# Study on radial fracture mechanism of saturated granite subjected to coupled static–cyclic impact loading: An experimental investigation

## TL;DR

This study investigates how granite fractures radially under combined static and cyclic impact loading, revealing key insights into rock failure mechanisms for underground engineering applications.

## Contribution

The study experimentally identifies radial tensile-dominated failure in granite under coupled static-cyclic impact loading and explains the role of stress waves and water in crack propagation.

## Key findings

- Granite primarily exhibits radial tensile-dominated failure under coupled static-cyclic impact loading.
- Stress wave analysis shows nonlinear propagation due to tensile stress waves.
- Free water at crack tips enhances crack propagation and affects fracture surface smoothness.

## Abstract

The rock failure mode under coupled static-cyclic impact loading is not unified, and the radial fracture mode is a distinct type. In this study, cyclic impact tests were performed using a modified Split-Hopkinson Pressure Bar system under various axial pressures and confining pressures. Results showed that granite primarily exhibited radial tensile-dominated failure under coupled static-cyclic impact loading, with compression-shear failure at the specimen ends. Stress wave analysis revealed nonlinear propagation attributed to tensile stress waves. Numerical simulations confirmed that the velocity field exhibited a symmetrical transition with velocity vectors oriented in opposite directions on either side of a central zone. Two zones appear in the middle of the specimen in the displacement field, which correspond to the plastic stage in the stress-strain curve. Meanwhile, the free water in crack tips assists in enhancing crack propagation. In addition, before the final impact loading, the peak of the transverse relaxation time spectrum of micro-pores has returned to its initial state approximately. Fracture surface shows smoother surface under higher axial and confining pressures. The study provides reference for stability evaluation in underground engineering.