Carbon fiber reinforced composites are widely used in the aerospace industry, due to their low weight and high strength. Porosity often occurs during the manufacturing of composite plates, which can compromise the structural integrity of the plate and affect its mechanical properties. In the aerospace industry, a typical requirement for structural components is for the porosity content to be kept below 2%. Non-destructive evaluation (NDE) techniques are used to estimate the porosity content in composite structures, the most common being ultrasonic imaging and X-ray computed tomography (CT). Ultrasonic imaging is a practical NDE method, but the relatively low resolution (typically order of 100µm) can affect the detection and quantification of porosities below 1%. X-ray CT offers a much higher resolution and as a result can detect smaller pores, but typically requires long scanning time and a restricted sample size.&nbsp;Edge illumination X-ray Phase Contrast Imaging (EI XPCi) was previously used for damage detection in composite plates, showing the complementarity offered by the differential phase and dark field signals to the conventional attenuation signal. The dark field signal corresponds to ultra-small-scattering due to features in the sub-pixel scale and represents the variation in inhomogeneity. Planar EI XPCi was used to quantify the porosity content in woven carbon fiber reinforced composite plates by comparing the retrieved X-ray signals to ultrasonic attenuation and matrix digestion. A new metric was introduced, the standard deviation of the differential phase (STDVDP) signal, which represents the variation of inhomogeneity in the plates for features of a scale equal to or above the system resolution (12µm).&nbsp;The dark field and STDVDP were compared with ultrasonic signal attenuation and matrix digestion for porosity specimens with porosity ranging between 0.7% and 10.7%. The SDTVDP was found to have a very high correlation with porosity content estimated from matrix digestion and ultrasonic attenuation. This represented an improvement compared to the dark field signal normally expected to represent porosity, likely due to the porosity being of a scale equal to or above the system resolution.

Edge Illumination X-Ray Phase Contrast Imaging and Ultrasonic Attenuation for Porosity Quantification in Composite Structures

Paper Proceedings: https://asmedigitalcollection.asme.org/qnde/QNDE2021/volume/85529

ASME 2021 48th Annual Review of Progress in Quantitative Nondestructive Evaluation (QNDE2021)

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