Heat Treatment Temperature Effects on Three‐Point Bending of 3D ‐Printed Onyx/ HSHT Fiberglass Honeycomb Composites

This study addresses the pressing demand for lightweight unmanned aerial vehicle (UAV) structures through the application of continuous fiber‐reinforced thermoplastics (CFRTs). Regular hexagonal honeycomb structures were fabricated via fused deposition modeling (FDM). To enhance structural performance, systematic heat treatments were applied at 130°C, 150°C, and 170°C. An integrated analytical framework combining crack path fractal dimension quantification, sequential thermo‐mechanically coupled finite element simulations, and experimental bending tests was developed to enable a comprehensive evaluation. The results reveal a non‐monotonic performance trend, wherein the 150°C treatment yields optimal mechanical properties, including the highest elastic modulus, along with significant improvements in strength and interfacial toughness. These enhancements are corroborated by pronounced fiber pull‐out features and an increase in crack path fractal complexity (fractal dimension = 1.594 ± 0.045). Mechanistic analysis indicates that the finite element simulations confirm that the 150°C treatment achieves an optimal balance between matrix crystallization enhancement and residual stress alleviation, whereas treatment at 170°C leads to interfacial degradation. Overall, this work establishes quantitative correlations between fractal geometric characteristics and material performance, elucidates the underlying thermo‐mechanical regulation mechanisms, and provides novel design strategies for the additive manufacturing of high‐integrity aerospace composite structures.