Influence of Water Absorption on the Impact Response and Failure Mechanisms of <scp>3D</scp> ‐Printed <scp>PLA</scp> ‐Based Honeycomb Sandwich Composite Structures

ABSTRACT This study investigates the influence of water absorption on the impact response and failure mechanisms of 3D‐printed sandwich composites with hexagonal honeycomb cores composed of polylactic acid (PLA)‐based materials, focusing on the comparative performance of natural (PLA–Wood) and synthetic (PLA–Carbon) reinforcements in moisture‐prone environments. The objective was to assess the effect of filler type on energy absorption, deformation, and failure progression after 30 days of water immersion under low‐velocity impact testing. The results indicate that water absorption has a material‐dependent impact on the mechanical performance. PLA–Wood exhibited the highest moisture uptake (21%), resulting in the greatest energy absorption (3.863 J) and end‐displacement (11.211 mm) owing to filler swelling and interfacial weakening. PLA–Carbon exhibited moderate water uptake (11%) with comparable energy absorption (3.856 J) but reduced end‐displacement (9.128 mm), indicating improved load transfer and stability. PLA demonstrated the lowest water uptake at 6% and energy absorption at 3.618 J, with minimal damage observed. Fourier‐transform infrared spectroscopy (FTIR) confirmed hydrolytic degradation, whereas scanning electron microscopy (SEM) and optical imaging revealed interfacial debonding and microstructural deterioration. These findings offer engineers critical insights into filler–matrix interactions and inform the design of impact‐resistant and moisture‐tolerant composites for aerospace, marine, and other high‐humidity structural applications.