Analysis of roughness-induced crack closure based on asymmetric crack-wake plasticity and size ratio effect

Asymmetric arrangements of stored crack-wake dislocations and low values of the size ratio SR, the characteristic microstructural distance divided by the plastic zone size, were found to be of basic importance for the misfit of crack flanks causing the roughness-induced crack closure. According to newly derived formulae including these effects, an estimation of a maximal level of roughness-induced crack closure can be made for metallic materials in the near threshold crack growth regime. On the basis of statistical considerations, the assessments can be extended for the whole fatigue crack propagation regime. A negligible level of roughness-induced crack closure in nanomaterials is predicted as a partial result of the statistical analysis.