JEC COMPOSITES MAGAZINE - Issue #117 - November/December 2017 - 63

Health monitoring of CFRP using printed circuits

Fig. 5: Force and resistance change of the four measured
channels versus displacement

Fig. 6: Light microscopy observation of polished sections after testing. Left: region above electrodes
2 and 3 (middle electrodes), inter-fibre failures and delaminations. Right: region above electrodes 1
and 4 (outer electrodes), only inter-fibre failures

Mechanical and electrical measurements for a representative
specimen are plotted in Figure 5. The resistance changes are
different for the four measured channels. For channel 1 (from
top electrode to low electrode 1) and channel 4 (from top
electrode to low electrode 4), there is no significant resistance
change until the final fracture where the resistances suddenly
increase to infinity. The resistance change of channels 2 and 3
(from top electrode to lower middle electrodes) increases significantly with increasing displacement up to 26% and 17.5%
before final failure, respectively.
Close to electrodes 1 and 4, no delaminations and inter-fibre
failures interrupting the current flow in the thickness direction are present. For channels 2 and 3, the resistance increase
indicates that damages occur inside the material close to the
most stressed areas in the centre of the specimen. This can be
seen in light microscopy observations (see Figure 6). Above
electrodes 2 and 3 (centre electrodes), inter-fibre failures in
the three lower 90° layers and delaminations in-between the
0° and 90° layers are found. Above the outer electrodes (1 and
4), only inter-fibre failures are detected. Since the resistance
increases only for measurements with electrodes close to the
most loaded areas where delaminations occur, delaminations
can be detected by a significantly higher resistance change
compared to areas where only inter-fibre failures occur, which
are not detected by the through-thickness measurements.

Conclusion
Inkjet-printed silver nanoparticle ink on CFRP allows for
structural health monitoring and for the detection of both
surface cracks and delaminations. If inter-fibre failures occur
on the surface, the electrical resistance measured along single printed paths increases due to interruptions of the printed
paths, which have a significantly lower resistance than CFRP.
Failures inside the material can be detected by measuring the

electrical resistance through the material. With through-thickness measurements, delaminations can be detected by an increase of the electrical resistance. If multiple electrodes are
printed on the material surface and several measurements are
conducted synchronously, a localization of the defects is possible. Hence, in case of tailored-designed printed paths additionally to the detection, inter-fibre failures and delaminations can
also be localized in CFRP.

Acknowledgements
The authors acknowledge the financial support from the
Landesforschungsförderung Hamburg (grant number LFF-FV
05). Furthermore, they acknowledge the Institute of Automation
Technology (Helmut Schmidt University) for printing conductive paths and Hexcel for supplying prepregs.
More information:
dx.doi.org/10.1080/20550340.2017.1362508
www.tuhh.de/kvweb
till.augustin@tuhh.de
References
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Online monitoring of surface cracks and delaminations in carbon
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Advanced Manufacturing: Polymer & Composites Science 2017;
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[2] Diamanti K., Soutis C. Structural health monitoring techniques
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[3] Chung D.D.L. Structural health monitoring by electrical
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[4] Schulte K., Baron C. Load and failure analyses of CFRP
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Composites Science and Technology 1989; 36(1):63-76.
[5] Kim H.S., Kang J.S., Park J.S., Hahn H.T., Jung H.C., Joung J.W.
Inkjet printed electronics for multifunctional composite structures.
Composites Science and Technology 2009; 69(7-8):1256-64.

N°117 November - December 2017

/ jec composites magazine

http://dx.doi.org/10.1080/20550340.2017.1362508 http://www.tuhh.de/kvweb

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