Dynamic mechanical properties and microscopic damage characteristics of deep skarn after high-temperature treatment

The skarn at a depth of 700 m is taken as the research object to study the dynamic behaviors of deep rocks under high temperature. The impact compression tests at different impact air pressures (0.8, 1.0 and 1.2 MPa) are carried out on the skarn at room temperature and after high-temperature treatment (200 ℃, 400 ℃, 600 ℃ and 800 ℃) by using the split Hopkinson press bar experimental device. The fracture surface is observed by the SEM scanning electron microscope and XRD phase characteristic analysis technology to explore the micro-failure mechanism of the skarn under high temperature and dynamic load. The test results show that under the same impact air pressure, the strength of the skarn deteriorates and the ductility increases with the increase of temperature. And at the same temperature, both the strength and deformation of the skarn increase with the increase of impact pressure, showing obvious strain rate effect. With the increase of impact pressure or temperature, the crushing degree of the skarn becomes more and more intense, and the fragmentation becomes smaller and smaller, and especially smaller particles are mainly crushed at 800℃. The change of internal composition and structure is the main reason for the change of mechanical properties of the skarn. The brittle failure of the skarn is mainly transgranular and intergranular fracture at 25℃ ~ 400℃. 400℃ ~ 600℃ is the threshold temperature range of skarn transformation from brittle to plastic. When the temperature degree is up to 600℃ ~ 800℃, it transforms into dimple and slip fracture.