# Study of Cyclic Plasticity and Creep Ratchet Behavior of PTFE
## 3 Results and Discussion
### The Cyclic Plasticity Behavior at Different Temperatures
Furthermore, LC1 is lower than LC2, and LC5 is higher than LC4, which indicates that an equal increase in the average stress level has a greater effect on ratchet strain and strain rate than an equal increase in the stress magnitude level. One possible explanation is that the average stress tends to be associated with creep. Higher average stresses result in larger creep responses. In the load ranges discussed, the effect of changes in mean stress on ratchet strain is more pronounced than that of changes in amplitude stress, and the effect on ratchet strain rate is similar to that of ratchet strain, whether the load is increased or decreased. The difference between the effects of mean stress and magnitude stress on ratchet strain is progressively magnified as the temperature increases. When cyclic loading is returned to no load at five temperatures, there is almost no difference in deformation between LC1 and LC2; LC4 and LC5, and the difference between mean stress and amplitude stress has little effect on the recoverable deformation due to simple molecular units. The results of LC3 at different temperatures not less than 50 \({}^{\circ}\)C are depicted in Figure 6. After 200 cycles, the ratchet strain reaches 5.44%, 5.62%, 6.8%, 11.2%, and 18.5%, respectively, which shows that the PTFE ratchet behavior is very sensitive to the temperature response, and the ratchet deformation is progressively larger as the temperature increases with the loading of the load at the same stress level; there is no significant difference in the ratchet behavior before 100 \({}^{\circ}\)C, and after 100 \({}^{\circ}\)C, the ratchet strain increases significantly. The evolution of the ratchet strain rate is close to that expected according to the rule, i.e., in the first cycle up to 50 cycles, the rate is rapidly reduced, and then maintains a relatively stable rate of slow decline. In general, below 150 \({}^{\circ}\)C, the ratchet strain rate difference is not significant, but when the temperature reaches 200 \({}^{\circ}\)C, the ratchet strain rate will exhibit nearly three times the increase. PTFE special high-temperature characteristics force us to consider the impact of the cyclic plastic loading process caused by the creep behavior, which may occur due to the influence of the cyclic plastic loading process. This may be an important factor affecting the cyclic plasticity test results. Both the ratchet strain and the strain rate increase with increasing temperatures. However, as shown in Figure 6b, the rate of ratchet strain increase rises significantly above 100 \({}^{\circ}\)C. This is because PTFE's modulus of elasticity decreases significantly once the ambient temperature surpasses 100 \({}^{\circ}\)C. The increase in temperature alters the structure of the crystal arrangement, and according to [PERSON] et al., this material undergoes a glassy transition at around 130 \({}^{\circ}\)C [34]. Meanwhile, the amorphous organization between the PTFE crystals and the crystals of other materials is progressively parallel to the slip in the crystal region; the higher the temperature, the greater the degree of slip [32]. As slippage occurs, the tendency of crystals to deform in the axial direction of tensile stress through rotation becomes more pronounced. The maximum creep strain at 23 \({}^{\circ}\)C is 2.3, 3.1, 5.9, and 7.8 times the minimum creep strain, respectively, which can be seen to increase substantially with the increasing stress level. The maximum creep strain at 50 \({}^{\circ}\)C was 1.34, 1.92, 2.68, and 3.58 times the minimum creep strain, respectively. The values at 100 \({}^{\circ}\)C were 1.38, 1.86, 2.75, and 3.68. The values at 150 \({}^{\circ}\)C were 1.46, 2.07, 3.15, and 4.32. The values were 1.5, 2.25, 3.13, and 4.25 at 200 \({}^{\circ}\)C. It can be seen that at 50 to 100 \({}^{\circ}\)C, the different levels of creep strain were similar. The stress response to temperatures between 150 and 200 \({}^{\circ}\)C is more sensitive, and the rule of change is similar.