## 5 Analysis of Test Results
### Influence of the Spreading Amount of Viscosity-Level Oil  
In order to further study the influence of different spreading amount of the viscosity-level oil on interlayer interface characteristics under vertical load, the maximum adhesion coefficient \(K_{\text{max}}\) was selected as the evaluation index of interlayer adhesion capacity, and relevant tests are carried out. The experimental data are shown in Figures 11 and 12.  
Figure 11: The curves relating spreading amount of viscosity-level oil A and adhesion coefficient.  
Figure 10: Influence of temperature on the bonding coefficient of oil B bond specimen.  
Figures 11 and 12 show the following features:  
1. When the ambient temperature is \(-10\)\({}^{\circ}\)C, the change in adhesion coefficient of viscosity-level oil A is not obvious. When the spreading amount increases from 0 to 0.5 kg/m\({}^{2}\), the adhesion coefficient increases by 25.7%. However, when the spreading amount changes from 0.5 to 1.5 kg/m\({}^{2}\), the change in the adhesion coefficient is small. In contrast, the adhesion coefficient of viscosity-level oil B is more regular, and the adhesion coefficient increases first and then decreases, with an obvious peak value.
2. When the ambient temperature is 0 \({}^{\circ}\)C, the adhesion coefficient of viscosity-level oil A shows an obvious regularity. The adhesion coefficient increases first and then decreases with the spreading amount increasing from 0 to 1.5 kg/m\({}^{2}\). Similarly, the regularity of the adhesion coefficient for viscosity-level oil B is consistent with viscosity-level A.
3. When the ambient temperature is 25 \({}^{\circ}\)C, the adhesion coefficient increases by 90.9% with the spreading amount of viscosity-level oil A increasing from 0 to 0.5 kg/m\({}^{2}\). When the spreading amount ranges from 0.5 to 1.0 kg/m\({}^{2}\), the adhesion coefficient increases by 41.3%. When the spreading amount increases from 1.0 to 1.5 kg/m\({}^{2}\), the adhesion coefficient decreases sharply by 64.4%. However, when the spreading amount of viscosity-level oil B increases from 0 to 0.5 kg/m\({}^{2}\), the adhesion coefficient increases by 66.5%. When the spreading amount increases from 0.5 to 1.0 kg/m\({}^{2}\), the adhesion coefficient decreases by 29.8%. When the spreading amount increases from 1.0 to 1.5 kg/m\({}^{2}\), the adhesion coefficient decreases by 26.1%.
4. When the ambient temperature is 50 \({}^{\circ}\)C, the adhesion coefficient of viscosity-level oil A is consistent with that at 25 \({}^{\circ}\)C. When the spreading amount increases from 0.5 to 1.0 kg/m\({}^{2}\), the adhesion coefficient increases by 37.7%. When the spreading amount increases from 1.0 to 1.5 kg/m\({}^{2}\), the adhesion coefficient decreases sharply by 69.3%. The change in adhesion coefficient of viscosity-level oil B is not obvious, but it still shows a trend of first increasing and then decreasing.  
In general, the spreading amount of viscosity-level oil has a certain effect on the adhesion coefficient. From 0 to 1.5 kg/m\({}^{2}\), the adhesion coefficient increases gradually first and then decreases, which basically shows a downward parabola form. Therefore, there is an optimal spreading amount. By fitting the curves of Figures 11 and 12, the  
Figure 12: The curves relating spreading amount of viscosity-level oil B and adhesion coefficient.  
polynomials are shown in Table 9, and the optimal amount of viscosity oil can be obtained under different working conditions.  
It can be seen from Table 9 that the spreading amounts of the viscosity-level oil A and oil B corresponding to their maximum adhesion coefficients, which are about 0.8 and 0.6 kg/m\({}^{2}\), respectively, at different temperatures. Therefore, the optimal spreading amount of the viscosity-level oil is suggested to be 0.6\(\sim\)0.8 kg/m\({}^{2}\).