# Quasi-Static Sliding Wear Analysis of 3D Rough Surface Considering Changes in the Point of Contact
## 4 Conclusions  
The purpose of this study is to analyze adhesion wear with a deterministic method and predict changes in surface parameters by considering the change in contact points of asperities that occur in the periodic sliding motion. The pressure distribution in the sliding process varies according to the location of the upper moving surface, and the prediction is more precise because the wear depth is evaluated at each position. To consider the characteristics of a rough surface, a very small area at the level where periodicity is established is set as the analysis area, and CGM and CC-FT are used for pressure calculation. In order to examine the effect that occurs as the contact points of asperities are changed, the data of the upper moving surface are moved over the lower stationary surface as in the actual sliding phenomenon, and the sliding wear following the Archard wear model is analyzed as a quasi-static process by dividing one cycle into small steps. In addition, the results of the truncation model and deterministic wear models are compared and analyzed. The conclusions are as follows:  
1. The simulation results of three models are analyzed and compared for the sliding wear of a plane and single asperity, and limitations of the truncation model are suggested. As a result of the analysis of sphere contact, the truncation model predicts more wear depth than the deterministic fixed model, and the truncation model shows excessive wear depth on rough surfaces. This is because, although the shape of the asperities gradually changes from the sphere during the wear process, the contact pressure is obtained as the Hertzian equation for the contact between the sphere and the plane. In addition, as the worn area increased, the error for the radius estimation accumulated, which indicates that the analysis result is not accurate. 2. Wear analysis is performed on numerically generated Gaussian, positively skewed, and negatively skewed surfaces. The sliding distance difference according to the presence or absence of movement of the surface is considered. As a result, the positively skewed surface, where the pressure concentration due to the shape of the asperities occurs the most, has the fastest decrease in RMS roughness. As the peaks on the surface disappear with wear, the skewness increases in the negative direction, and the kurtosis initially decreases and then increases. 3. In periodic sliding motion, the wear progress of the lower stationary surface is relatively slow because the sliding distance between the upper moving object and the lower stationary object is different. As a result, wear scars from asperities on the lower stationary surface appear on the upper moving surface, which is either deep or shallow depending on the surface. 4. Since the plastic contact area occupies a large proportion of the total contact area in the initial wear cycle, plastic contact must be considered in the contact analysis of rough surfaces. However, plastic contact does not occur after the contact area is sufficiently large due to wear. Therefore, the analysis time can be shortened by performing only elastic contact analysis instead of elastic-plastic contact analysis. This model can be applied to the analysis of wear between objects in the periodic sliding motion, such as a piston-liner, a shaft, and the bearing surface of sliding bearings. In addition, it is possible to analyze the effect of the shape of the surface more precisely with relatively better wear resistance on the rough shape of the mating surface. Conceptualization, Y.K. and Y.Y. ; Methodology, Y.K., B.L., K.P. and Y.Y. ; Software, Y.K. and B.L. ; Validation, Y.K., B.L. and Y.Y. ; Investigation, Y.K., B.L. and K.P. ; Writing--original draft, Y.K. ; Writing--review & editing, J.S., B.L. and Y.Y. ; Visualization, Y.K., Y.C., K.P. and Y.Y. ; Supervision, J.S. and Y.Y. ; Funding acquisition, J.S., Y.C. and Y.Y. All authors have read and agreed to the published version of the manuscript.