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.

Krishnan Balasubramaniam

Department of Mechanical Engineering

C V Krishnamurthy

Department Of Physics

Chebolu Lakshmana Rao

Algorithms

Cracks

Fatigue of materials

Imaging techniques

Inspection

Nondestructive examination

AUTOMATED DEFECT SIZING ALGORITHM

EMBEDDED SIGNAL IDENTIFICATION TECHNIQUE

THIN PLATES

Ultrasonics

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

Insight: Non-Destructive Testing and Condition Monitoring

Experimental probability of detection (POD) and probability of sizing (POS) curves are developed for the detection and sizing of surface-breaking cracks in components having complex geometry. A manual ultrasonic time of flight diffraction (TOFD) inspection system has been used to develop these POD and POS curves. Initially, it was assumed and subsequently verified that signal responses have a normal distribution. The effects of probe angle and probe center-to-center spacing on both POD and POS were observed. Unlike the PODs previously reported for conventional ultrasonic amplitude based flaw sizing techniques, the PODs associated with TOFD in the range of defect sizes considered here, exhibit a decreasing trend for a fixed set of experimental parameters. It is important to emphasize that the curves obtained in this work are specific to the geometry, specimen dimensions, set of notches and the specific probes used in the experiment. However, when using a manual TOFD inspection system, these curves can be useful for planning the risk-based inspection of components having complex geometry (such as a steam turbine rotor shaft). © 2009 Elsevier Ltd. All rights reserved.

NDT and E International

Reliability assessment of manual ultrasonic time of flight diffraction (TOFD) inspection for complex geometry components

The basic aim of this current research is to reliably detect and size defects in complex geometry welds using the well-known ultrasonic time of flight diffraction (TOFD) technique. A complex geometry weld specimen with various artificial defects was designed and fabricated. Different combinations of probe angles and probe center spacings were used in experiments for determining the optimum one. TOFD models were also developed for sizing the defects and experimentally verified. Copyright © 2009 by ASME.

Journal of Pressure Vessel Technology, Transactions of the ASME

Detection and sizing of defects in complex geometry weld by manual ultrasonic time of flight diffraction inspection

A hybrid-GA method, based on signal parameterization, has been reported here for the improved detection and sizing of surface cracks of small sizes/depths in thin sections. The method relies on parameterizing the composite reference from the defect into its individual components i.e., the crack tip diffracted echo and the corner trap echo and subsequently use the relative arrival time technique (RATT). The phased array ultrasonic technique was employed in the investigation. Both experimental and simulated signals were used in the study. It is shown through both simulations and experiments that the hybrid-GA is successful in parameterizing both non-overlapping and overlapping echoes encountered in thin sections. It is additionally shown that the hybrid-GA improves the signal to noise ratio and correct for under-sampling of data. © 2007 Elsevier Ltd. All rights reserved.

Theoretical and Applied Fracture Mechanics

Inverse method for detection and sizing of cracks in thin sections using a hybrid genetic algorithm based signal parametrisation

Sizing a surface-breaking crack in a complex geometry component, for example a steam turbine's solid rotor shaft, is a challenging inspection task. This paper deals with experimental work for the evaluation of the Time-of-Flight Difftaction (TOFD) technique for sizing of surface-breaking cracks in such a complex geometry component. The experimental results show that with the help of the mathematical model explained here, TOFD can size such cracks with reasonable accuracy.

Sizing of surface-breaking cracks in complex geometry components by ultrasonic Time-of-Flight Diffraction (TOFD) technique

Phased array ultrasonics can be used as a rapid tool for imaging and sizing crack-like defects. This paper reports the simulation of phased array ultrasonic wave interaction with the defects using the finite-difference time domain (FDTD) method. Experiments were conducted to validate modeling results for pulse-echo simulations of the phased array transducer on a mild-steel (MS) pipe sample with circumferential internal surface notches of three different sizes. Experiments were carried out on the MS pipe specimen using a conventional ultrasonic technique with a 5 MHz transducer at 45° refracted angle within the specimen and the defects were imaged and sized using the relative arrival time technique (RATT). The experimental B-scans obtained using the conventional ultrasonic techniques were compared with the experimental B-scans obtained using the phased array instrument. Simulation studies were also carried out by steering the beam to the requisite angles by the phased array transducer to study the effect of various angles of incidence on the defect definition, i.e., with respect to imaging and sizing, using the RATT. © 2007 Elsevier Ltd. All rights reserved.

International Journal of Pressure Vessels and Piping

Simulation of ultrasonic phased array technique for imaging and sizing of defects using longitudinal waves

IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control

Time of flight diffraction imaging for double-probe technique

Signal Processing

Cumulative contents of volume 36

NDT & E International

TOFD technique covered by British standard

NDT International

Changes in ultrasonic defect location and sizing

Diffraction of elastic waves by cracks: application to time-of-flight inspection

Ultrasonic TOFD flaw sizing and imaging in thin plates using embedded signal identification technique (ESIT)

Journal	Insight: Non-Destructive Testing and Condition Monitoring
ISSN	13542575
Open Access	No