Effect of microwave irradiation on dynamic mode-Ι fracture parameters of Barre granite

Microwave irradiation has been considered as one of the most promising approaches to assisting mechanical rock breakage in rock engineering. Understanding the influence of microwave-induced damage on rock dynamic fracture properties is thus desirable. Using the notched semi-circular bend (NSCB) method, dynamic fracture tests were carried out on rock specimens irradiated by microwaves with different durations. Prior to the dynamic tests, X-ray micro-CT scanning and P-wave velocity measurement were employed to quantify the microwave-induced damage. Both the CT value and the P-wave velocity decrease with the increase of the irradiation duration. During the dynamic tests with loads exerted by a split Hopkinson pressure bar (SHPB) system, a laser gap gauge (LGG) technique was used to monitor the crack surface opening distance (CSOD). The results show that the dynamic initiation fracture toughness increases linearly with the loading rate, and the microwave irradiation has a significant weakening effect. Moreover, the propagation fracture toughness and fracture energy are also sensitive to the irradiation duration and the loading rate, which both increasing with the loading rate while decreasing with the increase of the irradiation duration. In addition, the dynamic fracture velocity increases with the loading rate, whereas the limiting fracture velocity and the fracture arrest toughness are significantly reduced by the microwave irradiation.