Comparison of different segmentation methods for porosity evaluation in CFRP-reference samples with real porosity samples

The main objective of this work is quantitative evaluation of porosity in carbon fiber reinforced polymers (CFRP) with the help of X-ray computed tomography (XCT). For this purpose two types of sample were compared. Industrial porosity sample was obtained from an aeronautical industry. Artificially induced porosity samples were created by drilling holes with diameter 0.2 mm and 0.3 mm in non-porous samples. The reference porosity was obtained by measurement of diameters and its standard deviation using light optical microscopy (LOM) and XCT at different places on and within the sample for various Combinations plates of CFRP samples. Reference porosity limits were obtained for the range of 0.96 to 4.81 vol. %. Voxel variation scans were made on both types of samples between voxel sizes (2.75 μm) and (120 μm) and these were analysed using mainly six thresholds from TH 1 to TH 6. Our final conclusion is that TH 3 is the most robust threshold for both types of samples and shows least deviations over a wide range of voxel sizes. Porosity evaluation in CFRP depends mainly on XCT acquisition parameters, morphology of the voids present and segmentation method used. By stabilising XCT acquisition parameters for optimum visualisation and analysing morphology and individual void volumes; TH 3 segmentation can be adapted to obtain porosity values within expected porosity limits.