冷挤压变壁厚药筒件的超声兰姆波探伤

详细介绍了超声兰姆波的主要特点和多种传播模式,通过对小口径弹药筒壁厚尺寸与缺陷的分析和兰姆波特征曲线的求解,选择合理的药筒兰姆波探伤模式。采用3种标准伤样件验证了药筒管壁内、外表面探伤灵敏度的变化规律,内外表面探伤灵敏度差异,以及探伤灵敏度与标准伤刻痕深度的关系,论证了超声兰姆波单模式探伤的可行性和模式选择。     

Guided wave nuances for ultrasonic nondestructive evaluation

Recent developments in guided wave generation, reception, and mode control show that increased penetration power and sensitivity are possible. A tone burst function generator and appropriate signal processing are generally used. Variable angle beam and comb-type transducers are the key to this effort. Problems in tubing, piping, hidden corrosion detection in aging aircraft, adhesive and diffusion bonding, and ice detection are discussed. Additionally, sample configurations, inspection objectives, and logic are being developed for such sample problems as defect detection and analysis in lap splice joints, tear straps, cracks in a second layer, hidden corrosion in multiple layers, cracks from rivet holes, transverse cracking in a beam, and cracks in landing gear assembly. Theoretical and experimental aspects of guided wave analysis include phase velocity, group velocity, and attenuation dispersion curves; boundary element model analysis for reflection and transmission factor analysis; use of wave structure for defect detection sensitivity; source influence on the phase velocity spectrum, and the use of angle beam and comb transducer technology. Probe design and modeling considerations are being explored. Utilization of in-plane and out-of-plane displacement patterns on the surface and longitudinal power distribution across the structural cross-section are considered for improved sensitivity, penetration power, and resolution in nondestructive evaluation. Methods of controlling the phase velocity spectrum for mode and frequency selection are available. Such features as group velocity change, mode cut-off measurements, mode conversion, amplitude ratios of transmission, and reflection factors of specific mode and frequency as input will be introduced for their ability to be used in flaw and material characterization analysis.     

Probabilistic Fatigue Life Prediction and Structural Reliability Evaluation of Turbine Rotors Integrating an Automated Ultrasonic Inspection System

The paper presents a general method and procedure for fatigue reliability assessment integrating automated ultrasonic non-destructive inspections. The basic structure of an automated ultrasonic inspection system is presented. Fatigue reliability assessment methodology is developed using uncertainty quantification models for detection, sizing, and fatigue model parameters. The probability of detection model is based on a classical log-linear model coupling the actual flaw size with the ultrasonic inspection reported size. Using probabilistic modeling, the distribution of the actual flaw size is derived. Reliability assessment procedure using ultrasonic inspection data is suggested. A steam turbine rotor example with realistic ultrasonic inspection data is presented to demonstrate the overall method. Calculations and interpretations of assessment results based on risk recommendations for industrial applications are given.     

Treatment of false calls in evaluating nondestructive inspection proficiency

A test designed to evaluate nondestructive flaw detection proficiency by ultrasonic and eddy current methods has been conducted. Test data for each participant are reduced to contingency table format, and analysis of these tables via traditional measures of association is used to rank individual performances. The presence of false calls in an inspection record introduces a random inflation in flaw detection results. Measures are required which compensate for that fact. Proficiency rankings based on two such measures, Somers'd coefficient and the mean square contingency coefficient, show reasonable consistency with intuition-based rankings by experienced observers. Finally, a weighted generalization of Somers'sd is suggested, although optimal selection of weights remains an open problem.     

Using Markov Chain Monte Carlo methods to solve full Bayesian modeling of PWR vessel flaw distributions

We present a hierarchical Bayesian method for estimating the density and size distribution of subclad-flaws in French Pressurized Water Reactor (PWR) vessels. This model takes into account in-service inspection (ISI) data, a flaw size-dependent probability of detection (different functions are considered) with a threshold of detection, and a flaw sizing error distribution (different distributions are considered). The resulting model is identified through a Markov Chain Monte Carlo (MCMC) algorithm. The article includes discussion for choosing the prior distribution parameters and an illustrative application is presented highlighting the model's ability to provide good parameter estimates even when a small number of flaws are observed.     

