Noncontact Air-Coupled Guided Wave Ultrasonics for Detection of Thinning Defects in Aluminum Plates

Ultrasonic guided waves are gaining increasing attention for the inspection of platelike and rodlike structures. At the same time, inspection methods that do not require contact with the test piece are being developed for advanced applications. This paper capitalizes on recent advances in the areas of guided wave ultrasonics and noncontact ultrasonics to demonstrate a superior method for the nondestructive detection of thinning defects simulating hidden corrosion in thin aluminum plates. The proposed approach uses micromachined gas (air)-coupled capacitive transducers for the noncontact generation and detection of guided plate waves. Interesting features in the dispersive behavior of selected guided modes are used for the detection of plate thinning. It is shown that mode cutoff measurements provide a qualitative detection of thinning defects, while frequency shift measurements allow quantification of thinning depth. Measurement of the mode group velocity can be also used to quantify thinning depth. Similarly, thinning length can be determined by mode time-of-flight measurements.     

Phased Array Ultrasonic Testing for Post-Weld and OnLine Detection of Friction Stir Welding Defects

Nondestructive evaluation (NDE) techniques of phased array ultrasonic testing (PAUT) and digital X-ray radiography were employed on friction stir (FS)-welded Aluminum Alloy (AA)-2219-T87 specimens. PAUT intricacies required for scanning of FS-welded specimens with a 10-MHz 32-element transducer are discussed. The time corrected gain (TCG) calibration is required for scanning with an increase in index offset to compensate for decrease in A-Scan signal peak amplitude. Calibration techniques to find small defects with appropriate size tolerances are also established. The NDE technique of digital X-ray radiography is compared to PAUT, where it was found that a calibrated PAUT system is able to discover defects less than 0.2 mm where X-ray radiography could not. Incomplete penetration (IP), wormhole (WH), surface cavity (SC), and internal void (IV) defects are analyzed. Furthermore, an online PAUT system for FSW has been developed and successfully tested. The work provided herein will provide a gateway for an ultimate goal of an automated PAUT online sensing system.     

铝合金搅拌摩擦焊接头缺陷的超声检测方法研究综述

铝合金搅拌摩擦焊技术广泛运用于航空航天、汽车、船舶等制造领域,在国防工业的发展中扮演着重要角色,而超声波检测技术在对搅拌摩擦焊接头质量评估和控制方面起着不可或缺的作用。综述了铝合金搅拌摩擦焊接头缺陷的超声检测方法。介绍了接头缺陷的复杂多样的特点,分别阐述了超声检测A信号分析,超声C扫检测和超声相控阵检测方法在搅拌摩擦焊缺陷检测的应用,并介绍了3种检测方法检测能力,明确了搅拌摩擦焊缺陷超声检测尚需解决的突出问题并展望了未来研究的发展方向。     

复合材料制件拐角部位超声检测技术

复合材料在航空、航天等领域应用不断增加,制件的结构形式越来越复杂,在很多复杂结构中存在拐角部位,这些拐角部位的检测给无损检测带来困难.通过对资料的分析和试验,介绍了解决复合材料制件复杂结构拐角部位无损检测的方案和思路,并对比分析了各种检测方法的优缺点,认为超声相控阵技术在未来复合材料拐角部位无损检测上具有比较好的应用前...     

Lamb波在铝板缝类缺陷检测中的应用

为了研究Lamb波在缺陷板检测中的应用,建立非线性Lamb波检测系统.该系统用于检测具有不同深度裂纹的铝合金板和具有不同拉伸载荷循环的铝合金板.通过快速傅里叶变换(FFT)对获取的时域波形进行分析,得到两种缺陷对Lamb波非线性效应的影响.测试结果表明,对于裂纹缺陷,缺陷深度增加将增大试件超声非线性效应.当裂纹深度超过...     

