## 4 Analysis of Test Results
### Analysis of Uniaxial Compression Test Results  
#### 4.2.1 Deformation Characteristics  
Figure 7 shows the uniaxial compression full stress-strain curves of group A samples after 25 \({}^{\circ}\)C, 100 \({}^{\circ}\)C, 200 \({}^{\circ}\)C, 300 \({}^{\circ}\)C, 400 \({}^{\circ}\)C, 500 \({}^{\circ}\)C, 600 \({}^{\circ}\)C, 700 \({}^{\circ}\)C, 800 \({}^{\circ}\)C and 900 \({}^{\circ}\)C. It can be seen from Figure 7 that the variation of the stress-strain curve of the uniaxial compression of the group A samples after different high temperatures generally goes through four stages: compaction, elasticity, yielding and failure. 1. Compaction: The curve shows upward concave because of the closure of cracks existed under compress. Higher temperatures have long compaction phases, which indicate that the higher the temperature, the more micro-cracks are generated inside the sample. 2. Elasticity: The stress-strain curve at this stage is a straight line, showing a good linear relationship, showing the elastic characteristics of the material. The slope of the straight line segment at this stage is called the elastic modulus (also known as Young's modulus) and is the mechanical parameter of the material. 3. Yield: The stress-strain curve bends downward, and the specimen presents inelastic deformation. The material with lower internal strength of the rock specimen first yields and destroys gradually, and the increase rate of axial stress decreases gradually. 4. Destruction: The axial stress increases to the limit capacity that the specimen can withstand. The micro-cracks inside the specimen penetrate to form a macroscopic slip. In the initial stage of the slip, stress occurs in the longitudinal direction of the specimen, and failure occurs locally [33]. The stress dropped rapidly and the sample as a whole lost its bearing capacity. Figure 6: The relationship between damage factors and temperature of high temperature samples. Figure 7: _Cont._  
For comparison, Figure 8 shows the uniaxial compression of group A samples after 100-900 \({}^{\circ}\)C. The stress-strain comparison curve is obtained (one sample at the same temperature). Figure 8: Complete stress–strain curves of one sample at same temperature under uniaxial compression. Figure 7: Complete stress–strain curves of samples under uniaxial compression. It is not difficult to find from Figure 8 that after the sample is subjected to high temperature at 100-500 \({}^{\circ}\)C, the four stages of the stress-strain curve deformation process are basically similar, and the elastic modulus is roughly equivalent. It indicates that in this range, the effect of high temperature on the deformation characteristics of the sample during uniaxial compression is not obvious. The effect of high temperature on the bearing capacity of the sample is significant, compared to that at room temperature of 25 \({}^{\circ}\)C. Although the test results are largely discrete, they still have obvious general rules, and the bearing capacity of the sample increases with the increase in temperature. This can be explained as being within 500 \({}^{\circ}\)C, when the temperature increases, the hot melt deformation can gradually close part of the primary cracks, reduce the number of cracks, improve the contact state between the mineral particles, enhance the friction characteristics, and strengthen the bearing capacity of the sample. When the temperature exceeds 500 \({}^{\circ}\)C, the whole stress-strain curve shape begins to change greatly, which is mainly reflected in the initial resistance to deformation resistance, the stress-strain curve in the compaction phase increases, the stress-strain curve shifts to the right, the peak strain increases significantly, and the bearing capacity decreases. This can be understood as the thermal expansion of the sample mineral particles after the 500 \({}^{\circ}\)C high temperature causes the thermal expansion of the grain boundary to be uncoordinated, thereby causing thermal stress between the particles and the thermal stress will produce micro-cracks.