Modeling Ultrasonic Pulse-Echo Signals from a Flat-Bottom Hole in Immersion Testing Using a Multi-Gaussian Beam

This paper proposes an ultrasonic measurement model that can predict the pulse-echo signals from a flat-bottom hole in an isotropic, homogeneous solid specimen immersed in water in a computationally efficient manner. To develop such a model, a measurement model approach is adopted based on two important assumptions: the paraxial approximation for the transducer beam and the small flaw assumption for the flat-bottom hole. The modular model that results from these two assumptions contains three terms: a diffraction correction term, a far-field scattering amplitude term and a system efficiency factor term. The diffraction correction is defined based on a multi-Gaussian beam model which allows the rapid evaluation of the wave field incident on the hole. The far-field scattering amplitude of the flat-bottom hole is obtained using the Kirchhoff approximation together with the small flaw assumption. The system efficiency factor is determined by deconvolution of an experimental front surface reflection signal by a reference reflector model. Here, the contribution of each of these three terms to the overall measurement model are described in detail and the accuracy of the proposed model is verified by the comparison of the model-based predictions to experiments.     

An Ultrasonic Angle Beam Method for in situ Sizing of Fastener Hole Cracks

Ultrasonic testing is generally recognized as being the preferred nondestructive evaluation (NDE) method for measuring the size of cracks in metals, particularly when access is restricted. Using ultrasonic methods for structural health monitoring imposes the requirement of fixed transducers, which limits the articulation of transducers that is common for NDE. Here we consider the specific problem of in situ sizing of fatigue cracks emanating from fastener holes in aluminum structural components. A dual angle beam through transmission technique is employed whereby the regions of expected crack initiation are interrogated with vertically polarized shear waves. Fatigue cracks partially block the leaky creeping wave spiralling around the hole, and thus reduce the energy of the received signal. The reduction in received energy is directly related to the extent and shape of any open cracks, and this energy is modulated by the applied load as the cracks open and close. The ratio of energy received from the specimen under load to that received under no load is monitored, and this ratio is empirically related to the total crack area. A model is developed to explain this relationship for known crack shapes by assuming an ultrasonic energy profile in the plane of the crack. Data calculated from the model show very good agreement with the experimental results.     

超声体模的日常维护保养

本文就在实际工作中实际情况,对超声体模的日常维护保养提出自己的观点。     

Detection of Fibre Waviness Using Ultrasonic Array Scattering Data

Composite materials owe their success to the ability to favour mechanical properties in specific directions whilst minimising the weight of components. Although the composite manufacturing process has been progressively improved, subtle defects such as fibre waviness are still commonplace. Any localised departure of a ply from the desired lay-up direction is known to adversely affect strength. Therefore, manufacturers and end users are interested in detecting defects such as fibre waviness at various stages during prototyping and as part of the manufacturing process. In this paper, an ultrasonic array is used to both image the composite and extract information that characterises the scattering of the interior structure. The scattering information is encoded in the scattering matrix: defined as the far field amplitude of scattered signals from a defect as a function of the incident and scattering angles. A method for extracting the scattering matrix from experimental array data over a spatially localised region is presented. Ultimately this could lead to the ability to map the distribution of scattering behaviour within the composite. The method is demonstrated on composite samples containing various levels of waviness. It is also shown that use of the differences in the scattering matrices can offer the possibility to statistically differentiate wavinesses of different nature and severity.     

颗粒超声层析成像的散射特征分析

用数值方法对颗粒超声层析成像进行模拟研究,对单个球形颗粒散射特征的数值解与解析解作对比,验证数值方法的准确性、可靠性,进而对管内放置有单个和3个球形颗粒的散射声场特性进行的数值模拟和分析,并由二值逻辑反投影图像重建算法对其进行空间分布的重建,分析重建图像的误差。结果表明:基于边界元方法的数值模拟和重建方法是可行和有效的。     