CIRCUMFERENTIAL SHEAR HORIZONTAL WAVE AXIAL-CRACK SIZING IN PIPES

Circumferential shear horizontal (SH) waves are used for the inspection and sizing of axial cracks in pipelines. Experiments on two sample pipes having notches with different depths and lengths were carried out utilizing magnetostrictive sensor (MsS) technology for generating circumferential shear horizontal guided waves. A simplified two-dimensional model for crack sizing in pipes was studied through wave-reflection amplitude coefficients. The wave-reflection amplitudes are affected by both defect depths and lengths. To estimate the defect depth, which is critical, length compensation was taken for defects shorter than the beam width. An axial scan was carried out for the defect length estimations and the length compensation. Based on this axial scan, an approximate two-dimensional theory has been developed that has improved the defect depth estimation greatly. Two-dimensional boundary element modeling analysis and normal mode expansion technology are used to study defect sizing theoretically in a pipe-like structure by calculating reflection coefficients. The theoretical results agree with the experiments quite favorably.     

Utilization of prior flaw information in ultrasonic NDE: An analysis of flaw scattering amplitude as a random variable

Probabilistic approaches to flaw detection, classification, or characterization often assume prior knowledge of the flaw distribution. It is implicit that there is a scattering amplitude distribution associated with the flaw distribution. In a number of previously published probabilistic analyses, it has been assumed that scattering amplitude is an uncorrelated, Gaussian random variable with zero mean and known variance. In the work reported here, these assumptions are evaluated for the case of a lognormal distribution of spherical flaws. The correlation, mean, variance, and nature of the scattering amplitude distribution are considered as a function of frequency and as a function of the breadth of the assumed flaw distribution. It is shown for the assumed flaw distributions that scattering amplitude is not uncorrelated and does not have zero mean. It is shown that errors in estimating the flaw distribution variance affect both the scattering amplitude mean and variance. Using both analytical and numerical procedures, the scattering amplitude distribution is shown to be lognormal at long wavelength for a lognormal distribution of spherical scatterers. At high frequency, the distribution is shown to have a bimodal character.     

The application of synthetic focusing for imaging crack-like defects in pipelines using guided waves

This paper deals with quantifying the performance of a technique for detection, location, and sizing of circumferential crack-like defects in pipelines using synthetically focused guided waves. The system employs a circumferential array of piezoelectric transducer elements. A torsional probing guided wave is excited using the array, which subsequently interacts with the reflecting features of the pipe, such as defects or weld caps. The recorded backscattered signals are synthetically focused to every point of interest in the pipe wall, to form an image of the reflecting features of the pipe. The defect image amplitude is used to estimate the defect depth, and the full width at half maximum of the defect image circumferential profile is used to estimate the circumferential extent of the defect. The imaging system is tested with data from finite element simulations and from laboratory experiments. It is found that reliable sizing of circumferential cracks in finite element simulations and experiments can be achieved if the circumferential extent of the defect is greater than 1.5 lambda_S, where lambda_S is the shear wavelength at the frequency of inspection. This result is theoretically valid for any pipe size, any axial defect location, and any inspection frequency. Amplitude gains of around 18 dB over an unfocused system have been observed experimentally in an 8-inch pipe with a 9 dB SNR improvement.     

超声频率一致性分析及其在缺陷分类中的应用

超声检测中,需要根据不同的情况,如试样厚度、分辨率、缺陷深度及方向等而使用不同中心频率的探头。这成为信号自动分类中的一个主要问题。因为大多数模式分类算法与信号的形状密切相关,而信号的形状很大程度上随检测频率的变化而变化。为使分类系统不受检测频率的影响而能识别不同频率的同一类缺陷信号,文中采用了基于时间尺度化的频率一致性分析方法把不同频率的信号映射到同一参考频率。采集了两个焊接缺陷样本库也即尺度化处理样本库和没有尺度化处理样本库,并用类别可分性判据做定量对比。实验结果验证了频率一致性处理方法的有效性,能够消除换能器频率对分类的影响。     

Technique for generation of unipolar ultrasonic pulses

A transmit-receive switch has been developed that permits the generation and detection of broadband unipolar ultrasonic stress pulses in a pulse-echo mode. Results obtained with conventional planar transducers show that the bandwidths obtained are significantly larger than those realized with conventional ultrasonic pulse-echo techniques. The broadband technique is expected to be applicable to flaw sizing problems encountered in nondestructive evaluation (NDE) and to the measurement of gradients in material properties that can be related to changes in the acoustic impedance.     

