Correction of dynamic Brazilian disc tensile strength of rocks under preloading conditions considering the overload phenomenon and invoking the Griffith criterion

Abstract

Dynamic tensile failure is a common phenomenon in deep rock practices, and thus accurately evaluating the dynamic tensile responses of rocks under triaxial pressures is of great significance. The Brazilian disc (BD) test is the suggested method by the International Society for Rock Mechanics and Rock Engineering (ISRM) for measuring both the static and dynamic tensile strengths of rock-like materials. However, due to the overload phenomenon and the complex preloading conditions, the dynamic tensile strengths of rocks measured by the BD tests tend to be overestimated. To address this issue, the dynamic BD tensile strength (BTS) of Fangshan marble (FM) under different preloading conditions were measured through a triaxial split Hopkinson pressure bar (SHPB). The fracture onset in BD specimen was captured through a strain gage around the disc center. The discrepancy between the traditional tensile strength (TTS, determined by the peak load Pf of the BD specimen) and the nominal tensile strength (NTS, obtained from the load Pi when the diametral fracture commences in the tested BD specimen) was applied to quantitatively evaluating the overload phenomenon. The Griffith criterion was used to rectify the calculation of the tensile stress at the disc center under triaxial stress states. The results demonstrate that the overload ratio (s) increases with the loading rate (σ˙) and decreases with the hydrostatic pressure (σs). The TTS corrected by the Griffith criterion is independent of the σs due to the overload phenomenon, while the NTS corrected by the Griffith criterion is sensitive to both the σs and σ˙. Therefore, it is essential to modify the tensile stress in dynamic confined BD tests using both the overload correction and the Griffith criterion rectification to obtain the accurate dynamic BTS of rocks.

Keywords

• Dynamic brazilian disc test
• Overload phenomenon
• Dynamic tensile strength
• Hydrostatic pressure
• Griffith criterion