Acoustic Emission of Structural Materials Exposed to Open Flames.
Acoustic Emission of Structural Materials Exposed to
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
fire detection; acoustic properties; acoustic sensors;
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.