Poster from the ICTMS2015 conference.

1. Distance transforms and correlation maps for advanced
3D analysis of impact damage in composite panels.
Fabien Léonard1
and Jasmin Stein2
1
BAM – Federal Institute for Materials Research and Testing, Unter den Eichen 87, 12205 Berlin, GERMANY
2
TWI Ltd., Granta Park, Great Abington, Cambridge, CB21 6AL, UK
Introduction
The development of better composite materials for aerospace
applications requires an improved understanding of how dam-
age is generated within composite laminated structures follow-
ing a low velocity impact event.
Whilst most non-destructive techniques provide only 2D in-
formation, X-ray computed tomography can provide a full 3D
characterisation of the damage within a composite panel.
However, new CT data processing methods must be developed
to extract the relevant metrics and link the damage to the
composite structure (ply-by-ply damage separation).
Objectives
• Assess non-destructively and in 3D impact damage
• Link damage to structure (ply-by-ply damage separation)
• Extract meaningful damage metrics
Experimental details
The specimens are composite panels used as primary structures for aerospace applications. The reinforcement is a unidirec-
tional carbon fibre fabric bound with glass fibre yarns in a high glass transition temperature epoxy resin matrix.
Each panel consisted of 8 plies with ply angles of
0◦
and 90◦
, giving a complete lay-up sequence of
[(0◦
/90◦
)2]s detailled in Figure 1. The composite lam-
inates were manufactured by vacuum assisted resin
film infusion (VARFI).
Impact tests were carried out at 5 J, 10 J, 15J, and
20 J, according to the methodology of Prichard and
Hogg [1] with a specimen size of 89 mm x 55 mm
x 3 mm, an impactor mass of 5.048 kg and a hemi-
spherical tup 20 mm in diameter.
After impact test, the specimens were CT scanned
on a Nikon Metrology 225 kV system with the follow-
ing settings: 35.7 µm voxel size, Cu target, 60 kV,
175 µA, 2s exposure time, and 3142 projections.
Ply No. Angle (◦
) Interface
1 0
1
2 90
2
3 0
3
4 90
4
5 90
5
6 0
6
7 90
7
8 0
(a) Ply number, fibre orientation and interface numbering (b) Lay-up sequence
Figure 1: Overview of lay-up sequence of composite panels.
Data processing
The approach proposed here relies on the combination of two
distance transforms taken from different reference points into
a single map, called damage correlation map.
This approach provides a 2D map (Fig. 2e and 3) that more
clearly represents the complex 3D morphology of the impact
damage than previous work [2].
It also improves the accuracy of the damage separation and
subsequent analysis, as the panel distortion is better accounted
for. An overview of the data processing methodology is given
in Figure 2.
(a) Raw 2D slice
(b) Labelled damage
(c) Damage distance transform from impact face
(d) Damage distance transform from damage centre line
(e) Damage correlation map
Figure 2: Data processing workflow for panel impacted at 10 J.
Results
• Damage correlation map
The damage correlation map approach proposed here, gives an improved representation of the impact damage occurring within
the composite panel. Figure 3 clearly shows the greater impact damage in the panel tested at 15 J, as well as the greater
distortion close to the panel centre line and the wider delamination opening, compared to that of the 5 J panel. The damage
correlation maps can also be used to separate the segmented damage for each individual plies, as can be seen in Figure 4.
(a) 5 J (b) 15 J
Figure 3: Damage correlation maps for panels impacted at 5 J and 15 J.
• Ply-by-ply damage separation
The damage can be related to each individual ply and therefore, the evolution of the damage created versus the impact energy
can be measured qualitatively and quantitatively. In addition to global measurements, local measurements such as damage
volume, maximum delamination length and width, or projected damage area, can be obtained for each ply of the structure.
These measurements are required to improve our understanding of the type (failure mode) and extent of the impact damage.
(a) 5 J interface 1 (0◦
/90◦
) (b) 5 J interface 2 (90◦
/0◦
) (c) 5 J interface 3 (0◦
/90◦
) (d) 5 J interface 5 (90◦
/0◦
) (e) 5 J interface 6 (0◦
/90◦
) (f) 5 J interface 7 (90◦
/0◦
)
(g) 15 J interface 1 (0◦
/90◦
) (h) 15 J interface 2 (90◦
/0◦
) (i) 15 J interface 3 (0◦
/90◦
) (j) 15 J interface 5 (90◦
/0◦
) (k) 15 J interface 6 (0◦
/90◦
) (l) 15 J interface 7 (90◦
/0◦
)
Figure 4: Ply-by-ply damage separation according to damage correlation map for 5 J and 15 J impact energies.
References
[1] Prichard and Hogg The role of impact damage in post-impact
compression testing. Composites, 21(6) : 503–511, 1990.
[2] McCombe, Rouse, et al. X-ray damage characterisation in self-
healing fibre reinforced polymers. Composites Part A: Applied Science
and Manufacturing, 43(4):613–620, April 2012.
Contact details
fabien.leonard@bam.de
+49 30 8104 4627
+49 30 8104 1837
BAM website: http://www.bam.de
Conclusions
• Impact damage in composite panels can be fully assesses in 3D using X-ray computed tomography.
• An innovative data processing methodology using distance transforms and correlation maps has been developed to
provide qualitative and quantitative measurements for each individual ply of the laminates.
• The separation of the impact damage ply-by-ply is needed to improve our understanding of the type (failure mode) and
extent of the impact damage.
• The information provided here is essential both in terms of understanding the capacity of composites to absorb energy under
impact and to predict the residual strength/capability of composite laminates.
• Such data processing methodology is not limited to polymer composite laminates and could be applied to fibre metal
laminates (FML) or composite parts with complex geometries.