NDTnet 1998 Aug, Vol.3 No.8

Abstract

Lamb waves are attractive for large structure inspection because a significant area of structure can potentially be inspected from a single transducer position. However, it is essential to control the mode which is excited and the direction of propagation in order to obtain simple signals which can be interpreted easily.

Figure 1. Interdigital transduce ; Figure 2. Example of electrode pattern

The authors have developed interdigital transducers (1) which can be bonded permanently to a structure. They can be used selectively to excite and receive a specific Lamb mode and to insonify a particular region of a plate. Typically, pulse-echo measurements could be used to detect reflections from defects such as cracks or corrosion. The concept of the transducer is illustrated in Figure 1, and Figure 2 shows an electrode pattern designed for a focused or divergent beam. The transducers have been developed to be suitable for 1-2 mm thick plates and are being developed for thicker plates of up to 10 mm. They therefore offer potential for inspection of large plate structures as well as thin-skinned structures such as aircraft.

The paper examines the selection of the appropriate mode for defect detection and the design of suitable electrode patterns to enable a single transducer to be used to inspect in all directions around it, aiming to indicate both the distance and the direction of any defects. Experimental measurements and model predictions are used to validate the designs.

(1) R S C Monkhouse, P D Wilcox, P Cawley, Review of Progress in Quantitative NDE. 199 16A: 877-884.

Abstract Source:
Book of Abstracts, 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN: 87-986898-0-00

Full-Text Source:
Proceedings of the 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN:

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