DETERMINATION OF ELASTIC CONSTANTS IN A MATERIALS SUBMITTED TO HIGH TEMPERATURES WITH AN ULTRASONIC METHOD
Marie-Helene Nadal, Cyril Hermerel, Christian Gondard and Luc Paradis
CEA, BP 12, F 91680 BRUYERES, France
Keywords: Ultrasonic, Elastic constant, NDT, Composite, Elastic Constant
ABSTRACT The design of new materials leads to the use of specific characterisation tools. The knowledge of the elastic constants is an important data allowing the choice of elaboration and implementation parameters of these materials. For those which are submitted to high temperatures, most of the conventional measurement methods, such as mechanical testings, are unsuitable. Now, it is well known that the propagation velocities of different acoustic waves are directly linked to the elastic constants of the materials [1]. This nondestructive method applies to as well as isotropic and anisotropic materials [2]. The first device that we have developed allows the measurement of shear and compression waves speeds up to 1000°C on cylindrical specimens. The thermal insulation of the transducers is obtained with steel wave guides [3] for which it was necessary to optimise the dimensions in order to improve the signal to noise ratio. The measurement of wave time of flight in the specimen is obtained by a time averaging technique on different paths on transmission and reflexion which allows to exclude the effects of temperature gradients in wave guides. Several data processing algorithms were adjusted in order to take into account various deformations undergone by echoes (especially phase rotation and frequency scattering). This device was used for metallic and composite material. The accuracy on elastic constants is in the order of 5%. In some cases, it was possible to perform comparisons with data obtained with conventional techniques, and the validity of our results was confirmed. Another device based on the same principles, but adjusted to a working temperature upto 3000°C, is under development. It is characterised by new wave guides, special transducers working up to 350°C, and specific coupling medium. This technique is therefore very promising, especially because it is nondestructive and relatively simple to be implemented.
REFERENCES
- E. Carnevale, L. Lynnworth and G. Larson, Ultrasonic Measurements of elastic moduli at elevated temperatures using momentary contacts, J. Acous. Soc. Am., Vol. 36, No. 9, pp 1678-1684, 1964
- C. Malmstrom, R. Keen and L. Green, Some mechanical properties of graphite at elevated temperatures, J. Appl. Phys., Vol. 32, No. 5, 1951
- R. Thurston, Elastic waves in rods and optical fibers, Journal of sound and vibration, Vol. 159, No. 3, pp 441-467, 1992
Publication Source: Trends in NDE Science & Technology; Proceedings of the 14th World Conference on Non-Destructive Testing, New Delhi, 8-13 December 1996.Vol. 4, pages 2259 - 2262
Publisher: Ashgate Publishing Company
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