Roughness induced crack Closure: A review of key points

•It provides a review of key points on roughness induced crack closure (RICC).•The RICC model does not have the important environment component.•The gap, behind the crack tip below Kcl allows for the environment to enter.•The RICC does not validate the data in vacuum where environmental effects are absent. In this article we review and discuss the key points on the roughness induced closure (RICC) that is considered to affect crack tip shielding. While the RICC has been suggested as a mechanical obstruction in the wake of the crack during cyclic unloading for planar slip alloys at the threshold region, the emphasis on the access of the environment to the crack tip for an environmental damage was not considered. The question is how much the role of RICC alone versus the environment that can affect the overall damage needs some discussion. Dislocation-based models have indicated that the crack tip shielding effect from a single asperity is small. In addition, the location of such an asperity (rigid or deformable) behind the crack tip and multiple asperities also affects the shielding. Existing examples of threshold ΔKth data in a good vacuum (less than10-5 Pa) suggest that RICC is not a significant factor to reduce ΔKth with R in planar slip alloys at ambient temperature. The same alloy in moist air/dilute chemical environment do exhibit ΔKth reduction with R. This comparative observation indicates that the factor of environmental access dominates in the crack opening behind the crack tip affecting the near threshold region for fatigue damage. Near threshold region is where the time dependent environmental damage is significant.