Time-of-flight diffraction ultrasonics

About: Time-of-flight diffraction ultrasonics is a research topic. Over the lifetime, 544 publications have been published within this topic receiving 3189 citations.

Classification of TOFD Signals by Artificial Neural Network

Abstract: TOFD is one of the advanced ultrasonic NDE techniques widely used in weld inspection. Signal and image evaluation in TOFD requires adequate knowledge and experience. It is well known that artificial neural networks can be used for defect classification and sizing. However, review of literature indicates that very little work has been done in the area of application of ANN for TOFD signals and images. This work focuses on the application of multi layer feed forward network with Levenberg-Marquardt algorithm for the classification of TOFD signals from defect types such as Lack of Fusion and Lack of Penetration. TOFD signals from austenitic stainless steel weld pads with the above mentioned defects were acquired using an AEA micro plus TOFD equipment. Time scale features were extracted from the resultant TOFD A scans. Increasing the number of hidden layers in the network from 0 to 4 resulted in classification accuracy better than 95%. The results are a pointer to the promising application of this for automatic defect classification by TOFD technique. This paper provides the approach and analysis methodologies and the results obtained.

TOFD Echo Signal Processing to Achieve Superresolution

Abstract: It is proposed to use the method of maximum entropy (ME) and the method for constructing the AR model of the TOFD echo spectrum together with the method of splitting the spectrum to increase its resolution and, consequently, information content. The effectiveness of the approach proposed is demonstrated in model experiments. As a result, the resolution of TOFD echo signals has increased by at least two times, and the noise level has decreased by 6 dB. The higher resolution of TOFD echoes allows for phase analysis of echoes and conclusions about reflector type.

Design and adsorption force optimization analysis of TOFD-based weld inspection robot

Abstract: To meet the requirements of large metal tank weld inspection, a robot design scheme was proposed to walk on the outer surface of the tank and carry TOFD probe. The wall-climbing module, connecting frame module and TOFD weld inspection module are specifically designed. In this paper, the permanent magnetic adsorption principle and four-wheeled mechanism are both adopted in the wall-climbing module, meanwhile, the magnetic wheel's adsorption force is analyzed under multiple parameters. The main parameters affecting the adsorption force are obtained. To ensure the minimum size and the lightest quality of magnetic wheel, the adsorption force is also optimized based on the main parameters which are related to the permanent magnet itself. The above work provides a reference value for the research and development of intelligent weld inspection products of large metal tanks.

Enhancement of Time Resolution in Ultrasonic Time-of-Flight Diffraction Technique With Frequency-Domain Sparsity-Decomposability Inversion (FDSDI) Method

Abstract: The lack of time resolution restricts the quantitative detection of shallow subsurface defects with ultrasonic time-of-flight diffraction (TOFD) technique due to the superposition between lateral wave and diffracted waves from upper and lower tips. In this article, the frequency-domain sparsity-decomposability inversion (FDSDI) method was proposed to enhance the time resolution in TOFD based on the sparsity and decomposability of the ultrasonic reflection sequence. An optimization problem was formulated in the frequency domain by combining ${l}_{{1}}$ - and ${l}_{{2}}$ -norm constraints. The simulation was performed with a carbon steel model containing a series of shallow subsurface cracks at the depths of 2.0, 2.5, 3.0, 3.5, and 4.0 mm. The relative measurement errors of defect depths and heights were no more than 6.57%, and the depth of the dead zone was reduced by 70%. Subsequently, the feasibility of the FDSDI method was experimentally verified on a carbon steel specimen with an artificial defect. The defect depth and height were calculated with relative errors within 6.0%. Finally, the detection capacity of the FDSDI method was discussed, and the effects of frequency bandwidth, regularization parameter, and noise on inversion results were analyzed by experiments. It is concluded that the FDSDI method decouples the multiple overlapped signals and significantly improves the time resolution to quantify the small defects in the dead zone.

Results of the 2015 UT modeling benchmark obtained with models implemented in CIVA

Abstract: This communication presents the results of the 2015 UT benchmark obtained with the models implemented in CIVA. The benchmark addresses the TOFD technique. To calculate the diffraction echoes, field by applying the pencil-model and diffraction on notches edges is modelled by GTD (Geometrical Theory of Diffraction). We present comparisons between experimental and simulated results. We discuss the results obtained with and without applying the so-called “plane wave approximation” on the incident field.