Phase aberration correction in ultrasonic phased array non-destructive testing systems

Phase aberration correction for medical ultrasound systems has attracted a great deal of attention. Since phased array techniques are now widely employed for industrial non-destructive testing （NDT） applications in various fields, the problem of phase aberrations in the process of NDT testing is considered. The technique of cross-covariance for phase aberration correction is presented. The performance of the technique for phase aberration correction is tested by means of echo signals obtained in practical non-destructive testing experiment. The results show that the technique has the better accuracy of phase correction.

Model and optimization of ultrasonic phased array parameters

Beam focusing is one of the unique characteristics of ultrasonic phased array compared with conventional ultrasound.On the basis of two-dimensional radiated sound field of phased array,the three-dimensional radiated sound field was simulated in the paper,and then the effect of different frequencies,different number of array elements and different element spacings on focal spot,the depth of focus and the effect on horizontal and vertical resolution were analyzed.The optimal results of transducer parameters have certain reference value for the design of phased array probe.

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.

Ultrasonic Scattered Field Distribution of One and Two Cylindrical Solids with Phased Array Technique

The scattered fields of plane waves in a solid from a cylinder or sphere are critical in determining its acoustic characteristics as well as in engineering applications. This paper investigates the scattered field distributions of different incident waves created by elastic cylinders embedded in an elastic isotropic medium. Scattered waves, including longitudinal and transverse waves both inside and outside the cylinder, are described with specific modalities under an incident plane wave. A model with a scatterer embedded in a structural steel matrix and filled with aluminum is developed for comparison with the theoretical solution. The frequency of the plane wave ranged from 235 kHz to 2348 kHz, which corresponds to scaling factors from 0.5 to 5. Scattered field distributions in matrix materials blocked by an elastic cylindrical solid have been obtained by simulation or calculated using existing parameters. The simulation results are in good agreement with the theoretical solution, which supports the correctness of the simulation analysis. Furthermore, ultrasonic phased arrays are used to study scattered fields by changing the characteristics of the incident wave. On this foundation, a partial preliminary study of the scattered field distribution of double cylinders in a solid has been carried out, and the scattered field distribution at a given distance has been found to exhibit particular behaviors at different moments. Further studies on directivities and scattered fields are expected to improve the quantification of scattered images in isotropic solid materials by the phased array technique.

An application of ultrasonic phased array imaging in electron beam welding inspection

The basic principle and features of ultrasonic phased array imaging are discussed in this paper. Through the ultrasonic phased array technology, the electron beam welding defects and frozen keyholes characterization and imaging were realized. The ultrasonic phased array technology can detect kinds of defects in electron beam welding (EBW) quickly and easily.

Detection of Cracks in Aerospace Turbine Disks Using an Ultrasonic Phased Array C-scan Device

Crack detection in an aerospace turbine disk is essential for aircraft-quality detection.With the unique circular stepped structure and superalloy material properties of aerospace turbine disk,it is difficult for the traditional ultrasonic testing method to perform efficient and accurate testing.In this study,ultrasound phased array detection technology was applied to the non-destructive testing of aviation turbine disks:(i)A phased array ultrasonic c-scan device for detecting aerospace turbine disk cracks(PAUDA)was developed which consists of phased array ultrasonic,transducers,a computer,a displacement encoder,and a rotating scanner;(ii)The influence of the detection parameters include frequency,wave-type,and elements number of the ultrasonic phased array probe on the detection results on the near-surface and the far surface of the aerospace turbine disk is analyzed;(iii)Specimens with flat-bottom-hole(FBH)defects were scanned by the developed PAUDA and the results were analyzed and compared with the conventional single probe ultrasonic water immersion testing.The experiment shows that by using the ultrasonic phased array c-scan to scan the turbine disk the accuracy of the detection can be significantly improved which is of greater accuracy and higher efficiency than traditional immersion testing.

Inspection system for welded tubular joint based on ultrasonic phased array

A manual inspection of large-diameter tubular joints is difficult. As a result a scanner with three degrees of freedom （ DOFs） was developed based on the scanning principle of ultrasonic phased array. The weld tracing is realized by a 2DOF motion of scanner. The pose of ultrasonic probe is controlled by the third one. The control strategy is put forward based on a programmable multi-axis controller. Four kinds of scanning modes can be implemented simultaneously employing this ultrasonic inspection system. Experiments on reference blocks of tubular joints reveal that the automatic ultrasonic phased array inspection system has the same inspection accuracy as a manual ultrasonic inspection. This system is superior to the manual ultrasonic system in terms of reliability and repeatability. The artificial dejects of weld at tubular joint can be detected accurately with the presented inspection system.

The radial self-positioning algorithm of intelligent ultrasonic probe array in oil/gas pipeline

The working principle of the pipeline intelligent pig and the structure of ultrasonic probe array used to detect defects in oil/gas pipeline are introduced. The effects of the array＇ s radial position in pipe on defect resolution are analyzed. The causes leading to radial positioning error are investigated. An algo- rithm for the radial self-positioning is presented. The experimental results show that the radial self-positioning algorithm can eliminate the array＇ s space position error effectively and improve the defect resolution.

Measurement and Characterisation of a Diffuse Acoustic Field Using a Phased Array

A diffuse acoustic field has been increasingly used to infer temporal changes in the structures,such as early dislo-cations and microcracking.This study explores three different techniques to characterise acoustic field by using a single ultrasonic phased array.The first two techniques are proposed to measure spatial uniformity of wave field by examining differences in the integral of energy and the maximum energy respectively at multiple inspection loca-tions.The third one is developed to evaluate the degree of phase coherence between propagating waves transmitted sequentially by two neighbouring array elements.The efficacy of these techniques are investigated by examining their metrics on simulations and well-known samples.The results suggest that two selected metrics can be used to quantitatively estimate the diffuse field start time as well as the field size by comparing their value with the idealised diffuse state(15%for the energy integral metric,ηarea and 1 for the phase coherence metric,ηphase)and identifying the convergence start point.

