Study on Densification Mechanism of Braided Needle‐Punched Preform Based on Digital Element Method

ABSTRACT This study addresses the challenges of dynamically characterizing the internal structure of needle‐punched preforms and understanding poorly defined compression and rebound mechanisms. The digital element method is utilized to quantitatively characterize the fiber structure and stress, allowing for the analysis of stress dissipation patterns and fiber rebound behavior in different structures. The simulation results show that after densification and spring‐back stabilization, the yarn curvature near the perforated hole decreases by 44.45% and the aperture decreases by 27.26%. These changes reduce stress concentration and improve the flatness of the preform. The densification mechanism and mechanical stability effect of the needling process on the precast were systematically studied, and the rivet effect of the needling fiber bundle was proposed. Experimental results show that the method can effectively suppress the rebound rate and delamination in the composite structure. The maximum fiber volume fraction of the precompressed needled preform is 30.64%, which is 20.87% higher than that of the existing needled preform. The density reached 0.51 g/cm 3 , an increase of 15.91%. The study revealed the mechanism of needle densification and summarized the dynamic evolution of fiber structure and stress of preform parts under different densification processes. The precompression needling process can effectively increase the fiber volume fraction.