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Acoustic Emission of Structural Materials Exposed to Open Flames.


pdf icon Acoustic Emission of Structural Materials Exposed to Open Flames. (371 K)
Grosshandler, W. L.; Jackson, M. A.

NISTIR 4984; 26 p. December 1992.

Fire Safety Journal, Vol. 22, No. 3, 209-228, 1994.

Available from:

National Technical Information Service
Order number: PB93-138980

Keywords:

fire detection; acoustic properties; acoustic sensors; material properties

Abstract:

The use of acoustic emission (AE) as an early indicator of structural materials exposed to a flame has been investigated and found to be possible. Piezoelectric transducers have been mounted directly on 0.5 m long, simply supported beams of aluminum, gypsum board, wood and plastic, and have been used to record ultrasonic events resulting from a small flame placed under the beam. The number of AE events in a minute and the cumulative energy released during the heating cycle provide a good measure of the overheated state of some of these materials even before a temperature increase is indicated. The measured signals varied in energy and number with the type of material, the thickness of the specimen and heat flux. Wood was particularly susceptible to acoustic emission, producing more than 1000 events/min in a solid fir board and 30/min in 13 mm thick plywood when the flame exceeded 1 kW. A gypsum board produced 16 events in a minute. An aluminum plate did not respond above the background level (0.3 events/min) even though it reached the highest temperature. The differences in cumulative energy were equally striking, with the plywood being four times more energetic than the gypsum board even though the heating period for the wood was half as long, and 30 times more energetic than the aluminum. Some critical issues which remain to be investigated before this technique can be adapted to practical fire detection are mentioned.