超声A扫描信号建模及其缺陷识别方法研究

针对超声检测中A扫描信号依靠经验评定结构缺陷、识别缺陷类型困难等问题,提出一种A扫描信号建模方法,计算出缺陷A扫描信号。该方法基于超声检测系统建立A扫描信号数学模型,应用多元高斯声束法计算模型中缺陷表面超声波传播质点速度,运用基尔霍夫近似理论描述模型中缺陷散射振幅,从而获得缺陷超声A扫描信号。应用CSII-1/20标准试块平底孔(缺陷)超声A扫描表明:该方法计算获得试块平底孔5#(缺陷)A扫描信号与试验测量结果在缺陷位置和幅度基本吻合,是识别结构孔洞类缺陷的一种有效方法。     

金属材料内部缺陷试块的热压扩散连接制备方法

针对空腔类缺陷的人工模拟无损检测试块的研制,提出热压扩散连接技术的制备方法。利用热压扩散连接方法,制备内部含有三种不同规格尺寸人工模拟缺陷的试块。分析结果表明,试块连接区域熔合较好,熔合线难以区分;基体组织未发生明显变化;试块内缺陷尺寸发生变化且呈现一定变化规律,变形率与缺陷边界夹角和缺陷所呈角度大小有关。试块宏观尺寸呈现一定的形变,无损检测及金相分析结果显示人工缺陷边界清晰,基体连接区域扩散连接充分且组织无有害缺陷。热压扩散连接法应用于空腔类缺陷的人工模拟无损检测试块的研制工作具有可行性。     

基于机器视觉的砌墙砖自动检测系统

针对传统方法检测砌墙砖外观缺陷和几何尺寸存在效率低和准确度差的问题,设计一种基于机器视觉的砌墙砖自动检测系统。以OpenCV和PyQt为系统上位机开发平台,首先通过高分辨率的单目工业相机采集砌墙砖图像,再对图像进行阈值分割、边缘提取等图像处理,控制机械臂将标准块置于试样截面形心处,通过检测算法计算出试样的长度、宽度和高度以及识别缺陷区域,其后移开标准块,将缺陷区域坐标转换为运动导轨位移量,控制固定于运动导轨的精密激光传感器扫描缺陷区域实现精确测量缺陷深度数据。该系统已投入检测机构进行试检测,完成多批砌墙砖产品的检测实验,大量的实验结果表明,该检测系统技术成本低、性能稳定、精度高、结果稳定可靠,满足国家标准≤0.5mm的精度要求,尺寸测量重复性为0.09mm,缺陷测试重复性为0.10mm,相比于人工测量分别提高5.4倍和7.8倍,检测时间最多降低99.28%,能快速准确地对砌墙砖完成外观质量和几何尺寸的检测。     

汽轮机轮缘超声相控阵检测中缺陷方向识别

利用超声相控阵检测系统对含有裂纹缺陷的外包菌型低压汽轮机叶轮圆盘实验试块进行检测.针对超声波脉冲反射法中缺陷方向难以确定,尺寸容易误判等问题,提出一种频谱分析方法,研究线状缺陷方向变化对于超声回波的影响.对于3种倾斜角度的裂纹缺陷回波信号,分析其功率谱并进行小波包的分解和重构,用"频率-能量"的方法提取各方向缺陷回波信号的能量特征.实验结果表明,各方向缺陷回波信号的能量特征差别明显,并绘制出声束轴线与缺陷的夹角和高频带所占能量之间关系曲线.该方法实现了缺陷方向的识别,并为后续线状缺陷的准确定量提供依据.     

奥氏体不锈钢焊缝的超声相控阵检测及定量分析

奥氏体不锈钢管道焊缝缺陷的检测已引起无损探伤人员的密切关注.今利用超声相控阵技术对奥氏体不锈钢管道焊缝缺陷进行检测,并与20#碳钢检测成像效果进行比对.结果表明,相控阵超声波在20#碳钢中有很好的穿透性,而在奥氏体不锈钢焊缝中超声波信号衰减较为严重.奥氏体不锈钢焊缝区域缺陷信号信噪比最大值为9dB,当探伤深度大于30mm时,其信号衰减符合衰减方程描述.对于焊缝区域深度大于50mm,尺寸小于2mm的横通孔,超声相控阵技术无法清晰地探伤到此类缺陷.对于奥氏体不锈钢焊缝,横波检测成像的信噪比要高于纵波.     

