Defect and Porosity Determination of Fibre Reinforced Polymers by X-ray Computed Tomography

The porosity of carbon fibre-reinforced polymers is a very important topic for the practical applications of this material since there is a direct correlation between porosity and mechanical properties, such as shear strength. Therefore the porosity values of carbon fibre-reinforced composites for practical use in aircraft and cars must be lower than a certain level, usually 2.5-5 %. The most common nondestructive method for measuring the porosity is ultrasonic testing, since there is a mostly linear correlation between ultrasonic attenuation and porosity. However, the ultrasonic attenuation coefficient depends not only on the porosity, but also on the shape and distribution of the pores and the presence of other material inhomogeneities. This can lead to significant errors in the determination of the porosity. Acid digestion and materialography are also used for porosity measurement, but both methods are destructive. This paper deals with the application of X-ray computed tomography for the characterization of carbon fibre-reinforced composites, in particular for the quantitative determination of porosity with a reasonable degree of accuracy. In order to attain this, different segmentation methods were applied, systematic computed tomography investigations on a broad variety of composite samples with different measurement parameters were performed and the results are compared with results obtained by standard porosity measurement methods, such as ultrasonic testing and acid digestion. In addition, the possibility of characterizing the size, shape and position of all individual pores and other material inhomogeneities in three dimensions are demonstrated.