Shear-wave time of flight diffraction (S-TOFD) technique

Ultrasonic time of flight diffraction (TOFD) for sizing defects is based on the time of flight of the diffracted echo that is generated when a longitudinal wave is incident on a crack tip. This technique has the limitation during near-surface inspection due to signal superposition. Here, this limitation is overcome by using the shear wave-diffracted signal (instead of longitudinal wave) and hence called S-TOFD. Experiments were conducted on samples with defect tip closer to the surface of a flat plate sample to illustrate the utility of the S-TOFD technique. An increase in the flaw sizing accuracy, by using the shear wave-diffracted echoes from the tip and through the application of a signal processing technique (ESIT), was demonstrated.     

铝合金焊缝超声TOFD检测的信号特征

针对厚板铝合金焊接接头的检测，研究了超声衍射时间差法（TOFD）检测时的信号特征及衍射规律，并探讨了最佳检测工艺参数和缺陷测量精度。研究结果表明，缺陷尺寸的测量结果与真实值基本吻合。其研究为实际焊接接头的检测奠定了基础。     

Noncontact laser ultrasonic inspection of Ceramic Matrix Composites (CMCs)

Ceramic matrix composites (CMCs) are poised to revolutionize jet engine technology by enabling operation temperatures well beyond those possible with current superalloys, while reducing active cooling requirements and engine weight. Manufacturing of parts formed by silicon-carbide (SiC) fibers in a SiC matrix is now well advanced, with the first non-structural static components entering service in 2017 with the CFM Leap^® engine that uses SiC/SiC turbine shrouds. In order to expand the scope of application of CMCs to rotating parts, such as turbine blades, much work is being conducted to understand and characterize the modes of failure of these materials at temperatures beyond $\sim 1100°\mathrm{C}$. In this context, the ability of nondestructively monitoring the formation and progression of damage in CMCs specimens during high-temperature mechanical testing is critical. However, the elevated temperature precludes the possibility of using sensors placed in direct contact with the specimen and therefore severely restricts the range of available NDE techniques. This paper provides the first experimental assessment of the feasibility of noncontact laser ultrasonic inspection of SiC/SiC flat coupons. An Nd: Yag laser is used to excite ultrasonic waves on one side of the specimen while a Michelson interferometer detects the signals emerging on the other side at the epicenter position. The lasers are mounted on synchronized linear stages to form C-scans as in conventional immersion ultrasonics while ablation damage to the surface of the specimen is prevented by operating the lasers at low power density. Despite the complex microstructure of the SiC/SiC material it is found that the measured waveforms are remarkably similar to those observed when conducting the same tests in aluminum specimens. Moreover, it is shown that it is possible to image interlaminar defects caused by impacts, and monitor crack opening under tensile load. Finally, very good signal stability is observed when temperature is increased from 25 to 1250 °C which confirms the feasibility of laser monitoring at high temperature and is consistent with the good thermal stability of ceramic materials.     

面状缺陷超声TOFD法信号和图像的特征与识别

针对铝合金厚板焊缝中易于出现的几种典型的面状缺陷,研究了其超声衍射时间差法（TOFD—time of flight diffraction）的检测特征,对获得的A扫描信号和B、D扫描图像的特征进行了分析和解释,并对B、D扫描图像进行了线性化处理。结果表明,结合A扫描信号和B、D扫描图像的特征,能够有效地对面状缺陷进行识别、定位和定量。线性化处理技术有效地提高了图像的时间分辨力,使面状缺陷的信号和图像的特征更明显,进而使定位定量更为精确。     

基于最快衍射波时差法的实时定量化疲劳裂纹监测(英文)

由于受循环载荷及长期极端环境的作用,飞机的金属结构常会产生疲劳裂纹,进而对飞机结构造成严重破坏。疲劳裂纹的位置和尺寸定量化监测对于飞机制造商以及飞机维护人员具有十分重要的意义,因为它可以大幅度地提高飞机结构的安全性和可靠性,并降低飞机的维护成本。近年来,在疲劳裂纹的大致位置监测方面国内外的研究人员已经取得了较大的进展。但是疲劳裂纹的尺寸监测仍是一个具有挑战性的问题。发展了最快衍射波时差法来定量化监测疲劳裂纹的尺寸。最快衍射波时差法用一个粘接在结构表面的传感器网络激励和接收超声波信号,当超声波经过裂纹尖端时会产生衍射波,然后通过所提出的先进算法分析接收到的衍射波信号就可以获得裂纹的位置和尺寸等信息。结果表明,用最快衍射波时差法获得的裂纹尺寸与裂纹的真实尺寸非常接近。     