超声无损检测技术在金属材料焊接检测中的应用

在焊接金属材料的过程中,温度变化会改变金属材料的晶粒结构,导致其内部应力分布发生变化,构件强度降低,存在安全故障隐患。因此需要对金属缺陷进行快速、准确地检测,其中无损检测法应用广泛,其包括超声波检测和射线检测。在未焊接表面裂纹缺陷检测中,辐射超声波技术具备较高的检测效率。超声无损检测(UT)技术可以在不破坏产品、构件质量的前提下,对缺陷进行检测,为确定焊缝尺寸提供参考,在生产过程中消除风险,该文对超声无损检测技术在金属材料焊接中的应用进行了研究。     

复合材料层压板分层缺陷超声相控阵检测与评估

针对碳纤维增强树脂基复合材料分层缺陷的无损检测与评估问题,通过制备预埋分层缺陷的标准试样,利用超声相控阵技术对缺陷进行无损检测与定量评估,并对测量误差进行分析。首先,在层压板铺层中间埋入聚酰亚胺薄膜制备分层缺陷试样;然后,对试样进行超声相控阵检测,通过超声S扫和C扫图像对缺陷进行定性分析与定量测量,并结合声场仿真对检测误差进行分析。结果表明:所制备试样内分层缺陷形状规则、埋深及大小与预设一致;超声相控阵步进方向检测尺寸比较准确,而扫查方向尺寸误差较大;超声相控阵技术能够准确识别分层缺陷的形状、尺寸及位置,具有很高的检测精度,对较小缺陷具有很好的检测效果。     

奥氏体不锈钢焊缝超声回波信号的匹配追踪处理

研究了奥氏体不锈钢焊缝组织的金相显微结构及其对超声检测的影响,利用超声相控阵检测技术对定制的奥氏体不锈钢对接焊接接头对比试块中不同深度(10、30、50、70 mm)、φ2 mm×30 mm的横通孔缺陷进行了不同波型(横波和纵波)的检测,采用匹配追踪后处理方法对超声回波信号进行了处理。结果显示:奥氏体不锈钢焊缝组织结构复杂,晶粒粗大,各向异性明显,对超声检测产生严重的声能衰减,纵波检测奥氏体不锈钢焊缝中较深缺陷(50 mm)的能力强于横波检测,且匹配追踪对奥氏体不锈钢焊缝超声检测回波信号的处理不仅能有效抑制噪声信号、提高信噪比,还能提取出被淹没在噪声信号中的缺陷信号。     

超声波检测焊缝缺陷深度的不确定度评定

采用GUM法对超声波检测焊缝缺陷深度的测量不确定度来源进行了分析,并对检测过程中的测量不确定度进行了评定。结果表明:超声波检测焊缝缺陷深度的不确定度来源主要有超声波探伤仪水平线性误差、斜探头性能以及试块规格;为了得到精确的测量结果,测试前应对超声波探伤仪水平线性误差进行检查并确保其在合适范围内,然后选用合适的探头及试块。     

基于改进PSO的某前副车架自动检具参数优化

汽车前副车架生产过程中需要在线检测其几何参数,但在检测过程中,多种因素导致测量值与真实值有偏差,为了提高效率,采用自动检测系统。利用气缸将检测机构送进到结构件上的孔、轴或其他位置。当相对尺寸变化时,会带动检测机构运动,通过与检测结构连接的传感器读出相应数据,再经过信息处理方法计算出结构件的相关几何参数。测量中发现,压紧、推动、翻转等气缸的气压大小会直接影响检测的测量精度,为了提高测量精度,在不同气压下,对某型号前副车架进行了检测,得到了主要尺寸的测量值,计算了测量值与真实值的偏差;采用多项式回归分析法,得出了气压和前副车架主要尺寸的偏差的关系式;利用改进粒子群优化算法,以前副车架主要尺寸的总体偏差和为适应度函数,迭代寻优得到最佳气压值为0.4578 MPa。     

细铜棒内部缺陷超声自动检测系统设计

目的　检测细铜棒内部缺陷 .方法　采用组合超声检测法 ,结合多探头数据融合技术 .结果　实现了细铜棒内部缺陷的定性、定量自动检测 .结论　利用组合超声法和数据融合技术可以提高细铜棒的检测精度 .     

Defect tolerance of friction stir welds in DH36 steel

Friction stir welding of steel is in the early stages of development. The aim to commercialise this process creates a trade-off between welding time, cost and quality of the joint produced. Therefore, it becomes critical to analyse the lower quality bound of steel friction stir welds in conventional square edge butt welding configuration. Work has been undertaken to evaluate the microstructure and fatigue performance of 6 mm thick DH36 steel plates friction stir welded with sub-optimal process conditions, resulting in the development of embedded and surface breaking flaws. The defective weldments were characterised to understand the nature of the flaws and a programme of mechanical testing was undertaken (including fatigue assessment) to determine the relationship between the flaw geometry, location and weld quality. A number of characteristic flaws were identified and seen to interact with the samples' fatigue fracture mechanisms. Samples with wormholes at the weld root produced the lowest fatigue performance. Fracture from incomplete fusion paths at the retreating side of the welds' top surface was seen to correspond to the highest recorded fatigue lives. The work provides an insight into the complex nature of characteristic flaws in steel friction stir welds and their interaction with fatigue behaviour.     

模糊模式识别在轮箍超声横波探伤中的应用

轮箍是铁路机车运行的重要部件,在制造和使用过程中出现的各种危害性缺陷会严重威胁到列车的行驶安全.用超声无损检测缺陷,回波的识别易受轮箍标记、闸瓦、轮轨接触点及表面波等多种因素的干扰.在超声横波探伤基础上,可将模糊模式识别应用到机车轮箍的无损检测中.以内燃机车轮箍为实验检测对象,使用了多个标准人工伤模拟轮箍自然缺陷.通过提取缺陷回波频域相关特征建立典型缺陷的模糊子集,并运用基于贴近度的择近原则对未知缺陷进行分类识别.实验结果证明了该方法有效.对同一缺陷重复检测的正确识别率达92.5%.     

