Please wait. Contacting image service... loading

Article text

PHITS off to a flying start
By MARTIN AUBURY
RACKS and corrosion are
l| the bane of aircraft main
tenance; so much so that
the US Federal Aviation Adminis
tration is spending millions to
find better ways of detecting de
fects before they become danger
ous. Now $247,000 of the money
has come to Canberra to boost de
velopment of a portable holo
graphic interferometric testing
system (PHITS) pioneered at Aus
tralian Defence Force Academy
by the Aerospace and Mechanical
Engineering Department, Univer
sity of NSW.
A team led by Associate Profes
sor John Baird has demonstrated
that holographies can pinpoint
defects in typical aircraft struc
ture with equipment which is
portable practical and cheap -
about $3000. Holographic inspec
tion has been around for 20
years, but hitherto was hampered
by vibrations, whereas the UNSW
approach is practical for field
use.
The technique involves project
ing a laster beam through a pho
tographic plate on to suspect
structure, such as riveted joints
or regions prone to hidden corro
sion. On the film, the incoming
reference beam interferes with
light reflected from the structure
to produce fringe patterns called
interferograms, which replicate
minute contours of deformation.
' By gently loading the structure
while the film is exposed, any ir
regularities in the structure are
revealed as irregulation in the
fringe pattern. Because the holo
graphic film is mounted on the
structure just clear of its surface,
any background vibrations shake
the specimen and film identically
and so have no adverse effect on
the interferograms. Initial results
show that the technique is sensi
tive enough to detect cracks
starting at a rivet hole, well be
fore the crack emerges from un
der the rivet head. And unlike
current methods, holographies
can readily cover large area's.
Although the initial FAA con
tract is for one year, satisfactory
progress will trigger a five-year
funding program to fully validate
PHITS as an attractive new in
spection tool.
Technical officer Joe Van Dyke operates the AAS. The grey cylinder at the front of the machine is the furnace. Senior technical officer Bob Clark, left, and Associate Professor John Baird with the PHITS svstem at ADFA. Help
Senior technical officer Bob Clark, left, and Associate Professor John Baird with the PHITS svstem at ADFA.
$