Analysis of the fracture properties of additively manufactured carbon fiber reinforced thermoplastic composites

ENG- The primary objective of this thesis was to experimentally determine the elastic in-plane mechanical properties and interlaminar fracture toughness in modes I and II of Markforged® continuous Carbon Fiber reinforced PolyAmide (CF/PA) composites. Prismatic samples with paper end tabs yielded the best results for in-plane properties. For mode I fracture toughness, thin and thick specimens were tested, with thin specimens showing stable crack propagation and lower toughness values compared to mode II. This aligns with traditional FRP composites but contradicts previous literature. The second part of the thesis involved analyzing mode I interlaminar fracture toughness in multidirectional specimens using numerical simulations to prevent matrix tensile failure and crack jumping. Finite Element (FE) simulations guided the design based on interfacial angles, confirmed by experimental tests. Results showed that interface layer orientations affected toughness initiation and propagation, though variability made trends difficult to establish. The third part analyzed mixed-mode I/II interlaminar fracture toughness using the Mixed Mode Bending (MMB) test for 25%, 50%, and 75% ratios. While the 50% ratio values fell between mode I and II, the 25% and 75% ratios did not follow the expected trend. Fractographic analysis indicated no fabrication or testing errors, yet no logical explanation for these results could be established