# Crack Extension Analysis of Atmospheric Stress Corrosion Based on Peridynamics
## 2 Materials and Methods
### Simulation of Atmospheric Stress Corrosion Fracturing in 304 Stainless Steel
#### 2.2.2 Calculation Model Setup  
To simplify the model and improve the computational efficiency, we set the numerical simulation model as a rectangular plate of \(150\times 4\times 100\) mm\({}^{3}\). As shown in Figure 6, the initial crack length was 25 mm and a constant load was applied at the top and bottom edges of the plate. A layer of nodes to the right of the initial crack was used as the initial corrosion area, and the metal ion concentration in the initial corrosion area was set to zero and maintained at zero throughout the corrosion process. Zero-flux conditions were applied to the rest of the boundaries. The region describing the material was discretized using a uniform grid with nodes situated in the center of each cell, which was equivalent to employing Gaussian quadrature with a single point in the vicinity.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**C** & **Si** & **Mn** & **P** & **S** & **Ni** & **Cr** & **Fe** \\ \hline
0.06\% & 0.61\% & 0.95\% & 0.028\% & 0.011\% & 8.12\% & 18.10\% & Bal. \\ \hline \hline \end{tabular}
\end{table}
Table 1: Chemical composition of the specimen.  
Figure 5: SEM image of the sample surface.  
The region defining the material was discretized with a uniform grid with the nodes located in the middle of each cell, which was equivalent to using a single-point Gaussian quadrature in the neighborhood.  
The computational model consisted of 60,000 material points of 1 mm size, with eight particle layers at the bottom and top edges as loading layers, with a grid spacing \(\Delta x=1\) mm and a near-field radius \(\delta=3\) mm (corresponding to \(m=3\)), which was uniformly discretized in the \(x\), \(y\), and \(z\) directions with \(\Delta x\). The [PERSON]'s modulus of 304 stainless steel \(E=194020\) MPa and the Poisson's ratio \(v=0.3\); we chose \(C_{solid}=143\) M, \(C_{sat}=5.1\) M, and \(\lambda_{0}=30\) um, which are typical values for stainless steel, and applied \(C_{sat}\) at the location of the crack tip and along the newly created crack node. We assumed that the solubility of the corrosion front was 0.02 um\({}^{2}\)/s, and to improve the modeling rate, by referring to the calculation in [57], we used \(k_{H}=1.07\), \(k_{\sigma}=1.001\), and \(k_{H,\sigma}=1.08\). Typically, the plastic deformation of steel must be accounted for in the fracture model. However, as the plasticity of stainless steel decreases in corrosive environments, the ductile fracture transforms into a quasi-brittle fracture, necessitating the use of the intrinsic force model of brittle material with linear and nonlinear mechanical behavior in the solution process.  
In the process of stress corrosion, the time for corrosion diffusion is much longer than the time for crack expansion; therefore, the time t for corrosion diffusion calculation in the computational model should be much larger than the time \(T\) for the mechanical solution step. Moreover, the given initial liquid film thickness \(\lambda_{B}\) has a great influence on the results of the numerical simulation. Therefore, we conducted experiments to determine the appropriate time interval and initial liquid film thickness in the following section.