MATERIAL DISSOLUTION AT THE CRACK TIP

Despite a long-documented history of environmental effects, an understanding of the controlling mechanisms remains clouded. At fault are several challenges. First, multiple mechanisms can act simultaneously, e.g., dissolution, oxide fracture, oxide formation, material redeposition, and hydrogen embrittlement. Second, the scale of the material separation process on which the environment acts is atomistic, inhibiting direct observation. Considering these challenges, atomistic modeling can serve as a powerful probe to illuminate the mechanisms governing environmental effects and providing a means to study the material separation processes under the action of isolated mechanisms. Here, we report on the results of atomistic simulations specifically constructed to illuminate the role of material dissolution at the tip of a long crack. In cases of both brittle and ductile materials, we find that material dissolution can free arrested cracks. Beyond this, we find material dissolution to play a dole role, accelerating crack growth in the cases of brittle materials under sub-critical loading and accelerating crack tip blunting in the case of ductile materials. We find the result to be largely independent of loading magnitude and type, i.e. static vs fatigue. In total these results provide guidance for the development of continuum scale crack growth rules.
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