Ultrasonic Attenuation Due to Grain Boundary Scattering in Pure Niobium

Experimental confirmation of various grain scattering theories exist but there are still outstanding questions concerning the characterization of microstructure using ultrasound. In this study, high purity niobium serves as a model material devoid of extrinsic scattering centers (e.g., voids, precipitates, second phase particles etc.) A range of microstructures were obtained by annealing in ultrahigh vacuum at different temperatures (600–800°C) after routine cold-rolling and recrystallization heat treatment. Ultrasonic attenuation is measured as a function of a frequency for each sample. For the samples with an intermediate grain size (typically ∼50 μm), attenuation follows a power law dependence on frequency with an exponent of n∼1.6, which is close to the prediction, n=2, of classical Stochastic scattering theory. However, quantitative comparison shows that the observed attenuation is higher than predicted by the classical theory. The Stanke-Kino unified grain scattering theory may provide an explanation for the lower frequency dependence than traditional theories predict, though it still under predicts the magnitude of the attenuation. In any event, the resulting empirical relations provide a useful approach for practical grain size measurement with an acceptable level of uncertainty. The effect of a layered microstructure typical of some sheets/plates is discussed.     

A Model for Non-Rayleigh Scattering Statistics

The independent-scatterer K -distribution model, which has been introduced to describe a variety of scattering situations, is extended to include the effects of correlation between scatterers and finite illumination size. A model in which the array of scatterers is represented by a Γ -lorentzian cross-section fluctuation is proposed. In the appropriate limits this reduces to the independent K -distribution model. Following scattering by the Γ -lorentzian surface, the autocorrelation function and moments of the detected intensity for radiation of arbitrary beamwidth and wavefront curvature are derived. The results are compared with the predictions of the independent K -distribution model and the implications of the differences, which reflect the fact that the independent model cannot represent spatial averaging over the correlations within the surface, are discussed.     

Ultrasonic Wave Scattering by a Line Crack in a Solder Joint

A numerical procedure for the solution of a wave propagation problem in a solder joint with a line crack in its base layer is presented. The two-dimensional ``in-plane' wave propagation problem for a finite, multilayered body with a line crack in one of the layers is solved by the combined usage of the displacement and the traction BIEM. The discretization of the boundary with parabolic elements far from the crack edge and with quarter-point crack-tip boundary elements containing the correct behavior for displacement variations at the crack edge is used. Numerical results for a solder joint with real geometry and physical properties are presented. The relations between the wave scattering problems, the solder joint fatigue state estimation, and the reliability and quality of electronic packages is discussed.     

Ultrasonic Wave Scattering by a Line Crack in a Solder Joint

Abstract

A numerical procedure for the solution of a wave propagation problem in a solder joint with a line crack in its base layer is presented. The two-dimensional “in-plane” wave propagation problem for a finite, multilayered body with a line crack in one of the layers is solved by the combined usage of the displacement and the traction BIEM. The discretization of the boundary with parabolic elements far from the crack edge and with quarter-point crack-tip boundary elements containing the correct O() behavior for displacement variations at the crack edge is used. Numerical results for a solder joint with real geometry and physical properties are presented. The relations between the wave scattering problems, the solder joint fatigue state estimation, and the reliability and quality of electronic packages is discussed.     

Experimental Investigation into the Hole Quality in Ultrasonic Machining of WC-Co Composite

This study has focused on the evaluation of the influence of different input variables (cobalt content, thickness of workpiece, tool profile, tool material, size of abrasive grains, and power rating) on the hole quality (dimensional and form accuracy) obtained in ultrasonic machining of WC-Co composite material. Taguchi's approach has been employed for planning the experiments and optimization of the experimental results. Three measures of hole quality (hole oversize, out of roundness, and conicity) have been investigated under controlled experimental conditions. The experimental results showed that abrasive grit size and power rating were most influential for the hole quality. Hole quality has been found to be improved at higher cobalt content, whereas it is found to be degraded with the use of coarse grit size.     

Ultrasonic Propagation and Scattering in Duplex Microstructures with Application to Titanium Alloys

A general model for elongated duplex microstructures is proposed for modeling scattering-induced ultrasonic longitudinal attenuation in hexagonal polycrystals for application to titanium alloys. The material system consists of microtextured regions (MTRs) which are formed by much smaller ?? crystallites with preferred orientations. Their preferred orientation is represented by a modified Gaussian orientation distribution function. Scattering induced by MTRs and by crystallites is added to obtain ultrasonic attenuation in the medium. The effective elastic properties of MTRs are determined and used to obtain the scattering-induced MTR attenuation and backscattering. Crystallite attenuation is estimated by the untextured attenuation coefficient factored by a texture transition function. The total attenuation is obtained by combining solutions for microtextured region attenuation and crystallite attenuation. Spectroscopic attenuation and backscattering measurements are performed on a forged sample of titanium alloy. Reasonable agreement is found between experiment and the model predictions with a given texture parameter.     

