# Crack Extension Analysis of Atmospheric Stress Corrosion Based on Peridynamics
## 3 Results and Discussion
We used \(T=40t\) and \(\lambda_{B}=0.5\)\(\upmu\)m and numerically simulated the atmospheric stress corrosion of 304 stainless steel in a laboratory environment with a relative humidity RH of 35%. We used \(T=40t\) and \(\lambda_{B}=5\)\(\upmu\)m and numerically simulated the atmospheric stress corrosion of 304 stainless steel in a laboratory environment with a relative humidity RH of 75%. The results are shown in Figures 9 and 10. We found that the results of the numerical simulation of the model and the experimental results displayed good agreement. Both were dominated by transverse cracks and had some similarities in the direction of branching cracks. Figure 9: Energy diagram ((**a**) \(t=400\), (**c**) \(t=800\), (**e**) \(t=1200\), (**g**) \(t=1600\), and (**i**) \(t=2000\)), crack propagation path ((**b**) \(t=400\), (**d**) \(t=800\), (**f**) \(t=1200\), (**h**) \(t=1600\), and (**j**) \(t=2000\)), and an SEM image of the sample surface (**k**) when the RH was 35%, with \(T=40t\) and \(\lambda_{B}=0.5\) μm. Figure 10: Cont. [PERSON] et al. [5], through the study of stress corrosion of X70 pipeline steel in a near-neutral environment, found that the stress corrosion process can proceed both according to the anodic dissolution mechanism and according to the hydrogen embrittlement mechanism. 304 stainless steel samples due to local anodic dissolution on the surface formed the initial corrosion areas, these initial corrosion areas are the original defects of crack generation. In these defect areas, will cause a large stress concentration. At the same time, the hydrogen atoms generated during the anodic dissolution process will be enriched in the stress concentration area, and the hydrogen atoms will diffuse through the defects to the metal interior under the effect of concentration gradient and stress gradient. [PERSON] et al. [59], through a positron annihilation lifetime spectroscopy study on 304 stainless steel, confirmed that hydrogen diffuses into a deeper region after the application of tensile stress. Simultaneously, vacant hydrogen complexes are generated in this region and develop into vacant clusters. This study corroborated the role of hydrogen and stress in anodic-dissolution-dominated SCC. [PERSON] et al. [60] studied the stress corrosion of iron-containing chloride ion rust layers that occurred in humidity-controlled air. The results of the study showed that the relative humidity affected the rate of hydrogen uptake by the rust layer of iron. In the region of 42-74% RH, the hydrogen uptake rate increased with increasing RH. The pH of the rust layer was weakly acidic in the range of 4.2-4.3 during the corrosion in the tested RH range. Therefore, the higher the relative humidity within the range of 42-74%, the more hydrogen the metal absorbed during the stress corrosion. The greater the stress gradient and concentration gradient (hydrogen diffusion in metal mainly occurs via stress diffusion), the greater the diffusion range of hydrogen atoms in the metal. Under tensile stress, the direction of the crack extension remained essentially the same as the direction of diffusion of hydrogen atoms. This was highly similar to our simulation tests. [PERSON] et al. [61], in their study of X80 pipeline steel hydrogen embtitlement, found that when hydrogen embtitlement occurs in this material, the hydrogen originated from internal hydrogen and surface-absorbed hydrogen. When the material was charged with hydrogen, hydrogen atoms were first adsorbed on the metal surface, and then hydrogen penetrated the metal and became internal hydrogen. When the hydrogen charging was stopped, the absorbed hydrogen on the surface disappeared and the internal hydrogen atoms diffused outward. We set the boundary conditions with zero concentration of hydrogen atoms outside the model, i.e., only hydrogen atoms existed inside the model. In this case, the diffusion direction of hydrogen should be toward the right outer boundary of the model under the stress gradient and concentration gradient.