The meso-structure mineral composition and fracture mechanism of uniaxial compressed mudstone samples at high temperature were analyzed by XRD and scanning electron microscopy. The effect of tem- perature on mudstone composition and fracture mechanism were studied from a meso-structural per- spective, and the relationship between meso-structure and macro-mechanical characteristics at high temperature was revealed. The findings demonstrated that the fluctuation in diffraction intensity of kao- linite in the mudstone caused the fluctuation in its mechanical properties. The overall structure under- went a phase change around 600℃, which led to the sudden change in the mechanical properties of mudstone samples. When the temperature reached 600 ℃, the crystalline state worsened and kaolinite disappeared; however, some illite was produced, indicating that the chemical reaction of the structure and sudden drop of bearing capacity of the mudstone. Mudst0ne fracturing at high temperature involves mainly intergranular and transgranular fractures, which are typical in micro-brittle tensile failure. Con- sidering the macro-fracture characteristics of mudstone, the results suggested that macro-fracture under external force corresoonds to the meso-fracture.
The uniaxial compression tests for mudstone specimens are carried out with four different loading rates from room temperature to 400℃ by using the Rock Mechanics Servo-controlled Testing System MTS810 and high temperature furnace MTS652.02.The mechanical properties of mudstone with various loading rates are studied under different temperature conditions.The results show that when temperature increases from room temperature to 400℃ and loading rate is less than 0.03 mm/s,the peak strength of mudstone specimen decreases as loading rate increases,while the various peak strengths show significant differences when loading rate exceeds 0.03 mm/s.At room temperature,the elastic modulus decreases at the first time and then increases with loading rate rising.When the temperature is between200 and 400℃,the elastic modulus presents a decreasing trend with increasing loading rate.With increasing the loading rate,the number of fragments in mudstone becomes larger and even the powder is observed in mudstone with higher loading rate.Under high loading rate,the failure mode of mudstone specimens under different temperatures is mainly conical damage.