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。     

基于变窗口函数的仿人体组织材料超声散射信号处理研究

基于仿人体组织材料超声散射成像,提出了一种变窗口函数算法。该算法首先对散射信号进行阈值变换处理,再进行窗口漏检调和,最后对信号进行量化成像。实验表明该技术能够使图像有效区域与噪声明显区别开来,满足后期边缘提取及三维重建要求。     

Damage-Free Hole Making in Fiber-Reinforced Composites: An Innovative Tool Design Approach

Drilling is an inevitable machining technique that facilitates the assembly of composite parts. Drilling with the traditional tools causes significant damage to the composite parts. The forces that are produced during drilling are mostly accountable for the damage or rejection of the parts. Therefore, the main aim of the present investigation is to reduce the forces and subsequent damage that is induced during drilling operation. Thus, new tool geometry has been conceptualized, designed, developed, and implemented to investigate the drilling behavior of sisal-epoxy and nettle-epoxy laminates. A comparative analysis has been made to compare the performance of the developed tool with the widely used twist drill. The performance has been compared based on the forces and associated drilling-induced damage. It was found that the developed tool geometry gives better results than the traditional twist drill in terms of minimization of forces and damage as well.     

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.     

Measurement Models and Scattering Models for Predicting the Ultrasonic Pulse-Echo Response From Side-Drilled Holes

A side-drilled hole (SDH) is a commonly used reference reflector in ultrasonic nondestructive evaluation. In this paper, we will develop reciprocity-based measurement models along with scattering models that allow us to predict the ultrasonic response from a SDH in a pulse-echo immersion setup. Two measurement models will be derived, one suitable for large SDHs where variations of the incident fields over the cross section area of the SDH are considered, and a second model which neglects those variations. Two scattering models are also used along with these measurement models. These include an explicit model based on the Kirchhoff approximation, as well as an exact model obtained using the separation of variables method. Examples of the model-based received waveforms and peak-to-peak voltage responses are presented for a number of SDHs of different sizes and compared with experimentally determined SDH responses.     

AZO与ITO薄膜电磁散射特性对比试验研究

基于非平衡磁控溅射技术在浮法玻璃表面沉积了系列掺铝氧化锌 (AZO) 和氧化铟锡 (ITO) 薄膜, 从电磁隐身角度出发, 确定了两种薄膜的电磁散射测试方法和分析方法, 并测试了10、15 GHz的HH、VV的极化雷达散射截面 (RCS) 曲线, 以试验数据为基础, 研究了方块电阻对两种薄膜电磁散射的影响特性。试验结果表明, AZO与ITO散射曲线具有相似性, AZO散射曲线震荡性更明显;两种薄膜RCS增益随着方块电阻的增大而变小, AZO和ITO的RCS增益曲线均震荡性降低;方块电阻合适时, 两种薄膜均可实现座舱玻璃隐身。     

Microscopic Structure in Liquid Hydrogen and Deuterium: An X-Ray Scattering Study

The static structure factors S(Q) of liquid normal H₂ and D₂ have been measured in the wave-vector region 5 nm^–1<Q<30 nm^–1 through X-ray scattering using two independent sets of data. While the first set has been derived using a standard liquid diffraction geometry, the second has been worked out integrating the dynamic structure factors S(Q, ), measured through inelastic X-ray scattering spectroscopy. In the latter case the first spectral-moment sum rule has been used to obtain directly absolute static structure factor values. A comparison with quantum and classical Monte Carlo simulations shows that a quantitative agreement with the experimental data for both H₂ and D₂ can be obtained only if quantum effects are properly taken into account.     

RLC Ladder Model for Scattering in Single Metallic Nanoparticles

In this paper, we present a new modeling technique for plasmon-based metallic nanoparticles under the influence of an electromagnetic field. The model approximates the coefficients of the admittance rational function. The proposed model utilizes spherical wave functions to describe the field and it provides an equivalent ladder-form RLC realization. Simulation results show that our model matches very closely with the exact solution. Our newly developed model can be used as a basic building block to develop an equivalent circuit model for metallic nanoparticle-based plasmonic waveguides.