Cracking behavior of an inclined open crack in transparent 3D printed rock-like specimen

To observe the aspect of crack growth in rock is the main purpose of this study. Due to the geological nature of rock, rock specimens present scattered testing results. On the while, artificial rock-like specimens, for instance mortar specimens or 3D printed specimens, have advantages that allow reproduction with the identical and/or desired properties at high accuracy and resolution. The Objet30 Pro 3D printer from Stratasys was used in this study along with VeroClear, a transparent PMMA printing material. Transparent 3D printed specimen was expected to allow visual examination of crack behavior inside the specimen as it is affected under compressive loading. When PMMA 3D printed specimen is tested under compressive loading in frozen condition, it is known to show more of brittle behavior than in room temperature. Therefore, in this study, specimens containing single open crack with 30, 45 and 60 degrees in inclination angle were tested under frozen condition. The crack tip shape was either square or sharp with the tip angle of 20°, 45°, and 90°. Specimens under uniaxial compression test were filmed by a high-speed camera with the resolution of 640x352 and the frame speed of 30,000 f/s to observe the cracking behavior. Through compressive loading test, strength of the specimens with higher tip angles and 45° inclination angle was found to be the weakest. It was also observed that the decrease in inclination angle or the increase in tip angle resulted in higher wing crack angle development.