Ultrasonic Time of Flight Diffraction (TOFD) for sizing defects is based on the time of flight of the longitudinal diffracted echo(es) that is (arc) generated when a longitudinal wave is incident on a crack tip. TOFD technique so far has been commonly applied for the inspection of thick sections (>15 mm) and thickness below 5 mm from the scanning surface. This paper focuses the applications of the TOFD technique to thin and near surface inspections using shear wave diffracted echo (es) from the defect tips. Experimental result for simulated and realistic defects in thin samples will be presented. © 2006 American Institute of Physics.

Krishnan Balasubramaniam

Department of Mechanical Engineering

C V Krishnamurthy

Department Of Physics

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Inspection Using Shear Wave Time of Flight Diffraction (S‐TOFD) Technique

AIP Conference Proceedings

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. © 2006 Elsevier Ltd. All rights reserved.

NDT and E International

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

It is necessary to size the cracklike defects accurately in order to extend the life of thin-walled (< 10 mm) components (such as pressure vessels) particularly for aerospace applications. This paper discusses the successful application of ray techniques to simulate the ultrasonic time-of-flight diffraction experiments for platelike structures. For the simulation, the diffraction coefficients are computed using the geometric diffraction theory. The A and B scans are simulated in near real time and the different experimental parameters can be interactively controlled due to the computational efficiency of the ray technique. The simulated results are applied to (1) defect signal identification for vertical defects, (2) inspection of inclined defects, and (3) study the effect of pulse width or probe frequency on experimental results. The simulated results are compared with laboratory scale experimental results. Copyright © 2005 by ASME.

Journal of Pressure Vessel Technology, Transactions of the ASME

Ray based model for the ultrasonic time-of-flight diffraction simulation of thin walled structure inspection

The ultrasonic Time-of-Flight Diffraction (TOFD) technique is a well developed technique for sizing defects in thick sections (thickness >10 mm). Attempt has been made here to extend this technique for thin sections (6-10 mm). An automated defect sizing algorithm using the Embedded Signal Identification Technique (ESIT) was developed for separating partially superimposed signals often encountered in thin sections and the results were compared with the manual sizing method. Both EDM notches and more realistic fatigue cracks in thin section were used to evaluate the proposed technique.

Journal	AIP Conference Proceedings
ISSN	0094243X
Open Access	No