An Experimental Investigation and Characterization of 3D ‐Printed Short Carbon Fiber‐Reinforced Epoxy Composite Sandwich Structures Featuring Diverse Core Geometries Fabricated Using Customizable Inks

ABSTRACT This study explores the fabrication and characterization of lightweight, moderate‐to‐high‐strength short carbon fiber‐reinforced epoxy composite sandwich structures with tailored core designs using the direct ink writing (DIW) 3D printing technique and engineered composite inks. Customized composite inks containing 10–40 wt.% carbon fibers were developed, exhibiting viscoelastic and yielding properties for precise layer‐by‐layer deposition of complex core geometries (corrugated, rectangular, triangular) with integrated skins, eliminating the need for adhesives. DIW enables mold‐free production with enhanced control over material deposition and geometric complexity. The printed sandwich structures showed superior surface quality to other 3D‐printed continuous carbon fiber‐reinforced thermoplastic composite structures. Mechanical testing revealed that increasing core layer (L) counts from 1 L to 2 L significantly enhanced flexural stiffness and peak load‐bearing capacity. Enhancements in the base material properties of the inks led to increased peak load, flexural stiffness, and modulus in 1 L and 2 L DIW‐printed sandwich beams. In contrast, sandwich structures with varying core geometries yielded mixed strength results. Yet, the DIW‐printed carbon fiber‐reinforced epoxy composite sandwich structures exhibited excellent and/or comparable flexural properties to competitive published studies. This research highlights the potential of engineered inks combined with the DIW technique to create composite structures with tailored properties for lightweight, high‐performance structural applications.