A comparison of X-ray attenuation, differential phase, and dark-field contrast imaging for the detection of porosity in carbon fiber reinforced cyanate ester

In this work we explore the capabilities of Talbot-Lau grating interferometry (TLGI) radiography for the inspection of porosity in structural specimens of cyanate ester carbon fiber reinforced polymer. The influence of system resolution and varying specimen thicknesses on mean values and standard deviations (STDV) in all three image modalities acquired by TLGI are addressed. Results show that mean absorption contrast (AC) values are highly affected by specimen thickness and strong negative correlation (r ≤ −0.8) is found only after correction via preliminary thickness measurements. Although dark-field contrast (DFC) is affected by changes in specimen thickness as well, the signal can be corrected by normalization with the inherently available AC. Consequently, strong positive correlation with porosity was found both in high- and low-resolution imaging (r = 0.83 and 0.71 respectively). Without the need for high image resolution or thickness measurements, the normalized DFC is a promising option for large field of view inspections. Investigations of STDV revealed strong positive correlations between porosity and AC STDV as well as differential phase contrast (DPC) STDV (r = 0.95 and 0.92 respectively) but high image resolution is required. Furthermore, results suggest increased robustness against variations in specimen thickness of AC and DPC STDV analyses.