# Dynamic Mechanical Properties of Heat-Treated Shale under Different Temperatures
## 1 Introduction
Since hydraulic fracturing technology is mostly used in the exploitation of shale gas abroad, research on the mechanical properties of shale is mainly focused on static research, and the exploration on the dynamic mechanical behavior of shale is relatively rare. Although our country started late in shale research, some substantial progress has been made. [PERSON] et al. [11; 12; 13; 14] conducted uniaxial and triaxial compression tests on shale, analyzed the mechanical properties, strength, and failure mode of shale, and revealed the anisotropic failure mechanism of shale. [PERSON] et al. [15] divided the pyrolysis weight loss of oil shale into three stages based on the new technology of in situ thermal injection mining of oil shale. When the temperature exceeds 200 \({}^{\circ}\)C, the influence of temperature on bulk density, specific gravity, porosity, etc., increases. When the temperature exceeds 300 \({}^{\circ}\)C, there is a significant increase in the number, length, and width of shale fractures. At the same time, microcracks are formed in the direction perpendicular to the bedding plane. [PERSON] [16] et al. studied the anisotropy of shale generated by layered waves and gave the  
Figure 1: Physical model of fracture propagation under high-energy gas fracturing [3]. P-wave and S-wave velocities of samples in different directions under different conditions. [PERSON] [17] found that fracturing fluid intrudes into rock mass along with fractures, which is the main reason for the decline in shale strength. [PERSON] et al. [18,19] carried out uniaxial compression mechanical experiments of shale under four kinds of low strain rates and analyzed the influence of shale strain rates on the relevant mechanical parameters of shale. [PERSON] [20] conducted the separation Hopkinson bar compression experiment for the high strain rate of shale, and preliminarily explored the dynamic constitutive relationship of shale. [PERSON] et al. [21] used the separated Hopkinson pressure bar system to carry out impact tests on shale. It was concluded that the damage degree of shale significantly increases with the increase in impact velocity under different strain rates, and that the ductility and failure resistance of rock materials are improved under passive confining pressure. Crack initiation and its effects on the dynamic behavior of rock, particularly regarding ultrasonic wave velocity, have been studied extensively in recent years. Numerical manifold method (NMM) simulations have been used to investigate the propagation of stress waves through the fractured rock mass [22]. A study by [PERSON] [23] demonstrated that the stress wave velocity is affected by the size and orientation of the fractures, as well as the properties of the surrounding rock's matrix. Micro-fractures have also been found to impact the dynamic behavior of rocks significantly. A study by [PERSON] [24] on wave propagation through rock mass with micro-fractures found that the velocity and amplitude of the waves are affected by the orientation and distribution of the micro-fractures. Thermal shock-induced damage is another factor that can affect the dynamic behavior of rocks. The spatial gradient distribution of damage to granite induced via thermal shock has been studied. It was found that the thermal shock-induced damage significantly affects the ultrasonic wave velocity and attenuation [25]. Finally, experimental investigations of thermal effects on the dynamic behavior of granite have demonstrated that changes in temperature can cause significant changes in the ultrasonic wave velocity, attenuation, and dispersion [26]. These studies have contributed to a better understanding of the effects of crack initiation and thermal shock-induced damage on the dynamic behavior of rocks. Different material grains have different anisotropy and thermophysical properties, which leads to incongruuous deformation across grain borders and thermal stress between or within grains [27].