Associated with IMaST, and involved in the Regional Apulian Call “Support for Regional Technological Cluster for Innovation” for financial support, specifically COGEA-Composite Certification in General Aviation (OES4AM4), under the supervision of Dr C. Giannini, senior researcher at IC-CNR. This activity was carried out thanks to the collaboration with Dr M. Nacucchi and Ing. F. De Pascalis, researchers at ENEA, Centro ricerche di Brindisi (Italy), both expert of X-ray computational tomography and image analysis. ENEA is the owner of the X-ray CT instrument and of the Avizo Software license.

Institute of Crystallography of CNR in Bari and ENEA uses Avizo Software to perform porosity analysis of CFRP-based composites and demonstrate the efficiency of non-destructive X-ray CT for material structural analysis

The aim of the study is to show the versatility of X-ray computed tomography (CT) to inspect, without any material destruction, the internal structure of carbon fiber reinforced polymer (CFRP)-based composites in two type of configurations, layered and sandwich, widely used in aviation as structural elements.

For the certification of composite materials to be used in general aviation, the international regulation involves the use of destructive testing (DT) methods, such as acid digestion, to determine the porosity of the composite. With this research, we aim to demonstrate that all types of composite structured elements can be non-destructively inspected by X-ray CT, thereby permitting investigation of the volume distribution of the pores/voids in the analyzed sample, providing, after a post-analysis data processing and 3D sample reconstruction, an interactive 3D exploration and quantitative analysis of porosity by the complete 3D volume rendering of the analyzed composites.

Avizo Software “was chosen for its versatility and feasibility for data processing and image analysis.”

Thermo Scientific Avizo Software was used for the image processing of the datasets, segmentation, and analysis procedures. It was chosen for its versatility and feasibility for data processing and image analysis. Indeed, it permitted not only visualization but also, after an accurate segmentation procedure of the grayscale histogram relative to the X-ray CT acquired images, allowed the acquisition of a specific data analysis. The reported case included the labeling of pores and a mathematical and statistical analysis of the detected pores, evaluating their shape, their volume, etc., and visualizing them in the 3D reconstructed analyzed object.

Avizo Software has permitted us to obtain not only the 3D volume rendering of the entire analyzed object, but also, by using specific image processing and analyses, the individuation and the label voids/pores in the region of interest and the determination of their volume, whose data have been needed to evaluate the total object porosity.

Conclusions

The accuracy of the porosity results has been evaluated for both structures. For the monolithic element, the porosity value has been compared with that obtained by the standard acid digestion procedure. For the sandwich structure, since it could not be correctly analyzed by the standardized acid digestion because of foam in the interlayer, the porosity accuracy has been indirectly evaluated, comparing the foam porosity calculated by the 3D sample reconstruction after the X-ray CT analysis with the value reported in the commercial foam datasheet.

The obtained results have demonstrated that X-ray CT represents an efficient and accurate non-destructive alternative technique with respect to the standard destructive inspection methods in aviation application. X-ray CT has been shown capable of providing information on the inner structure of composites, thus allowing for a complete material structural analysis.

Porosity determination in CFRP skins of sandwich hybrid composite. Porosity equals 0.11%. Top left and right: before and after segmentation. Bottom: grayscale histogram after masking the foam sandwich layer.

Porosity determination in CFRP skins of sandwich hybrid composite. Porosity equals 0.11%.
Left and right images: before and after segmentation. Histogram: grayscale histogram after masking the foam sandwich layer.

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By Dr. Elena Dilonardo, Politecnico di Bari, Italy.

Images and text are courtesy of the IC-CNR and ENEA.
Reference: https://doi.org/10.1016/j.compscitech.2020.108093
High resolution X-ray computed tomography: A versatile non-destructive tool to characterize CFRP-based aircraft composite elements, E. Dilonardo, M. Nacucchi, F. De Pascalis, M. Zarrelli, C. Giannini, Composites Science and Technology, 2020, vol. 192, 108093.

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