A Comprehensive Experimental Study on Mechanical Anisotropy and Failure Mode of 3D Printed Gypsum Rocks: From Composition and Microstructure to Macroscopic Mechanical Properties Response.

3D printing (3DP) technology is a groundbreaking technology that can offer valuable insight into rock characterization and theoretical model verification due to its specimen reproducibility and unprecedented flexibility in manufacturing various structural shapes. Previous studies have explored the effect of printing direction on the mechanical properties of 3D-printed rocks, but the underlying cause of macroscopic mechanical anisotropy in 3D-printed gypsum rocks remains unclear. In this study, the effect of the movement direction of the printer head and bedding plane on macroscopic mechanical behavior and failure modes of 3D printed gypsum rocks were investigated. Uniaxial compression tests were conducted to investigate the mechanical properties of 3D-printed gypsum rocks. Along with the mechanical studies, the composition change of the raw powder before and after printing was studied based on particle size diameter (PSD), x-ray diffraction (XRD), and thermogravimetric differential thermal analysis (TG–DTA) experiments. Furthermore, Micro-CT imaging was conducted to investigate the microstructural characteristics of 3D-printed rocks (e.g. pore size, pore shape, and pore anisotropy). The results indicated that 3DP gypsum specimens printed on the yoz plane, which were only affected by the bedding direction, exhibited the lowest strength and mechanical anisotropy. In contrast, specimens printed on the xoy plane, influenced solely by the movement direction of printer head, showed the highest strength. Specimens printed on the xoz plane displayed the greatest mechanical anisotropy due to the joint effect of the bedding direction and the movement direction of the printer head. In terms of strength and mechanical anisotropic properties of 3D-printed specimens, the movement of the printer head was found to be more significant than the bedding direction, whereas the bedding direction was more crucial for peak strain. As for the failure mode, most of the 3D-printed specimens failed by shear failure of which the bedding planes played an important role in the specimens with small inclined angles. Highlights: This study investigated the effect of the movement direction of the printer head and bedding planes on mechanical anisotropy and the failure mode of 3DP gypsum rocks. Three types of experiments were conducted to enhance the understanding of how material composition and microstructure impact the macroscopic mechanical response of 3DP gypsum rocks. Micro-CT scanning tests were performed to reveal the failure mode and microstructural characteristics of 3D printed gypsum rocks. [ABSTRACT FROM AUTHOR]