Damage effect of hypervelocity projectiles on granite at different impact angles

Investigation of the damage effects of bursting layer materials represented by granite under hypervelocity oblique penetration is important for the design of underground protective engineering. Through hypervelocity oblique penetration tests, this study systematically reveals the damage mechanism and dynamic mechanical response of granite targets under different striking angles. Tests were conducted at striking angles of 0°, 15°, 30°, and 45° using a two-stage light gas gun, with velocities ranging from 1838 m/s to 2664 m/s, while high-speed photography and 3D scanning were employed for quantitative characterization of penetration damage. For striking angles of 0°, the differences in anti-penetration properties between medium-grained and fine-grained granite were compared. The experimental results indicate that striking angles greater than 30° significantly decrease damage parameters. A velocity threshold exists at 45°, where increasing velocity from 2343 m/s to 2436 m/s causes the penetration depth and the volume loss to plummet by 34.66% and 59.99%, respectively. Multivariate regression analysis revealed linear correlations between normal velocity ( V 0 cos β ) and damage parameters. Furthermore, based on the Extended Dynamic Cavity Expansion Model (EDCEM), a penetration depth prediction model was modified to consider the striking angle. Among the four designed velocity gradients, the average penetration depth, crater area, volume loss and peak strain of fine-grained granite are all smaller than those of medium-grained granite. Their failure modes were observed microscopically, demonstrating superior anti-penetration properties of fine-grained granite. The experimental results address a gap relative to traditional vertical penetration studies and provide essential data for the performance assessment of granite subjected to oblique penetration.