## 3 Results and Discussion  
### Effects of Environmental Media on Dissipation Energy Characteristics  
#### 3.1.1 Hysteresis Loops of Tangential Force versus Displacement Amplitude  
It is clearly seen from Figure 1 that the displacement amplitude is composed of an elastic deformation part (DT) and relative slip (RS) between contacting wires [19; 20]. Hysteresis loops of tangential force versus displacement amplitude (\(F_{t}\)-\(D\)) present shapes of parallelogram, ellipse and straight line, which indicates the gross slip, partial slip and adhesion state, respectively. All points at the refuting contact interface move relative to each other in the case of gross slip, while the partial slip state indicates the adhesion at the contact center of contacting wires and the micro-slip at the contact edge. In each environmental medium, the hysteresis loop presents the parallelogram at the initial stage of the tension-torsion cyclic loading test, which indicates the gross slip at contact surfaces of steel wires. As loading cycles increase, the hysteresis loop changes to the ellipse, which reveals a decrease in the relative slip range and an increase in the adhesion zone, i.e., partial slip state. As compared to the case of air medium, solutions and deionized water require fewer loading cycles for the transition of hysteresis loop from parallelogram to ellipse, which reveals easier removal of protection film at the wire surface and easier transition from gross slip to partial slip at the refuting contact surface in cases of solutions and deionized water. The maximum tangential force between steel wires decreases in the order: air, alkaline and neutral solutions, deionized water and acid solution (Figure 1e,f and Table 3). In cases of distinct media, the relative slip decreases in the order: acid, neutral and alkaline solutions, deionized water and air (Figure 1e and Table 3). In acid solution, wire surface wear is similar to \"pickling and polishing\". Coupled roles of solution medium and SO\({}_{4}\)[2] lubricating film cause the good lubrication at the refuting contact surface, and thereby induce a smaller maximum tangential force and a larger relative slip [21; 22]. In the case of deionized water, it presents the worse lubrication and no electrolyte ion effect as compared to the case of acid solution, which indicates a larger maximum tangential force and a smaller relative slip. In cases of neutral and alkaline solutions, interactions between Cl\({}^{-}\) electrochemical corrosion and SO\({}_{4}\)[2] lubrication film cause the decreases in the maximum tangential force and relative slip [21; 22]. The case of air medium presents the maximum tangential force and minimum relative slip attributed to the rough contact surface, discharge of accumulated debris and poor lubrication effect. The dissipation energy attributed to cyclic tensile loading with refuting contact is characterized by the area inside \(F_{t}\)-\(D\) loop; the dissipation energy is mainly released in the form of friction heat due to material removal [23]. At loading cycles of 20,000, dissipation energies in cases of air, deionized water, acid, neutral and alkaline solutions are \(1.0\times 10^{-3}\) J, \(1.32\times 10^{-3}\) J, \(1.46\times 10^{-3}\) J, \(1.48\times 10^{-3}\) J and \(1.62\times 10^{-3}\)J, respectively. Therefore, in distinct environmental media, the dissipation energy decreases in the order: alkaline, neutral and acid solutions, deionized water and air. It is known that the dissipation energy is positively correlated with the product of maximum tangential force and relative slip. Larger dissipation energy indicates more difficult removal of surface material, which coincides with change trends of wear depth and wear coefficient as depicted in Section 3.1.3.