JEC COMPOSITES MAGAZINE - Issue #83 - August/September 2013 - 72

NDT

Fig. 6: SAUL compensation for a misaligned curved array

do not address part-to-part variability.
It is also common for systems to have
features that allow repositioning of the
part or adapting the scan plan where
necessary. This, however, requires time
and actions that must be performed in
the tank, leading to an increased cycle
time and loss of system availability to
inspect parts.
Figures 4 and 6 show the results of
experiments performed to demonstrate
SAUL’s ability to correct for probe misalignment. The top figures in Figure 4
show the position of a linear probe for
two measurements, as well as the delay
laws applied to the probe’s elements
(indicated by the red bars). For the
first measurement, the probe was oriented parallel to the composite-plate
test specimen and fired with no delay
laws applied. The resulting B-scan is
shown in the lower-left image. For
the second measurement, the probe
was tilted 5 degrees from normal as
indicated in the top-right image. In this
case, SAUL was activated to calculate
the delay laws required to compensate
for the tilt of the probe. As described
above, the objective of the SAUL
delay-law optimization is to generate a
wave front that is normal to the front
surface of the test specimen. The same

principle is used for curved surfaces,
where the incident wave fronts are
optimized locally to match the surface
(see Figures 5 and 6).
The experimental setup for measurements made with a curved array and
a composite tube are shown in Figure
4 (top images), along with a picture
of the release-film defects that were
placed mid-laminate in the tube (bottom image). The probe curvature is a
good match to the tube, and all four
defects were detected and imaged
when the curved array was well centred
on the test specimen as shown in the
first column of Figure 5. When the
probe was shifted 3 mm off-centre, all
return signals were lost as shown in the
centre column. Maintaining the probe
in the offset position and activating
SAUL completely restores the signals
as shown in the third column.
Comparing the images in the first and
third columns shows that the scans obtained with SAUL for the probe in the
offset position agree very well with the
images obtained when the probe was
correctly centred on the test specimen.
The results of laboratory experiments
and modelling were used to optimize
SAUL for the wide range of composite-

72 jec composites magazine / No83 August - September 2013

part geometries encountered in the
aerospace sector. This effort included
M2M’s design and optimization of the
4x16 matrix probe shown in the lowerleft corner of Figure 3. This probe
is being used to inspect hundreds of
different composite parts in the first
fully-automated SAUL implementation
at the EADS composites production
facility in Aquitaine, France. The advantage of the 2D array is that geometry compensation is performed in
two directions, allowing the probe to
be used on a variety of complex parts
including those with small radii. The
probe also successfully compensates
for part variability, greatly improving
productivity compared to installations
using multiple probes and/or manual
part manipulation.
Figure 7 shows two views of a part
inspected using SAUL with the 2D matrix probe described in Figure 3. The
part is an L-shaped composite panel
with a tight radius, most easily seen
in the 3D image (left-hand picture).
Although not easy to see in the figure,
the part is curved in the X-Y plane.
Amplitude and time-of-flight C-scans
obtained for the part are displayed in
Figure 8. To facilitate interpretation,
the C-scan images have been separated

JEC COMPOSITES MAGAZINE - Issue #83 - August/September 2013

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