Process-induced degradation of tensile strength in 3D-printed carbon fiber–reinforced PA6: Experimental and numerical study

Continuous carbon fiber–reinforced composites (CCFRCs) produced by 3D printing offer design flexibility but often exhibit reduced mechanical performance due to process-induced defects. This study examines the effect of the printing process on the tensile strength of a CCFRC with polyamide 6 as the matrix using both numerical and experimental techniques. The experiment comprises two phases: 3D printing and tensile testing. The first phase is further divided into three stages, referred to as before (Stage 1), during (Stage 2), and after printing (Stage 3), with samples collected at each stage for tensile testing and analysis. Microscopic structure analysis was conducted using powerful X-ray imaging at the synchrotron radiation facility “NanoTerasu,” revealing the effects of the printing process. Based on these observations, simulations are performed using a spring element model (SEM) that incorporates process-induced initial fiber breakage and voids. For Stages 1 and 2, the simulation predicts the strength with high accuracy; however, for Stage 3, a 20% overestimation is observed. This result suggests that Stage 3 may introduce changes in the probabilistic strength distribution of the fibers and may cause degradation of the fiber/resin interface due to the presence of voids, which cannot be modeled using the current numerical approach, leading to a further reduction in the tensile strength. The findings of this study contribute to elucidating the degradation mechanisms of tensile strength induced by the 3D printing process in CCFRCs.