EVALUATION OF POROSITY IN OUT-OF-AUTOCLAVE CURED CFRP LAMINATES USING THROUGH-TRANSMISSION ULTRASOUND AND X-RAY MICROTOMOGRAPHY

Voids in composite laminates can influence damage initiation, propagation and lead to catastrophic failure. It is therefore important to characterize the morphology and content of voids reliably in order to decide deployment or disposal of a composite component. In this work, thin carbon/epoxy non-crimp-fabric laminates with varying void contents/porosities are manufactured using an out-of-autoclave curing method and then employed to evaluate the robustness of through-transmission ultrasound and X-ray Computed Tomography (micro-CT) scans. The porosity post-processed using a micro-CT 'ambient occlusion' strategy is compared with the volumes captured by an Otsu's grayscale thresholding strategy and the standard acid digestion test. The micro-CT results show that the occlusion method captures the volume of enclosed and open (i.e. near/at laminate surface) voids and thus provides a more comprehensive assessment of voids content and their morphology. The results show a good correlation between ultrasound attenuation and the porosities measured from micro-CT and acid digestion methods.