# Crack Extension Analysis of Atmospheric Stress Corrosion Based on Peridynamics
## 3 Results and Discussion  
In order to study the effect of the corrosion diffusion time \(t\) with mechanical loading time \(T\) and the initial liquid film thickness on the numerical simulation of the stress corrosion process, we performed the simulation solution based on the data model with RH = 35% relative humidity under the condition that all the boundaries were not set to zero flux. We first studied the effect of the corrosion diffusion time \(t\) and mechanical loading time \(T\). Four sets of simulations were done: \(T=30t\) (40\(t\), 50\(t\), 60\(t\)) when \(t=30\) (40, 50, 60), i.e., the corrosion diffusion solver ran 30 (40, 50, 60) time steps after the fracture solver ran once. The results are shown in Figure 7. The red-brown part of the energy sketch (left) indicates the mechanical damage release energy. The red-brown part of the corrosion diffusion domain diagram (right) corresponds to the region where the metal ion concentration in the metal matrix became zero. Figure 6: Geometry and boundary conditions. Figure 7 shows that in the case of a coupled solver with the same running time, the longer the corrosion diffusion solver ran, the greater the corroded region. The direction of fracture expansion was toward the region of corrosion diffusion in this investigation. Taking \(\lambda_{B}=0.5\)\(\upmu\)m (\(5\)\(\upmu\)m, \(50\)\(\upmu\)m, \(500\)\(\upmu\)m), \(T=40t\), setting the initial corrosion region metal ion concentration to zero, and applying zero flux to the rest of the boundary, we did four sets of simulation experiments to determine the effect of the initial electrolyte film thickness, and the simulation results are shown in Figure 8. As shown in Figure 8: As \(\lambda_{B}\) increases, the simulation results are shown in Figure 8.  
Figure 7: Energy diagram ((**a**) \(T=30t\), (**c**) \(T=40t\), (**e**) \(T=50t\), and (**g**) \(T=60t\)) and corrosion diffusion field ((**b**) \(T=30t\), (**d**) \(T=40t\), (**f**) \(T=50t\), and (**h**) \(T=60t\)) in the 500-time-step test. becomes larger, the area of corrosion diffusion also becomes larger, and is accompanied by the appearance of branching cracks. When \(\lambda_{B}\) to increase to a certain extent, the same time step under the area of corrosion diffusion in turn becomes smaller. This is in line with the effect of electrolyte film thickness on corrosion rate. Figure 8: Energy diagram ((**a**) \(\lambda_{B}\) = 0.5 \(\upmu\)m, (**c**) \(\lambda_{B}\) = 5 \(\upmu\)m, (**e**) \(\lambda_{B}\) = 50 \(\upmu\)m, and (**g**) \(\lambda_{B}\) = 500 \(\upmu\)m) and crack propagation path ((**b**) \(\lambda_{B}\) = 0.5 \(\upmu\)m, (**d**) \(\lambda_{B}\) = 5 \(\upmu\)m, (**f**) \(\lambda_{B}\) = 50 \(\upmu\)m, and (**h**) \(\lambda_{B}\) = 500 \(\upmu\)m) in the liquid film thickness test at 1200 time steps. [PERSON] et al. [58] demonstrated that oxygen plays a key role in the nucleation and extension of stress corrosion cracks. For IGSCC cracks, oxidation first occurs before the SCC crack tip. The crack then expands by connecting with microcracks within the grain interface oxide. For TGSCC cracks, the nucleation and growth of microcracks in the oxide along the deformation zone is an important mechanism for TGSCC crack extension. This was consistent with the partially discontinuous cracks in Figure 8b,d,f,h in the simulation experiments, further justifying the model. Through simulation experiments, we found that the thickness of the electrolyte liquid film not only affected the rate of stress corrosion to a great extent but also affected the sprouting and evolution of branching cracks during the stress corrosion process. Through the above two simulation experiments, we found that the selection of the appropriate time interval and the initial liquid film thickness had an important influence on the simulation solution. Based on the above simulation experiments, the metal ion concentration in the initial corrosion region was set to zero and zero flux was applied to the boundary of the remaining prefabricated cracks.