Guided Wave Tuning Principles for Defect Detection in Tubing

Dispersion diagrams for longitudinal modes and several flexural modes are given. A partial loading oblique incidence technique was introduced for non-axisymmetric guided wave generation. Acoustic fields for partially loaded generation of guided waves were obtained along a sample Inconel steam generator tube surface. The axial field and the circumferential fields were non uniform. Even though the acoustic field was much more complicated than in the case of axisymmetric modes, the study of non-axisymmetric mode cannot be avoided; excitation of a single symmetric mode is often difficult due to limited access and transducer efficiency and there is also mode conversion after scattering from defects. For 100% inspection coverage of tubing and piping, three dimensional tuning (distance, frequency, and incident angle tuning), was employed. A single combination of incident angle, position, and frequency may miss defects in blind spots. However, complete inspection coverage of a whole cross sectional area over a certain distance of tubing was successfully demonstrated through a multi crack detection experiment by using the three dimensional tuning concepts. Also, the use of non-axisymmetric guided waves for a large distance inspection capability was successfully demonstrated.     

超声相控阵全聚焦无损检测技术概述

超声相控阵全聚焦成像技术基于接收信号后处理的思想,对检测回波数据进行离线分析成像,是超声检测领域里的一项新技术。因其成像分辨率高、覆盖面广、对小缺陷灵敏度高等优势,在航空航天、高铁、石油管道、核电站等工业领域已有初步应用。文章介绍了全聚焦成像技术的检测原理及优缺点,介绍了其国内外发展历程,总结了研究热点及发展趋势。     

Effect of ultrasonic nanocrystal surface modification on the characteristics of AISI 310 stainless steel up to very high cycle fatigue

Effects of ultrasonic nanocrystal surface modification (UNSM) on the very high cycle fatigue response of AISI 310 stainless steel have been investigated. The higher impact force used in UNSM treatment showed a higher fatigue life improvement. The fatigue life improvement was higher in crack initiation from the surface of specimens. The subsurface crack initiation depth in the alloy increased with increase in the fatigue failure cycles. It was concluded that UNSM treatment can increase the life of the alloy significantly up to very high cycle fatigue.     

应力波在泡沫铝夹层三明治板中传播规律的数值研究

根据 Gibson 理论模型确定出泡沫铝的力学参数,设计出不同密度组合的5种数值计算模型,利用非线性动力学程序 LS-DYNA 研究了爆炸载荷作用下,应力波在泡沫铝夹层三明治板中的传播规律。对其缓冲吸能、衰减应力波特性进行对比分析。研究结果表明：由 Gibson 理论模型确定出的泡沫铝力学参数,在 CrushableFoam 本构模型中能够较好地反映应力波在不同介质界面间的反射与透射情况,与弹性波理论吻合度较高。在总体密度相同的情况下,H-M-S 梯度结构对爆炸冲击波具有更好的缓冲效果。其对应力波的持续削弱能力和爆炸冲击能量的持续吸收能力都要强于其他结构。     

钢包耳轴根部焊缝的相控阵超声检测与信号处理

采用匹配追踪算法和小波变换对低信噪比(2dB和-5dB)钢包耳轴根部焊缝缺陷检测信号进行预处理对比分析,在定制试块上采用64阵元超声相控阵探头对深度为230mm的耳轴根部焊缝进行检测,并且结合基于Gabor原子库的匹配追踪算法对回波信号进行消噪后成像.结果表明,在低信噪比(-5dB)条件下,匹配追踪算法较小波变换有更好的预处理效果;对深度位于220mm和230mm处的钢包耳轴焊缝缺陷的实际检测信号进行去噪处理时,匹配追踪算法能够准确定位缺陷位置并显著提高缺陷处信噪比.     

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.     

低频相控阵超声检测用于船用复合材料缺陷定量分析研究

研究了低频相控阵超声检测技术用于船用复合材料缺陷定量分析的问题。首先针对典型船用复合材料的相控阵聚焦声场进行分析,包括典型材料声速对小缺陷检出能力的影响、不同频率和合成孔径对近场长度的影响以及不同聚焦深度的声场仿真,提出不同厚度典型船用复合材料的相控阵超声频率和合成孔径推荐原则。为了验证该原则的准确性,通过实测不同深度的Φ3 mm的小缺陷,运用TCG校准的方式对TCG曲线的线性和小缺陷的检测效果进行验证。实现了对典型船用复合材料近表面和内部缺陷的定量分析,达到了较好的检测效果。     

Quantitative Detection of Internal Defects in Automotive Tires by an Interferographic Technique

Because of to the advantages of high sensitivity, nondestructive evaluation, and whole-field analysis, the interferographic technique is superior to other nondestructive evaluation (NDE) techniques. In this article, precut cracks 25 mm and 40 mm long that did not cut through the tire and that extended in different directions inside the tire were made. The interference fringes caused by the tire cracks under different pressures were obtained. By applying the proposed intensive characteristic model to the tires with internal defects, the position, length, and direction of the cracks can be evaluated. Results showed that the errors of experimental data are in good agreement; all were less than 7.6%.     

