## 1 Introduction
To address these limitations, researchers have proposed new improvement methods, primarily by altering particle shapes and constitutive relationships within the model. For instance, [PERSON] [25] developed the Flat-Joint (F) contact model, which simulates the mechanical behavior of bonding, failure, and local contacts within a polygonal crystal structure by assuming finite-length segments and finite-area surfaces. To simulate expansion and interlocking forces by changing grain shapes, [PERSON] et al. [26] introduced the Cluster and Clump elements. The Cluster element involves the aggregation of multiple particles to simulate boundaries, while the Clump element allows particles within the unit to overlap freely without undergoing failure under force. These methods offer certain advantages but still fail to accurately reproduce the failure processes occurring within and at the boundaries of rock crystals. Therefore, [PERSON] et al. [27] proposed the Grain-Based Model (GBM), which consists of crystals represented by different polygons. Within the mineral crystals, particles are connected by parallel-bond (PB) contacts, while the boundaries between crystals are defined by smooth-joint (SJ) contacts, allowing for deformation and failure of the crystals. This model not only simulates the mechanical behavior within crystals but also replicates the interactions between crystals, providing a more realistic representation of rock mechanical behavior. Consequently, GBM is currently considered one of the most suitable tools for studying the mechanical response mechanisms of rock materials, particularly crystalline rocks. [PERSON] et al. [28; 29] established a GBM granite model based on granular flow, studying the evolution of the cracks and stress-strain curves of granite with different crystal grain sizes and under different high temperatures. [PERSON] et al. [30] improved the traditional Voronoi GBM model using digital image processing techniques to consider the actual microscopic structure of rocks, integrating discrete crack networks into the model to account for the influence of microcracks. [PERSON] et al. [31] developed a thermo-mechanical grain-based model (TM-GBM) that reflects the actual mineral distribution to study the multi-scale damage of granite during heating, cooling, and uniaxial loading processes. Their findings revealed that, under the same thermal shock temperature, the thermal stress magnitude and the number of thermal cracks during the heating process were significantly lower than those during the cooling process. From the above analysis, it can be observed that it is challenging to fully capture the entire damage and fracture process of granite in real-time high-temperature environments through indoor experiments alone. Therefore, numerical simulation methods are needed for analysis. However, current high-temperature simulation studies on granite are mainly focused on post-high-temperature conditions, while there is relatively less research on the micromechanical behavior of granite under real-time high-temperature conditions. However, the mechanical properties of rocks differ between real-time high-temperature and post-high-temperature exposure conditions. [PERSON] et al. [32], [PERSON] et al. [33], and [PERSON] et al. [34] found that compared to samples cooled naturally after high-temperature exposure, the degradation of various mechanical properties of real-time high-temperature specimens is more pronounced when the temperature is below 400 \({}^{\circ}\)C. However, after reaching 400 \({}^{\circ}\)C, samples cooled naturally exhibit a temperature turning point, with the degree of degradation higher than that of real-time high-temperature specimens. Based on the above considerations, given the geological conditions of real-time high-temperature exploitation in deep dry hot rocks, it is essential to conduct research on the microscopic damage of rocks under real-time high-temperature conditions.