# The Preparation of Active Support-Based Sealing Material and Sealing Effect Analysis
## 3 Analysis of Mechanical Characteristics of Sealing Material  
### TriAxial Strength and Deformation Characteristics  
Based on the ratio of the sealing materials obtained via orthogonal tests, the test specimens with different expansion rates, namely, 0%, 1%, 3% and 5%, were obtained by changing the content of expanding agent. The MTS815 electronic servo test system was used to conduct triaxial tests on the specimens, as shown in Figure 5. This test system mainly consists of oil sources, a testing machine, a confining pressure control cabinet, and a data acquisition system. The test specimens for the triaxial test were in a standard cylinder with a diameter of 50 mm and a height of 100 mm. The actual test scheme is as follows: Triaxial tests are carried out on the specimens with an expansion rate of 0%, 1%, 3% and 5%, respectively, and the loaded confining pressure grade gradients are 1 MPa, 2 MPa, and 3 MPa. Three tests are conducted for each group of specimens, with a total sample size of 36 specimens. The confining pressure is loaded at a rate of 0.01 MPa/s until it reaches the set value and then remains unchanged. Then the vertical load is applied via displacement control. In order to reflect the gradual and natural loading in the field, the loading rate was set at 0.01 mm/s until the specimen was damaged. The triaxial test results for the sealing materials with different expansion rates are shown in Figure 6. As can be seen, the properties of the sealing materials change significantly with the size of the confining pressure. At a low confining pressure, the materials show the characteristics of brittle materials, and the stress decreases significantly with the increase in strain after specimen failure. When the confining pressure is relatively higher, the material shows the characteristics of a viscous material, and the post-peak stress is still more than 90% of the peak stress. With the increase in the confining pressure, the peak strength of the material also increases significantly. When the expansion rate is 1% and the confining pressure is 3 MPa, the peak strength is 10.14 MPa, and the corresponding peak strain increases as well. In general, the larger the lateral stress is, the more the curve of the elastic phase shifts to the left on the stress-strain curve. Accordingly, the greater the confining pressure is, the greater the elastic modulus of the material becomes and the stronger the deformation resistance of the material is. The annular strain of the specimen decreases with the increase in the confining pressure. Under the same confining pressure condition, the larger the expansion rate of the material is, the smaller the annular strain is. With the increase in the confining pressure, Poisson's ratio of the specimen decreases gradually. This is because the lateral pressure exerted on the specimen restricts its circumferential deformation to a certain extent under the higher confining pressure. The specimen's Poisson's ratio displays a downward trend with the increase in the expansion rate. This is because the larger the expansion rate of the specimen is, the more pores there are in the specimen, and the higher the compaction degree is under triaxial compression. Figure 5: MTS815 electronic servo test system. Figure 7 shows the curve of the elastic modulus of the sealing materials with different expansion rates when the confining pressure changes. As can be seen from the figure, the elastic modulus increases as the confining pressure rises; the higher the expansion rate is, the more the elastic modulus increases with the rise of the confining pressure. At a confining pressure of 3 MPa, the elastic modulus of the specimen with an expansion rate of 0% reaches 12.74 GPa, 38.6% higher than that of uniaxial compression. Similarly, at the same confining pressure, the elastic modulus of the specimen with an expansion rate of 5% reaches 1.53 GPa, 50% higher than that of uniaxial compression. By contrast, the increase in amplitude is greater than that of 0%.