Development of material verification test procedure for edge glow protection performance

When a high current density flows in a Carbon Fiber
Reinforced Plastic (CFRP) part, the resulting voltage drops
within the material associated with the strong electrical
anisotropy of the laminate can lead to electrical breakdowns
or hotspots at the cut edges of the material or on the inner
surface of the panel. The phenomenon occurring at the edge is
called “Edge Glow” which can be considered as an ignition
hazard.

In order to limit its intensity or even better, to avoid the
phenomenon to occur, much work has been performed in
order to improve the equipotentiality of the carbon layers in
the bulk of the laminate by increasing the transverse
conductivity (i.e. Z-conductivity) through the introduction of
electrical contacts between plies.
In order to validate a new CFRP material, the performance
assessment was based on a lightning test performed on several
T-joints which were very expensive and time consuming to
manufacture, making the overall development process slow
and not compatible with the program objectives and
constraints.
In order to support the development of new carbon material in
a more efficient way, a simplified assessment test is presented
in this paper that focuses only on the performance against edge
glow independently from the final assembly solution. In that
respect, the Edge Glow protection performance becomes
inherent to the material properties and does not depend any
more on the detailed design of the part, which is exactly the
target set for future composite tank developments.
With this new method, the sample is made of one small
coupon of CFRP with 2 fasteners installed in interference fit
and misaligned to enhance voltage drop apparition under
direct current injection. Although it was not possible to link
directly macroscopic parameters such as the voltage drop and
current with the microscopic phenomenon associated with the
apparition of light at cut edges, this method, based on camera
measurements, enabled a quick and economical assessment of
the performance for a new material against edge glow.