## 3 SB as SE Process--Review and Discussion
### Correlations in the Integrated SE Approach  
#### 3.2.1 Basic Concepts and Rationale of Correlations  
It is necessary to define and clearly distinguish the terms method and process used in the literature regarding SB. The definitions were given in our previous review paper [32]. A method is a coherent time-space arrangement of two bodies (a deforming component and a treated surface) in the mechanical sense, with defined geometry and physical and chemical properties, whereas a process is an energy and mass exchange resulting from the coherent interaction between two bodies with clearly defined quantitative characteristics. Using the same method, but with different quantitative parameters (governing factors), many processes can be implemented, and, as a result, the processed components will have different SI, and thus a different OB. Of the three components of SE (Figure 10), one can control only one, namely, the process through which the desired SI and OB can be obtained, which can be measured (recorded). Therefore, the finishing process is at the input of the system, and the OB is at the output.  
The purpose of structural and machine elements is to fulfil a set functional purpose, satisfying the necessary requirements for operational life. The main task in SE is to define a cost-effective finishing process that satisfies the desired performance characteristics of the component, i.e., the output information is known, and the input information is sought.  
\begin{table}
\begin{tabular}{l l l l l l l} \hline \hline \multirow{2}{*}{**Alloys**} & \multirow{2}{*}{**R\({}_{\omega}\) \(\mu\)m**} & \multicolumn{2}{l}{**Surface**} & \multicolumn{2}{l}{**Residual Stresses [()]\({}^{\text{{\text{{\text{{\text{{\text{{\text{\text{{\text{\text{{\text{{\text{{ \text{{  }}}}}}}}}}}{{{{{{{{{{{{{{{{{}}}}}}}}}}}}}}}{{{{{{{{}}}}}}{{{{{}}}}}{{{{}}}}{{{{}}}}{{{{}}}}  
In other words, the task to be solved is inverse, i.e., a task of synthesis. The first way to solve this task is to study the direct correlation 'finishing-OB' (Figure 1). This approach seems shorter on the face of it. The main disadvantage is that SI characteristics are not quantified. Thus, the 'finishing-SI' and 'SI-OB' correlations remain hidden. For this reason, the obtained information about the 'finishing-OB' correlation (a specific combination of the magnitudes of the process governing factors was found) can only be used for another analogous case. The second way of solving the task involves the longer path of research 'finishing-SI-OB' (Figure 1), since the characteristics of SI are also determined in a quantitative and qualitative aspect. This approach allows the assessment the influence of the main features of SI on the OB. For example, it is known that larger residual compressive stresses in SL provide greater fatigue strength, negative skewness and kurtosis greater than three provide higher sliding wear resistance in boundary lubrication friction condition, and so on. It is important to note that quantification of SI characteristics generally requires less time, effort, and resources than OB evaluation tests. The resulting SI-OB correlation database allows predicting OB for other cases based on the finishing-SI correlation. Therefore, in the majority of cases, the given task can be solved only on the basis of the correlation 'finishing (process)-SI'. The components of SE, the correlations between them, and the necessary optimizations to solve the main task of synthesis of a suitable finishing process are visualised in Figure 13.