Modeling tools for ultrasonic inspection of welds

Developments in quantitative ultrasonic nondestructive testing (NDT) of welds require simulation tools for cost-effective research and engineering works. The present paper reviews the specific developments in modeling of weld inspection at the French Atomic Energy Commission (CEA), made in keeping with the general pattern of CEA in simulation studies of ultrasonic examination. Two models have been developed for several years at CEA for this purpose. One is dedicated to the computation of the ultrasonic field radiated by arbitrary transducers into pieces (possibly anisotropic and heterogeneous) under examination. We specifically discuss how the metallurgical structure and associated elastic properties of welds is taken into account. The other simulates a testing experiment. It accounts for the interaction of the beam with defects (within a piece made of isotropic material) and specimen boundaries and simulates the transducer scan over the piece for synthesizing images comparable with measurements. We specifically discuss the influence of the possible complex geometry of the back-wall of a weld. Examples of application are given. They demonstrate the usefulness of such modeling tools in ultrasonic NDT of welds to study and optimize testing configurations, and to help NDT experts to interpret actual data.     

超声TOFD图谱多普勒频移估计及增强算法研究

为了提高超声TOFD平行扫查(B扫)图谱的横向分辨率、区分横向接近的不同缺陷,采用合成孔径聚焦技术(SAFT,Synthetic Aperture Focusing Technique)对B扫图谱进行波束锐化和图像增强,推导了缺陷尖端衍射回波的参数模型和多普勒频移,提出了B扫图谱多普勒频率随缺陷深度呈非线性关系.在经典SAF重建的基础上,对合成孔径两侧的缺陷信号进行增益补偿,修正波束衰减引起的B扫图谱灰度梯度下降.研究结果表明:该方法能有效提高孔径合成图谱中缺陷信号的横向分辨率和对比度,精确表征缺陷在被检测体中的横向位置及缺陷高度.     

Application of modeling techniques for ultrasonic austenitic weld inspection

After a brief discussion of the fundamental equations of elastic wave propagation in anisotropic (transversely isotropic) materials and their basic solutions in terms of plane waves and Green functions, we point out and demonstrate the usefulness of Huygens’ principle in conjunction with the results obtained by the numerical Elastodynamic Finite Integration Technique (EFIT)-code for an intuitive physical understanding of ultrasound propagation in austenitic steel. EFIT is briefly explained and then validated against a weld transmission experiment; applications to pulse echo simulations for various canonical and real-life geometries and structures with and without backwall entering notches are to follow. Further, we have been able to confirm the existence of the second qSV-wave, as predicted by plane wave theory, through EFIT-modeling as well as experiments.     

New dual-focalization ferroelectret-based array for air-coupled ultrasonic inspection of textiles

This work presents a design methodology for half-curved airborne ultrasonic arrays based in cellular ferroelectret film. The geometry of the array proposed allows us focus naturally in the vertical plane and electronically in the horizontal one, obtaining similar spatial resolution in both directions. Theoretical predictions and simulated results were validated with a developed array prototype designed to operate at frequencies between 50 kHz and 300 kHz. The potential of the device is shown by inspecting different textile samples in transmission mode. This multitransducer design is a low cost alternative to the use of composite 2D arrays in noncontact ultrasonic inspections.     

Study of ultrasonic phased array inspection imaging technology for NDT

A research about the ultrasonic phased array imaging principle from A-scan signal to B-scan image for non-destructive testing （NDT） was conducted in this paper, the ultrasonic phased array inspection imaging system used in industrial field was developed and the experiment was performed on the steel testing block by the system with 64 elements, 5 MHz phased array transducer. Experimental results show that the flaws could be accurately detected and the flaws size could be estimated from the B-scan images, and the B-scan images could clearly show the location of the flaws, but the quality of B-scan images needs to be enhanced by digital signal processing and controlling dynamic focusing for improving the image resolution.     

An ultrasonic array-based system for real-time inspection of carbon-epoxy composite plates

A real-time ultrasonic imager operating at a frequency of 3.5 MHz to test composites in immersion has been developed. It is based on linear array transducers and provides either B-scan or transmission images of composite plates of a few centimeters thickness. The electronic scanning has a pitch of 1.25 mm and an amplitude of 80 mm, and the electronic focusing as well as the acoustic lens on the arrays are set to work at a depth of 40 mm in water. Tests made on composite and plastic plates of 5 to 17 mm thickness show that the system allows the detection of different types of defects and that the interpretation of the ultrasonic signals can be performed on line.     

A probabilistic approach for the optimisation of ultrasonic array inspection techniques

Ultrasonic arrays are now used routinely for the inspection of engineering structures in order to maintain their integrity and assess their performance. Such inspections are usually optimised manually using empirical measurements and parametric studies which are laborious, time-consuming, and may not result in an optimal approach. In this paper, a general framework for the optimisation of ultrasonic array inspection techniques in NDE is presented. Defect detection rate is set as the main inspection objective and used to assess the performance of the optimisation framework. Statistical modelling of the inspection is used to form the optimisation problem and incorporate inspection uncertainty such as crack type and location, material properties and geometry, etc. A genetic algorithm is used to solve the global optimisation problem. As a demonstration, the optimisation framework is used with two objective functions based on array signal amplitude and signal-to-noise ratio (SNR). The optimal use of plane B-scan and total focusing method imaging algorithms is also investigated. The performance of the optimisation scheme is explored in simulation and then validated experimentally. It has been found that, for the inspection scenarios considered, TFM provides better detectability in a statistical sense than plane B-scan imaging in scenarios where uncertainty in the inspection is expected.     