UPA based 3D visualization of discontinuities in great thickness EBW seam

Electron beam welding （EBW） is a fusion welding process in which a beam of high-velocity electrons is applied to two materials to be joined. It is a complex high-temperature metallurgical process, and the quality of welding may deteriorate because of defects caused by improper welding parameters, especially in the EBW of thickened aluminum alloy plate. Ultrasonic phased array（UPA） technology has been applied more widely in the field of nondestructive testing because of its ability of effectively controlling the shape and direction of the emitted ultrasonic beam. In present research, a specimen with EBW seam on thickened aluminum plate was tested with a linear array ultrasonic phased array probe, and a large number of B-scan images of the weld were acquired by electronic scanning in probe combined with the mechanical scanning of the probe along the weld direction. This large number of B-scan images were stacked to construct the volume data, with which the 3D image of the weld discontinuities were reconstructed, and the 3D visualization was realized. More details about weld discontinuities＇ spatial distribution and orientation were revealed, and this approach also made the results of non-destructive ultrasonic testing more easily to understand.

Model-based optimization of phased array ultrasonic testing

Simulation of phased array beams in dovetail and austenitic welds is conducted to optimize the setup of phased array ultrasonic testing（PAUT）.To simulate the beam in such material with complex geometry or with characteristic of anisotropy and inhomogeneity, firstly,linear phased multi-Gaussian beam（LPMGB） models are introduced and discussed. Then,in the case of dovetail,wedge is designed to maximize the stable amplitude of the beam along the steering path;in the case of austenitic weld,modified focal law are developed to solve the problem of beam screwing and defocusing due to the material properties.To verify the effectiveness of the modified focal law,beam fields are calculated using LPMGB model in austenitic welds.

Ultrasonic guided wave inspection with array sensors

Ultrasonic guided wave becomes one of promising tool for monitoring various types of structures such as large steel plates, vessels, and pipes in oil, chemical or nuclear industry, because guided waves have ability to travel wide range of the target structure in a single position. However, analysis of guided wave signals acquired from structure is difficult on account of low S/N ratio and its dispersive nature. To improve S/N ratio and overcome dispersion effect, focusing techniques for guided waves are needed. Thus, in this study, focusing techniques for guided waves were developed in order to improve long range inspection ability, and performance of the developed techniques was verified by experiments.

Feature Extraction of Sectorial Scan Image of Thick-Walled Electron Beam Welding Seam Based on Principal Component Analysis

A feature extraction method was proposed to sectorial scan image of Ti-6Al-4V electron beam welding seam based on principal component analysis to solve problem of high-dimensional data resulting in timeconsuming in defect recognition. Seven features were extracted from the image and represented 87. 3% information of the original data. Both the extracted features and the original data were used to train support vector machine model to assess the feature extraction performance in two aspects: recognition accuracy and training time. The results show that using the extracted features the recognition accuracy of pore,crack,lack of fusion and lack of penetration are 93%,90.7%,94.7% and 89.3%,respectively,which is slightly higher than those using the original data. The training time of the models using the extracted features is extremely reduced comparing with those using the original data.

The study of complex focussing acoustic field of a convex phased array probe used in ultrasonic diagnostic B-scanner

This paper reports a study of complex focussing acoustic fields of a convex phased array probe widely used in ultrasonic diagnostic B-scanner. The time delay necessary for electronic focussing and for geometric focussing of complex focussing is given. By means of Helmholtz's integral formula, the expressions of acoustic fields were obtained for the electronic focussing and complex focussing.With Simpson's numerical integral, a great deal of computations was carried out with an 86 / 330 computer. By means of using different parameters, an optimum focal range and beam width of a 4 sequences electronic and complex focussing acoustic system was selected. With an EUB-40 ultrasound diagnostic B-scanner produced by the Hitachi company, the lateral focussing acoustic field and lateral resolution in an echoic tank were photographed by latticing method and the experimental result is consistent with the theory.

The pitch-catch nonlinear ultrasonic imaging techniques for structural health monitoring

Nonlinear ultrasonic imaging techniques in pulse-echo configuration have recently shown their potential to allow the effective separation of nonlinear and linear features in a nonlinear image.In this study,two ultrasonic phased arrays are implemented to produce an image of elastic nonlinearity through the parallel-sequential subtraction of the coherently scattered components in the through-transmission acoustic field at the transmission or subharmonic frequency.In parallel mode,a physical focus at each pixel is achieved by firing the transmitters with a predefined delay law.In sequential mode,each transmitter is fired in sequence and all the receivers are employed to capture the data simultaneously.This full matrix captured data can be post-processed and focused synthetically at the target area.The images of parallel focusing and sequential focusing are expected to be linearly identical and hence any differences remained on the subtracted image can be related to the nonlinearities arising from the defects.Therefore,the imaging metric here is defined as the difference between parallel and sequentially focused amplitudes obtained from forward coherently scattered fields at each target point.Additionally,the negative influences due to the instrumentation nonlinearities are investigated by studying the remaining relative phase and amplitude at undamaged pixels.A compensation method is implemented to suppress these noises,significantly enhancing the selectivity of nonlinear scattering features.The proposed techniques are then implemented to monitor fatigue crack growth in order to explore the capability of these methods as measures of elastic nonlinearity induced by different sizes of small closed cracks.The promising results suggest that nonlinear imaging can be used to monitor crack growth and improve the detectability at early stages.