Flaw detection close to the interface using ultrasonic echography

The detection of flaws by ultrasonic echography becomes difficult when the flaw is at a shallow depth. The time delay between the interface and flaw echos is less than the width of the impulse-response time of the transducer, and the flaw echo generally has an amplitude much smaller than the dominating interface echo. When the surface is not too rough, the interface echo can be assumed to be known, and its comparison with the signal interface and flaw echo permits the detection of the flaw. In this article it is shown that signal processing techniques allow small flaws to be detected very close to the surface (0.5 mm). Two methods are proposed, the first one is based on the minimization of the mean-square error, and the second on the spectral substraction of the two echos.This work has been supported by the French Ministry of Defense.     

磁轭式磁粉探伤机提升力测量装置的研制

磁粉探伤是一种重要的无损检测方法,在生产实际中得到了广泛应用。磁粉探伤机的性能指标稳定并满足工作要求,是保证其检测结果准确可靠的前提,磁粉探伤机最关键的性能指标就是其磁轭的磁化能力,目前国内常用的磁化能力校验方法是提升力测试法。本文根据磁轭式磁粉探伤机提升力的定义,利用智能传感器和高速数据采集技术,研制出了一种磁粉探伤机提升力测量装置,本装置操作简便,结果直观,不用再使用笨重的提升力测量试块,大大提高了校验效率,取得了良好的社会效益和经济效益。     

Improved method of estimating the product quality after multiple inspections

A complex product is often inspected more than once in a sequential manner to ensure the product’s quality. Based on the number of defects discovered during each round of inspection process, we can estimate the number of defects still remaining in the product. For each defect, the probability that the defect will be detected during each inspection cycle is usually assumed to be a known ‘constant’. However, in many practical situations, some defects are easily detected, while others are much more difficult to identify. In this paper, we propose a ‘beta-geometric’ inspection model in which the heterogeneity in detection probability is described by a beta distribution. In a numerical study, we show that our more realistic inspection model clearly outperforms traditional estimation methods that are based on the assumption of a constant detection probability.     

Approximate model of eddy-current probe impedance for surface-breaking flaws

A theoretical model is derived for the prediction of eddy-current probe impedance changes caused by three-dimensional, surface-breaking flaws. Magnetic scalar potential theory and the surface impedance approximation are used to calculate fields on the flaw surface for arbitrary probe position and flaw geometry. Impedance changes are determined by a first-order perturbation calculation, with skin depth being the perturbation parameter. The end result is a relatively simple, three-dimensional model for simulating an eddy-current inspection. Numerical results for rectangular slots include maps of the impedance signals obtained in raster scan patterns and studies of skin-depth effects as a function of probe size, lift-off, and flaw dimensions.     

混凝土结构缺陷的融合识别研究

混凝土结构缺陷的无损检测是一项非常困难的工作,尤其是小尺寸或浅层的缺陷检测非常困难,由于仅用一种检测方法往往难以给出令人信服的结论,因此,本文同时采用超声检测和脉冲回波检测两种方法对不同大小的剥离和空洞缺陷进行了探测,并用小波分析方法对这两种信号进行了特征抽取,以第三阶尺度上的极大模作为信号的特征微量;随后,用一个多层前馈神经网络进行了单种检测方法的软决策,定义并计算了以该软决策为基础的概率分配函数;最后,用证据理论方法进行了两种检测方法的决策级融合识别,分类试验结果表明融合识别确实好于单一方法的识别。     

