JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - 57

kissing bonds can only be revealed by
shearography. Therefore, the methods
are complementary. The following
example demonstrates the successful
combination of both methods for the
complete inspection of a composite
aircraft wing (Figure 6).

Fig. 5: Aluminium honeycomb panel with
simulated defects, tested using a combination of thermal and partial vacuum loading
shearography

rials and very stiff materials with a low
thermal expansion coefficient (e.g.
C-SiC ceramics). In some cases, only
a combination of loading techniques
leads to optimum defect visualization.
Figure 5 shows this approach for the
inspection of an aluminium honeycomb panel.
The shearogram reveals the debonding of the cover (front side and far
side, Figure 5, left) as well as resinfilled honeycomb (Figure 5, middle)
and two inserts, one of them being
debonded (Figure 5, right). This result
was generated by a combination of
thermal and partial vacuum loading.
Many types of defects are detectable
by both thermography and shearography, but there are some flaws that
can only be revealed by one of them.
Porosity, inhomogeneous fibre volume
content and wall thickness can be
detected by thermography, but not
with shearography. On the other hand,
out-of-plane fibre undulation and

The standard approach to check the
bonding of the wing after manufacturing consists in drilling a hole
into each fin field to endoscopically
determine if there is sufficient adhesive between the spar, fins and cover,
leaving the brand new wing perforated after the test. Shearography and
thermography made it possible to
perform this inspection task faster, in
a non-destructive way and providing
more information. Thermography
was used for the monolithic GFRP
part of the cover on top of the spar.
The results show an out-of-tolerance
narrowing of the adhesive seam at
several spots between the spar and the
cover (Figure 6, right). Shearography
was suitable for the inspection of the
adhesion between the GFRP/foam
sandwich cover and the fins. While
endoscopy can only check if there is
a sufficient amount of adhesive, shearography can distinguish if there is
adhesion or not. In the case described,
it revealed one fin with no adhesion to
the cover (Figure 6, bottom).
Both methods are not only suited for
fibre-reinforced plastic composites,
but also for metal and metal/FRP
structures (depending on the thickness
of the material). They can be applied
at different stages of production (for
example, preforms can be inspected

Fig. 6: GFRP/foam sandwich wing of an ultralight aircraft tested using both shearography
(bottom) and thermography (right). Courtesy of
IKT, University of Stuttgart

efficiently using thermography), but
also in maintenance and after repair.
In addition, many other applications
are possible, like testing of Li-ion
batteries (detection of air pockets,
particle detection). Depending on the
application, automated measurement
and evaluation are possible using both
methods. Standards for active thermography and shearography were recently
established or are currently under revision. Standards for the certification
of personnel are also available (EN
4179 for aerospace and ISO 9712 for
industrial applications). n

No92 October - November 2014 /

More information:
www.edevis.com

jec composites magazine 57
http://www.edevis.com http://www.teicomposite.com
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014
