Experimental study on interface failure behavior of 3D printed continuous fiber reinforced composites

Additive manufacturing (or 3D printing) for continuous fiber composite exhibits great potential for fabrication of next-generation lightweight sophisticated structural components. Nevertheless, understanding of interface characteristics of printed parts has remained an open research question for broader applications of this new technology in engineering practice. This study aimed to evaluate the interfacial quality of 3D-printed carbon fiber reinforced plastic (CFRP) composites from two aspects: interlaminar fracture toughness in a pure mode and interfacial failure mechanism in a mixed mode. Prior to the experimental tests, the microstructural quality of the 3D printed specimens was characterized, which showed that the void content and shape of different materials are different. There is a clear boundary line where the short fiber matrix layer and the continuous fiber reinforced layer are in contact, while the interface formed between the same material layers has no evident connection traces. The standard specimens were printed for testing pure mode I and mode II interlaminar fracture toughness, through which the G Ι C and G IIC of interface between continuous carbon fiber layers was characterized. It was found that the fiber bridging phenomenon presented in the double cantilever beam (DCB) experiments, resulting in a higher initial mode I fracture toughness. The end notched flexure (ENF) tests found that the fracture toughness of initial mode II in between the 0° continuous carbon fiber layers was relatively low. The scanning electron microscope (SEM) analysis revealed that the separated surface had only a small area of the matrix being sheared. The single lap specimen printed directly was proposed as a simplified model for simulating complex structural parts subjected to mixed stress of peel and shear. The mechanical responses and failure characteristics of the interfaces composed of different materials and different fiber angles under mixed stress were studied. It is found that each specimen presented some mixed failure modes, and the interface characteristics of different materials and different fiber orientations were completely different. The results gained in-depth understanding on the interfacial properties of 3D printing fiber reinforced structures, thereby providing key data and knowledge for practical applications. • Different layering methods with different interlayer morphology and void shape. • The critical strain energy release rates of type I and typeⅡwere obtained. • Continuous fiber bridging enhances type I fracture toughness. • The shear resistance of the interface between continuous fibers and matrix is very weak. • Reinforcement materials and fiber angles affect the interfacial bond strength and failure.