Numerical simulation of the effects of residual stress on the concentration of hydrogen around a crack tip

For this study we used finite element analysis to show how the residual stress affects the hydrogen concentration around a crack tip in a plastically deformable material after a fatigue process. Following a 9. cycle fatigue process, hydrogen diffusion analysis was carried out at the highest applied fatigue stress. This showed hydrogen invading the crack surface and diffusing into the material. The concentration of hydrogen was higher close to the crack tip and its behavior was largely affected by the residual stress in the material. Tensile residual stress accelerated the hydrogen invasion and increased its concentration, while compressive residual stress simulated as the stress induced by peening clearly suppressed them. This is due to the affect the residual stress has on the hydrostatic stress around the crack tip which is a dominant factor in the hydrogen diffusion behavior. Peening, which is a surface treatment used to introduce compressive residual stress to enhance the mechanical properties of a material, such as its resistance to stress corrosion cracking and its fatigue strength, may, therefore, suppress the embrittlement caused by hydrogen.