X-Ray Tomography-Based Characterization of the Porosity Evolution in Composites Manufactured by Fused Filament Fabrication

Fused filament fabrication delivers composites with incomplete interface bonding prone to delaminate under loading due to the non-isothermal molecular entanglement during deposition.

We aim to localize the mesoscale porosity in 3D-printed composites and quantify its volumetric growth under loading to investigate whether incomplete filament adhesion can lead to delamination.

We measured the porosity volumic content by X-ray tomography testing. To distinguish between damage nucleated at the crack tip and mesoscale interface delamination, we quantified the local, 3D strain concentration region size at the crack tip by 2D digital image correlation of slice images over orthogonal planes.

Through image segmentation, we observed that the mesoscale porosity resulting from the deposition process clustered at the filament interfaces and doubled from roughly 7% to 14% from an applied opening load of 700 N to 1400 N due to the stress concentration at the filament interfaces. Digital image correlation emphasized the strain concentration over a reduced area at the notch, up to the damage nucleation for an applied load of 1400 N, before the sudden brittle failure.

The presented contactless characterization technique emphasizes that mesoscale porosity concentrates at the filament interface, which is a critical delamination nucleation site under loading. This fracture mechanism is even more severe for high-performance composites such as carbon fiber reinforced PEEK.