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TOFD (Time of Flight Diffraction), one of the most advanced technologies in the field of NDT (Nondestructive Testing), is widely used in science and industry to evaluate the properties of material, component or system without causing damage. Experiments on TOFD show that signal is greatly disturbed by the noise received by the receiving probe. Based on the performance analysis of four different kinds...
Computational simulations and reliability analysis were used to optimize an automated ultrasonic system used in pipe inspections in a manufacture plant in operation. Through the application of these tools the quality of the final product could be improved from more efficiency inspections. The main purpose was to establish the influence of each variable involved in the capacity of the ultrasonic system...
One of the main drawbacks of EMATs is their inefficiency in generating ultrasounds. To solve this problem, a new surface-wave EMAT design, whose magnet width is less than the coil, is proposed. The principle of the new EMAT is studied based on finite element simulation, which indicates that the EMAT is more efficient by taking advantage of both horizontal and vertical magnetic fields of the magnet...
The accuracy and speed of nondestructive testing can be improved by using multiple Lamb wave electromagnetic acoustic transducers (EMATs) instead of a single one. However, the methods for the arrangement of the multiple transducers have been seldom reported. In this paper, the acoustic field excited by the Lamb wave EMAT is described by a 3-D finite element (FE) model. Based on this acoustic field,...
It has been shown that the complicated nonlinear vibration phenomena in mechanical workpieces under excitations of intense ultrasonic pulses increase greatly the detectability of defects (cracks). To study the nonlinear vibration phenomena of plates induced by the ultrasonic pulses, an electrical circuit model is proposed to simulate the mechanical vibro-impact motions between the transducer horn...
A technique of completely non-contact laser ultrasonic imaging was proposed to detect austenitic stainless steel with an artificial defect. Austenitic stainless steel was scanned by using the pulse of Nd:YAG laser, and the ultrasonic wave was received by the interferometer. The ultrasonic vibrations image at different locations away from the damages was analyzed in detail, and then taking discrete...
The main objective of this work is to assess the possibility of improving the achievable image quality using synthetic aperture (SA) approach and to evaluate the performance of the modified algorithm. The modified algorithm is based on the coherent summation of back-scattered RF echo signals with weights calculated for each point and for all possible combinations of transmit-receive pairs. Weights...
An online health monitoring system (OHMS) was tailor-made and implemented for structural health monitoring (SHM) of train structures. A sensor network made up of miniature piezoelectric wafers was configured on the bogie frames of China's latest high-speed train model. Ultrasonic guided waves were generated through the sensor network, and a variety of signal features were retrieved and fused by the...
Total focusing method (TFM) is a post-processing algorithm for ultrasonic imaging, usually used for processing linear array data. In this paper, TFM is extended to obtain three-dimensional (3D) image based on two-dimensional array data. However, it takes a long time to get 3D information from large amount of 2D array data by TFM. So Sub-aperture matrix capture (SMC) and sparse array are taken into...
The Full Matrix Capture (FMC) method can provide the original complete information which is detected by the ultrasonic array and can recover with the Total Focusing Method (TFM). This technique has better detection sensitivity and resolution relative to conventional scanning method and is valuable for improving the quality and reliability of industrial non-destructive testing. However, it has low...
The Total Focus Method (TFM) is a post-processing algorithm which uses all elements in the array to focus in both transmission and reception at every image point. The time-domain signals is captured in a process termed Full Matrix Capture (FMC). In this paper, the main objective is to research the effects of directivity function on the TFM. The TFM algorithm is based on the FMC data with weights calculated...
In this paper, a design concept of sparse array is applied to total focusing imaging technique. During the process, the elements of a phased array are partially selected according to the theory of effective aperture, in order to reduce the amount of captured data and shorten the processing time of TFM imaging. Simulated imaging with Field II program and experimental verification on two standard phased...
This article presents a laser-based ultrasonic technique (LBUT) in ablation regime for inspection of internal defects using the pulsed high-power laser (HPL) and two wave mixing (TWM) detector. Pulsed HPL source has been recognized as a good ultrasonic generator to overcome weakness of the conventional contact transducer in harsh environment such as high temperature and rough surface of measurement...
In this paper, time-reversal with multiple signal classification (termed TR-MUSIC), the widely used time-reversal based imaging algorithm, has been introduced into the area of ultrasonic NDE. This method can break diffraction limit which is given by Rayleigh criterion and achieve super resolution imaging. Here, resolution means the ability of an imaging method to resolve closely spaced targets. A...
The materials of testing specimen are nonuniform, which leads to phase aberration in ultrasonic signal. The resolution of ultrasonic image decreases as a result of phase aberration, this paper proposes a method that can correct the phase aberration through calculating signal correlation. In this method, we calculate the correction function between the reference signal and other signals and choose...
An automated ultrasonic scanner based on the non-contact air-coupled technique is designed and developed in order to perform nondestructive characterization of the surface of different structures and to detect the surface defects. The measurement is carried out without any contact with the examined part. The paper presents the scanner and several examples of its applications: the on-site characterization...
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