Evaluation on dynamic Brazilian splitting tests in rock materials under three loading modes by digital image correlation

The validity of the dynamic tensile strength in rock materials is problematic in dynamic Brazilian splitting tests. The purpose of this study is to understand the failure law and effectiveness of the dynamic Brazilian disc (BD) test for five different rock types under three typical loading modes, including platform loading (mode-I), steel bar loading (mode-II) and arc loading (mode-III). Based on the digital image correlation (DIC) technique and high-speed camera, the deformation localization and rupture evolution of the BD specimen under impact loading were obtained, and two rupture characteristics of the specimen were summarized. The loading mode significantly affects the crack initiation location of the disc in the dynamic BD test. The experimental results show that loading mode-III is the most consistent with Brazilian test theory in the dynamic BD test, while loading mode-II violates the test principle. At the same incident energy, the loading rate and dynamic tensile strength are functions of loading mode and lithology, which are highest in loading mode-III, followed by loading mode-I, and the lowest in loading mode-II. The strain and displacement field after peak load were extracted by DIC, and it was found that there were four typical failure modes in dynamic BD tests.