X-ray CT-Based Defect Evaluation of Continuous CFRP Additive Manufacturing

The spread of additive technologies from prototyping to manufacturing has made the development of new products possible, but still needs effective methods in order to allow their characterization. In particular, porosity is considered a crucial aspect of AM products. A prototype system for the deposition of continuous carbon fiber-reinforced polymers with a thermoplastic matrix has been recently developed at Mechanical Engineering Department of Politecnico di Milano. This application is of interest, as it would avoid the expensive development and manufacturing of specific molds. The mechanical performance of the manufactured components depends mainly on porosity and on non-correct adhesion among filaments, even in the case of conventional manufacturing processes. The additive deposition shows even more relevant issues of this kind. Hence the need for a characterization of the process. The conventional approach considers a destructive test to characterize the composite mechanical properties or porosity. The aim of this paper is proposing original approaches to evaluate both porosity and non-correct adhesion by means of X-Ray computed tomography. The method is validated by comparing the porosity with the reference destructive method defined in the ASTM D3171 standard. It is also shown that the amount of defects is correlated to the mechanical properties of the obtained components, thus the approach can be used for a non-destructive evaluation of the manufactured parts.