Experimental Investigation of Damage Evolution and Strain Fields of 3D-Printed Rock-like Specimens Based on X-Ray Computed Micro-Tomographic Imaging and Digital Volume Correlation
Authors: Shao Yulong , Kim Jineon , Song Jae-Joon , He Chen 
Published: August 2024

ABSTRACT:
Some researchers have explored the feasibility of replicating the crack behavior of natural rocks with defects using three-dimensional (3D) printing technology. However, few have investigated changes in strain fields during compression experiments, even though this is crucial for understanding the crack behavior of 3D-printed rock-like specimens. This study examines the crack evolution and strain field distribution in the 3D-printed rock-like specimen to address this gap during the compression tests. In this study, a set of in-situ uniaxial compression tests was performed on 3D-printed rock-like specimens with an initial flaw with various inclined angles (α = 30°, 45°, 60°) using the high-resolution Micro-CT scanner with a loading apparatus. Based on the CT images of 3D-printed rock-like specimens obtained at different scanning steps, the 3D reconstruction and digital volume correlation (DVC) processes were applied to illustrate the damage evolution and quantify the 3D interior deformation of 3D-printed rock-like specimens. The results indicated that within the 3D-printed specimens, tensile cracks were first initiated near the internal flaw, followed by shear cracks or tensile-shear mixed cracks at the flaw tips. The characteristics of internal strain distribution before cracking indicated strain localization, and the cracking process of specimens was strongly correlated with radial strain distribution.

1. BACKGROUND
Currently, methods for studying rocks' crack behavior, damage characteristics, and failure mechanisms in compression experiments include experimental approaches (such as rock coring and rock analog materials) and numerical simulation methods (such as finite element methods, discrete element methods, and finite difference methods). Due to their superior control and reproducibility, rock analog materials offer a better understanding of the crack behavior of rocks in compression tests. Traditional rock analog materials, including gypsum, sand, and cement-based materials, are prepared by casting methods. However, this method is low-precision, time-consuming, ineffective, and cannot produce samples with complex internal structures. 3D printing technology, one of the representative technologies of the Fourth Industrial Revolution, has been widely used in various fields, including rock mechanics and geotechnical engineering (Jiang et al., 2016; Song et al., 2018; Zhu et al., 2018). Researchers (Shao et al., 2023; Song et al., 2020; Zhou et al., 2020) have found through uniaxial and triaxial compression experiments that powder-based 3D-printed specimens exhibit lower strength, with their mechanical properties only matching those of low-strength sandstones, while resin-based 3D-printed specimens can match the high strength of natural rocks. Asadizadeh et al. (2019) studied the full-field strain evolution and crack propagation behavior of 3D-printed gypsum specimens with different initial defects in Brazilian split tests using Digital Image Correlation (DIC) technology based on powder-based 3D printers. They concluded that tensile cracking dominates fracturing under loading, while shear cracking is challenging. Song et al. (2023a) explored the mechanical response and deformation-cracking behavior of 3D-printed sand specimens with prefabricated flaws, shedding light on how fracture characteristics impact strength and failure modes. The results indicate that the fracture mode of 3D-printed sand specimens strongly depends on the inclination angle of the initial defect.