Anisotropic properties of 3D-printed rock-like materials under dynamic Brazilian disc tests

Rock materials are commonly endowed with anisotropic structures, like beddings, flaws and fillers, which casues difficulty when trying to predict strength, deformation and fracture properties under dynamic loading. Considering the structural complexity and randomness in rock materials, it is difficult to get samples for experimental studies. 3D printing (3DP) is emerging as a promising method to replicate the complicated meso- and micro- structures found in natural geological materials, but which is able to repetitively fabricate identical specimens. In this study, 3D printed rock-like specimens are fabricated into cylinders for Brazilian disc testing (diameter: 50 mm and thickness: 25 mm) using extrudable geomaterials (extrusion width 1 mm and layer thickness 0.5 mm). By combining a split Hopkinson pressure bar and a high-speed camera, Brazilian disc tests were conducted on the 3DP specimens with bedding angle α (i.e. angle between impact direction and bedding orientation) taking a variety of values (0˚, 30˚, 45˚, 60˚, and 90˚) to investigate anisotropic mechanical and fracturing properties. Results show that the dynamic peak strength gradually increases as the bedding angle α increases from 0˚ to 90˚. Failure patterns of 3DP specimens exhibits tensile dominated failure in both bedding angles 0˚ and 90˚, and mixed tensile-shear failure in other bedding angles (30˚, 45˚ and 60˚). The experimental results are consistent with a previous study using natural rock materials, indicating that the 3D printing technology has promise to allow more controlled studies of rock materials under dynamic loadings, avoiding the structural inconsistencies in natural rock specimens.