中厚钢板超声波探伤不合格原因分析

针对中厚钢板超声波探伤出现的两类典型缺陷,通过低倍检验和金相检验等手段,并结合实际探伤过程中缺陷的分布位置对探伤不合格的原因进行了分析。结果表明:点状密集型缺陷主要与连铸坯的中心偏析有关,侧边条型缺陷则主要来源于连铸坯的三角区裂纹或靠近三角区的中心裂纹,钢板体部的条型缺陷则是由连铸坯的中间裂纹造成的。     

Nondestructive Characterization of Planar Defects Using Laser-Generated Ultrasonic Shear Waves

This paper introduces a laser scanning technique to characterize internal planar defects in a specimen with parallel boundaries. Based on the principles of laser-based ultrasonic shear waves and shadowing, a procedure to determine flaw location, size, and orientation is described. The key feature of this scheme is the use of an optimum wave propagation angle where the maximum shear wave propagates. The feasibility of the approach is evidenced by testing specimens with various controlled and natural internal flaws. The experimental results are promising, in that the flaw characteristics can be determined with good accuracy. It is found that the scheme is especially useful for characterizing transverse-type flaws. The limitations of the technique are also addressed.     

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.     

Frequency-Wavenumber Migration of Ultrasonic Data

In ultrasonic nondestructive evaluation (NDE), the depth of the image is usually calculated by multiplying the traveling time of the echoes with the velocity of the medium. If the flaw is not a horizontal plane, the flaw images may be distorted and mislocated. Although the lateral resolution and sizing accuracy of the flaw image can be improved using the digital signal processing methods, e.g., the utilization of the blocking filter or deconvolution filter, these methods do a little favor about the distortion and mislocation problems. The migration, an image-processing method used widely in reflection seismology, is introduced to process the ultrasonic data in this study. Since the signals are coherent and the noises are random, the flaw image can be transformed from its apparent position to the true position using the migration method and the resolution of the image may be improved. Not only the real positions of the oblique cracks can be found upon applying the frequency-wavenumber (F-K) migration to process ultrasonic data, but, in addition, the dimensions of the flaws can be estimated more accurately. Results presented in this study show that the migration method can be applied successfully to the ultrasonic data processing and can improve the quality of ultrasonic image in both size and location of the flaws.     

Nondestructive Characterization of Planar Defects Using Laser-Generated Ultrasonic Shear Waves

Abstract

This paper introduces a laser scanning technique to characterize internal planar defects in a specimen with parallel boundaries. Based on the principles of laser-based ultrasonic shear waves and shadowing, a procedure to determine flaw location, size, and orientation is described. The key feature of this scheme is the use of an optimum wave propagation angle where the maximum shear wave propagates. The feasibility of the approach is evidenced by testing specimens with various controlled and natural internal flaws. The experimental results are promising, in that the flaw characteristics can be determined with good accuracy. It is found that the scheme is especially useful for characterizing transverse-type flaws. The limitations of the technique are also addressed.     

Sizing of disbonds at a thin-layer substrate interface from spectral peaks

An ultrasonic through transmission technique is used to inspect the interface of a thin layer and a substrate. An experiment is performed using a specimen constructed of a 0.040 inch (1.02 mm) polycarbonate layer bonded by an adhesive film to an aluminum plate. Circular flaws are induced with paper placed between the adhesive film and the polycarbonate layer to create disbonds. The flaws range in size from 0.5 inches (12.7 mm) to 0.067 inches (1.70 mm) in diameter. A through transmission ultrasonic inspection technique, which uses a flat transducer as a transmitter and a focused transducer as a receiver, is employed. Time signals from the receiving transducer are recorded for each flaw, transformed to the frequency domain by use of a fast Fourier transform (FFT), and are linearly deconvolved with the FFT of the time signals of the aluminum plate alone. The peaks of the resulting frequency response functions for each flaw predict the resonant frequencies of the flaws. The area of the thin layer above a disbond is modeled as a thin plate which is excited by the incident ultrasonic wave motion at its edges. The resonance peaks at the center of the plate are related to the size of the flaw. The principal result of the paper is that, based on the theory presented here, the size of the disbond can be obtained from measurements of the resonance peaks.     

Flaw identification using the boundary element method

In this paper a new boundary element formulation is presented for the identification of the location and size of internal flaws in two-dimensional structures. An introduction to inverse analysis is given, with special reference to methods of flaw identification, along with a brief review of the optimization methods employed. Both the standard boundary element and the dual boundary element method are presented, with the dual boundary element method proposed as the basis for the new formulation. The flaw identification method is presented, along with the computation of the boundary displacement and traction derivatives and the specialized analytical integration used for cracked boundaries. Examples are given to demonstrate the accuracy of the sensitivity values and the performance of flaw location.