In-situ characterization of additively manufactured continuous fiber reinforced tensile test specimens by X-ray computed tomography

Continuous fiber reinforcement of fused filament fabricated specimens combines the flexibility of additive manufacturing with the increased strength and stiffness of composite materials. However, special attention must be paid to defects and irregularities typically occurring in additive manufactured parts to avoid excessive dropout. For this work, specimens from nylon matrix with continuous carbon, glass, and aramid fiber reinforcement were manufactured and tested under tensile load. X-ray in-situ investigations were performed to assess the feasibility of fiber breakage detection via X-ray radiography. Three-dimensional characterization of additive manufacturing quality was performed via X-ray microcomputed tomography. It has been shown that layer thickness has only minor influence on tensile properties compared to variations in continuous fiber material. Glass fiber and carbon fiber reinforcement result in similar tensile strength at fiber failure, superior to aramid fiber reinforcement. Increased porosity within the processed carbon fiber bundles suggests low impregnation quality of the pre-impregnated continuous fiber source material. Glass-fiber bundles showed notably better impregnation quality. However, all processed continuous fiber materials showed significant in-plane waviness of up to 30° from the intended fiber orientation causing additional shear stress in components. Lastly, we found that additive manufacturing quality varies in printing direction causing a notable increase in porosity towards the upper surface layers of the specimens.