卷积神经网络在印刷品缺陷检测的应用

目的 为了改善传统机器检测印刷产品缺陷存在误费率高的不足。方法 提出以卷积神经网络为控制核心的印刷品缺陷检测系统。设计可在实际检测中应用的卷积神经网络,设计在线印刷质量检测系统的硬件结构。结果 对结构相同而训练次数、学习率不同的卷积神经网络进行了缺陷检测的性能对比,验证了该卷积神经网络在学习率小于0.01时,可以获得较好的识别效果;在学习率大于0.05时,网络不容易收敛。网络训练次数越多,精度越高,相应的训练时间也较长。在满足快速性和精确度的条件下,确定了适应某印刷品的缺陷检验网络训练次数为50,学习率为0.005,此时的识别率为90%。结论 经过实验证明,该检测系统具有良好的缺陷识别能力,缺陷类型的分类准确率较高。该系统具有一定的实用价值。     

A unified constrained inversion model for ultrasonic flaw sizing

Equivalent flaw sizing using ultrasonic waves is an approach whereby shape and orientation information of a defect are obtained in terms of a best-fit simple geometry that is able to represent the major aspects of the flaw. Separate examples of this approach have previously been developed for volumetric flaws and cracks using the Born and Kirchhoff approximations, respectively. Here, these separate algorithms are unified into a single algorithm capable of sizing both volumetric flaws and cracks. Some examples of the performance of this unified algorithm on both synthetic and experimental data are also given.     

复合材料蜂窝板脉冲热像检测和调制热像检测的比较研究

为了探索适合复合材料蜂窝板缺陷检测的红外热像检测法及热像信号处理方法, 对蜂窝板的脉冲热像检测(PT)、调制热像检测(MT)及几种热像信号处理方法的缺陷检测能力进行了比较。在脉冲热像检测中, 用脉冲相位法进行热像序列处理, 并与最佳原始热像进行比较。在调制热像检测中, 提出用离散傅里叶级数法和相关系数法进行热像序列处理, 并与经典的四点法进行比较。研究结果表明, 在蜂窝板脱粘缺陷的检测中, 调制热像法的检测效果好于脉冲热像法。在调制热像法的信号处理中, 离散傅里叶级数法和相关系数法的应用效果均好于四点法。在最佳调制频率下, 以"调制热像-离散傅里叶级数"法进行蜂窝板脱粘缺陷的检测具有最大的缺陷探测能力。     

Approach to Lamb Wave Lateral Crack Quantification in Elastic Plate Based on Reflection and Transmission Coefficients Surfaces

Ultrasonic guided wave is promising in structure integrity management, but there is still much to learn about it because of its complex mechanism. Defect sizing or quantification is very important for structure inspection using ultrasonic guided waves, and this inverse problem is also very difficult to solve. The work presented in this article aims to resolve the lateral crack quantification problem in the inspection of thin elastic plate using Lamb wave. First, two-dimensional (2D) boundary element method (BEM) simulation was used to study the interaction of one chosen pure mode Lamb wave with lateral crack defect, and this could be defined as the forward problem. Then reflection and transmission coefficients surfaces were built from the results of the numerical simulation. Finally, an approach for lateral crack quantification based on these reflection and transmission coefficients surfaces was proposed. The quantification examples show that the presented approach gives acceptable accuracy. Some limitations of this approach are also discussed.     

Frequency domain methods for reducing transducer variability

A major objective of quantitative nondestructive evaluation is to formulate defect detection, classification, and sizing algorithms that are insensitive to variations in transducer characteristics, material type, and defect depth. With the data used in this research, ultrasonic signals were found to vary significantly with changes in the transducer and only secondarily with changes in material and depth. It is shown that the method for minimizing signal variations due to transducer and material changes is to deconvolve the test signal with respect to the transducer response from a reference defect in a block of the same material. Since depth variation primarily affects signal amplitude and has minor impact on shape, detection, classification, and sizing, insensitivity to depth is achieved by avoiding the use of amplitude-dependent parameters. The notion of a standard transducer is introduced. Its mathematical properties and methods of realization are given. It is shown how the effects of variability from different test transducers can be removed by signal processing. When these procedures are applied to the test transducer, the effect is to cause it to resemble the standard transducer and, thereby, to place all ultrasonic waveforms on a common basis.