A parametric study of segmentation thresholds for X-ray CT porosity characterisation in composite materials

Porosity in composites is a critical manufacturing defect that leads to a reduction of mechanical performance. Non-destructive testing (NDT) techniques are used to inspect composites after manufacture to identify defects and to help assess their impact on mechanical performance. Micro X-ray computed tomography is a promising NDT technique which provides information about pore location, size and morphology. To identify and characterise voids, an image ‘segmentation’ must be applied to the full CT dataset, which is simply a rule-based decision about whether a voxel is inside a pore or not. This work uses a simple model to analyse and compare the effectiveness of previously accepted threshold methods for segmentation across a range of material and porosity parameters. A new CT-segmentation thresholding method is proposed and evaluated for characterising voids in a wider range of composites. The sources of uncertainties are investigated and recommendations are made to minimise these uncertainties.