Mechanistic study of fiber damage evolution in 3D printing of two-matrix continuous carbon fiber-reinforced composites based on electrical conductivity changes

This study addresses the critical issue of fiber breakage defects that significantly affect the mechanical performance of 3D printed two-matrix continuous carbon fiber-reinforced composites. A conductivity-based method is proposed to characterize the extent of fiber fracture during the printing process. The entire process is segmented into five stages, from the raw two-matrix prepreg filament (Stage 1) to the final printed part (Stage 5). The relationship between fiber breakage and electrical conductivity at different stages is systematically investigated, verifying the effectiveness of electrical conductivity as an indicator for assessing fiber continuity and damage severity. Experimental analysis under varying processing parameters further reveals that the electrical conductivity of printed part is highly sensitive to both printing speed and temperature. These findings indicate that conductivity monitoring can effectively capture the degradation in mechanical performance caused by microscale defects, offering valuable guidance for process parameters optimization. Within the given process and parameter range in this paper, the optimal process parameter combination is a printing temperature of 210°C and a printing speed coefficient of 3. Finally, by integrating thermal property analysis and microstructural characterization, the study elucidates a damage evolution mechanism dominated by epoxy softening-induced interfacial failure and thermo-temporal stress accumulation. This mechanism collectively drives the fracture of continuous carbon fibers during printing, laying the groundwork for future multiscale modeling of damage evolution in two-matrix continuous carbon fiber-reinforced composites.