites with Spectral Analysis of Backscattered Laser-Induced Ultrasonic Pulses

The laser-ultrasonic method for nondestructive quantitative local porosity assessment for CFRP composites is proposed and realized experimentally for only one available flat surface of a specimen or a product. This method combines the laser thermoelastic generation and the high-sensitivity piezoelectric detection of broadband pulses of longitudinal ultrasonic waves and does not require the detection of the backwall echo ultrasonic signal. The generation and the detection of ultrasonic pulses is carried out with the specially designed laser-ultrasonic transducer, which allows one to obtain both the temporal profile and the frequency spectrum of a part of the ultrasonic signal backscattered by gas voids in a composite specimen. The frequency spectrum of backscattered ultrasonic pulses is analyzed for three sets of CFRP specimens with different epoxy matrix fractions and porosity. The empirical relation between porosity of CFRP specimens and the spectral power (structural noise power) of ultrasonic signals backscattered by voids is obtained for porosity values up to 0.15. This relation allows one to evaluate the local porosity from measured structural noise power both for CFRP specimens and products fabricated from the same composite material. The proposed laser-ultrasonic setup demonstrates a basis for a system of CFRP porosity assessment in field conditions. It can be very useful especially for nondestructive detection of structural changes of composite materials that will allow evaluation of products during their life time.     

Surface roughness evaluation via ultrasonic scanning

Despite extensive applications of ultrasonic waves to various nondestructive testing and evaluation of materials, scattering of focused ultrasonic waves due to surface roughness has not been fully investigated. This paper presents an analytical and experimental evaluation of surface roughness measurement using focused ultrasonic beams. The characteristics of focused ultrasonic waves are analyzed by using the impulse response method with a sine-modulated Gaussian pulse as source. First, the beam profile in the focal plane of the focused ultrasonic transducer is analyzed both numerically and experimentally. Second, peak amplitude distribution and reflected waveforms from a flat surface with various incident angles are analytically generated and compared with experimental results. Then, the peak amplitudes of the ultrasonic waves reflected from cusped surfaces which are easily found among machined surfaces are analyzed and compared with experimental data for the first time. The analysis shows good agreement between analytical and experimental results. The excellent correlation between the measurements using a profilometer and the proposed ultrasonic system demonstrates a good potential for surface roughness measurement by ultrasonic sensing.     

Ultrasonic Study of Environmental Damage Initiation and Evolution in Adhesive Joints

This article reports on an experimental study of environmental degradation of adhesive joints by an ultrasonic angle—beam technique. The technique is based on measurements of the frequency response of the reflection of obliquely incident ultrasonic signals from a joint bondline. Ultrasonic measurements were performed using a special ultrasonic goniometer with only one ultrasonic transducer. By this method, the degradation of single lap adhesive joints was studied as a function of exposure in NaCl solutions at 68°C under static tensile load. It was found that joint degradation is accompanied by a shift of the ultrasonic reflection spectrum minimum to a lower frequency. Two stages of adhesive joint environmental degradation can be distinguished: a) a relatively slow adhesive joint degradation dominated by adhesive creep, and b) delamination along the adhesive/adherend interface, leading to failure. Several degradation mechanisms are found in the first stage to affect the position of the spectral minimum. The first is adhesive creep caused by normal-to-bond-plane stress concentration at the joint overlap edges. This mechanism is found to have the dominant effect on the ultrasonic signature. Second, changes of the effective density and elastic moduli of the adhesive layer also affect the spectrum of the reflected signal. The third mechanism is the degradation of the adhesive—adherend interface. In the second stage of the joint degradation process, delamination along the adhesive/adherend interface occurs and is followed by joint failure. While the time span of the first stage changes significantly from joint to joint, the time span of the second stage (failure by delamination) in our conditions is about 30—40 h. The delamination results in a significant additional spectral minimum shift to a lower frequency that can be used as an indicator of failure initiation.     

精密硬态切削过程中已加工表面变质层生成研究

精密硬态切削过程中刀具与工件发生剧烈的热力耦合作用,使得一定条件下已加工表面出现变质层.为揭示变质层的生成机制,研究了PCBN刀具硬态切削淬硬模具钢Cr12MoV的工艺过程.通过实验手段揭示了表面变质层生成机理,得到了不同刀具磨损情况下变质层中白层厚度的变化规律;采用MATLAB数学分析软件构建了已加工表面温度场分布曲线,预测了特定切削条件下变质层中的白层厚度.实验验证结果表明:该模型预测精度较高,可以为精密硬态切削加工过程中工件加工质量的控制提供依据.     

