JID:CSNDT AID:35 /FLA [m3G; v1.176; Prn:19/05/2016; 13:34] P.1(1-9) Case Studies in Nondestructive Testing and Evaluation ••• (••••) •••–••• Contents lists available at ScienceDirect Case Studies in Nondestructive Testing and Evaluation www.elsevier.com/locate/csndt Dual energy CT inspection of a carbon fibre reinforced plastic composite combined with metal components Daniel Vavrik a,b,∗ , Jan Jakubek b , Ivana Kumpova a , Martin Pichotka b a Institute of Theoretical and Applied Mechanics, v.v.i., Centre of Excellence Telˇ c, Czech Republic b Institute of Experimental and Applied Physics, Czech Technical University in Prague, Czech Republic a r t i c l e i n f o a b s t r a c t Article history: Available online xxxx This work is focused on the inspection of carbon fibre reinforced plastic composites (CFRP) combined with metal components. It is well known that the high absorption of metallic parts degrades the quality of radiographic measurements (contrast) and causes typical metal artefacts in X-ray computed tomography (CT) reconstruction. It will be shown that these problems can be successfully solved utilizing the dual energy CT method (DECT), which is typically used for the material decomposition of complex objects. In other words, DECT can help differentiate object components with a similar overall attenuation or visualise low attenuation components that are next to high attenuation ones. The application of DECT to analyse honeycomb sandwich panels and CFRP parts joined with metal fasteners will be presented in the article.  2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). 1. Introduction The inspection of sandwich structures composed of a metallic honeycomb core and a CFRP skin, widely used in the aerospace industry, will be presented in this work as the first show case. In particular, the combination of a CFRP skin and an aluminium (Al) core is investigated due its superior strength-to-weight ratio and excellent impact resistance. Possible skin-to-core disbonds may have a crucial influence on the structural integrity of such structures. However, their identifi- cation can be problematic when utilizing standard non-destructive techniques (NDT) like ultrasound, thermography, or tap testing methods due to their relatively low resolution and the intrinsically high heterogeneity of honeycomb sandwich struc- tures. The standard X-ray computed tomography (X-ray CT) technique provides good results if the inspected object is flat and tilted in the optimal position to identify disbonds searching the reconstructed volume slice by slice. Direct 3D visuali- sation is rather problematic, especially if the object is not flat. It will be shown here that this restriction can be successfully overcome utilizing the dual energy computed tomography method (DECT). Furthermore, the identification of disbonding can be achieved by employing a single photon counting detector with a spectroscopic capability, allowing multi-energy CT. The porosity of CFRP skin is obviously another parameter which has to be analysed. It will be shown that a porosity analysis based on X-ray CT data can be significantly influenced by the porosity present in the resin layer bonding skin and the core of the sandwich structure. Yet again, this problem can be solved utilizing the DECT method. The identification of disbonding present between CFRP components, with a copper (Cu) grid on the top, glued together and joined with metal fasteners, will be shown here as another show case. The identification of disbonding due to a lack of resin is complicated by metal artefacts as well as by the beam hardening effect caused by the significantly differing * Corresponding author. E-mail addresses: vavrik@itam.cas.cz (D. Vavrik), jan@jakubek.cz (J. Jakubek), kumpova@itam.cas.cz (I. Kumpova), pichotka@utef.cvut.cz (M. Pichotka). http://dx.doi.org/10.1016/j.csndt.2016.05.001 2214-6571/ 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).