Development of an ultrasonic system for submarine hull acoustic cladding inspection

A computer controlled ultrasonic measurement and data analysis system has been developed to establish the bonding characteristics of polymer based tiles used on the external hulls of UK submarines to reduce sonar reflection and radiated noise. This paper describes the evolvement of the system from laboratory to field site and discusses the selection of hardware components, system integration and the development of the specialized software necessary to initiate and monitor the scanning procedure. The system has been developed to have the versatility to survey either individual or a number of adjacent tiles. Measurement of disbond characteristics is accomplished by the use of C-scan techniques supported by B-scan data and other software processes. Absolute and percentage disbond areas can be calculated to allow acceptance criteria to be applied. The system can also be used as a training and QA tool. Trials on a submarine in refit have demonstrated the efficacy of the technique and early results are given.     

Enhancement of ultrasonic images for sizing of defects by time-of-flight diffraction

A signal processing technique is presented for significantly sharpening the resolution of ultrasonic images, similar to those acquired in the nondestructive evaluation of girth welds in oil/gas pipelines. This enhancement allows a much improved estimate of the exact size of any detected anomaly in the weld, such that fracture mechanics can be used to gauge the probability of weld failure. The algorithm is based on the synthetic aperture focusing technique (SAFT), combined with a variation of Wiener filtering and autoregressive spectral extrapolation. An analytical model of the transducer is used to construct an appropriate reference spectrum for the deconvolution operation, and accounts for the dependence of a beam's frequency spectrum on the position of a flaw relative to the transmitter. Experimental results are used to provide an estimate of the improvement in flaw sizing accuracy.     

压力容器焊接工艺评定的监督检验

现行的《锅炉压力容器产品安全性能检验规则》及上级监察部门的相关文函,均未对压力容器焊接工艺评定的监督检验工作给出具体的规定.在此根据对焊接工艺评定标准的理解和焊接工艺评定实践,结合国家对压力容器监督检验工作的意图,阐述焊接工艺评定监督检验的目的、内容和方法.     

环焊缝超声检测系统实时性设计与实现

对基于 PC的管道环焊缝超声检测系统实时性进行全面的分析研究 ,从软件和硬件两方面确定了解决系统实时性的几种途径 ,开发了 Windows环境下的系统实时控制软件及运动控制软件 ,并设计实验验证了系统实时性设计的有效性     

圆钢相控阵超声漏检因素分析

介绍了圆钢全自动相控阵超声的设备结构及其主要技术参数,结合具体的相控阵探头参数,主要从聚焦法则、周向覆盖率、轴向覆盖率3个方面,对影响相控阵超声检测漏检的关键因素进行了分析,并且从聚焦法则、轴向分辨率、检测速度等参数的设置方面给出了具体解决措施,为相关人员理解相控阵、操作类似相控阵设备提供了经验参考,同时为产品实现无缺陷交货提供了理论依据。     

Development of ultrasonic waveguide sensor for under-sodium inspection in a sodium-cooled fast reactor

The reactor core and in-vessel structures of a sodium-cooled fast reactor (SFR) cannot be examined visually due to the opaque sodium. The examination of the in-vessel structures is possible using ultrasonics to penetrate the sodium. A plate-type ultrasonic waveguide sensor using a leaky Lamb wave (A₀ mode) has been developed for under-sodium visual inspection of the reactor core and in-vessel structures. In the plate waveguide sensor, the A₀ leaky Lamb wave is utilized for the single mode generation and the effective radiation capability in a fluid. The liquid wedge is applied for the generation of the A₀ mode in the low frequency range. The long pulse tone-burst excitation should be applied to minimize the dispersion effect in 10 m long distance propagation of the A₀ Lamb wave. And a novel technique which is capable of steering a radiation beam of a waveguide sensor without a mechanical movement of the waveguide sensor has been suggested. The control of the beam angle can be achieved by a frequency tuning method of the excitation pulse in the dispersive low frequency range of the A₀ Lamb wave. A 10 m long ultrasonic waveguide sensor module which consists of a plate waveguide, a liquid wedge, an ultrasonic sensor, and an acoustical shielding protection tube has been designed and manufactured. The possibility of applying the ultrasonic waveguide sensor module to an under-sodium visual inspection has been investigated. The experimental tests such as the long distance propagation test of A₀ Lamb wave, the beam profile measurements, and C-scanning experiments in water have been carried out for the performance of the ultrasonic waveguide sensor. The feasibility of the ultrasonic waveguide sensor technique has been successfully demonstrated.