Synergistic Effects of Elongational–Shear Hybrid Flow Fields on Enhancing Processability and Impact Resistance of Polyamide 612/Carbon Fiber Composites

ABSTRACT Carbon fiber‐reinforced polyamide composites (PA612/CF) are vital for lightweight, high‐performance applications. This study evaluates a novel screw (ES) with periodic channel geometry against conventional screws (CS) for processing PA612/CF. Through rheological, fiber retention, crystallization, and mechanical analyses, the ES screw's elongational flow–dominated shear field enhanced melt flowability (longer spiral flow) and reduced molecular entanglement. Processing PA612 with the ES screw yields higher molecular weight due to shear optimization that minimizes degradation, thereby enhancing mechanical properties and crystallization potential. The ES screw minimized fiber breakage, achieving longer retention lengths than CS, while improving fiber dispersion and interfacial bonding. Impact strength tests revealed the ES screw outperformed the CS screw at 0–40 wt% fiber content due to reduced stress concentration and delayed crack propagation. The ES screw combines efficient mixing with low fiber damage, offering a breakthrough for high‐fiber‐content engineering plastics. This work provides critical insights for optimizing screw design to enhance composite performance in aerospace and automotive industries. This research integrates equipment design (ES screw), process innovation (elongational–shear hybrid flow fields), and performance breakthrough (high retained fiber length/low entanglement melt), enabling cross‐scale innovation from basic theory to industrial applications.