Volumetric fracturing behavior of 3D printed artificial rocks containing single and double 3D internal flaws under static uniaxial compression

In nature, rock discontinuities, e.g., cracks, voids and joints, are usually three-dimensional, which to a large extent control the volumetric fracturing behaviors of rock masses. Understanding their growth behaviors and effects on rock volumetric fracturing properties is crucial for the stability assessment of rock engineering. In this study, three-dimensional printing (3DP) method was adopted to fabricate resin-based artificial rocks containing single flaw and double pre-existing penny-shaped 3D internal flaws. Static uniaxial compression tests were, subsequently, conducted on these samples to investigate the influence of flaw number, flaw angle (alpha) and ligament angle (beta) on the volumetric fracturing behaviors of the 3DP artificial rocks. The results indicate that flaw geometry has remarkable influence on the mechanical and fracture behaviors of the flawed samples. The single flawed sample with alpha equal to 60 degrees has the lowest compressive strength (sigma(c)) and axial strain at the peak stress (epsilon(a)). sigma(c) and epsilon(a) of the double flawed sample generally increase when beta changes from 45 degrees to 105 degrees. When the flaw number increases from one to two, the initiation stress of the first wing crack, sigma(c) and epsilon(a) decrease. With the aid of high-speed cameras, we studied 3D crack growth inside the transparent 3DP resin samples in real-time for the first time. Wing and anti-wing cracks wrapped around the flaw edge could only propagate for approximately 1-1.5 times the length of the initial flaw. Wing cracks generated at the inner tips of the flaws cannot coalesce, except for the sample with beta of 105 degrees. The maximum crack propagation velocity in single flawed specimens is higher than that in double flawed samples. The continuous propagation of the secondary cracks developed after the peak stress lead to the burst-like failure of the flawed samples. This study could enhance our understanding of volumetric fracturing behaviors of rocks.