Regulating Mechanical Behavior of Onyx Hexagonal Honeycombs via Heat Treatment: A Thermo‐Mechanical Study

ABSTRACT Additively manufactured honeycomb structures offer exceptional lightweight and high energy‐absorption capabilities for aerospace applications. However, their mechanical performance evolution and damage‐suppression mechanisms under elevated temperatures remain poorly understood. This study bridges a long‐standing gap by combining systematic experiments and thermo‐mechanical finite‐element simulations to quantify the effects of heat‐treatment temperature, post‐treatment cooling duration, and compression‐pretreatment sequence on both microstructural evolution and macroscopic mechanical behavior of FDM‐printed short‐fiber‐reinforced Onyx honeycombs. Five specimen groups underwent heat treatment followed by either 5 or 30 min ambient cooling, with and without 5 mm or 20 mm pre‐compression. Mechanical testing revealed that short‐duration cooling reduced tensile strength by 12.2% and decreased specific energy absorption by 15.3%. Conversely, extended cooling enhanced energy absorption by 275%. Compression pretreatment further increased bearing strength by 13.6%. SEM analysis indicated that heat‐induced thermoplasticization of the nylon matrix strengthened fiber–matrix interfacial bonding, shifted failure modes toward fiber fracture, and that pore coalescence promoted crack deflection and material toughening. Thermo‐mechanical simulations encompassed both stepwise and synchronous loading scenarios, confirming that optimized heat treatment mitigates local stress gradients, and that synchronous loading synergistically compacts defects and stabilizes strain distributions. However, simulations slightly overestimated the strengthening effect in compression‐treated groups due to omission of pore damage. These findings establish a quantitative process–property framework and offer a theoretical foundation for pre‐processing design strategies to optimize the thermo‐mechanical performance and service life of lightweight honeycomb components such as UAV wings.