Abstract: Understanding the dynamic tensile behavior of rock is essential for studying the response of rock masses under blasting and seismic loading. Granite specimens were subjected to dynamic Brazilian splitting tests using a combination of ultra-high-speed camera and digital image correlation (DIC) techniques. Stress equilibrium and central crack initiation were assessed through strain gauge measurements and high-speed photography. The evolution of the deformation field on the microsecond timescale was analyzed using high-speed DIC, and the rate-dependent mechanisms at the crystal scale were investigated through polarizing microscopy. The results show that the tensile strength–strain rate relationship of granite can be divided into three regimes. In Regime II, the behavior conforms to the unified dynamic strength model, with a characteristic strain rate of 48.3 s^-1 and a dynamic increase factor of 0.97. Notably, the average fragment size remains nearly constant with increasing strain rate. The ratio of residual kinetic energy to total dissipated energy ranges from approximately 23% to 47%. At the crystal scale, meso-scale failure modes include transgranular cracking, crack deflection, crack clustering into bands, and grain pulverization. With increasing strain rate, the failure process transitions from central crack initiation to boundary-dominated failure. When the strain rate exceeds a critical threshold, stress equilibrium and central initiation conditions are no longer met, resulting in an apparent decrease in dynamic tensile strength. This indicates that test validity may be compromised under such conditions, and results must be interpreted with caution.

Key words: rock mechanics, impact load, strain rate mechanism, unified dynamic strength model, dynamic fragmentation