NDTnet 1998 Aug, Vol.3 No.8

Abstract

Introduction
The use of the surface ultrasonic waves seems to be convenient for the identification of surface and subsurface defects. However, this method has not found wide practical application. It is connected with the fact that the surface waves are weakened by soil on the surface itself. In addition, the methods of testing by the surface waves does not yield to automation due to the difficulties of the acoustic contact creation. The aim of this work is the creation of the surface waves transducer for the automated testing.

Conditions of surface waves excitation
Under the surface waves excitation the fluid for the acoustic contact must be located only in the places of contact, otherwise the influence on the amplitude will be uncontrolled. When the surface waves excited through the slot gap, the basic attentions must be drawn to the analysis of the contact liquid front meniscus position relatively of the acoustic beam exit extreme point.The investigations has been shown that the optimum location of the meniscus is within the range -0.1a/cos and 0.3a/cos. (fig. 1 a- the piezoelement radius, - the angle of prism slope).

Fig. 1 The scheme of surface wave excitation

The supply of acoustic contact
The implementation of the described sound duct is performed by the use of the magnetic liquid as the contact medium. The magnetic systems must held the magnetic fluid within the above specified limits. It was made on the base of the permanent magnets and located in the body of the transducer [1]. The equivalent solenoid method was used in the calculations [2].

Conclusion
The described method allows to achieve the constancy of the conditions of the surface waveformation. Using the described transducer in the complex with the system of the acoustic contact control, system of the contact liquid supply as far as it is consumed has allowed to increase the time of the aircraft engine compressor wheel disks testing on the several tens times.

References
1.Prokhorenko,P., Baev,A, Konovalov, G. 11-th WCNDT, Las-Vegas, USA, 1985, 4:385-388
2.Mayorov A. NDT - 89 - Int. Conference - Plovdive, Bulgaria, 1989, 2: 583-586.

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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