Research of Inter‐Track and Macroporosity, and Fluid Content in Determining Mechanical Performance of 3D‐Printed Unit Cells: Insights From In Situ 4D X‐Ray Tomography

This study investigates the influence of macropore geometry, orientation, and pore content (air vs. water) on the mechanical behavior and structural evolution of additively manufactured cubic unit cells under uniaxial compressive loading. A cubic elementary cell containing a single ellipsoidal macropore was selected as the model structure, with pore orientations varying from 0° to 90° relative to the loading direction. The internal pore was filled with either air or water to evaluate the effect of pore content on mechanical performance. In situ 4D XCT was employed to capture real‐time changes in pore morphology and mechanical response across different loading stages. In air‐filled specimens, mechanical loading induced significant reorganization of inter‐track pores, with smaller pores (~0.03 mm) expanding and intermediate‐sized pores (~0.045 mm) collapsing. Larger pores (~0.06–0.12 mm) expanded in 45° and 90° relative to the loading direction. Water‐filled specimens exhibited structural stability, with minimal pore deformation due to hydrostatic pressure effects. Inter‐track porosity was found to be more sensitive to mechanical deformation than macropores. The presence of liquid in the macropore significantly influenced mechanical properties, preserving structural integrity and delaying pore collapse. The evolution of pore morphology was geometry‐dependent, with 45° and 90° specimens showing distinct patterns of pore expansion and collapse compared to 0°, likely due to differences in macropore orientation relative to the loading direction. These results highlight the importance of incorporating pore‐scale deformation mechanisms into numerical models to improve the accuracy of mechanical behavior predictions for porous additively manufactured components. This work provides a foundation for calibrating numerical models of porous structures and enhances the understanding of fluid–structure interaction in additively manufactured materials under mechanical loading. The integration of XCT, mechanical testing, and numerical simulation enables a comprehensive analysis of multiscale pore behavior, offering insights applicable to biomedical, structural, and functional porous material design.