Under-estimation of crack growth rate due to negligence of timescale distinction during hydrogen assisted cracking through diffusion

Some alloys in mechanical and civil applications are observed to fracture easily in the presence of hydrogen. Many diffusion-based models have helped describe this phenomenon. The crack grows when critical hydrogen concentration ahead of the crack tip is reached. In existing models, the crack growth is constantly coupled with hydrogen diffusion. However, diffusion and crack growth are observed to occur at distinct timescales - diffusion being a much slower process. This motivates the use of distinct timescales to describe crack growth and diffusion. It is found that the crack growth rate predicted is underestimated if timescale distinction is ignored.