基于智能手机APP的图像法检测混凝土表面裂缝研究

提出了一种基于Android APP的混凝土表面裂缝无损检测方法.利用智能手机摄像头模组采集裂缝区域图像,通过灰度化、滤波降噪、泛洪填充等图像处理算法提取裂缝目标,根据裂缝像素点坐标间的几何关系以及裂缝所包含的像素点个数,并结合拍摄手机的单位像素点尺寸来计量裂缝特征值,实现裂缝无损检测.新开发的APP裂缝检测技术能计量...     

Design of an Orthotropic Piezoelectric Composite Material Phased Array Transducer for Damage Detection in a Concrete Structure

ABSTRACT

In order to verify the feasibility and effectiveness of the sensor used in complex concrete materials, an innovative application of ultrasonic phased array detection for a concrete structure was investigated. Comparing with the traditional piezoelectric composites, orthotropic piezoelectric composite material (OPCM) can be used as transducers in damage detection show clear advantages because of their high sensitivity and directivity along the polarization direction. A low frequency ultrasonic phased array transducer consisting of 16 OPCM elements is studied. The optimal array parameters, such as the phased array element interval, the array element width, and number of elements, are obtained by studying the total displacement changes as various parameters change at the focus point in the concrete structure. This configuration allowed the variation and control of the wave field directivity in the concrete structure during the measurements. The measurements were taken on concrete specimens using a precise time-delay device. The experimental measurements were compared to theoretical calculations to investigate the influence of different array element parameters. The results show that an OPCM phased array transducer can be used to detect damage in a concrete block.     

水利工程中金属焊缝缺陷的超声检测方法比较研究

为研究基于超声的无损探伤方法在水利工程金属结构焊缝缺陷识别中的应用,利用常规超声检测技术、超声相控阵技术、衍射时差法(Time of Flight Diffraction, TOFD)超声检测技术对水利工程金属结构焊接试块缺陷进行识别,分析了各种缺陷在超声无损探伤技术中的特征显示。研究结果表明:常规超声检测技术、TOFD检测技术均能对各种缺陷实现信号显示,超声相控阵检测技术对气孔和横向裂纹的显示不够明显,但对其它缺陷的检出效果较为明显;常规超声检测技术对操作人员的要求较高,对缺陷的定性困难,精度不高;TOFD检测结果中气孔和横向裂纹的显示呈现出一种特殊的弧形,有一定高度的内部裂纹和未熔合的信号由上下尖端衍射波组成,根部未焊透上下尖端信号不够明显;相控阵检测结果直观,可以较精确地测量缺陷的埋藏深度、自身高度、长度等,但在扫查点状缺陷或者与超声声束平行的裂纹缺陷时,检出率极低。     

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。     

利用PVDF检测激光声表面波的实验方法

提出一种利用聚偏二氟乙烯(PVDF)传感器检测激光声表面波的实验方法,并介绍其构成和检测方法.将PVDF薄膜附在微型刀劈上,钳紧在金属固定块上,引出两个电极,从而实现信号的声电转换.利用Nd:YAG脉冲激光器激发声表面波,分别对金属铝板和缺陷铝板进行检测,得到了具有很好信噪比的超声信号.实验结果表明,信号灵敏度高,并可用于表面缺陷的检测.     

Fatigue growth of surface cracks in nickel-based superalloys

The fatigue growth of surface cracks in three nickel-base superalloys has been monitored using a DC electrical potential-drop technique at both 200°C and 600°C in air. A three dimensional finite element analysis stress intensity calibration has enabled these growth rates to be compared with standard data obtained from though-cracked compact tension specimens. Good agreement has been found between surface and through-crack growth rates over the range from threshold to $\text{～25}\text{MNm}{}^{\mathrm{<mtext>?3</mtext><mtext>2</mtext>}}$ although for applied stress intensity ranges in excess of this the surface cracks propagated more slowly than expected, particularly at 200°C. This retardation has been suggested to arise from the increased proportion of a plane stress crack growth for the shorter surface cracks leading to both increased closure effects and a change in the crack growth mechanism.