JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - 54

NDT

analysed using the second grating (G2) and
the digital X-ray detector. In the presence of
a sample, the interference pattern is modified due to the absorption, refraction and
scattering of the beam within the sample,
so that two new images can be extracted in
addition to the conventional X-ray image:
the refraction and scattering images .

Ultrasound

Steel
Foreign
materials

Aluminium
PTFE

Resin-poor area
Resin-rich area
Fibre
misalignment

Out-of-plane
In-plane
1mm

Cut fibre

2mm
<2%

Porosity

2-5%
>5%
Cracks

54 jec composites magazine / No106 July 2016

Computed
tomography

Radiography

X-ray
Phased array

XPCI

Tab. 1 Defect detectability compared to other
NDI methods

Active infrared
thermography

Figure 3 shows the example of a door
hinge manufactured by compression
moulding out of chopped prepreg
tapes. The manufacturing process was
developed by the University of Applied
Sciences and Arts Northwestern Switzerland (Eguémann et al. 2013). Resin-rich
areas can be detected in the scattering
image while they stay invisible with
conventional X-ray systems.
Throughtransmission
ultrasonics

Fig. 3: X-ray phase contrast radiography images
of a CFRP door hinge produced by compression
moulding (Eguémann et al. 2013)

The additional images bring the following
advantages:
- Higher contrast for weakly absorbing
materials such as polymers and carbon
fibres,
- Sensitive to micro- and macrostructural
features such as porosity, cracks or fibre
misalignment.
These new insights in the material translate
into better detectability of critical defects for
a broad range of applications.

Water jet

Fig. 2: Schematic representation of the imaging
principle used in XPCI

EVITA project
Within the EVITA project, a prototype
was built to inspect components up to 1
× 0.75m. Using typical measurement parameters, an inspection speed up to 5m2/
hr can be achieved with the demonstrator - with further speed improvements
planned in future system generations.
XPCI was compared to conventional
NDI techniques such as water jet C-scan,
through-transmission ultrasonics, phased
array, conventional X-ray radiography
and tomography, and active infrared
thermography. The benchmark was made
on 4mm-thick monolithic CFRP panels,
where defects had been artificially
created. The results of the benchmark are
shown in Table 1.
As a summary, XPCI is a contact-free
transmission NDI technique without
coupling agent. It has the related advantages of being more sensitive than
other NDI methods and having a higher
penetration depth, thus allowing the inspection of thicker parts (>30mm). The
current demonstrator was developed for
a stationary use due to the safety requirements that involve an X-ray cabinet or
bunker. In terms of detectability, XPCI
is more sensitive to cracks, porosity and
foams compared to other NDI techniques. n
More information:
www.csem.ch
vincent.revol@csem.ch

References
- CSEM, 2015. EVITA project (grant number 314735).
www.evita-project.eu.
- Eguémann, L. et al., 2013. Manufacturing of complex
composite parts for aerospace application with novel and
recycled thermoplastic materials. In Proceedings of 19th
international conference on composite materials 2013.
- Frost & Sullivan, 2013. The Global Nondestructive
Testing Equipment Market for Composite Inspection
(9840-30).
- Pfeiffer, F. et al., 2006. Phase retrieval and differential
phase-contrast imaging with low-brilliance X-ray sources. Nature Physics, 2(4), pp.258-261. www.nature.com/
doifinder/10.1038/nphys265 [Accessed March 5, 2012].
- Revol, V. et al., 2010. Noise analysis of grating-based
x-ray differential phase contrast imaging. Review of Scientific Instruments, 81(7), p.73709. Available at: http://
www.ncbi.nlm.nih.gov/pubmed/20687733.

http://www.csem.ch http://www.evita-project.eu http://www.nature.com/doifinder/10.1038/nphys265 http://www.nature.com/doifinder/10.1038/nphys265 http://www.ncbi.nlm.nih.gov/pubmed/20687733 http://www.ncbi.nlm.nih.gov/pubmed/20687733

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #106 - July 2016