Experimental evaluation of intrinsic and nonstationary ultrasonic Doppler spectral broadening in steady and pulsatile flow loop models

Intrinsic and nonstationary Doppler spectral broadening, and the skewness of the spectral representation, were evaluated experimentally using porcine red cell suspensions as ultrasonic scatterers. Theoretically, the relative Doppler bandwidth, defined as the intrinsic bandwidth divided by the mean Doppler frequency shift, should be velocity independent. The relative Doppler bandwidth invariance theorem was experimentally verified with an in vitro steady laminar blood flow model. It is shown that the relative bandwidth is both independent of the flow velocity and blood hematocrit. Using a pulsatile laminar flow model, the authors demonstrated that the relative Doppler bandwidth invariance theorem did not hold during flow acceleration and deceleration. In addition, a positive skewness of the Doppler spectra was observed during acceleration while a negative skewness was measured during the deceleration of blood. The effect of the window duration used in the Fourier spectral computation, on nonstationary broadening, is characterized.     

Experimental investigations into the ultrasonic assisted jet electrochemical micro-drilling process

The present article deals with fabrication of ultrasonic assisted jet electrochemical micro-drilling process setup, a special nozzle assembly to pass the ultrasonic vibrations in the electrolyte jet and a work-piece fixture. A detailed experimental study of the newly developed process has been carried out. Effects of process parameters like voltage, inter-electrode gap, electrolyte concentration, electrolyte pressure and pulse on time of ultrasonic vibrations have been studied on process responses, namely, MRR and hole taper. From the results obtained after experimentation, it was observed that MRR improved with an rise in pulse on time of ultrasonic vibrations whereas the hole taper decreased with the rise in pulse on time. It was concluded that combining ultrasonic vibrations with the Jet-ECMD resulted in an enhancement of the process capabilities in terms of improvement of MRR and reduction in the hole taper.     

Theoretical analysis of ultrasonic vibration spectra from multiple particle-plate impacts

Many industrial processes involve particles in a carrier fluid, and it is often of interest to monitor the size of these particles noninvasively. The aim of this paper is to develop a theoretical model of multiple particle-wall impact vibrations that can be used to recover the particle size from experimental data. These vibrations have been measured by an ultrasonic transducer attached to the exterior of a vessel containing a stirred-particle-laden fluid. A linear systems model is derived for the response of the piezoelectric ultrasonic transducer, which has a single matching layer. The acceleration power spectrum of these vibrations has been shown experimentally to contain information on the size of the impacting particle. In particular, the frequency of the main spectral lobe is inversely proportional to the particle size. We present a theoretical model that agrees with this empirically observed phenomenon. The theoretical model is then used to simulate multiple particle-wall impacts, with each particle impacting at a randomly chosen location. A set of theoretical vibration spectra arising from multiple particle-wall impacts are integrated and compared with the experimental data. The ability of this approach to distinguish between different particle sizes is clearly shown.     

Characterization of Structural Noise Patterns and Echo Separation in the Time-Frequency Plane for Austenitic Stainless Steels

The aim of this study is to characterize the structural noise for a better flaw detection in heterogeneous materials (steels, weld, composites...) using ultrasonic waves. For this purpose, the continuous wavelet transform is applied to ultrasonic A-scan signals acquired using an ultrasonic non destructive testing (NDT) device. The time-scale representation provided, which highlights the temporal evolution of the spectral content of the A-scan signals, is relevant but can lead to misinterpretation. The problem is to identify if each pattern from the wavelet representation is due to the structural noise or the flaw. To solve this problem, a detection technique based on statistical significance testing in the time-scale plane is used. Information about the structural noise signals is injected into the decision process using an autoregressive model, which seems relevant according to the spectral content of the signal. The approach is tested on experimental signals, obtained by ultrasonic NDT of metallic materials (austenitic stainless steel) then on a weld in this steel and indeed enables to distinguish the components of the signal as flaw echoes, which differ from the structural noise.     

Filler–matrix debonding in glass bead-filled polystyrene

The debonding process in a glassy polymer filled with glass beads during constant strain rate tensile loading has been analysed both theoretically and experimentally. A model which combines concepts of damage mechanics and the time dependence of interfacial strength has been proposed and compared with experimental results on glass bead-filled polystyrene. The stress–strain behaviour and the debonding could be modelled using a Bartenev-type relation for the destruction of the interfacial bond and by considering the gradual transformation on the initially well-bonded composite into foam. A good agreement between calculated and experimental data was achieved. This revised version was published online in November 2006 with corrections to the Cover Date.     

用吹气法研究脱脂乳粉的结块特性

为了研究脱脂乳粉的结块特性,建立了一套测试粉体结块特性的吹气动力学实验装置,对脱脂乳粉和混合添加剂的脱脂乳粉的结块特性进行了实验研究,应用非晶态粉体玻璃化转变理论分析实验数据,确定脱脂乳粉结块的影响因素和结块特征。正交实验及方差分析结果表明,相对湿度和温度是影响脱脂乳粉的两个主要因素;得到了相对湿度、温度、时间,以及添加剂种类及用量对脱脂乳粉结块指数的影响规律。