## 4 Results
### Effect of Deep Rolling Pressure  
Figure 14a illustrates the effect of deep rolling pressure on the material surface, combining both a pressure distribution map (top side) and a time-based pressure variation graph (bottom side). In this analysis, the deep rolling pressure applied experimentally is 150 bar, while the pressure from the FEA reaches 1.57 \(\times\) 10\({}^{7}\) Pa (approximately 157 bar). Figure 13: Stress distribution in FEA of deep rolling. This comparison provides valuable insights into the behavior of the material under different rolling pressures and how accurately the FEA model simulates the experimental conditions. Pressure Distribution on the Material Surface (Top Side of the Image): The color-coded pressure distribution map shows the varying pressure levels exerted by the deep rolling tool on the material surface during the process. The pressures range from \(1.57\times 10^{7}\) Pa (in red, the maximum pressure) to \(-1.56\times 10^{7}\) Pa (in blue, the minimum pressure). The red areas indicate where the deep rolling tool exerts the highest pressure, which is recorded at approximately 157 bar. This zone directly beneath the tool is where the most significant deformation of the material occurs, as the pressure is applied to induce compressive residual stresses, enhancing the material's resistance to fatigue and crack propagation. The high-pressure zone covers a small, localized area, indicating that the effect of deep rolling is concentrated under the tool. The blue and green areas represent zones with minimal or negative pressure, located further from the direct contact area of the tool. These areas experience less deformation, as the pressure dissipates farther away from the tool. This pattern is typical in deep rolling processes, where the induced pressure is highest at the point of contact and gradually decreases as it spreads across the surface. Time-Based Pressure Variation (Bottom Side of the Image): The graph on the bottom depicts the pressure variation over time, measured in seconds, as the deep rolling tool moves across the material. The green line shows how the pressure fluctuates, peaking and dipping periodically as the tool applies force dynamically during the process. The fluctuations in the graph reflect the dynamic nature of the deep rolling process. Each  
Figure 14: (a) Pressure distribution on the material surface during the deep rolling process. (b) Time-based pressure variation during the deep rolling process. peak in the graph represents a moment where the tool applies maximum pressure (about 157 bar), while the valleys show instances where the pressure decreases as the tool moves across the material. Periodic loading and unloading are characteristic of rolling processes, where the tool's movement causes variations in applied pressure. Comparison Between Experimental and FEA Pressures: The experimental pressure is set at 150 bar, while the FEA simulation estimates a slightly higher maximum pressure of 157 bar. The graph shows that the FEA model accurately captures the pressure fluctuations and provides a close approximation of the experimental conditions. This indicates that the FEA simulation is a reliable tool for predicting pressure distribution and behavior during deep rolling, especially under high-pressure conditions. The application of high pressure (150-157 bar) during deep rolling has several key effects on the material. The high-pressure zones under the tool cause significant plastic deformation of the surface layers. This deformation leads to the formation of compressive residual stresses, which are beneficial in preventing crack initiation and improving the material's fatigue life. The pressure is highly localized, with the most substantial effects confined to the areas directly under the tool. This localized pressure ensures that the deep rolling process primarily affects the regions of the material that are most vulnerable to stress-related failures, such as surface cracks.