FIFTH CANADIAN CONFERENCE ON NONDESTRUCTIVE ... - IAEA

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COMPUTER CONTROLLED CARBON COMPOSITE PANEL TESTERS
5. VaWalle.
Canadian HVL Technology Limited, Rzxdate, Ontario
When we speak of composites these days we generally refer to panels composed
of a number of layers of cloth made of carbon, graphite or kevlar fibers held
together and impregnated with a binder or adhesive which after the
application of heat and pressure within a vacuum becomes a strong light
panel.
Since the price of the materials from which these panels are made and the
construction as well as the testing has been very costly, the use of these
panels has been restricted primarily to military airplanes, frames and skins.
However as the cost of the material and construction is coming down and more
applications are being found more aluminum and other metal components are
being replaced with this superior material.
The superiority of these panels for their function in airplanes or other
structures are in their weight-to-strength ratio as well as in the rigidity
in one direction versus flexibility in other directions.
However, the graphite or carbon composites can exhibit these properties only
if the layers are bonded together perfectly. Even small areas of unbond
between adjacent layers can significantly weaken the panels. Particularly if
these multilayer composites are glued against both sides of a metal or fibre
honeycomb, this so called composite sandwich can only be inspected by means
of ultrasonic through-transmission.
The heart of all present ultrasonic panel testing systems consists of two
transducers, one transmitter and one receiver, connected to an appropriate
ultrasonic instrument.
Since the honeycomb centered panel is extremely light and often very large,
up to 50" x 8" wide or larger, it is difficult to submerge it and perform an
immersion test on it.
Therefore, the two transducers are housed in so called water jets or
squirters. These water coupling devices produce a small diameter water
column in front of the transducers which allows the sound beam to be conveyed
from the transmitter transducer to the receiver.
When the panel is placed between the transducers, the sound beam passes
through the panel except where it is interrupted by an area of unbond. This
loss of signal amplitude is related to an amount or area of unbond.