01/03/2018
Picture of a composite panel with several impact damages

Composite panel (center) and separation of impact damage for each layer of the panel, where damage geometry and extent can be seen

Source: BAM, Division Micro Non-Destructive Testing

The aerospace industry has always needed to be at the forefront of materials research and development, driven by the requirement for ever lighter, yet stronger, structures. In the light of this, carbon fibre reinforced polymers (CFRP) have begun to replace conventional light metal alloys, such as aluminium and titanium, for aircraft structures. The growing use of CFRPs has arisen from their high strength- and stiffness-to-weight ratios compared to those of light alloys, but also from the ability to tailor their structure to produce more aerodynamically and mechanically efficient components. These advantages are however balanced by a lower impact damage tolerance, mainly due to the layered and heterogeneous structure of CFRP laminate panels. Characterising impact damage in composite structures is thus one of the major challenges that the aerospace industry faces, especially as for low velocity impact events, significant damage can be generated inside a composite component whilst there can be little indication of external surface damage.

A technique with great potential to assess damage in composite components is X-ray computed tomography, as it allows imaging the full damage non-destructively and in 3D. However, for curved or deformed composite panels, such as a panel after an impact event, it can be difficult to extract meaningful data. The present paper introduces a new methodology for X-ray computed tomography data processing, that allows a full description of the impact damage within a composite panel in 3D, by separating the damage according to the structure of that panel. The methodology is based on a distance transform approach, to provide a full description of the 3D morphology and amount of damage for each individual layer of the composite panel. This new approach significantly extends our ability to characterise impact damage and extract meaningful measurements from X-ray computed tomography datasets.

By better understanding how the energy of an impact event is absorbed by a composite structure and develops into damage, we can engineer composite panel architectures better suited to impact resistance, and validate numerical models and simulations of impact failure. This is needed to ensure the safety of the current generation of airplanes and develop the next generation of composite materials for safer tomorrow’s airplanes.

The quantification of impact damage distribution in composite laminates by analysis of X-ray computed tomograms
Fabien Léonard, J. Stein, C. Soutis, P.J. Withers
Composites Science and Technology, Volume 152, 10 November 2017, Pages 139-148
BAM Department Non-Destructive Testing, Division Micro Non-Destructive Testing